NBSIR 75-798 (R)

New Polymers

Martin G. Broadhurst, Editor

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

October 1975

Final

Prepared for Office of Naval Research

Arlington, Virginia 22044

NBSIR 75-798

NEW POLYMERS

Martin G. Broadhurst, Editor

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

October 1 975

Final

Prepared for Office of Naval Research

Arlington, Virginia 22044

U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton, Secretary

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Table of Contents

Page Number

Introduction 1

Preparation of Polyorganosiloxanes from Inorganic Mineral Silicates 2 by B. R. Curre'll

Polycarboranesiloxanes , Part 1 11

by J. F. Ditter

Polyelectrolyte Mosaic Membranes, Part II 49 by J. F. Ditter

Electrical Property Studies of Planar Metal Complex Systems ... 71

by L. V. Interrante •

The Synthesis and Electrical Properties of Metal Mercaptides of 92

1,4-Dimercaptobenzene

by G. N. Schrauzer and E. Prakash

(Halomethyl) Arsenic Compounds. I. Primary and Secondary .... 117

by A. L. Rheingold

(Halomethyl) Arsines II. Preparation and Characterization of . . 147- Pentakis (Chloromethyl) Cy clopentaarsine

by A. L. Rheingold

Synthesis of Poly (Arylaminophosphazenes ) 168

by J. E. White

New Polymers

Introduction

This report contains manuscripts of talks that were presented at

the Annual Program Review of the Office of Naval Research. Part of

the program focused on piezoelectric measurements and applications of

polymers and those papers were compiled previously in an Interagency

Report, NBSIR 75-760. The papers in this present report are concerned

with the chemical syntheses and characterization of potentially useful

new polymers. Together, these two reports are the final reports from

NBS to ONR as prescribed in contract number NAonr-44-75.

Commercial materials are identified in. this paper to adequately

specify the experimental procedure. Such identification does not imply

recommendation or endorsement by the National Bureau of Standards.

- 1 -
Preparation o f Poiyorgar.osiloxanes from Inorganic Mineral Silicates.

J

B.R. Currell.

Thames Polytechnic,

Wellington Street, London, SE18 6PF.

Many mineral silicates may be regarded as inorganic polymers; chains, double

chains, sheets and networks are well known (Figure 1).

Triaethylsilylation involves the conversion of =Si-0- sites to =Si-0-»S«.Me

3* The general interest in triniethylsilylation is based on two objectives:

(a) to provide additional information on silicate structures by the determination

of chain lengths and

(b) to prepare new polybrgunosiloxane based materials.

Lentz reported that triicethysj lylarion may be achieved using a reaction mixture < concentrated hydrochloric acid, water, isopropyl aichchol and hexamethyldisiloxane.

He attempted to apply this reaction to a measurement of silicate chain lengths in

1 2 sodium silicate solutions and hydrated portland cement pastes by converting the

silicate; anion to a polyorganosiloxane the molecular weight of which could be

measured (I). Masson, with a modified reaction mixture used trimethylsiylatrion tc 3

measure the chain lengi'n in lead siicjate glasses.

0"SL

I C-

-0

0

I

o

-J

- Si - o

\b

X

X X

I

I X

X

/ _ <r

X

X

-2-
If trimethylsilyl derivatives can be prepared while still retaining the

original backbone structure of the silicate there is considerable potential

for the preparation of polyorganosiloxanes of both conventional and novel structure

4 e.g. double chain or ladder polymers, and also sheet polymers. Holliday has

discussed the physical properties of the whole polymer spectrum and demonstrated

that htcx»- is a very wide gulf between the properties of, for example, the

polyorganosiloxanes and the inorganic silicates. No materials have been prepared

which fill this gulf. It is possible that materials of this type may be prepared

by partial trimethylsilylation of inorganic silicates.

This paper is a report of a study designed to assess the applicability of the

trimethylsilylation technique to a wide range of macromolecular silicates taking

examples of chains, double chs.ings and sheets. The silicates which were examined

are as follows.

Sheets

Daphnite

Vermiculite

Prehnite

Apophyllite

Biotite

Phlogopite

Talc

Kaolinlte

Muscovite

Margarite

Thuringite

Single chains

Diopside

Hedenbergite

Hypersthene

Bronzite

Wollanstonite

Double chains

Anthophyllite

Tremoli te

Trimethylsilylation is carried out by hea.ting the mineral (10 g) wih a mixture of isopropyl alcohol (50 ml), hydrocholric acid (d = 1.18, 50 ml) and

hexamethyldisiloxane (66.6 ml).

The ideal trimethylsilylation reaction may be represented as shown in (II) and

(III) using a single chain silicate as an example. The ideal reaction involves

complete removal of cations and the trimethylsiylation of the resulting polysilicic

acid with retention of the original silicon-oxygen backbone in the final product.
0"M r

I Sc-o

/0

J a

[

/

I

I 014

t * o

\

( o

I

Trimethylsilanol is formed from the hexamethyldisiloxane as shown in (IV)jfe',

H O/HCl

Me Si-0SiMe„ -> 2Ma! SiOH

o (IV)

The minerals examined showed varying degrees of reactivity towards trimethylo silylaticn at 75 and may be divided into three groups. Group I comprises bronzite,

hypersthene, diopside, treraolite, prehnite, talc and kaolinite and shows no reactivi

the mineral is recovered unchanged from the reaction mixture in each case. Group II comprises hedenbergije , wollastonite, anthophyllite, apoplr/llite and vermiculite in

which partial or complete cation removal occurs followed by partial trimethylsilylation to give an insoluble solid. Group III comprises daphnite, biotite,

phlogopite, muscovite, margarite and thuringite from which there is complete cation

removal to give triraethylsilylated products soluble in organic solvents. Except

for biotite, reaction at room temperature gave in each case little or no trimethylsi lylation with the recovery of the unreacted mineral.

In Group II minerals, degrees of trimethylsilylation were calculated from C,H

analyses. Further evidence for trimethylsilylation rests on infrared spectra and

DTA. The infrared spectra of all these products showed evidence for the presence

of unreacted Si-OH groups and there is the probability of the development of a silic

type structure formed by the condensation of adjacent Si-OH groups shown in (V).

E Si Of/ H0$iB (V)

-L-
Calculated degrees of trimethylsilylation are as follows:

Hedenbergite 14.8%

Wollastonite 14.3%

Vermiculite 89.3%

Apophyllite 16.5%

In the minerals in Group III all the cations were removed. Analytical figures

indicate the average representative structures shown in Figure 2.

All these structures receive support from elemental analyses, hydroxyl group

determination, molecular weight measurements, infrared, *H n.m.r. and mass spectra.

The success or otherwise of the trimethylsilylation depends in a very

complicated way on the structure of the silicate mineral used. The first requirement

is that the cations must be leachable by hydrochloric acid. Some general points

may be noted with regard to our present work; (a) cation removal is helped by the

presence of heavy metal ions, e.g. Fe (cf. hedenbergite, anthophyllite and

vermiculite), and (b) the less closely packed is the backbone the more likelihood

there is of acid attack (cf, wollastonite and apophyllite). Following cation

removal the accessability of the Si-OH sites to attack by Me^SiOH will be the

controlling factor. Polymerisation/depolymerisation equilibria of the silicic acid

will be competing w.Lth the trimethylsilylation reaction as shown in (VI).

In each case all possible reactons, no doubt, occur to varying degrees, but in the cases of wollastonite and hedenbergite this appears to be important. Apophyllite too falls in this category but here the sheet structure appears to be retained in the

product together with some unreacted Si-OH groups and it is possible that this

retention of the sheet structure might render the Si-OH sites inaccessible to the

incoming group for further reaction.

DM

I OU

I

/ on

-5-
Soluble products appear to be formed when there is a certain degree of

replacement of silicon by aluminium in the silicate sheet. Thus with relatively

3+ little Al in the tetrahedral sheet of vermiculite although the cations are removed no soluble products are formed. Biotite, phlogopite and muscovite have

approximate Al:Si ratios of 1:3 while margarite and thuringite have approximate

Al:Si ratios of 1:1; each of these gave soluble products. Presumably acid

attack occurs at the aluminium centre breaking the silicate sheet at these^ points

to form fragments small enough to allow attack by trimethylsilanol and give products

of molecular weight small enough to allow solubility in organic solvents. Assuming

that fission occurs at the aluminium centres in the silicate sheet, it should be

possible to correlate the average molecular weight of the products with the

distribution of aluminium in the silicate sheet. Thus margarite and thuringite

with high levels of aluminium in the silicate sheet gave low molecular weight

products compared with biotite, phlogopite and muscovite which with less aluminium

in the silicate sheet gave comparatively high molecular weight products.
The reactivity of the hydroxyl groups has been examined in reactions of

biotito and thuringite products with diphenylphosphine chloride,

trimethylchlorosilane, acetyl chloride, phenyl isocyanate and thionyl

chloride. This work is still in progress but some conclusions have

already been reached. Diphenylphosphine chloride, trimethylchlorosilane and

acetyl chloride each react to give replacement of the hydroxyl groups e.g.

HO

X 1*

x fl

> 'TVP O-Kj-o

X

->Pk Co Q-r-Sl- O

n

X

n

x

X

ft
The reactions involving phenyl isocyanate and thionyl chloride have

also been carried out, but as yet the picture if complicated and v/e are unsure of the type of reaction which has occurred. It is possible

that the replacements shown below are accompanied by an appreciable

amount of side reaction..

-HO-Si-0

x' -a

So a* ->

-5i- 0

X

I 0 H • // /

X

n

62 -

X

n

References

1. Lentz, C.W. Inorg.Chem . 1964, 3 (4), 574.

2. Lentz, C.W. Spl. Report 90, Highway Research Board , Washington DC 1966,266.

3. Gotz, J; Masson, C.R.; Jamieson, W.D. Proc Ann. Mtg. Intern. Comm. Glass , Totonto, Sept 3 -6, 1969, 69.

4. Holliday, L. Chcmy. Ind . 1972,921

-8-
-Si—0-

I 0.

Single chain

Si

I 0

I

Si

i 0.

Double chain

I 0

I SiIV

I0

I Si rr / \ \

°si/° o.oN V /

o.o o^o

S. Si Si

I I I 0 0 0

1 I I Si S

; Si ,o 6.o

n Y /0 6.0^0 q

Si Si Si

1 1 1 0 0 0

1 Si! Si

1 Si

Si

I 0

.0 o.o

' \ I /

Si

I 0

(

Sheet Figure 1. Structure of silicate anions.

-9-
HOX

I 0

I -SiI 0

I X

0--H X—O-Si-O-Si-O-X

(o).(b),(c) (e)

X

I 0

I Si

H

H?/

X-O-Si

I 0

I X-O-Si

I \

0

I H

0 9 0

S'

I c

I O-Si

I V

0

I H

Si

I 0

I Si / I Vo o

I X

?0

I Si / \ s- > 0

<

I H

X

Si

H

I 0

\ I Si-O-X

I o

I Si-O-X

/ I 0

I H

N I /

Si

I 0

IX

0

I Si-O-X

/\

0

H

I

X-O-Si

I 0

I X-O-Si

I V

Si ? o

oN ?y

X I 0

X

1

, Si / I v 0

I H

Si

I 0

I X

X

I 0

1 Si

X

Si

I 0

I X

Si-O-X

I 0

I Si-O-X

(f)

(d) Figure 2. Average representative structures, (a) n — 3, from phlogopitc; (A) n = 4, from thuringitc;

(c) « == 5, from biotitc (at room anil rellux temperature); (d) from biotite at reflux (75°) temperature;

(c) from margarite; (fj from daphnitc. X = SiMc,.
POLYCARBORANESILOXANES: Part

J. F. Ditter

Chemical Systems, Inc. 1852 McGaw Avenue

Irvine, California 92705

- 11 -

PART I

POLYCARBORANESILOXANES

Extracted from a General Treatise Being Written on Carborane Polymers.

- 12 -

I. INTRODUCTION

Many copolymers incorporating carborane molecules in the chain,

as discussed later, have been synthesized, but the copolymers evoking

the most interest, due to their high temperature properties, are the

polycarboranesiloxanes .. Structurally, the polymers can be visualized

simply as polysiloxanes with carborane moieties in the chain. In their physical and chemical properties, general chain structure, and

techniques of synthesis, they closely resemble the polysiloxanes.

However, because there are electron-deficient carborane molecules in

the chain, the polycarboranesiloxanes hold a considerable advantage

over the polysiloxanes in high temperature applications. For example,

as the stationary phase in gas chromatography, polycarboranesiloxanes

can effectively operate with high separation efficiencies at temperatures as high as 400° C. As elastomers, their operational limits lie

in the region of 300-350°C. As coatings, where oxidative crosslinking

can be utilized, they provide oxidative protection and electrical insulation for the substrate at temperatures in excess of 650°C and, in

applications involving stlicate/polycarboranesiloxane composites, at temperatures as high as 1100°C. Silicones cannot compete in these

regimes because of their propensity for chain fragmentation and cylization at temperatures as low as 250-300°C.

Other carborane copolymers, e.g., polyesters, polycarbonates,

vinyl-addition types, etc., have not shown particularly outstanding

properties. Consequently, relatively little research activity has

been centered on them other than syntheses and minimal characterization

studies

.

II. CARBORANES AMENABLE TO POLYMER SYNTHESIS

Carboranes are classified as closo- , nido- , and arachno- (Fig.

1-3) j corresponding, respectively, to closed-cage , nest , and web structures. Thermal stability and chemical resistance decrease in the order

closo- > nido- > arachno because of (and in proportion to the number of)

hydrogen bridges on the nido- and arachno-compounds . Consequently,

-13-

B6

H

10 CB

5 H

9 C

2

B4H

8

hexaborane-10)

Figure 2, Representative ni do -Carboranes
Figure 3. An arachno- Carborane

1

-16-
carborane copolymer systems have to date encompassed only the closocarboranes (Fig. 1) and primarily c

2 B ioH12' and C2 B

5 H7 ' Ths latter

two compounds have received the greatest emphasis firstly because of « their relatively greater availability and secondly because of the outstanding properties of some of their polymers. However, with the

possible exception of the relatively non-stable C^B^H^ compound, the

remaining closo- carboranes in Fig. 1 should also be capable of producing polymer systems comparable in many if not all respects to those of

C

2B1Q

H

12

and C^.

III. CARBORANE STRUCTURAL PARAMETERS

For any polymer system the monomer(s) first of all must have the

appropriate functionality to be capable of inclusion in the chain.

Closo- carboranes , with two carbon atoms in the molecular cage, possess

the requisite difunctionality for linear polymer systems. Short chain,

crystalline oligomers have been synthesized by direct carbon carbon

bonding between adjacent carborane cages, but the higher molecular weight

polymers which have been synthesized to date have ail utilized other

functional groups attached to the carbon atoms. Examples include dimethylchlcrosilyl groups for polycarboranesiloxanes , carboxyl groups for

polycarbonates and polyesters, etc., all of which are amenable to polymerization by polycondensation reactions. Similarly, vinyl addition car- borane polymers can be prepared from monomers in which a vinyl group is

appended to one of the cage carbon atoms.

The carbon-attached hydrogen atoms in closo- carboranes possess

sufficient acidity to permit substitution reactions to be carried out at these positions. Reactions with Grignard reagents, such as lithium

butyl, for example, proceed facilely and lead to formation of the dilithiocarboranes , and the lithium atoms in turn can be replaced with an almost unlimited array of other functional groups, including groups

amenable to polymerization reactions.

The electron distribution in closo- carborane cages was studied

first of all by electrophilic substitution reactions on ortho-and meta-

^2^10^12 ^ ' ut ili z in8 x-ray diffraction measurements (1) to determine substitution positions.

-17-
STRUCTURE FORMULA NAME

1,2-C

2

B 10H

12

(ortho)

1 ,2-dicarba- closo- dodecaborarte-12

1 ' 7" C

2

B10

H

12 (meta)

1 , 7-dicarba-closo- dodecaborane- 1

2

Figure 4. Nomenclature and Numbering System for Carboranes

-18-
j.-itial substitution w±s 1v*und to occur on the boron atc;i;s opposite the carbon atoms , indicating these to bo the positions of highest

l r ~t;v,. density on the cage. Considerable dipole moment \ves observed

(

,*"• » with the carbon constituting the positive pole. On j^rf-C^gH^,

' here the carbons are located directly opposite one another end where

•11 the boron etc-ns are equivalent, oiectrophilic rvbstitu-'r'.i occurs

randomly. All possible geometric isomers were fo, ' in <..'- --"titles

r. dieted on a statistical basis.

The electrons in the cage that are r.ot engaged in ..or.;':.-.! cov;*.l - fit

j...! 'no -re celocalizcd throughout the cage and give it a three-

•/ ..:1f n-.l

K sucer-arozati c" character (3), which accounts fir the re-

;.le chemical and thermal stability of these compounds

«

Sir.n'«i;rly, analysis by ' S-nmr of the products of Friecel -C; eft

;.;•=." ••'.hirbctiiutic:! on the 5 ,6- borons. P.eplacesncnt of V : r.-*h"-rf-

• :hsn on the C-b ln H 1r compounds, as discussed in U .

:v ~:::z>is r

.;:r; availasjuty of clo£0-carcora::es ".

. . c: v:

/.P LICAi IONS

The closo-carborane, L,4-C,b,rb 5 is .7' Resized by direct '<?•: . &etiW: ' ,ri oentaborans- S a:;! .-.:.etylcnj s op£U c -st:c: • a hr.

'. fin-; system: v: which p tvbcra.n:. •

' -• r--\ty? = " h

-

. h':ati. * :.t Kh"'C •.';»• aLast e socc::d {4}. ATe; : -..it'

prefe-

,. ;m' 1 ,5r C. r?.,""K j qiicng wit::, t; . on-c-Tn•:- i,f hi chcr

1

:

SSrC bor .; i~s {C.,B dh a&j A~so

: b:-vsn : (b) •y = hj

'i . .i<# liwl^vCev

*. 1.

-19-
distillation on a multi-plate column. Boiling points at 760 mm are

.:: J C for C

2S

5

H7> 2?°C for 1 and -37°C for 1 ^-C^IL. Complete separation of CgBgHy from the methylated carborane by-products

has not been feasible, but fortunately the methyl groups all appear

to be attached to boron atoms and not to the carbon atoms of the car- bcranes. If even a email concentration of mono- methylated carborane,

in which the methyl is attached to a carbon atom, remains in the C 0 tl-H.T fraction, it would serve as a chain terminator in the final polymerization reaction. As little as 0.C5 mole percent of this impurity could

cut the desired molecular weight drastically. Removal of C-dimethyl

carbo rar.es from the ^2^5^*7 * on t ^' e °^er band, is not important since

these are non-functional and cannot interfere with polymerization.

Preparation of the iccsahcdral ^2^1 0^1 2 C£rb°ranes until recently

bas bjc.i carried out by solution ohasc reaction of dccaborane-K wit!)

acetyl are. The first step in the synthesis' involves preparation of a ciligand of decaborane, a typical synthesis being the reaction of decafcorano-14 with diethyl sulfide ( 7).

E,

0

H 14

* 2(C

2

H

5

) 2

S B10

ll 12 - 2[S(C

2

H

5

) 2T + H,

The next step involves addition of the acetylene, which is bubbled

ihi'CUfjh the solution over an extended period of time.

B10H

12 -2[S(C

?H

5

) 2

]

-! C

2H2 -^-C-*~ C

2

B 10M 12

+ H

2

i

In addition to the reaction of acetyl en 2 with the dil i/ard to give

C.-,C lrji TO carboranes, it is possible to use almost any acetyl enic compound

!;• this reaction and thereby obtain modified carboranes with pendant

groups on one or both cage carbon atoms. A specific example for polymer

chcrvistry is the reaction of vinyl acetylene with the diliyend, giving a '-vinyl carborane (Fig. 5)'. Vinyl addition polymers uslny tin's monomer

havt i: ecr: prepared, as discussed later.

Based on decaborane- K as starting material, trie yields of carboraae produce -j by the diVigand so*, triors chemistry tactwrkjite run about 80*.

This f igure, however 4 can be ?cfr:.wi;a t •••islea

: !tr:, "•>.* if the yield is

-20-
-21-
based on sodium tetrahydroborate, NaBH^, which is a precursor (via diborane) for the preparation of decaborane-14, then the yields of car- borane are more on the order of 20-30%. Consequently, ^2^10^12 car'30r" anes produced by this method are very expensive commodities. The same situation is true for the smaller carboranes based on pentaborane-9,

though not as severe because yields of pentaborane-9 from EH^ are about

threefold better than for decaborane-14 from BH^.

Recently, however, a greatly improved method for producing C^lO^l'

directly from BH^ and acetylene has been developed by Union Carbide

Corporation, although details of the syntheses have not been revealed.

Presumably, it is based on a technique first investigated by Call ery

Company ( 8) wherein BH7 is transformed into a higher molecular weight

2-

ion or neutral molecule, such as B-|qH-|q , B-jqH-j^ or

^iq^-j

3"^ "iQand. If

the intermediate is ionic, then neutralization with an acid would be re- quired to form the corresponding neutral borane before treatment with

acetylene to produce the ^10^12 carb° rane - The overall process, in

any event, represents a significant advance in lowering the cost of car- boranes and making them available in the near future in reasonably large

quantities. Even a yield of 40-50% would be a big improvement over the

old method because of the simplicity of the process.

The three C2B 10

H 12 carb° rane isomers are all solids at room temperature. Melting points are 295°, 270°, and 260°C, respectively, for

the ortho, meta and para configurations. The ortho compound converts

quantitatively into meta by thermal rearrangement above 450°C, but con- version into the para compound requires significantly higher temperatures and is a low yield reaction accompanied by fragmentation and cage

fusion, Purification of the parent carboranes can be accomplished by

recrystallization from ether or acetone.

V. DILITHI0CARB0RANE5 - MONOMER PRECURSORS

The dilithio derivative of a closo- car borane is prepared by re- acting the parent carborane with a lithium alkyl, usually the butyl

derivative, in an ether/hydrocarbon solvent.

:;CB n

l! n

CII + 2LiC

4

H

g LiCB

n Hn CLi + 2C^

Q

-22-
The dilithio derivative of ^2-5^7 "* s 9 enera "l1y synthesized at -30°C,

while that of C 2^inH 12 rea. IJ "' res

The carborane is dissolve- in a 60/40 diethyl ether/hexane solution, and then, in an inert atmosphere and with vigorous stirring and

supplementary cooling, a 15 weight percent solution of lithium butyl in

hexane is added at a rate sufficiently slow to preclude any increase in

temperature above the initial level. Approximately \Q% excess lithium

butyl above the calculated stoichiometric amount is added to insure

near-quantitative conversion of the carborane into the dilithio salt.

The mcno-l ithium salt forms almost immediately, but substitution of the

second lithium atom requires extended time and somewhat higher temperature. Generally, after all of the lithium butyl has been added, the

reaction is allowed to digest overnight at room temperature.

The mo no -1 ithium salt is soluble in the ether/hexane solvent, but

the dilithio salt forms a yellowish gummy ether complex, which must be

kept suspended by vigorous stirring. V,'ith the ^2^^7 carDorane > the

dilithio salt/ether complex is spontaneously flammable in air, but re- moval of the last vestiges of ether permits handling in air. The ^10^1

derivative, on the other hand, is not spontaneously flammable even as the

ether complex.

The dilithio salt can be concentrated by removing all or part of

the ether/hexane solvent by vacuum evaporation, or it can be left in the

solvent mixture for the next step, i.e., formation of the monomer. Bis -

silyl monomers, for example, are formed by reacting the dilithio salt of

the carborane with dimethyl dichlorosi lane, as fallows:

LiCBgHgCLi + 2 Ci

2 Si(CH

3

) 2 -20°C

si a ether

(CpBr-monomer)

-23-
VI. IMPORTANT PARAMETERS FOR CARBORANE POLYMER SYNTHESES

The vast majority of carborane-containing polymers are synthesized

by polycondensation reactions, i.e., by splitting out a molecule, usu- ally water, from the propagating chain. For condensation-type polymerizations, three very important factors must be considered for the achievement of high molecular weights. These are:

• High monomer purity, i.e., extremely low concentrations

of chain-terminating species;

• Precise stoichiometry between reacting co-monomers when

copolymers are synthesized;

• High conversion rates for polymerization.

Consider first the problem of purity and, for purposes of illustration, assume a polycondensation reaction involving dimethyl si lane diol, which

forms when dimethyldichlorosilane is hydrolyzed. If the reaction mixture contains 90 mole percent of the desired monomer, (CHg^SiC^and

10 mole percent of the chain-termination species, (CH-^gSiCii, then, on

a statistical average, nine molecules of the dimethylmonomer will join

together until terminated at one end by a molecule of the tri methyl

compound. An additional nine dimethylmonomers will then propagate on the live end of the above chain until it too is terminated by a second

trimethyl compound. The number of repeating units in this chain, ex- cluding the terminating species, will be 9x2 = 18 and the molecular

weight will be 18x74 = 1332. Similarly, if there is only one mole

percent of chain-terminating species, the number of repeating units

will be 99x2 = 198, and the molecular weight will be 198x74 = 14,652.

The table below shows the relationship between molecular weight and

various concentrations of chain-terminating molecules for polydimethyl

siloxane synthesis.

| -24-
Table 1. Effect of chain-terminating impurity in

the preparation of polydi methyl si loxane

Monomer

Concentration

Chain-Terminating

Species

Average No. of

Repeating Units

Average

Molecular Weight

90 mol %

99

99.9

10 moT %

10.1

0.05

0.025

0.010

1 ,998

3,998

7,998

19,998

18

198

1 ,332

14,652

148,000

296,000

592,000

99.95

99.975

99.990 1 ,500,000

A desirable molecular weight for this polymer for many applications is

about 600,000, which represents 8,000 repeating units. If as little as 0.05 mole percent of trimethylmonomer is initially present, the molecular

weight will be only half of the desired value; if 0.1 mole percent is

present, the molecular weight will be one-fourth as much as desired.

Molecular weight differences of these magnitudes can mean significant

differences in the polymer's physical properties, e.g., large differences

in viscosity if it is an oil and differences in strength if it is to be an elastomer.

Consider next the problem of stoichiometry in the polymerization

of two co-monomers and assume that the final product is a polyester made

by copolymerizing adipic acid, H00C(CH

2

) 4C00H, with a carborane diol,

such as bis- hydroxymethyldodecaborane:

H00C(CH

2

) 4C00H + H0CH

2CB

1Q

H 10CCH

2 0H

r

0

II 0 CC(CH

2

) 4C-0-CH

2 CB 1Q

H 10

CH

2 0 —

Schematically, this can be represented as

nA + nB *- (AB)

n + (n-l)H

20

-25-
In this case the molecular weight of A is 146, while that of B_ is 204;

molecular weights of the participating units in the polymer chain are 146-18 = 128 for A and 204-18 = 186 for B.

If the reacting mixture contains only half as many moles of A as

B_, then the polymer chains will, on the average, grow to only three

units long, i.e., BAB , before terminating. If the reaction mixture

contains 40 mole percent of A and 60 mole percent of B_ (2:3 ratio),

then the polymer chains will grow to five units, i.e., BABAB . Table 2 shows the influence of the relative monomer concentrations on chain

length and molecular weight — assuming 100% conversion into polymer, a feat which experimentally can be approached but never achieved (9),

Table 2. The influence of monomer stoichiometrics on chain

length and molecular weight of the carborane polyester, fC0C(CH2 )it C00-CH2 CH 10 H 10 CCH 2

(>}-n represented

as (AB) . and assuming 100% conversion.

mole % A mole % B chain units molecular weight

33 67 3 500

40 60 5 814

49 51 50 7,850

49.5 50.5 100 15,700

49.9 50.1 500 78,500

49.95 50.05 1,000 157,000

49.99 50.01 5,000 785,000

49.995 50.005 10,000 1,570,000

The chain length in the previous table is calculated simply by the ex- pression:

No. of units Mole fraction B - Mole fraction A

The percent conversion of monomer into polymer is also a very important factor in determining the final chain length in polycondensation

reactions (9). In table 2, for example, if the conversion were 99%

rather than 100%, then for the polymer consisting of 100 units, one out

of 100 links would not have been formed, and the molecular weight would

-26-
be only half of that shown, or 7,850. For the polymer consisting of

1,000 units, ten links would not have formed, and the molecular weight

would be only one-eleventh of that shown, or 14,300 rather than

157,000, a dramatic difference.

Similarly, for 99.5%' conversion, for 1,000 chain units five would

not have formed, and the molecular weight would.be 157,000 * 6 = 26,000.

Table 3 shows data from table 2 recalculated on the basis of 99.9%,

99.5% and 99% conversion.

Table 3. The effect of percent conversion on chain length and

molecular weight of the polyester shown in Table 2.

No. of Units per Chain Molecular Weight

Conversion: 100% 99.9% 99 . 5% 99% 100% 99.9% 99.5% 99

100 91 67 50 15,700 14,270 10,470 7,850

500 333 143 83 78,500 52,300 22,430 13,080

1,000 500 167 91 157,000 78,500 26,170 14,270

5,000 833 192 98 785,000 130,800 30,190 13,390

10,000 909 196 99 1,570,000 142,700 30,780 15,540

One of the primary reasons why completely quantitative conversions

in polycondensat-ion reactions are not realized is the fact that they are equilibrium reactions (10) where one mole of water is formed for each con- densation. Hence, the water must be removed from the equilibrium to in- crease the conversion and thereby achieve high molecular weights. However, even with high molecular weights a small amount of water still belongs to the equilibrium, and the amount of water remaining is a function

of the equilibrium constant (10).

In summary, the purity, the stoichiometry , and the degree of con- version are very important factors in polycondensation reactions, and

this covers the large majority of polycarborane syntheses. The achievement of high molecular weights has been a difficult problem until very

recently, particularly with polycarboranesi loxanes , and the reasons cited

here, particularly purity, have been responsible for this problem. Up

-27-
until as recently as 1973, polycarboranesiloxane molecular weights above

20,000 were rarely achieved, and the desired strength and toughness of

the elastomers were consequently lacking.

VII. POLYCARBORANESILOXANE SYNTHESES

Silicone Analogies . The methods of synthesis of silicone polymers, or polysiloxanes, are closely allied with the methods of synthesis

of polycarboranesiloxanes, and in fact the latter can be regarded as modified silicones. The carborane and si lane monomers possess the same types of functionalities, and hence their polymerization mechanisms are

similar.

A typical silicone polymerization is that of dimethyldichlorosilane, which is reacted with water to form the silanol. The silanol

then undergoes polymerization by condensation, splitting out one molecule of water for each condensation. The overall reaction is as follows

(CH

3

) 2 Sia

2 + 2 H 20

n (CH

3

) 2Si(0H)

2

With the simple addition of water to the monomer, generally in the

presence of an ether solvent such as dioxane, can vary from that of

low molecular weight trimers, tetramers, etc., up to fairly large values

that correspond to straight chain (linear) polymers. The addition of

catalysts, buffers, different solvents, etc. can change the distribution

of molecular weights over a large range. However, high molecular weight

silicones are best achieved by synthesizing low molecular weight cyclic

oligomers, generally trimers and tetramers, and subjecting these

oligomers to rigid purification procedures. The oligomers, in the

(CH

3

) 2Si(0H)

2 + 2 HC£

CH

3

Si -0 4- + (n-1) H20. CH.

-28-
presence of catalysts, then can be polymerized to very high molecular

weight linear. polymers (11). In this way the problems of purity,

stoichiometry and high conversion that are inherent in polycondensation

reactions are overcome.

Cyclic polysilcxar.e trimer, tetramer, etc. are formed in appreciable quantities in the polycondensation of hydrolyzed dichl oromonomer

,

and these are recovered (after HC£ evolution and solvent evaporation)

by distillation cf the product mixture. At 760 mm the boiling points

are 134C C for the trimer and 1 75°C for the tetramer; cyclic compounds

vri th higher values of n_ are recovered by distillation at reduced

pressures (12). Cyclic po"!ysi loxanes can also be obtained by heating

linear polysiloxanes to 350-400°C and removing the volatile fragmentation products from the still pot with a stream of nitrogen. Trimer and

tetramer are then subsequently recovered from this distillate by anotehr

fractional distillation, as above.

High molecular weights can be obtained from the cyclic oligomers

by either acid or base catalysis. In acid catalysis the oxygen atom in

the polymerizing chain is an electron donor for the proton of the acid,

while in base catalysis the base is a donor for the silicon atom,

thereby allowing the silicon to take on additional valency ( ). Both

phenomena are ionic in character but opposite in their polarizing

characteristics, i.e.,

I © e

- Si - 0 - Si —

1 A I

- Si - 0 - Si :

| f© le

H B

Base catalysis of the cyclic tetramer, for example, is achieved with

absolutely dry KOH (14), and the mechanism involves CH~ attack on a silicon atom and K attack on an adjacent oxygen. The ring opens into

a chain with K+ and 0H~ ends. These then catalyze further ring openings and polymerizations, and the net result is formation cf high mo- lecular weight polymers. V.

! ater is excluded from this system,

-29-
Similarly, a catalytic amount of concentrated h^SO^ can induce

the formation of high molecular weight polymers from these same oligomers, again in the complete absence of water ( ).

The point of this discussion is to emphasize the techniques for

achieving high molecular weights with silicones, utilizing the cyclic

oligomers to attain the requisite high purities and high conversions.

Carborane-siloxane polymers, on the other hand, do not generally cyclize

and hence cannot take advantage of this mode of purification. These

factors are important but have not generally been emphasized in previous

polycarborane literature.

Finally, it should be mentioned that high molecular weights are not necessarily always desired, and lower molecular weight polymers,

for example oils of certain specific viscosities, are sometimes required.

These materials, however, are also readily obtainable by the above same techniques but with the deliberate addition of controlled amounts of

end-capping monomers, such as trimethylchlorosilane, to limit chain

lengths. In this same context, it is frequently desired to impart

elastomeric properties to a polymeric resin, and for this purpose triand tetrafunctional monomers can be added to the reacting mixture to

impart specific amounts of crosslinking into the resin.

Ms-Si lyl Carborane Monomers . The dilithio salts (Section V) are suitable precursors for just about any category of condensation-type

monomers, including the bis- silylated carboranes from which polycarboranesiloxanes are made.

The preparation of the C^Bg-monomer from the dilithio salt is illustrated in Fig. 6. The ether/hexane slurry of the dilithio salt is

allowed to flow very slowly into an ether solution of dimethyldichlorosilane, maintained at -20°C. An excess of the silane compound is maintained to insure complete silylation.

When the reaction is finished, the ether, hexane, and unreacted

silane are stripped off at reduced pressures, and finally the monomer

is removed by vacuum distillation (B.P. 65°C at one torr) . The main

-30-

impurity (B.P. 46°C at 1 torr) is the monochloromonomer , wherein the

second chlorine atom has been replaced by a hydrogen atom. This impurity can be transformed into the dichloromonomer by distilling it

in the presence of aluminum chloride and acetyl chloride. •

The preparation of C2B-jQ-monomers involves the same general chemistry as that of the C2Bg-monomer except that with ^2^10 tnere are tnree

potential monomers, depending on whether C2^10^12 is to have ortho , meta

or para configuration (Fig. 4). m^B-igH-^ is quantitatively derivable

from o_-C2B-jqH-|2 by thermal rearrangement above 450°C, but it has been

found to be more convenient to prepare first the bischlorodimethylsilyl

derivative of c^^B-jqH^* which is the ortho^B-iQ monomer, then convert

it to the m-configuration because this rearrangement takes place at much

lower temperatures (*~300°C) than that of the parent carborane (15). The

sequence is shown in Fig. 7. Conversion of the m^B-ig-monomer into

•Pj"^2^10^12~mononier ' however, is not feasible because the requisite temperatures destroy the monomer. In this case it is necessary to prepare

first the Pj^B-iqH-^ parent compound, then synthesize its monomer by

normal lithiation and silylation procedures.

The experimental details of synthesis of the bis- silyl monomers of

the three isomers of £2^10^12 ^ ave ^ een extens '' ve ^y reported in the literature (16). The silylation reaction is carried out at 0°C, and the monomers can be purified by vacuum fractionation but are usually purified

by recrystallization from ether.

Carborane-Siloxane Polymerization by Ferric Chloride Catalyses . One of the earliest attempts to synthesize polycarboranesi loxanes involved

condensation polymerization of the bis-(chlorodimethyl silyl )-monomer of ortho-

^2^10^12 However, chain polymerization was unsuccessful due to the

tendency of the condensation product to form a f ive-membered exocycle

(Fig. 8) in almost quantitative yields. This compound was observed to possess extreme thermal stability, surviving 500°C with comparative ease. The same phenomenon occurred when the monomer was reacted with ammonia

except that the product here was a very stable cyclic imide. Electron resonance in this ring, enhanced tremendously by the electron deficient

-32-
to

O O

-33-
to 10

o\ /O o

C4 coVI

o S. >> QJ O E 0 o X c

UJ o

s: •o

0) o i- f—

<u co XI CM E OCD I . •z. o 1 XZ

01 +-> > u

f- o

u.

0) J= 4-> +J M-

«»-

O o

I/) c •<- o </> •r- >»

+J i—

(d o B U

i- -a o >>

COc
cage in conjunction with the siloxy moieties, gives it extraordinary

stability.

The exocyclic ring compound can be obtained in very high purity,

but whether the ring could be catalytical ly induced to open up and form

the linear high molecular weight polymer is problematical. If so, it

would be an ideal way to generate both the ortho and meta forms of this

homo-polymer, since the ortho form can be converted quantitatively to meta by heating above about 300°C.

When the ortho monomer was found to form the exocycle, research

efforts were switched to the meta monomer which does not cyclize because

the carbon atoms in the cage are nonadjacent. The first attempts to polymerize the meta carborane monomer involved hydrolysis of the bis(chlorodimethylsilyl ) derivative by the simple addition of water to an acetone

solution of the monomer at room temperature (18). The diol formed readily,

but it could not be induced to undergo polycondensation. Subsequently,

techniques that had worked in silicone chemistry (19), i.e., a ferric

chloride catalyzed polymerization reaction between dichloromonomer and

dimethoxymonomer (made from the dichloro-compound by methanolysi s) were tried and found to work (20). The reaction was carried out neat (no

solvents) at temperatures ranging up to 190°C. Methyl chloride is a product of the reaction.

Similarly copolymerization of the dimethoxy carborane monomer with

suitable proportions of dichlorodimethylsilane opened the way to synthesis of the entire family of "Si B polymers," which later were designated as Dexsil polymers for commercial sale. Experimentally, the liquid co-monomers were placed in a flask along with about 2 mole percent FeCz^,

then heated under vacuum with continued stirring for a period of about

four hours. Purification of the resin was carried out by recrystallization from hot xylene.

The "SiB" designation is a convenient method of identifying the

polycarboranesiloxanes. For example, 10-SiB-l indicates that the polymer

is based on the bis- silylated ^2^}0^]2 car'30rane anc' nas one oxygen atom

per repeating unit. 5-S1B-2 indicates the C

? BrH 7 carborane, with two

-35-
oxygens per repeating unit; it is made by co-condensation of the ^2^S~ monomer with dimethyldichlorosilane.

A number of years after the successful synthesis of the 10-SiB

polymers, when the smaller closo- carborane, C^^^j, became available in

sufficient quantities, this same ferric chloride catalyzed polymerization reaction was applied to C2B^-based carborajie monomers (21). The

technique was again successful, producing 5-SiB-l, a hard wax, as the

first Pentasil polymer. One important difference was immediately noted

in that the Pentasil polymer was more tractable and lower melting than

the corresponding Dexsil polymer. Whereas Tmwas 260°C for 10-SiB-l,

it was found to be only 70°C for 5-SiB-l. The transition temperatures

for the 5-SiB-l were roughly comparable to those for 10-SiB-3.

This observation then spurred efforts to try to develop a 5-SiB-l

elastomer, or at least an elastomeric polymer requiring substantially

fewer siloxy groups in the chain than did the Dexsil polymers. With

this end in mind, the idea of disrupting the chain symmetry of the

5-SiB-l polymer by randomly inserting large C2B-jg-moieties in the chain was originated. Hopefully, such a modified SiB-1 polymer would either

be elastomeric or could be made elastomeric under ambient conditions.

When this modified 5-SiB-l polymer was synthesized, again by ferric

chloride catalyzed reaction between the methoxy- and chloromonomers, it was indeed found to be an elastomeric resin. Its physical and chemical

properties were approximately the same as those of elastomeric 10-SiB-3

(Dexsil 300).

Unfortunately, in the case of both the Pentasil and Dexsil polymers

at that time, the high temperature synthesis and/or post-treatment introduced crosslinks into the polymer. The crossl inking probably is caused

by a Friedel-Craft type attack on the cage, wherein the ferric chloride

induces methyl group bridging between adjacent chains.

Except for the unmodified 5-SiB-l and 10-SiB-l, every polymer synthesized by ferric chloride catalysis was either elastomeric or intractable because of excessive crossl inking, and no two samples ever appeared to have the same. consistency. Fortunately, other techniques soon

-36-
were discovered (about 1970) which made available for the first time

long chain linear polymers. One technique was room temperature alcoholysis, suitable for synthesis of Pentasil polymers (22)-, another

was a low temperature (0°C) hydrolysis, devised for synthesis of certain

Dexsil polymers (23); a third was an acid-catalyzed condensation of

C^Bi ^-monomers (23). "ore recently a fourth approach, involving si lanes

with facile leaving groups, has been successfully applied to the synthesis of very high molecular weight 10-SiB-2 polymers (24-).

Synthesis of Pentasil Polymers by Alcoholysis . In carrying out a ferric chloride catalyzed polymerization, one of the preliminary steps

involves preparation of the dimethoxymonomer by reacting the dichloro- monomer with methanol. In the course of one such methanolysis reaction

with C^Bg-dichloromoner, it was noticed that a white precipitate had

formed after standing for several days (22). Infrared analysis then

showed this precipitate to be a Pentasil polymer with some additional

B-0 bonding attributable to B-OR groups on the carborane cage. The

methoxy monomer had undergone a polycondensation reaction and formed a 5-SiB-l polymer, but, unfortunately, the methanol had also attacked the

carborane cage. A systematic search then indicated that a tertiary

alcohol, such as t-amyl , was a suitable reagent for any and all 5 - S i

3

(random) polymers. Molecular weights up to 5,000 were obtained with this

method. Copolymers made with more than about 20 mole percent dimethyl - dichlorosilane were found to be oily liquids, while the addition of trior tetra-functional monomers made them elastomeric gums, a typical formulation being:

67 mole %

25 mole %

8 mole %

C^Bg Monomer

( CH^

) 2^ iC&2

CH o Si0i o

Polycarboranesi loxanes by Hydrolytic Polycondensation . The tfl}'

monomer, in contrast to the C 9 Br monomer, is not amenable to formation

-37-
of the 10-SiB-l polymer by alcoholytic condensation (22) just as the

C2B-|Q-disilanol monomer does not undergo hydrolytic polycondensation

(20). Apparently the influence of the C

2

B 1Q cage inhibits scission of

the Si-0, SiO-H, and/or SiO-R bonds on the monomer. Whether the reason

is steric in nature or due to electron charge smoothing is not known,

but the C2B-jQ-disilyl monomer resists hydrolytic and alcoholytic condensation. However, C2B-|g-monomers which contain additional siloxy groups

corresponding to Dexsil 300 or larger undergo hydrolytic polycondensation

in water/ether/THF solutions at 0°C, and linear polymers of 10-SiB-3 and

10-SiB-5 were first prepared in this manner (23). All of the 5-SiB poly- mers also can be prepared with this technique.

The experimental procedure involved the addition of water/THF to a solution of the appropriate monomers dissolved in ether. The reaction

flask is maintained at 0°C during the addition and then allowed to warm

to room temperature and digested for another 2-1/2 hours. The solvents

are stripped off by relatively low temperature (30-35°C) evaporation

under vacuum conditions. This procedure was found to eliminate the

problem of crosslinking during synthesis, and soluble (linear) 10-SiB

polymers with average molecular weights in the 10,000 range and peak

maxima around 16,000-20,000 were first produced in this manner. Copolymerization of these same monomers with phenylated silanes produced

the appropriate phenylated polymers.

. Acid-Catalyzed Polycondensation of Diols . The OH-terminated counterpart of the chloro-monomer that was used successfully to synthesize Dexsil

300 by hydrolytic condensation was found to undergo acid-catalyzed con- densation at elevated temperatures (23)- The OH-terminated monomer was first prepared by treatment of the chloromonomer with sodium bicarbonate

in moist ether. Polymerization was then effected by heating the monomer

for 20 minutes at 200°C and 4 hours at 170°C in vacuo in the presence of

a catalytic quantity of H^SO^ (^0.6 wt-%). In this synthesis the 170°C

temperature did not induce formation of a crossl inked gum. The Dexsil

300 polymer produced had a molecular weight distribution comparable to that produced by the hydrolytic condensation method. The peak maximum

was at MW = 16,000-20,000.

-38-
High Molecular Weight C2B-j Q-Based Polycarboranesiloxanes . Of the

various methods for synthesizing the polycarboranesiloxanes prior to a few years. ago, none produced polymers with molecular weights exceeding

100,000, and then only rarely. Generally, the molecular weights were between 5,000 and 20,000 and consequently possessed poor tensile properties. The reasons, in retrospect, were undoubtedly due to a combination

of factors such as lack of high monomer purity, incomplete conversion,

and, with copolymer systems, non-precise stoichiometry, as elaborated in

Section VI.

At Union Carbide the challenge of fabricating high molecular weight

polycarboranesiloxanes was met by reacting the disilanol of the C^B-jqsilyl monomer with di functional si lanes having appropriate facile leaving

groups ( ). A variety of silanes were investigated, but certain ureidosi lanes were found to be particularly attractive because they were non- basic and formed insoluble urea byproducts, which led to high conversions,

A typical polymerization reaction, utilizing an N-pyrrol idine derivative,

is as follows:

DCH. CH. 3 . 3

- Si(CH

3

) 2 + HOSi - CB

10

H 10

C - SiOH

J 2

CH. CH.

CH,

Si - CB

10

H 1QC - Si - 0 - Si

CH.

CHI ;

5i

I CH.

CH.

CH.

u

D

2 polymer (10-SiB-2)

Linear polymers with weight average molecular weights as high as 250,000 (720 repeating units, 1440 chain units) have been synthesized

in this way. Furthermore, substitution of 33 mole percent of either

-39-
di phenyl siloxane or methyl phenyl si loxane moieties in the chain produced

an amorphous polymer suitable for elastomer formulations.

Experimentally, the carborane monomer is converted to the diol by

hydrolysis, then the ureidosilane (powder) is slowly added to the diol

which is dissolved in chlorobenzene and maintained at 0 to -10°C. Reaction stoichiometry is carefully monitored by nmr, and on completion of

the reaction the insoluble byproduct is removed by filtration.

High Molecular Weight C^ B ^-Based Polycarboranesiloxanes . L i near polymers of C2B^-carborane with molecular weights in excess of 10,000 were rarely achieved by the previously discussed methods, again most

likely due primarily to impurities in the form of chain terminating trimethyl compounds. Recently at Chemical Systems high purity monomer,

purified by repeated distillations on a spinning band column, was prepared and polymerized by hydrolytic condensation into the 5-SiB-l homopolymer. The product was a linear polymer with VL = 182,000.

The preparation involved the slow addition of a water/dioxane so- lution to a vigorously stirred solution of the monomer also dissolved

in dioxane at room temperature. The water was precisely measured to react to a 1:1 molar ratio with the monomer. Stirring was maintained

for several additional hours, and then the temperature of the solution was slowly increased to dioxane reflux temperature (101°C) to induce

polycondensation and drive off HCx. formed in the reaction. The pressure was then reduced and the dioxane removed by distillation. The reaction

is as follows:

CaSi - CB^C - SiC£ + H0H

CH

3

- 0 - + HC£

-40-
VIII. POLYCARBORANESI LOXANE CHARACTERIZATION

The polycarboranesi loxanes constitute a class of outstanding heat

resistant polymers. In Fig. 9 are two members of this family of com- pounds, one (5-SiB-l) based on the ^2^^7 carborane and the other (10-

SiB-2) based on m^B-jgH-^ carborane. Structurally, these polymers can be visualized as silicones with bis- silyl ated carborane units inserted

in the chain. In an ordinary silicone, and this holds for silicates in

general, the Si-O-Si bonds develop substantial double bond resonance

character due to a shift of the extra electrons on oxygen toward silicon

and their accommodation in the unfilled 3d orbitals of the silicon atoms

(13). The bonds are shorter and stronger and the angles are wider than

would be anticipated by simple addition of atomic radii. The weakly

electron-donating methyl groups also contribute to strengthening of the

Si -0 bonds but at some sacrifice in the strength of the Si -C bond. The

decreased electron density at the methyls, however, makes them less re- active, particularly toward electrophil ic reagents and free radical

attack by oxygen molecules, at least compared with hydrocarbons. The

methyl groups, as might be expected, are the most vulnerable points in

the polymer. If, now, carborane moieties are interspersed along the

chain, there must be a further delocal ization of electrons in the form

of a shift toward the electron deficient carborane cage. This strengthens in particular the bond between the cage-carbon and the silicon,

but it must also further diminish the activity of the methyl groups be- cause the stability of the polymer increases dramatically. The methyl

groups remain the points of greatest vulnerability, thermally and oxidatively, but the activation energies for the reactions have to be significantly greater than in silicones. The stabilities of these compounds

are apparent in characterization studies, such as thermal gravimetric

analysis (TGA) , torsional braid analysis (TBA), modulus temperature

measurements, etc. as well as by spectroscopic analyses of degradation

products formed by various temperatures.

Thermal Gravimetric Analyses . TGA curves give dramatic testimony

to the heat resistant characteristics of the polycarboranesiloxanes.

Figs. 10 and 11 show typical weight changes as functions of temperature

-41-
c

oO

in o» r— rc»

ro r- c

x •<- <o UJ (/> CvJ <U i— I C I XI

• (0 XI' fcri i- -r- oo O 
 i CJ XI I o I. S-Wr- 3 f0

-42-


for various 10-SiB and 5-SiB polymers. Particularly with SiB-1 compounds and in the presence of air, the TGA curves are practically

straight lines up to 500°C and very little change thereafter. Silicone

polymers, by way of comparison, begin to lose weight as low as 200-300°C

and by 35O-400°C the losses become severe.

Evaluation of Data . All of the various techniques, TGA, DSC, TBA

and spectroscopic evidence by which the Dexsil and Pentasil polymers were

characterized brought out the following salient points:

t The thermal stability of a polycarboranesi 1 oxane is an inverse

function of the number of siloxy groups in the repeating unit,

as indicated by weight loss observed in TGA. Mass spectral

analysis' supports .his relationship by showing the cyclizing

groups split out of the chain in the higher S i 3 formulations.

» The methyl groups in the polymer are the points of greatest

vulnerability, oxidatively and thermally, and the farther

removed they are from the carborane cage, the more vulnerable

they become.

• Thermally, for a given Si 3 formulation, there appear to be

little differences between the stabilities of Pentasil and

Dexsil polymers.

• Thenno-oxidatively3 for a given SiB formulation, a Dexsil is

somewhat more stable with respect to the value of T than a ox Pentasil, 10-Si3-3 shows about the same resistance to oxidation as 5-SiB-l

.

• Polymers in inert environments can withstand temperatures substantially higher than in oxidative environments. The differences are generally on the order of 100° to 150°C.

• The SiB-1 formulation, both for C2B-Q and C£B- polymers is

extremely stable once it has been oxidatively cross! inked.

The TGA's of these polymers in air are practically straight

lines, showing very little gain or less of weight. This behavior is of practical importance in coatings.

-45-
• A C2BC polymer for a given Si B formulation is more tractable

than a C 0 B,~ polymer, i.e., it has a lower T and a lower T . L 10 r J g m

t The addition of small concentrations of silicon-pendant phenyl

groups improves the thermal and oxidative resistance of the

Dexsil polymers significantly. Dexsil 4000-j is more stable

than unmodified Dexsil 300 despite the fact that it has one more siloxy group in the chain.

• Proper compounding and curing improves oxidation resistance

tremendously. Without compounding or curing, the polycarboranesiloxane resins begin to crosslink oxidatively in the 270-300°C

region. With silica and iron oxide fillers and peroxide curing,

T

Qx can be raised 45-50°C.

• Para-carborane polymers are somewhat more temperature resistant

than meta-carborane polymers in that weight losses in TGA occur at somewhat higher temperatures. However, the total weight

loss that occurs up to 800°C is about the same for both polymers. Also, the para-carborane polymer has a disadvantage in

having3 a higher T and T . 3 g m

• The polycarboranesi loxanes are considerably more stable, oxidatively and thermally, than pure silicones.

e High molecular weight polycarboranesi loxanes with good tensile

strengths can be prepared by careful attention to monomer purity,

precise co-monomer ratios, and high conversion percentages for

the transition of monomers into polymer.

-46-
REFERENCES

1. (a) J. A. Potenza and W. N. Lipscomb, J. Am. Chem . Soc . , 86_, 1 874 (1964).

(b) J. A. Potenza, W. N. Lipscomb, G. D. Vickers and H. A. Schroeder,

J. Am. Chem . Soc , 88, 628 (1966).

2. R. Maruca, H. Schroeder and A. W. Laubengayer, Inorg . Chem . , 6_, 572 (1967).

3. H. A. Schroeder, Inorg . Macromol . Rev . , 1 , 45 (1970).

4. J. F. Ditter, E. B. Klusmann, J. D. Oakes, and R. E. Williams, Inorg . Chem ., 9, 889 (1970).

5. J. F. Ditter and R. E. Williams, Methyl -closo-Carboranes . Tech. Rpt. No. 7,

Chemical Systems, Inc., Office of Naval Research Contract N00014-70-C0109, June 15, 1971

.

6. S. A. Miller, Acetylene: It's Properties, Manufacture and Uses , Vol.1,

Academic Press, New York, 1965, p. 247.

7. (a) T. L. Heying, J. W. Ager, S. L. Clark, D. J. Mangold, H. L. Goldstetn,

'. M. Hillman, R. J. Polak and S. W. Szymanski , Inorg . Chem . , 2_, 1039

(1963).

(b) M. M. Fein, J. Bobinski, N. Mayes, N. Schwartz, and M. S. Cohen,

Inorg . Chem . , 2, 1111 (1963).

(c) M. M. Fein, D. Grafstein, J. E. Paustian, J. Bobinski, B. M. Lichstein,

N. Mayes, N. N. Schwartz and M. S. Cohen, Inorg . Chem . , 2, 1115 (1963).

8. (a) J. M. Makhlouf, W. V. Hough and G. T. Hefferan, Inorg . Chem . , 6, 1196

(1967).

(b) M. D. Marshall, R. M. Hunt, G. T. Hefferan, R. M. Adams and J. M. Makhlouf, J_. Am. Chem . Soc . , 89, 3361 (1967)

(c) E. L. Muetterties and W. H. Knoth, Polyhedral Boranes , Marcel Dekker,

1968, pp. 86-92.

9. B. Vollmert, Polymer Chemistry , Springer-Verlag, New York, 1973, pp. 212-214.

10. Ibid . , pp. 216-222.

11. W. Patnode and D. F. Wilcock, J_. Am. Chem . Soc . , 68_, 358 (1946).

12. W. R. Sorenson and T. W. Campbell, Preparative Methods of Polymer Chemistry , Interscience, New York, 1968 (2nd ed.), p. 385.

13. W. Noll, Chemistry and Technology of Silicones , Academic Press, New York,

1968, pp. 306-324.

14. W. R. Sorenson and T. W. Campbell, loc . cit . , p. 386.

15. R. M. Salinger and C. L. Frye, Inorg . Chem . , 4, 1815 (1965).

16. T. L. Heying, J. W. Ager, S. L. Clark, R. P. Alexander, S. Papetti , J. A. Reid and S. I. Trotz, Inorg . Chem . , 2, 1097 (1963).

-47-
17. S. Papetti and T. L. Heying, Inorg . Chem . , 2, 1105 (1963).

18. S. Papetti and T. L. Heying, Inorg . Chem . , 3_, 1448 (1964).

19. P. C. Servais, U. S. Patent No. 2,485,928.

20. S. Papetti, B. B. Schaeffer, A. P. Gray, and T. L. Heying, J_. Polym . Sci . A-l, 4, 1623 (1966).

21. R. E. Kesting, K. F. Jackson, E. B. Klusman, and F. J. Gerhart, J_. Appl . Polym . Sci . , 14, 2525 (1970).

22. R. E. Kesting, K. F. Jackson, and J. M. Newman, J_. Appl . Polym . Sci . , 15 , 2645 (1971).

23. K. 0. Knollmueller, R. N. Scott, H. Kwasnik, and J. F. Sieckhaus, J_. Polym . Sci . , A-l , 9, 1071 (1971).

24. E. N. Peters, E. Hedaya, J. H. Kawakami , G. T. Kwiatkowski , D. W. McNeil

and R. W. Tulis, Rubber Chemistry and Technology , 48, 14 (1975).
POLYELECTROLYTE MOSAIC MEMBRANES: PART II

J. F. Ditter

Chemical Systems, Inc. 1852 McGaw Avenue

Irvine, California 92705

-49-
ABSTRACT

Piezodi alysis is a unique mode of ion transfer through a membrane.

When a saline solution is forced to flow through a piezodialysis membrane, the

net flow of ions through the membrane exceeds the volume flow of water so that

the permeate becomes enriched and the feed becomes depleted in salt. Structurally, a piezodialysis membrane consists of a mosaic of alternating microdomains of cation and anion exchanging polyelectrolytes which preferably

extend uninterruptedly from the top to the bottom surfaces, thus providing

pathways for the cations and anions through the membrane.

Mosaic membranes have been fabricated in various ways, but one which

we have found to be relatively simple as well as amenable to many modifications

is made by a process called phase inversion. This consists of dissolving in a common solvent system a cation-exchanging polyelectrolyte and the precursor

polymer of an anion-exchangi ng polyelectrolyte, both synthesized with suitable

moieties that permit subsequent crossl inking, then casting this solution into a thin film and allowing the solvent to evaporate. At this point the polymers

begin to precipitate, the first one forming islands in a matrix of the second.

The membrane is then crossl inked by heating, and the precursor polymer finally

is quaternized by a simple gas phase reaction. Exploratory membranes to demonstrate feasibility have been synthesized in this manner, and salt enrichment

values up to 180% (ratio of brine water to product water) have been obtained.

-50-
SECTION I EXPERIMENTAL

1.0 PIEZODIALYSIS TYPE MASS TRANSPORT

If pure water is forced by pressure through an ion exchange membrane,

e.g., one made of sodium polystyrene sulfonate, the movement of v/ater forces

the Na counterions in the membrane to begin to move in the direction of the

water flow. The SO-" anion sites, however, are fixed in position and cannot

+ move, so the Na ions can travel only a short distance before the attractive

forces between the Na

+ and S0~~ inhibit further ion flow. There is a net

+ charge differential, 6 at the bottom of the membrane and 6 at the top, due

to the incremental displacement of the Na ions. This is the well known

streaming potential and is illustrated in Figure 1.

Figure 1. Streaming potential in an ion exchange membrane.

If a saline solution is then substituted for the pure water in Figure

1, the Na counterions in the membrane will again begin to move through the

membrane at the onset of flow, but now there are Na

+ ions in the feed to oc- cupy the vacated sites in the membrane. The Cl~ ions in the feed solution,

however, are restrained from moving into the membrane by the fixed SO^" sites

and by the streaming potential in the membrane. These forces act to retard

further flow of counterions so that both Na

+ and CiT are inhibited from moving

through the membrane. Consequently, if the water continues to flow, the feed

water becomes enriched in salt and the permeate becomes depleted (Figure 2).

-51-
1V ±

:ACI

S03-NA"

SO3-NA

4

"

S0

3 ~Na

+ IS"

Salt-Depleted Water

Figure 2. Salt rejection by an ion exchange membrane,

The effectiveness with which a given ion exchange membrane excludes coions determines its salt rejection capabilities, and rejections on the order of 50-

60% are readily attainable.

If now instead of a simple monofunctional ion exchange membrane we substitute one having alternating patches or domains of anion and cation ex- changing polyel ectrolytes , there will then be pathways for both the Na

+ and

the Ci~ ions (Figure 3), and these ions will continue to move stairstep

fashion into and through the membrane as long as they are neutralized and

r-.vo»..rv- .w

^•:oo.?.=

^+ ipiiti

Enriched

Brine

if ci - mOe.-

Figure 3. Salt enrichment by piezodialysi s.

52-
dispersed at the bottom surface. It is important to realize that the net

flow of salt through the membrane under these circumstances is greater than

the flow of water . The feed water, after salt depletion, becomes the product,

while the salt-enriched filtrate becomes the brine, or permeate.

A membrane of the type shown in Figure 3 is known as a irosaic membrane, while the ion transport process is termed pressure or piezodialysis.

For piezodialysis to occjr there are a number of requirements and important

factors to be considered.

• Pressure is the driving force which, by moving water through

the membrane, creates the charge imbalance and causes piezodialysis action to occur.

e The charge domains should extend uninterruptedly from the

top surface to the bottom. Within the membrane itself,

electrical neutrality is preserved between the fixed ion

sites and the counterions regardless of conditions outside

the membrane, so the pathways for the counterions can be

devious—so long as they are not discontinuous. If the ion

in its movement through the membrane encounters a discontinuity in the form of an adverse polyel ectrolyte, it may

cease flowing, causing localized salt rejection at that point.

e Adjacent domains should be in sufficiently close proximity

at the membrane's surfaces to provide charge neutralization

in the solutions (feed and brine) and prevent buildup of a streaming potential within a given domain. Dead space between domains should be minimal.

• The smaller the domains, the higher the mass transport of

ions because the centers of large domains are not as effectively neutralized as the edges and hence can carry less

ion flow, or current. However, there is also a lower limit

because along the interfaces between domains the polyel ectrolyte fixed sites will tend to neutralize one another and will

not be able to transport counterions. The optimum size has

not been determined, but it is generally believed to be

somewhere between 0.01 micrometers (100 Angstroms) and 1.0

micrometers.

Piezodialysi s-type flow in a mosaic was first predicted in 1932 by

Sollner [1]. Transport theories were developed by Kedem and Katchalsky [2]

and later greatly embellished and refined by Weinstein [3], by Dresner [4],

and by Leitz [5], and their respective coworkers. At the onset of our

program (August, 1972) experimental feasibility of desalination by piezodialysis action through mosaic membranes had already been demonstrated by

Weinstein [3b] and Leitz [5], utilizing various configurations such as ion

-53-
exchanger patches embedded in silicone, polyelectrolyte/latex strips, etc. Our initial approach [6] involved the synthesis of mosaic membranes utilizing

ionotropic gels [7-13] as templates on which to structure the mosaics. In the micro-capillaries of the gel, an SEM photo of which is shown in Figure 4, was inserted one of the polyelectrolytes ; in the matrix (which is 98% water

in the nascent gel) the water was replaced by the other polyelectrolyte.

Fabrication was possible on a very small scale, where the specimens could be

sliced to remove overlying surface films, but on a larger scale the approach

was fraught with difficulties. One of the polyelectrolytes always seemed to spread out on the surface, which is disastrous because even an ultrathin film

of one polyelectrolyte causes salt rejection (Figure 2). Work on this approach

was set aside when it was found the mosaic membranes could be made more practically by a phase inversion technique, as described below.

1.1 PHASE INVERSION TECHNIQUES

If an appropriate viscous solution consisting of a polymer, a swelling agent, and a volatile solvent is cast as a membrane, the polymer and the

swelling agent, because of solubility differences, will separate into domains

as the solvent evaporates [14]. If the swelling agent, which is a nonsolvent

for the polymer, is then removed either by evaporation or by leaching, the

membrane becomes perforated. Under the right set of solubility and volatility

conditions the perforations will be in the size range desirable for piezodialysis type membranes. The first test of the feasibility of this approach

[15] involved fabrication of a crude but porous phase inversion membrane

formed by dissolving equal amounts (4.25% of each by weight) of polyvinylalcohol and poly(2-methyl-5-vinylpyridine) in an organic solvent, then casting the

viscous solution as a 10-mil thick membrane. After drying, the membrane was washed with water to remove the polyvinyl al cohol . The leached membrane is

shown in Figure 5, wherein the white spots are the vacancies which had previously contained the polyvinylalcohol . The domains are on the order of 20-30

micrometers in diameter.

A porous membrane also can be produced by using a volatile swelling

agent in place of the non-volatile polyvinylalcohol. The sequence of events

is: (a) the highly volatile solvent evaporates quickly, as soon as the film

is cast; (b) as the solvent evaporates the polymer and swelling agent begin

to drop out of solution; (c) the polymer and swelling agent, if sufficiently

incompatible, coalesce and form separate domains; and (d) the swelling agent

-54-
m

Figure SEM photomicrograph of a cross-section of an ionotropic

gel membrane.

-55-
Figure 5. Phase inversion membrane formed by cast

ing a solution containing polymeric 2-methyl-5-vinyl pyridine

and polyvinylalcohol (PVA) followed by leaching with water.

White spots indicate prior location of PVA domains. 100X.

Y :

r ^^z^^'- —- 3

Figure 6. Phase inversion membrane formed by casting polymeric 2-methyl-5-vinylpyridine in a solution containing a volatile ether. The pores are very similar in magnitude

to those of the ionotropic gels. 100X.

-56-
evaporates, leaving holes in the film. Figure 6 shows a polyvinyl pyridine

membrane cast with a volatile ether as swelling agent and methylene chloride

as solvent. The capillary pores are on the order of 5-10 micrometers in

diameter.

Now, if the roles of organic polymer and swelling agent cited in

the previous examples could be taken by two suitable polyelectrolytes, then

the cast film would be transformed simply and directly into a piezodialysi

s

mosaic membrane as phase separation occurred in the film, as the solvent evap

orated. This would indeed be a significant achievement if it could be done . Polyelectrolytes, however, do not cooperate that readily, for in a solution

of two opposite polyelectrolytes the fixed ion sites on one tend to be neu- tralized by the fixed sites cn the other, which in turn leads to precipitation of both components from solution. It is possible to circumvent this

problem, however, by using only one polyelectrolyte in the casting solution;

the other exists as its organic precursor polymer, which is transformed into

the counterpart polyelectrolyte after the film has been cast and the domains

are locked in place. This is the approach that has been followed during the

past several months at Chemical Systems.

1.2 FABRICATION OF MEMBRANES

1.2.1 Selection of Polymers and Solvents for the Casting Solution

A wide variety of cation and anion exchanging polyelectrolytes

exist, but for initial experiments where feasibility was the first consideration the choice was sodium polystyrene sulfonate and poly (1 ,2-dimethyl -5-

vinyl pyridi ni urn chloride) because their monomers are readily available and are amenable to a wide variety of copolymerization reactions. Because of

the incompatibilities discussed in the previous section, only one polyelectrolyte can be tolerated in the casting solution; the other component

must be the precursor polymer for the other polyelectrolyte. Since

quaternization is a relatively simple treatment compared with sulfonation,

the decision was made to use sodium polystyrene sulfonate as polyelectrolyte

and poly(2-methyl -5-vinyl pyridi ne) as the precursor in the casting solution.

The first problem encountered with the above polymer combination

was the selection of a solvent or solvent combination that would dissolve

both polymers. The P(SSS) is soluble only in water, at least to the degree

-57-
required for membrane casting, while the other polymer, P(2M5VP), is soluble

only in organic solvents. Since one solvent must be water, the other obviously must be compatible with water, preferably miscible, and must also be

a good solvent for P(2M5VP). Since the mosaic pattern is created as the two

solvents evaporate, their volatilities should also be reasonably close together. Candidate solvents therefore had to include compounds such as low

molecular weight alcohols, acetone, dioxane, certain ethers ( tetrahydrofuran)

etc.

The various solvent combinations were studied, and the best one was

found to be methanol /water in the approximate ratio of 3:1. The casting so- lutions were made up by dissolving known concentrations of the two polymers

in their respective solvents, then mixing the two solutions together in the

desired proportions. The casting solution should be highly viscous but still

amenable to casting with a doctor blade.

1.2.2 Cross! inking Techniques

Once the membrane has been cast and the two polymers have agglomerated into their separate micro-domains, the next problem is to lock the

polymers in place so that later, when in contact with water, they cannot fuse

together and neutralize one another, cannot leach out, and cannot swell to the point where the membrane would wrinkle excessively or break loose from its

support. Initially attempts were made to crosslink the sulfonate polymer

ionically by treatment with barium chloride (barium sulfonate is insoluble),

but the domains were destroyed by the aqueous solution. Barium chloride

powder did not work either. Copolymers of SSS and 2M5VP with methacrylic

acid were then synthesized, and cross! inking attempts with hexane diamine

and hexanediol were made. Again, however, it was found that the treatment

destroyed the domains. The crosslinking agents were organic liquids, and un- fortunately they dissolved the vinylpyridine polymer before crosslinking re- actions were initiated.

The lack of success by these techniques then dictated the need for

crosslinking by non-destructive treatments, either by radiation (e.g., ultraviolet light) or by gas phase reactions which would not destroy the domains.

Hence, pendant functional groups such as vinyls, amines, methyl ol , or any

others amenable to crosslinking by these techniques, had to be included in

-58-
the chains. Cross! inking through vinyls could be effected by ultraviolet ra- diation, through amine groups by reaction with gaseous formaldehyde, through

methylol groups by reaction with gaseous HCx, or by simple heating, etc.

After considerable preliminary experimentation, two successful

crossl inking techniques that worked for both the polyanion and the polycation

chains were devised. These were:

Formaldehyde/Amide Crossl inking — This involved the reaction of

formaldehyde with pendant amide groups that had been incorporated into the

polymers by appropriate copolymerization of the primary monomers with acrylamide, i.e.,

CH~ = CH

2

I + C = 0 s»- Polyanion Copolymer

NH

2

Acryl amide

CH

2 == CH

I Polycation Precursor

+ C = 0 *— Polymer

INH

2

Acryl amide

As discussed later, crossl inking occurs when the amide is reacted with the

formaldehyde—after the membrane is formed.

Free Radical Initiated Crossl inking — This involved crossl inking

through pendant vinyl groups that had been incorporated into the chains by

copolymerization of the primary monomers with butadiene, completely analogous

to the previous equations except that butadiene was substituted for acrylamide.

Successful crosslinking v/as effected through pendant vinyls by adding an initiator and then heating.

CH

2M5VP

-59-
In addition to the foregoing successful methods, there were numer- ous unsuccessful attempts at crosslinking. In chronological order the vari- ous methods are discussed below,

1.2.2.1 Ultraviolet Crosslinking with Butadiene Copolymers — Copolymers of

butadiene (BD) with sodium styrene sulfonate (SSS) and of butadiene with 2- methyl-5-vinylpyridine (2M5VP) were synthesized, the first by emulsion polymerization and the second by solution polymerization. In copolymers of these

types a significant number of pendant vinyl groups occur because chain propagation through the first vinyl in the molecule occurs with greater facility

than through the second vinyl.

The P(2M5VP-BD) films were found to be amenable to crosslinking

by u.v. irradiation, particularly when benzophenone initiator was added.

Films of P(SSS-BD), however, could not be crossl inked, not even with benzophenone. Water interferes with ultraviolet-induced reactions, so in this case hydration of SO^

- probably prevented crosslinking.

1 .2.2.2 Crosslinking with Acrylate and Cinnamate Copolyers — Two

approaches have been utilized to try to crosslink the polymers by incorpor- . ating acrylate and cinnamate molecules in the polymer chains. The first

approach consisted of assimilation of the ally! ester in the chain during

polymerization, while the second involved synthesis of copolymers with

pendant hydroxyl groups, to which could then be attached the appropriate un- saturated moieties. In the first approach copolymers Of both SSS and 2H5VP were synthesized with difunctional vinyl monomers, i.e., with allyl methacrylate and allyl cinnamate.

CH

3 0

CH

2 = C — C — 0CH2 CH = CH2 CH = CH — C — 0CH

2 CH = CH2

Allyl methacrylate Ally! cinnamate

-60-
The polymerization reaction is supposed to occur primarily through

only one of the unsaturated linkages of each co-monomer, leaving the other

as a pendant group available for crossl inking. However, all attempts to cross- link them, either in bulk or in the membrane, failed, The second approach,

utilizing reactions between hydroxy! pendant groups and unsaturated chlorides,

was partially successful. Copolymers of vinylacetate with SSS and with 2M5VP were synthesized with no problems, and the acetate was easily hydrolyzed with

an aqueous acid to give OH functionality on the chain; likewise, copolymers

of SSS and MVP also were easily made with 2-hydroxyethylacrylate.

OH 0

I II CH

2 = C — C - 0CH

2 CH

3

.

The esterif ication of P(MVP-vtnylaTcohol), carried out in tetrahydrofuran

,

occurred readily, as follows,

--CHo - CH— + CH

OH

ch - c -a —CH

2 — CH

q

I II 0 - C - CH = CH,

J n

and films were actually cast and successfully crossl inked with ultraviolet.

However, esterification of P(SSS-vinyl alcohol) presented problems because

water is the only adequate solvent for the polyelectrolyte, whereas the an- hydrous chloride must be kept away from water. The reaction was therefore

run in formamide, which affords limited solubility of the polymer, but the

reaction was not particularly successful. Synthesis of the p-toluidine salt

of PSSS would seem to offer one way around the solubility problem, but past

experiments had indicated that the p-toluidine salt protonates the nitrogen

in the vinylpyridine ring of P2MVP. Tetraalkyl ammonium salts probably

could be used in this situation, but a more promising route to crossl inking

,

viz., acrylamide copolymers, was discovered, so the pendant vinyl approach

was set aside.

1.2.2.3 Crossl inking via Acrylamide Copolymers — Copolymers of acrylamide

with SSS and with 2M5VP were synthesized with the idea of crossl inking through

the amide groups by reactions with gaseous formaldehyde. The first step would

be formation of the N-methylolamide:

-61-
--CH

2 — CH 0

!l --CH

2 — CH

C = 0 + HCH 0

NH

The second step, cross! inking, would occur by splitting out water: —CH

2—CH— CHC = 0

A Crossl inked

Polymer

This technique was carried out successfully with both the P(SSSacrylamide) and P(MVP-acryl amide) in mosaic membranes. The membrane can be

simply placed in a closed container along with paraformaldehyde and heated at

160°C for several hours or, alternatively, basic formalin solution containing

K

2

S

20g initiator can be included in the original casting solution. In addition to crosslinking internally within a domain, this technique allows poly- mers to crosslink across domains, thereby greatly improving surface integrity.

The amide also contributes to the adhesion of the mosaic film to the supporting polyester paper, and the final product consequently has outstanding

physical strength and flexibility.

of the methylol derivative of each of the two bulk polymers by gentle, treatment with formaldehyde prior to casting. After casting, the membrane is

s.imply heated to induce crosslinking. The advantage lies in the fact that

post-treatment is simplified; the disadvantage is that some crosslinking inevitably occurs in the bulk phase prior to casting. A further modification

is to treat the methylol moieties in the membrane with gaseous HCs., which

catalyzes the crosslinking reaction. This reaction is generally unsatisfactory,

however, because protonation of the nitrogen in the pyridine ring occurs first,

causing the PMVP to become soluble in the water present in the membrane and

thereby immediately destroying the domains by combination with the polyanion.

A variation of the amide/formaldehyde linkage consists of synthesis

-62-
1.2.2.4 Free Radical Cross! inking Through Unsaturated ['pieties — As discussed in the next section, membranes made from polyelectrolytes cross! inked

by the acrylamide/formaldehyde reaction were the first successful phase inversion piezodialysis membranes. Free radical-induced crossl inking of

butadiene-containing polyelectrolytes was then re-investigated, and it was found that simple heating of the membranes (with an initiator) at about 150°C

for slightly over an hour was sufficient to produce a well -crossl inked membrane. This is in marked contrast to ultraviolet radiation, which had been

unsuccessful in inducing crossl inking in SSS polymers. The free radical

crossl inked butadiene-containing membranes had good physical properties and

negligible swelling tendencies. Moreover, subsequent testing showed that

salt enrichment values for these membranes were superior even to those of the

acrylamide-contai ning membranes

.

1.2.3 Quaternization Reaction

The quaternization of polymers of 2-methyl-5-vinylpyridine with

alky! halides is a fairly easy task. The order of reactivity with methyl

halides is iodide > bromide > chloride. The iodide goes at room temperatura,

while the chloride proceeds readily at temperatures of about 60°C (gas phase

reaction). The presence of other moieties in the chain does not appear to inhibit the reaction.

The membranes discussed in the previous section were generally

quaternized by heating in the presence of methyl chloride at 85°C for about

two hours. Calibration experiments involving weight changes in a known

quantity of P(2M5VP) on a membrane indicated that the above conditions were adequate for complete quaternization.

1 .3 DESALINATION TESTS

A large number of membranes were tested for their desalination

capabilities, but those demonstrating piezodialysis action were all fabricated from one or the other of the following systems:

a) Poly(sodium styrene sulfonate/acryl amide) +

pol y ( 2-methyl -5-vi nyl pyr i di ne/acryl ami de)

;

crossl inked with formaldehyde, either in gas state

or in formalin (in initial casting solution).

b) Poly(sodium styrene sul fonate/butadiene) + poly(2-methyl -5-vinyl pyridine/butadiene)

;

crossl inked by heating; free radical initiator.

-63-
The casting solutions were prepared by dissolving the particular copolymers

in separate solvents, then combining the solutions. For example, the P(2M5VPAA) is dissolved in methanol and the P(SSS-AA) in water, and these were com- bined to make up a casting solution in which the methanol /water ratio would

be about 3:1 by weight, while in the final mosaic membrane there would be

approximately equal volumes (to produce equal domains) of the two polyelectrolytes. The acryl amide concentration in each of the two polymers would be

about 30 mol percent because it had been found that this concentration produced domains that were on the order of 1-3 micrometers in diameter. A variation on this system involved the addition of butadiene polymer as a filler,

which served to tighten the membrane, remove holes or other defects, and generally decrease the water flux through the membrane.

After the solutions were made up they were cast as films, either

on glass plates for microscopic examination, or on porous polyester paper for

desalination testing. The solvents were allowed to evaporate for 15-20

minutes, then sections of the cast membrane were crossl i nked. With formaldehyde cross! inking, the membranes were heated in a closed container for several

hours at 160°C in the presence of paraformaldehyde or, alternatively, the same procedure but with formalin in the casting solution. Butadiene copolymers were crossl inked by the same procedure (150°C oven) except that azobis-isobutyronitri 1 e initiator was used in place of the formaldehyde treatment.

The crossl inked membranes were then quaternized at 85°C in an atmosphere of gaseous methyl chloride for about two hours. From calibration

experiments based on weight changes in the membrane, it had been determined

that the above conditions were sufficient for quaternization of the nitrogen

in the pyridine ring.

The apparatus for desalination testing consisted of an Amicon high

pressure cell equipped with a magnetic stirrer in the feed water section.

Salt concentrations in the feed and product water were determined by con- ductivity measurements and checked by chloride ion analysis, using silver

nitrate with potassium chromate indicator. The feed water was .01N in NaC£

(580 ppm) , and the highest enrichment achieved was 180% based on the ratio

of salt in the permeate (brine) to that in the depleted feed water. The test

data are shown in Table 1. The 180% enrichment value is comparable to values

reported by Leitz [16] for latex membranes and by Yama.be, et al [17], for

styrene-butadiene membranes.
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*—

c «d" CD CO •r— rcJ +-> o J3 CJ E Cu Q_ CL. E A3 "O •p— £Z o E "• -CI 4-* 4-* CD o fO +-) ,rT

its GJ >- 1 1 CO o QJ +-) *i to E o CD fO _. ,* GJ M 13 C CO ^* CO C_J t_J S- H3 CJ) " H

X !GJ

T sr. to

O GJ

LlI -cr r— T^. "O

CT + o CO •rC

Q_ CO o • GJ GJ o <; co o

~o co CO 4-* fO cz " * •* C >> s—** 13 !Z3 C3

to CO CO .Q -oC E E QJ 0) GJ a. o cu

CD QJ co "O ~o o o +-» +-> o CO CO CO LO fO •r—

</) CO o rO 03 =tts

X +-> >> >> 4-* s_ E E GJ cu cu to to 13 <_) S- S- "O CO CD CO -a

GJ o o fO c (13 CJ to o

t. 4->C *o <4- <+- n3 +-> -i- c CO e CO ro rd E OJ 4-> GJ c CL-iGJ S— E czc= cu O CO J, > JD •o nj fO O fO QJ fO E o E E 01 o_ Lu CO Z to x: to o

'o o CD to o o -a CO Ol CO s: Lu i- E

s_ o cu SS- c •r- o

GJ E uJ 4-> E GJ * * < < cC <c CO CO * * ?— CO * o >> oo

+-> CO r— C\J CO LO to

Te =tt= =«*=

-65-
SECTION 2 FUTURE WORK

2.0 SCOPE OF THE PHASE INVERSION TECHNIQUE

The fabrication of piezodialysis type membranes by the phase inversion technique is actually a relatively simple procedure, once the polymer

systems, swelling agents, etc., have been selected, synthesized and dissolved

in a suitable solvent. The big advantage of the phase inversion method lies

in the fact that the post-treatments of the membrane are minimal and relatively

easy. Membrane preparation simply involves spreading the viscous casting so- lution into a thin film, allowing it to dry, then crossl inking it by heating

or by a gas phase reaction, and finally quaternizing it by another gas phase

reaction. Moreover, since the ultimate goal is to use the membrane in a large

desalination element, e.g., a spiral wound module, then crosslinking and

quaternization could be carried out very easily after the spiral wound element

had been assembled. The element would be placed inside an oven and the requisite gases would be allowed to flow through it.

For laboratory experimentation, the phase inversion technique is

extremely versatile in scope and offers unusual opportunities to modify parameters and change the membrane's structure and composition to optimize desalting characteristics. The following possibilities exist:

• Domain size — Can be varied by making changes in polymer

molecular weights, by incorporating other moieties in the

polyelectrolyte chain (e.g., acrylamide), by utilizing

coupling agents (surfactants), or by using polymer

grafting techniques.

a Porosity, flux - Can be increased by using swelling agents

that leach out or will evaporate after the membrane is set; can be reduced by using fillers (e.g., polybutadiene)

,

which eliminate defects and reduce porosity; flux can also

be changed by changing membrane thickness.

0 Asymmetric skin — Can be produced by increasing the vaporization rate of the solvent or by post-treating the

membrane.

• Swell ing — Can be varied by varying the amount of crosslinking.

• Strength , pliabil ity, handling -Can be improved by adding

other moieties (e.g., butadiene) in the chains; moderate

improvements can be effected by adding a plasticizer (e.g.,

glycerol) which "lubricates" the membrane.
The previous discussions have been limited to flat sheet piezodialysis membranes, but there is no technical reason why they could not also

be extruded as hollow fibers. The substantially larger surface area per unit

volume of a hollow fiber desalination element versus a flat sheet, spiral

wound element, gives it a significant advantage— about 25-fold. A fiber

composed of polystyrene/polyvinylpyridine (butadiene copolymers) should have

the requisite strength to withstand the pressures in a piezodialysis desalination system. .

•

2.1 INCORPORATION OF AN ASYMMETRIC SKIN

The accomplishments that have already been achieved with exploratory

type flat sheet membranes were discussed in Section 1.3, and even with these

fairly primitive, relatively uncontrolled membranes enrichment values up to 180% were obtained. By careful variation of "one parameter at a time," if

such is ever really experimentally possible, significant additional improvements in salt enrichment should be practically a certainty.

One of the important requirements for good piezodialysis action, as discussed in the background data in Section 1.0, is that the polyel ectrolyte

domains should extend from the top to the bottom of the membrane to provide

continuous pathways for the transport of countericns. However, with a mem- brane that is 4 mils thick, which is close to minimal thickness for good

handling characteristics, it is virtually impossible to produce domains that

extend 100 micrometers (4 mils) through the membrane but which are only

1-2 (or preferably even less) micrometers in cross-section. The way around

this problem, however, would seem to be to put a thin skin on the surface, i.e.,

fabricate a membrane ,ei the r flat sheet or hollow fiber, which has a thin

asymmetric skin supported on a porous substructure, exactly analogous to the

structure of reverse osmosis membranes. In this structure the asymmetric skin

is the "working part" of the membrane, while the porous substructure merely

supports the skin and is actually superfluous for the piezodialysis transport

of ions.

-67-
REFERENCES

1. K. Sollner, Biochem, z., 244, 370 (1932),

2. 0. Kedem and A. Katchalsky., Trans. Farad, soc, 59_, 1919 (1963); ibid.,

59, 1931 (1963); ibid., 59, 1941 (1963).

3. (a) J. N. Weinstein and S. R. Caplan, science, 161 , 70' (1968);

(b) J. N. Weinstein, Ph.D. Thesis in Biophysics; "Charge Mosaic Membranes,"

Harvard University, Cambridge, Mass, (1971);

(c) J. N. Weinstein, B. J. Bunow and S. R. Caplan, Desalination, 11, 341

(1972) ; (d) J, N. Weinstein, B. M. Misra, D. Kalif and S. R. Caplan, Desalination,

12, 1 (1973);

(e) C. R. Gardner, J. N. Weinstein and S. R. Caplan, Desalination, 1_2, 19

(1973) ; (f) J. N. Weinstein, "Theoretical Studies of Mosaic Membranes for Piezodialysis," Stanford Medical Center, Final Report, Contract No. 14-30-

3145, Office of Saline Water, December, 1972.

4. L. Dresner, Desalination, 1_0, 47 (1972).

5. ja) F. B. Leitz and W. A, McRae, Desalination, 10, 293 (1972);

(b) F. B. Leitz and J. Shorr, "Research on Piezodialysi s ," Ionics, Inc.,

Annual Reports, Contract No. 14-01-0001-2333, Office of Saline Water,

May, 1972; 1973; 1974.

6. J. F. Ditter, "The Development of Mosaic Membranes (for Piezodialysis)

from Ionotropic Gel Templates," Chemical Systems, Inc., Final Report,

Contract No. 14-30-2725, Office of Saline Water, August, 1973.

7. H. Thiele and H. Micke, Koiioid-z, 111 , 73 (1948).

8. H. Thiele and G. Kienast, Kolloid-z, 127, 134 (1952).

9. H. Thiele and G. Anderson, z. Naturforschg, 10b, 677 (1955)

10. H. Thiele and K. Hallich, Koiioid-z, 15J_, 1 (1957).

11. H. Thiele and E. Schacht, a. Physik. chem., 208, 42 (1958).

12. H. Thiele and K. Hallich, Z. Naturforschg. , 13b, 580 (1958)

13. H. Thiele and K. Hallich, Koiioid-z, 163, 115 (1959).

14. R. E. Resting,. J,. Appl. Polym. Sci., 17_, 1771 (1973).

15. J. F. Ditter, op.. cit., First Quarterly Report, March, 1974

16. F. B. Leitz, Desalination, 13, 373 (1973)

17. T. Yamabe, K. Umezawa, Sh. Yoshida and N. Takai, Desalination, 1_5, 127

(1974).

18

-68-
18. "Development of Cellulose Triacetate Hollow Fiber Reserse Osmosis Modules

for Brackish '..'ater Desalination," Dow Chemical Corp., R&D Progress Rept.

No. 763, Contract No. 14-01-0001-2248, Office of Saline Water, December,

1971 .

-69-

SFfi :

-' 875

A REPORT SUBMITTED TO M. BROADHURST

,

NATIONAL BUREAU OF STANDARDS

by

L. V. INTERRANTE

GENERAL ELECTRIC CORPORATE

RESEARCH AND DEVELOPMENT

Schenectady, N.Y. 12301

-70-
ELECTRICAL PROPERTY STUDIES OF PLANAR

METAL COMPLEX SYSTEMS

Leonard V. Interrante

Physical Sciences Branch

General Electric Corporate Research

and Development

P.O. Box 8, Schenectady, N.Y. 12301

Abstract

The use of electrical property measurements to obtain information

regarding the conduction process and intermolecular interactions in molecular

solids containing planar metal complexes is discussed. The results of recent

electrical conductivity and thermopower studies on the compounds Pt(NH3

) 4 PtCl4

and (TTF)2NiS4C4H4 (TTF = tetrathiafulvalene) are described and used to

illustrate the application of electrical property measurements'.

-71-
Introduction

j The strong current interest in inorganic and organic compounds

which display pseudo-one dimensional solid state properties has been noted

in several other papers in this Symposium. This interest has been manifested

in a rather large number of special symposia^ and publications, particularly

in the physics journals, in the last few years.

In many of these compounds the "one-dimensional" solid state properties derive from interactions between planar molecular units which are

"stacked" together to form columns or even metal atom chains along one

direction in the solid. The tendency of planar molecules to stack in columns

can be understood simply from the standpoint of packing efficiency considerations although in certain cases specific bonding interactions have been

(9) evidenced by unusually short intermolecular separations. In the case of

planar transition metal complexes, the interactions among the metal and

ligand n-orbitals which occur within these stacks can provide a continuous

pathway for electron derealization along one direction in the solid, detectable

as anisotropic electrical conductivity. Such effectively one-dimensional solid

state interactions can result in unique properties and property combinations.

For example, in addition to pseudo-metallic conductivity and optical reflectivity

behavior along the stacking direction and effectively insulating character perpendicular to this direction, evidence has been obtained for unusual structural

distortions, analogous to Jahn Teller effects in molecular systems, which

(3) result in gradual metal to insulator transitions at low temperatures. In

certain cases these structural distortions are believed to give rise to

-72-
cooperative electron transport, via "charge density waves, " which presumably

enhance the conductivity at low temperatures above that which could be antic-

(3 4) ipated on the basis of ordinary one-electron scattering theory. '

In addition to systems with one- dimensional metallic properties, there

are a considerably larger number of planar metal complexes where stacking

interactions in the solid state give rise to unusual properties, including highly

anisotropic conducivity behavior, but where electronic or structural factors

(5) lead to thermally activated conductivities. Work on such "one-dimensional

semiconductors" constitutes an important area of study within the general topic

of "solids with one- dimensional interactions" and has provided much useful

information regarding structure-property relationships in these materials.

The primary objective of this paper is to illustrate, by means of

specific examples chosen from our past and current research, how electrical

property measurements can be of value in the study of the intermolecular

orbital interactions in transition metal complex systems of this type and in

deducing information regarding the solid state electronic structure. To

facilitate this discussion a brief description of electrical conductivity and some

other electrical properties has been included. For a more detailed account as

well as a description of the various experimental techniques which are used to

determine these properties, the reader is referred to any of several excellent

( 6 )

1 books on the subject.

THE MEASUREMENT OF ELECTRICAL PROPERTIES

Electrical Conductivity

The measurement of electrical conductivity is essentially the determination of the amount of charge transported per second across a unit area of
sample due to an applied unit electric field. Assuming the conductivity is

primarily "electronic" in nature (as opposed to "ionic"), as seems to be the

case for most transition metal complex solids, the charge carriers are either

electrons or their positive counterparts, "holes" and the conductivity is determined by the number of such species and their velocity (mobility) in the applied

field, i. e. , c a n u, where o is the conductivity, n is the number of carriers

and their mobility in cm2 /volt-sec. The mobility, in very simple terms,

reflects the facility with which the carrier can move through the sample and

thus, in a crystal comprised of molecular units, provides a good measure of

the intermolecular orbital interactions.

The reciprocal of the conductivity is the resistivity, p, which is the

resistance per unit cube and is measured in ohm cm; the unit of conductivity

is thus ohm-1 cm-1

. The conductivities of a number of representative materials

at 25°C are compared in Figure 1 on a logarithmic scale of ohm-1 cm" 1

. The

terms "metal, " "semiconductor, " and "insulator" imply a certain level of

conductivity, as is illustrated by the approximate ranges in Figure 1, but,

moreover, refer to the manner in which the conductivity varies with temperature as well as other characteristic electrical, optical, and magnetic properties. For a metal the conductivity generally decreases with increasing

temperature in the manner, o a l/T, whereas for semiconductors and

insulators the conductivity generally increases, often exponentially, i. e. ,

a a exp(-AE/kT).

As is indicated in Figure 1, molecular solids, and indeed most

organic and metal complex materials fall in this category, usually exhibit

-74-
rather low electrical conductivities (10 _1 ohm" 1 cm* 1

) reflecting the rather

weak Van dcr Waals interactions between the molecular units in the solid.

There are a number of molecular solids with substantially higher conductivities,

however, ranging up to ~ 800 .ohm-1 cm-1 for tetraselcnofulvalene «tetracyano-

(7) quinodimethane (TSeF • TCNQ).

In this compound and several other structurally analogous organic

and inorganic compounds the conductivity exhibits an inverse dependence on

temperature over a limited temperature region and other characteristically

"metal -like" properties are observed. Included in this group are polymeric

sulfur nitride, (SN)^, and a group of partially oxidized, square planar platinum

and iridium complexes, collectively referred to as "KCP" in Figure 1, both

of which are discussed elsewhere in this Symposium.

With the exception of these relatively few materials, most transition

metal complexes exhibit properties more typical of semiconductors with

conductivities usually less than 10" 2 ohm-1 cm-1 and a thermally activated

conductivity behavior. The thermal activation energy, which is derived from

plots of log a vs l/T, in thesecases , may result from either the production of

charge carriers, as, for example, by direct band gap excitation in an intrinsic

semiconductor, or from the carrier motion, as in systems where the conduction proceeds by a short range, thermally activated, hopping process.

In either case, extremely small amounts of impurities and crystalline

defects can play an important role in determining both the magnitude of the

conductivity and the activation energy. The elucidation of such effects is

often a difficult task, requiring careful control of sample purity and form as

well as experiments on samples in various stages of purification.

-75-
Other Electrical Properties

A characteristic feature of many semiconductors and insulators is

an increase in conductivity on absorption of light in a particular frequency

range. This "photoconducivity" usually reflects an increase in the number of

free carriers in the solid due to their photoexcitation from filled bands, donor

levels or trapping states. The spectral response and quantum efficiency of

the photoconductivity can be used to deduce information regarding the energy

band structure of a semiconductor and the carrier lifetimes (or mobilities)

.

Another electrical property of fundamental importance is the thermoelectric power, or Seebeck effect. Its sign, magnitude and temperature

dependence can provide information about the sign of the charge carriers and

their mobility as well as the band structure of the solid. It is essentially the"

voltage generated between two junctions of a material when the two junctions

are held at different temperatures and it is determined simply by measuring

the induced voltage and dividing by the temperature difference. The sign of

the thermopower is defined as the polarity of the cold junction and usually

corresponds to the sign of the majority carrier (i. e. , positive for holes,

negative for electrons). Its magnitude is characteristically small (< 100

M-V/degree) for metals and considerably larger (>100 nV/degree) for semiconductors. The temperature dependence is also usually larger for semiconductors where a relation of the type S = B/T + K (where S is the thermopower and B and K are constants) is often observed. Various theoretical

expressions of this general form have been derived on the basis of band theory

and used to relate the experimental data to such features of the conduction

-76-
process as the position of the Fermi level in relation to the band edges, the

effective mass of the carriers, the electron /hole mobility ratio and the nature

of the carrier scattering mechanism.

have been

A variety of other types of electrical measurements/employed in the

study of semiconductor materials. Hall Effect measurements have been used

to determine the sign and concentration of charge carriers as well as, in

conjunction with conductivity measurements, to deduce mobilities. The

mobilities, which are quite sensitive to the intermolecular orbital overlaps

in molecular solids, can also be determined directly, with less ambiguity, by

injecting a pulse of charge carriers, using light or an electric field, and measuring their transit time over a known distance in a known field. Although

such methods have proven quite useful in the study of many inorganic semiconductors they have not found wide application thus far in work on molecular

solids due, perhaps in part, to difficulties in obtaining suitable single crystal

samples of appropriate dimensions, as well as the somewhat higher degree of

sophistication required for their meaningful application. For details regarding

these and the various other electrical property measurement methods which

(6) are not discussed here, the previously mentioned reference sources should

be consulted.

THE APPLICATION OF ELECTRICAL MEASUREMENTS

TO THE STUDY OF SOME METAL COMPLEX SYSTEMS

Magnus' Green Salt

The crystal structure of Magnus' Green Salt (MGS), [Pt(NH3 ) 4 Pt Cl4 ],

is illustrated in Figure 2. Of particular interest are the linear chains of Pt

atoms which result from the columnar stacking of the constituent planar complex

-77-
units. The Pt-Pt separations within these chains (3.25A) 'is substantially

shorter than the separations between chains (6.39 A) suggesting the possibility

of highly directional solid state interactions. The first evidence for the

existence of such interactions was the green color of this compound which was

not the expected consequence of the combination of the colorless Pt(XH3

) 4 2+

and pink PtCl4

2 ~ ions. Spectral studies carried out over the past 25 years on MGS have led to the identification of the source of the green color as a

"window" in the absorption spectrum at ~ 20,000 cm-1 arising from a red

shift and intensification of the largely intramolecular "d -» d" transitions on

the PtCl4

2 " ion. (9)

In one of the earlier studies of this absorption spectrum an apparent

broad, strong, absorption band was observed in the near infrared region in

the vicinity of 6000 cm which was thought to be possibly intermolecular in

origin. This observation led to the postulation of an energy band description

for the electronic structure of MGS which has been widely used in subsequent

work on this and other "metal-chain" systems (Figure 3).

The extended interaction of the filled d o and emptv p orbitals on z, z

the platinum atoms in the linear chains is viewed here as giving rise to energy

bands of appreciable width in the solid, much like the energy bands in covalent

inorganic semiconductors, only highly directional in character. The "near

infrared absorption band" was attributed to transitions across the "forbidden

energy gap" between these bands, which then, presumably amounts to <1 eV.

The possibility that thermal or photoexcitation of electrons between

these bands could lead to mobile charge carriers in either or both bands, and

-78-
consequently anisotropic semiconductivity or photoconductivity, was

anticipated. Subsequent observations by Collman and co-workers^^ and by

(12) Gomm, Thomas, and Underhill verified these predictions and, moreover,

gave results which seemed to be in reasonable quantitative agreement with the

intrinsic band model description in Figure 3. This agreement was short lived,

(13) however, as later spectral studies on single crystals of MGS failed to

substantiate the earlier claim of a strong absorption band in the near infrared,

as would be anticipated from the presumed band gap of <1 eV, and semi-

(14) quantitative band structure calculations led to an estimate of 4.5 eV for the

d^" Pz band gap, which would be characteristic of a good insulator.

To answer the questions regarding the origin of the conductivity in MGS

and the nature of the solid state electronic interactions raised by these observations, the growth of suitable single crystal samples of MGS and a detailed

study of their electrical properties was undertaken. The subsequent develop-

(15) ment of a silica gel procedure for the growth of MGS- crystals permitted,

for the first time, the preparation of large, high quality crystals of appreciable

cross section. Rectangular parallelepiped crystals 1-2 mm long and up to

0.7 mm x0.7 mm in cross-section were obtained in this manner and, after

screening for defects by examination under a microscope and study of the

crystal morphology by x-ray precession methods, were mounted for conductivity

and thermoelectric power measurements. Conductivities were measured using

(6)

the standard four-electrode, voltage probe method, with two end contacts

and two voltage probes attached along one direction in the crystal, and also

( 1 C) by the Montgomery method with four electrodes at four parallel edges of
the crystal, to determine the conductivity anisotropy. Contacts were made

using Dupont silver paint #7941 and fine gold wire leads.

A typical log o vs l/T plot obtained in the voltage-probe studies is

illustrated in Figure 4. The linearity of this plot over the wide temperature

range studied (120° to 350°K) suggests that we are dealing with one thermally

activated conduction process in this temperature regime.

Measurement of the conductivity anisotropy both by four-probe mea-

' (16 17) surements on individual samples and by the Montgomery method ' gave

values in the range 18-* 25/1 for the ratio of the c (metal chain direction) and

a axis conductivities. This is somewhat less than the anisotropy exhibited

(3 18) by other one dimensional systems ' but is still basically consistent with

the suggestion that the predominant solid state interactions in MGS are along

the platinum chains.

A detailed study of the conductivity as a function of frequency was not

carried out; however, preliminary two electrode A.C. measurements at room

temperature on a single crystal sample indicated essentially no change from

(17) the D.C. conductivity value with A.C. frequencies up to at least 1000 hertz.

This observation is in agreement with expectations for band-type semiconductors

where the carriers are relatively mobile in an applied field.

In addition to these conductivity studies, measurements of the thermopower were carried out on several crystals as a function of temperature using

two small gold-Advance thermocouples attached to the ends of the crystal with

(17) silver paint. The crystal and thermocouples were suspended from single

crystal quartz blocks, one of which was electrically heated to provide the

-80-
required temperature gradient. In each case positive thermopower values

were observed, suggesting that holes are the majority carriers. The large

magnitude of the thermopower and its essentially linear dependence on 1 /T

(Figure 5) is consistent with previous observations on semiconductors and

with the expression, S = k/e [AE/kT + A], derived by Fritzsche for a semi-

(19) conductor in which only one band is involved in the conduction process.

The AE in this expression is basically the activation energy for charge carrier

production and, in the case of a band type semiconductor is equivalent to the

thermal activation energy for conductivity. The substantially higher value

observed for the conductivity activation energy in this same crystal could

arise, in part, from an activation energy associated with the charge carrier

motion, as in a narrow band, hopping type semiconductor.

The results of the voltage-probe D.C. conductivity measurements

on 19 different crystals of MGS obtained from 4 crystal growth preparations

are summarized in Table I. These data reveal several interesting features

regarding the conduction process in MGS. In particular, whereas the room

temperature conductivities of crystals obtained from the same preparation are

in reasonably good agreement, the variation from one preparation to the next

is as much as three orders of magnitude. A marked variation in the thermal

activation energy for conductivity is also apparent between preparations with,

in general, a lower thermal activation energy for the samples of higher conductivity. Careful examination of these crystals under a microscope and by

x-ray precession methods revealed no apparent structural or morphological

differences among the samples from different preparations. Microanalytical
determinations indicated small amounts (ppm level) of other transition

elements (primarily Fe, Cu, and Pd) but no obvious variations in composition

from one preparation to the next.

TABLE I

D.C. Conductivity Data for MGS Crystals

3,

c-Axis Thermal

Number of Conductivity Activation

Preparation Samples at 25°C (ohm-1 cm"1

) Energy (eV)

A 6 4.7(±2.4) x 10" 5 0.352 (±0.033)

B 3 8.5(±4.2) x 10" 4 0.257 (±0.025)

C 4 1.3(±0.3) x 10" 3 0.255 (±0.020)

D 6 7.5(±1.6) x 10~ 3 0.212 (±0.012)

aAverage values with average deviations in parentheses.

By means of additional experiments carried out using the same

Pt(NH3 ) 42+ and PtCl4

2 ~ solutions, it was shown that certain solutions consistently gave crystals of higher conductivity, suggesting that differences in

the composition of these solutions were responsible for the observed conductivity variations. On the basis of these findings and the previously

mentioned arguments against the intrinsic band model, it was suggested that

(13a, 20)

the conductivity in MGS was impurity dominated.

The first definitive information regarding the nature of these

impurities was provided by EPR measurements on MGS carried out on both

single crystal and powder samples prepared under different experimental

(21) conditions. An axially symmetric resonance was observed in the single

-82-
crystal samples which was identified, on the basis of the g- values and the

observed hyperfine pattern, as arising from an electron in a d^-like state

extending over several Pt atoms. Spectrophotometric analysis of the solutions used to prepare MGS and doping experiments suggested further that the

IV

source of these unpaired electrons were Pt complexes present in the solutions. These Pt^ complexes apparently induce a partial oxidation of the

Pt^ ions in the solid which is compensated by the addition of negative ions

(presumably halides), either at interstitial sites or as a replacement for the

neutral NH3 groups. The presence of such halide ions, particularly at

interstitial sites, could facilitate electron transfer between the platinum

chains, thus accounting for the observation of the substantially lower (18-25X)

but still significant conductivity perpendicular to the metal chain direction

IV II in MGS. The existence of Pt species in the nominal Pt complexes used

to prepare MGS was found to be a general occurrence, presumably due to air

IV

oxidation or to incomplete reduction of the Pt starting material in the

preparation of the Pt^ complexes.

EPR studies on some of the same crystals employed in the previously

mentioned conductivity studies revealed a general correspondence between the

intensity of the EPR resonance and the conductivity of the crystals, thus

establishing a relationship between the impurity induced conductivity effects

and the presence of "Pt^-like" states in the solid.

Using the available information regarding the nature of the "impurity"

states in MGS and the results of the semiquantitative band structure calculations,

a modified "band model" for the MGS electronic structure can be constructed

-83-
which appears to account for much of the available data.' This model (Figure 6)

is similar to the intrinsic band model proposed by Miller,

^

in that n &

z

2 and

n P

z

" bands of significant width are postulated; however, consistent with the

theoretical calculations and spectral observations^' here the d 9 - p z band gap is on the order of 4.5 eV and acceptor levels, corresponding to the

Pt^-like states localized in the vicinity of the charge compensating defects,

have been introduced close to the top of the d^band.

Intrinsic MGS in this context would be a good insulator and the observed conductivity is attributed entirely to the presence of the "impurity"

states. Thermal excitation of electrons from the d^ band into these acceptor

levels should lead to hole conduction in the d „ bands, consistent with the observed "p-type" conductivity behavior. Also the essentially frequency independent conductivity as well as the weak character of the photoconductivity

response observed by Collman^^ in the near infrared is understandable on

this basis, as is the lack of any strong absorption bands in this region, considering the relatively low concentration of impurity states present [200 ppm

n Pt^ n sites estimated by EPR

^ ]. It is also possible to account for the

apparently smaller thermal activation energies observed for the crystals of

higher conductivity by considering the likelihood of impurity banding in these

presumably more highly doped samples.

Although this extrinsic band model can be used to account for much

of the available information concerning the electrical properties of MGS,

especially in view of the thermopower data obtained, the alternative possibility

that conventional band theory is not appropriate to MGS and that a more

-84-
localized description of the electronic structure is required clearly cannot

be discounted at this point. A definite answer to this question must await

further studies on this system, including a direct determination of the charge

carrier mobility.

(TTF)2 NiS4C4H4

Bis(tetrathiafulvalene)-bis(l, 2-ethylenedithiolene)nickel [(TTF)2 NiS4C4H4 ]

is a member of a new series of n-donor-acceptor compounds prepared by the

interaction of tetrathiafulvalene (TTF) with neutral bis-dithiolene metal

(22) complexes. It crystallizes from acetonitrile solution as large (~2 mm on

a side) single crystals suitable for detailed conductivity measurements. The

results of such measurements, when examined in the light of the other solid

state properties and information obtained from a complete three-dimensional

crystal structure determination, suggest specific interactions- of a quite directional character among the constituent planar molecular units in the solid

and thus provide a good illustration of the utility of electrical conductivity as

a tool for investigating solid state interactions.

In addition to the conductivity studies, electronic absorption spectral,

magnetic susceptibility and esr measurements were carried out on this

compound. ^^a ^ The results indicated that charge transfer between the

neutral diamagnetic TTF and NiS4C4H4 units had occurred in the solid state

to give paramagnetic NiS4C4H4" ions. These were identified by both their

characteristic absorption spectrum and by their anisotropic g-values. The

magnetic measurements indicated essentially Curie type paramagnetism but

with a Curie constant appropriate for only one unpaired electron per

-85-
(TTl'^Ni^C^U formula unit. This was identified as the electron on the

NiS4C4

l[ 4 ~ ions on the basis of the esr and spectral results. The fate of the

+

electron left on the TTF units after charge transfer is suggested by the

(22b) results of the structural investigation.. This compound crystallizes in

the monoclinic space group C2 /m with a = 25.80A, b = 10.67A, c = 9.99A

and 3 = 119. 67A.

Views normal to the (010) and (100) planes are shown in Figures 7

and 8, respectively. The structure consists of four (TTF)2 XiS4C 4H4 formula

unit cell molecules

per / with the TTF and NiS4C4H4 / arranged in alternate strips parallel

to the (100) plane. The NiS4C4H4 units are oriented with their molecular

planes parallel to the (100) plane and are located at y = 0 and 1/2, well

separated from one another and the other molecules in the unit cell. Three

structurally distinct TTF molecules occur, labeled I, II, and III in the

figures.

The molecules I and II form a columnar stack along [010] with the

two units at II and 11' in Figure 8 rotated by 60° with respect to those at I and

in a fully eclipsed configuration. These two units (II and II') are separated by

3.48A, suggesting a significant bonding interaction. These are identified as

the TTF+

ions in the structure which are presumably held together in an

(23) eclipsed configuration by means of interaction of the half filled b lu orbitals

on the two units. The electrons left after charge transfer are thus presumably

paired up in the resultant bonding molecular orbital. These (TTF+

) 2 dimer

units are effectively connected to one another in two dimensional sheets parallel

to the (100) plane by means of the neutral TTF molecules at I and IE. Those

-86-
o f > at I are separated by 3. 60 A from the (TTF ) 2 pairs and could potentially

interact through overlap of the blu rr-orbitals on each unit. The ones at III + ° also make close sulfur- sulfur contacts to the TTF units in the dimer (3. 51 A)

thus bridging these dimers together along the [001] direction (Figure 9). In

this case the interaction, if indeed one occurs, must involve the n-orbitals

of the III unit and the a-orbitals of the (TTF+

) 2 dimer.

Using single crystal samples cut into rectangular parallelepipeds of

~1.0 mm x 0.7 mm x 0.4 mm dimensions, conductivity measurements were

(16) carried out by means of the Montgomery method, with contacts placed at

four parallel edges of the samples. Single crystal x-ray precession measurements were used to determine the relationship to the principal crystallographic

directions. In this manner the conductivities along the [010] and [001] direction and an approximate value for. the conductivity perpendicular to the

(100) plane were determined as a function of temperature. A thermally

activated conductivity behavior much like that in MGS was observed with a

thermal activation energy of 0. 23 ± 0. 02 eV which was approximately independent of direction. The conductivity, however, showed a strong direction

dependence and was found to be highest along the [010] or TTF stacking direction in the solid. The value observed here (7.4 x 10~ 3 ohm" 1 cm-1

) is

relatively high on the scale of molecular semiconductors and indicates an

appreciable n -orbital interaction among the TTF units in the stack. The

conductivity along the [001] axis, although definitely lower than that along

[010], is also appreciable suggesting that the TTF o -tt orbital interactions

in this direction also provide a pathway for electron derealization in the solid.

-87-
The lowest conductivity value determined (~5.0 10 : ohm" 1 cm" 1

)

is that perpendicular to the (100) plane, through the NiS4C4H4 units, where

the interatomic separations are relatively large and the orbital interactions

are weakest.

The origin of the conductivity in this compound is not yet known with

certainty, although it is tempting to speculate that the electron pair presumably

involved in the (TTF ) 2 binding can be thermally activated into conduction band

states to produce carriers. Alternative mechanisms, perhaps even involving

impurity species, certainly csmot be discounted at this point, especially in

view of the results obtained with MGS. Further investigations of this unusual

material are currently in progress.

ACKNOWLEDGEMENT

This work was supported, in part, by the Air Force Office of

Scientific Research (AFSC), United States Air Force, under contract

F-44G20-71-C-0129. The contributions of Drs. H.R. Hart, Jr., I. S. Jacobs,

J. S. Kasper, G. D. Watkins, and S.H. Wee to the work described herein are

also gratefully acknowledged.

-S3-
LITERATURE CITED

1. NATO Advanced Study Institute on "Low Dimensional Cooperative

Phenomena and the Possibility of High Temperature Superconductivity, " Starnberg, Germany, Sept. 19 74; German Physical Society Conf. on "One Dimensional Conductors, " Univ. ov Saarbrucken, July 10-12, 1974.

Symposium on "Conducting Organic and Transition Metal Salts, " Lake

Arrowhead, Calif., May 1974, ACS Symposium on "Extended Interactions Between Metal Ions in Transition Metal Complexes, 11 Los

Angeles, Calif. , April 1974, and "One- Dimensional Physics Workshop, " Boseman, Montana, July 1973.

2. Kistenmacher, T.J., Phillips, T.E., and Cowan, D.O., Acta Cryst. B,

30, 763 (1974); Krogmann, K. , Angew. Chem. Internat. edit. 8, 35 (1969).

3. Zeller, H. R. , Adv. Solid State Phys., 13, 31 (1973).

4. Tanner, D. B. , Jacobsen, C.S., Garito, A.F., and Heeger, A. J.

,

Phys. Rev. Letters 32^, 1301 (1974).

5. Interrante, L. V. , Proc. NATO ASI on "Low-Dimensional Cooperative

Phenomena on the Possibility of High Temperature Superconductivity"

Starnberg, Germany, Sept. 1974; ibid. Underbill, A. E.

6. Gutmann, F. and Lyons, L. E. , "Organic Semiconductors, " John Wiley

and Sons, Inc., New York (1967), "Methods of Exper. Physics. Solid

State Phys., K. Lark-Horovitz and V. A. Johnson, eds. , Vol.6, Pt. B,

Academic Press, N.Y. (1959); and references therein.

7. Engler, E.M., private communication; Chem. Engr. News, Sept. 30,

1974, p. 18.

8. Atoji, M., Richardson J.W., and Rundle, R. E. , J. Amer. Chem.

Soc. 3 01 ? (1957).

9. Martin, D. S. , Jr. , Rush, R.M., Kroening, R. F. , and Fanwick, P. F.

,

Inorg. Chem. 1_2, 301 (1973); Day, P., Inorg Chim. Acta Rev. 3_, 81 (1969);

Anex, B. G. , ACS Symposium Series, "Extended Interactions between

Metal Ions in Transition Metal Complexes, " American Chemical Society,

L. V. Interrante, ed. , Vol. 5 (1974); Day, P. , ibid; Martin, D. S. , ibid.

10. Miller, J. R. , J. Chem. Soc. 713 (1965).

11. Collman, J. P. , Ballard, L. F. , Monteith, L. K. , Pitt, C.G. , and

Slifkin, L. , in "International Symposium on Decomposition of OrganoMetallic Compounds to Refractory Ceramics, Metals and Metal Alloys, " K.S. Mazdiyasni, Ed., Dayton, Ohio (1968), pp. 269-283.

-89-
12. Gomm, P.S., Thomas, T.W. , and Underhill, A.E., J. Chem. Soc. (A)

2154 (1971).

13 a. Irishman, E. and Interrante, L.V., Inorg. Chem. 11, 1722 (1972);

b.Day, P., Orchard, A.F., Thomson, A. J., and Williams, A. J. P. , J. Chem. Phys. 43, 3763 (1965).

14. Interrante, L. V. and Messmer, R. P. , Inorg. Chem. 1_0, 1174 (1971).

15. Henisch, U.K., "Crystal Growth in Gels, " Pennsylvania State University

Press, Univ. Park, 1970.

16. Montgomery, H.C., J. Appl. Phys. 42, 2971 (1971).

17. We are indebted to II. R. Hart, Jr. and W. R. Giard of the GE Corp.

Res. and Dev. for carrying out these measurements.

18. Cohen, M.J., Coleman, L. B. , Garito.A.F. and Heeger, A. J. , Phys. Rev. BIO, 1298 (1974).

19. Fritzsche, H. , Solid State Commun. 9, 1813 (1971).

20. Interrante, L.V., J. C.S. Chem. Commun. 302 (1972).

21. Mehran, F. and Scott, B.A-. , Rev. Letters 31, 99 (1973);

Scott, B.A., Mehran, F., Silverman, B.D., and Ratner, M.A.,

ACS Symposium Series, "Extended Interactions between Metal Ions

in Transition Metal Complexes, " L. V. Interrante, ed. , Vol. 5 (1974).

22a. Interrante, L. V. , Browall, K.W., Hart, H. R. , Jr., Jacobs, I. S. Watkins, G. D. , and Wee, S.H., J. Am. Chem. Soc, in press.

b.Kasper, J.S., Interrante, L.V. , and Secaur, C.A., J. Am. Chem. Soc, in press

2.3 . Gleiter, R. , Schmidt, E. , Cowan, D.O., and Ferraris, L. P. , Elec.

Spectr. and Related Phenom. , 2, 207 (1973).

-90-
Figures

Figure 1. Approximate conductivity scale for some representative solid

state materials.

Figure 2. The crystal structure of Magnus 1 Green Salt.

Figure 3. Energy band model for MGS [Adapted from J. R. Miller,

J. Chem. Soc. 713 (1965)].

Figure 4. Representative log p vs 1 /T plot for a MGS crystal wired for

D.C. voltage probe measurements along the c axis.

Figure 5. The thermopower of MGS as a function of l/T. The slope of

the log p vs l/T curve for this same crystal is included for

purposes of comparison.

Figure 6. Extrinsic band model description for the electronic structure

of MGS. The acceptor levels correspond to localized n Pt* -

like" states, each containing one unpaired electron.

Figure 7. The unit cell of the (TTF)2 NiS4C4H4 crystal structure viewed

down [010], The molecules whose centers are at y = 1/2 are

darkened; except for molecules labeled II, all other molecules

have their centers at y = 0. The three types of TTF units discussed in the text are. identified by Roman numerals.

Figure 8. A view of the (TTF)2NiS4C4H4 structure normal to (100) showing

the three types of TTF molecules (labeled I, II, and III).

Figure 9. Interaction of TTF units in (TTF)2 NiS4C 4H4 .

91-
THE SYNTHESIS AND ELECTRICAL PROPERTIES OF METAL MERCAPTIDES

OF 1 ,4-DIMERCAPTOBENZENE

By G.N. Schrauzer and H. Prakash, Department of

Chemistry, University of California

at San Diego

Special Report to Mr. M.Broadhurst

National Bureau of Standards, Washington D.C.
AIC4032^A

REVISED.

THE SYNTHESIS AND ELECTRICAL PROPERTIES OF TRANSITION METAL MERCAPTIDES

OF 1 ,4-DIMERCAPTOBENZENE

* G.N. Schrauzer and H. Prakash

Department of Chemistry

The University of California, San Diego

Revelle College, La Jolla, Ca. 92037

ABSTRACT:

The synthesis of a number of new transition metal mercaptides of the

ligand 1 ,4-dimercaptobenzene is reported. Several of these mercaptides,

which are regarded as S-bridged polymers, behave like semiconductors within

the temperature range investigated. An interesting result of the study is

the relatively low electrical resistivity (P = 40 ohm* cm at 25°C) of the

Cu(I) complex of composition [Cu-S-C^H^-S-Cu]^. Copper thiophenolate

,

[C,H 1 r SCu] is also found to behave like a semiconductor, with an electrical

6 5

J n

' 4 ° - resistivity of 5.1 x 10 ohm-cm at 25 C. The reaction of 7,7,8,8-tetracyanop_-quinodimethane (TCNOJ with Cu(I) complexes cleaves the Cu-S bonds and

leads to the formation of the Cu(I) salt of the TCNQ radical anion, Cu

+TCNQ".

RECEIVED

MAY 21 1974 1NORG. Cri£M,

* To whom correspondence should be addressed.
INTRODUCTION: .

Extensive studies of the coordination chemistry of unsaturated or aromatic

2-5

1,2-dithiol ligands have been reported , and semiconductor behavior has

been noted for transition metal complexes of c-dithiodiketones , dithiooxamide

6-8

(rubeanic acid) and N-substituted dithiocarbamates . . However, no information

is available concerning 1,4-dimercaptobenzene and other aromatic polythiols

as potential ligands. We became interested in these ligands and their

coordination polymers with the object of finding new thermally stable materials

having semiconducting properties. The ligands chosen meet the requirements

to form complexes with these properties. First, they are thermally stable

and possess donor atoms separated by an aromatic ring. Secondly, each

ligand can bind two metal atoms, and substantial back-coordination of the

metal d electrons to the ligand-based antibonding orbitals as well as the

formation of sulfur-bridged metal chains could facilitate electron transport.

In this paper, we report the synthesis and the chemical and electrical

properties of a number of new polymeric mercaptides of 1,4-dimercaptobenzene

having the general formulae [M-S-C^H^-S-M]^ (M=Cu(I) and Ag(I)) and

[M-S-C^H-S-] (M=Cu(II), Hg(II), Pb(II), and Ni (11)) . For comparison, the

6 4 n properties of copper thiophenolate are also given.

(

-94-
EXPERIMENTAL:

Physical Measurements . The infrared spectra of the complexes were obtained

-1 from KBr pellets, using a Beckman Model IR-33 for the 4000-600 cm range

and Perkin-Elmer Models 180 and 457 for the 600-300 cm" range. X-Ray powder

patterns were obtained on a G.E. XRD-6 diffractometer with Cu K<* radiation

and a crystal monochromator to eliminate the Cu Kp line. The X-ray tube voltage

O was 45 kv; the amperage 15 ma; the entrance slit 1.0 medium resolution and

e the exit slit 0.2 . The proton magnetic resonance spectra were recorded on

a TR-60 spectrometer. Solid state absorption spectra of complexes wherever

possible were obtained on KBr pellets using a Beckman Model DK-2A

spectrophotometer.

Synthesis of 1 ,4-Dimercaptobenzene . The ligand 1 ,4-dimercaptobenzene was

prepared via the reductive cleavage of 1 ,4-bis (ethylthio)benzene according

9 to the method of Adams and Ferretti. A solution of p-dibromobenzene in

2,4-lutidine was treated with the sodium salt of ethyl mercapt an and catalytic

amounts of cuprous bromide to form the thioether.*^ The thioether was

subsequently cleaved by sodium in liquid ammonia. The sodium salt of 1,4-

dimercaptobenzene was isolated after evaporation of liquid ammonia. The

free dithiol was obtained by treatment of the aqueous solution of the

sodium salt with hydrochloric acid. The ligand was further purified by

o vacuum sublimation before use, mp 97.5-98.5 C.

Preparation of Metal Complexes . In general the metal complexes were prepared

by mixing under argon hot solutions of the appropriate metal compound (cupric

chloride, cuprous chloride, mercuric chloride, silver acetate, lead acetate,

and nickel tetracarbonyl) and dithiol in stoichiometric amounts. Argon was
a

toa—

cu

•J

cu

;>: 2o»-i E-i

i toz1H

CU=

cuo

COcu

—I

cuc§

CU<u»—I

to

>-Kcu

to

cuCO

>-

•J<

cu

cuEoo U CJ oo

I/) o co

en < u ou o

CNA^ CO O i-H

Oo o

to

toA

t-~ uO

O

rO

toA o

o»

UO00CM

L.T

O CO 00

O

(NtoA

CO LO

LO o oCO

CO o

CO CO

toA

Cl CM T LP,

LO

to to

co ^

r-^ lo

to ci Cl Cl

O Cl O Cl o o co oo

-OO LO UO

U0 CN CN CN 00 O CO

Cl Cl

LO UO

U0 U0 o o to to

L0

O

CO LO

CO c-i CN cs,

\0

LO CN o ci

CO CO

CM CN

CO CO co r-^

to to

CN CN

CN

O

LO L0 o to

CN CN

CO

O

U0 L0

—i cn ci r-» O ^ —I Cl L0 CN Cl

Cl CO

CN CN

to to

CN

O

CN Cl t to CN

O

to o

CN Cl Cl vCCl Cl

L0 U0CN

O L0

to —<

cn to O r»» o to O CN

L0 LO

to to

CN CN

to to CN CN CN CN

O O.

— —i

CN CN CM CM

—i O

CN CN \0 o to to c3Ou3O

CD CD OCN

CO

CN

C3 2

<J 1)o

c3

a o

>• c3OL< £0

CJ

4-> o 4-> CO *-> •(-> to es cd 3 en

CD 2 -3 o o o > 1 ,<i 1 • 1 1 LO o o o i—( o o > o CN CN o _CN CN o H

to CN to CN CN

u ent

u0O

i-l w

cct

ar c

L0to

f-i tn cu o a * H o ^

to c c c c +-> +J f 1 H • H rT c 3 Is 'a' c c in 1 U1 CJ1 u < c 1 1 1 1

rs od

3" CN i to1 to1 to to• to1 to1 to1 COI Vip>

0)1) on ry

COi _-*r <* >* CJ c 3 cu 4-1 ~o vO ~o ~\o C -a •H CJ

X cj

uu

Uu

u

u Isu c/l CJ

CD 1 1 1 1 1 1 1 u 1 •3

O 1 ( to CO to CO to to to CO to CJ E

•rt co CU 1 1 1 1 1 1 LO V i

+-> e t D 3 _6J5 H rt 2 O

X 3 o u 3 CJ < cu u o CJ u u ' 1 CJ

leu Its o-o mpl

-T3 >s n o o u "Z. 2 CJ

+-> c

cu f—l CN to L0 Cn 00 cn J3 2 *

CJ

CJ •aso

cuauxc3O3

cj-I touI toI 3

CJ

two

4)3

+JX

-96-
used to prevent the oxidation of dithiol in air. The complexes were filtered,

washed successively with ethanol and ether, and dried i_n vacuo at 150-200°C.

The Cu(I) complex was also synthesized by heating an intimate mixture of

freshly prepared cuprous chloride with excess dithiol under argon in the

temperature range of 120-200°C. The excess ligand was removed by vacuum

sublimation at 200°C. Copper thiophenolate was prepared by refluxing freshly

prepared cuprous chloride and thiophenol in ethanol under a blanket of

argon. The pale-yellow solid was filtered, washed with boiling ethanol

and benzene. The solid was dried in vacuo at 150°C. The analytical data, colors,

decomposition temperatures and solvents used are given in Table 1.

Reactions of 7,7,8,8, -Tetracyano-p-quinodimethane (TCNQ) with Cu(I) Complexes

of Thiophenol and 1 ,4-Dimercaptobenzene ,

In a typical reaction, a powdered mixture of [CuSC^H^]^ and TCNQ in 1:1.5

mole ratio was charged into a Pyrex test tube and heated to 100°C in^an oil

bath under a blanket of argon. After four hours, the white crystals which

deposited on the colder parts of the test tube were carefully removed and

identified as diphenyl disulfide, C

&H SSC6

H , mp 60-61°C. The melting point

reported for diphenyl disulfide is 61-62°C.** The blue reaction mixture was

then freed of unreacted TCNQ by vacuum-subliming the latter at 1S0-200°C. The

X-ray powder diffraction pattern of the blue-black solid left in the sublimation

pot was in agreement with that, of Cu

+TCNQ prepared by the method of Melby, et al . o The interplanar spacings (d values in A) were: 7.96, 5.64, 5.04, 3.97, 3.53,

3.11 for Cu

+TCNQ* obtained in this study, and 7.96, 5.65, 5.05, 3.98,

+ i 12

3.53, 3.12 for Cu TCNQ prepared by Melby, et al . , method. Similar reactions

occurred when [CuSC^H^]^ and TCNQ were suspended in benzene at room temperature

or heated in sealed Pyrex tubes above 45°C for several hours.

-97-
The Cu(I) complex of 1,4-dimercaptobenzene was similarly reacted with

TCN'Q in a sealed Pyrex tube in the temperature range of 120-160°C. The X-ray

powder diffraction pattern of the reaction mixture revealed the presence

of Cu

+TCNQ~ . It is reasonable to postulate that the other product was the

13

polymeric sulfide, -

C

S-C

6H4~ s ") n

> which is known to be amorphous. No further

attempt was made to characterize the polymeric sulfide as it could not be

separated from the reaction mixture.

Reactions of Metal Cc-plexes with Organic Halides. A typical reaction was

carried out by refluxing a sample of the mercaptide complex with excess

organic halide (allyl bromide for the silver complex and methyl iodide for

all other complexes) overnight. The insoluble solid residue in each case

was filtered, washed with chloroform and dried in air. The X^ray powder

diffraction pattern of the residue showed that it was either AgBr or Cul

depending whether the silver complex or the copper complexes were reacted.

The insoluble solid residue obtained from the reaction of Hg(II) complex

with methyl iodide was purified, twice from a N,N-dimethylfornamide-methanol

mixture. The very light yellow solid after drying melted at 145-145. 5°C. The

proton chemical shifts (in deuterated dimethylsulfoxide, t relative to

(CH^)^Si) were: 2.32 [quartet due to aromatic protons, J = 20 cps) and 7.10

(doublet due to methyl protons, J = 17 cps) in the area ratio of 9:30,

consistent with the dimethylsulfonium iodide salt of 1 ,4-bis (methylthio) benzene,

I (CH^) (CH^) 2^ • The residue obtained after evaporation of N,Ndimethylformamide and drying was shown to be Hg^ by its X-ray powder

diffraction pattern.

-98-
The filtrate after evaporation of the organic halide yielded a white solid

when methyl iodide was used and an oil when allyl bromide was used to cleave

the mercaptide complexes. The white solid after recrystallization from

o petroleum ether melted at 79-80 C. The reported melting point for

e 14_ 1,4-bis (methylthio)benzene is 84-85 C. The proton chemical shifts (in

CDClj, t relative to (CH^^Si) were: 2.87 due to aromatic protons and 7.55

due to methyl protons. The area ratio of 1:1.54 is consistent with 1,4-bis

(methylthio)benzene , H^C-S-C^H^-S-CHj. The oily residue obtained from the

reaction of silver complex with allyl bromide was identified as 1,4-bis

(allyl thio)benzene, H

2 C=CH-CH2 -S-C6

H

4 -S-CH

2 -CH=CH2

. The proton chemical

shifts (in CDClj, t relative to (CH^Si) were: 2. 8 7 (aromatic) , 6.55

(doublet, -CH

2 -), 4 . 18 (multiplet , =CH-) , 4. 90 (doublet , =CH

2

- trans to

=CH-), and 5.12 (=CH

2

~ cis_ to =CH-) . The area ratios C

6

H

4/-CH

2 -/-CH=/=CH2 were 1/1/0 .'6/1, consistent with 1,4-bis (allylthio)benzene.

Resistivity Measurements . Two-probe measurement -of d.c. resistivities were

made on compressed powder compacts pressed at 97,000 psi, employing brass

electrodes in conjunction with a "Keithley Model 600A Electrometer for

current measurements and a Keithley Model 160 Digital Multimeter for measurement

of the voltage drop across the sample. D.C. resistivities were taken as

averages before and after reversing the applied potential (usually 1.5 volts

with a dry cell) to eliminate polarization effects. The electrical contact

with the electrodes was made by G.E. Electronics Silver Print. The pellets

were mounted between the electrodes and clamped in a small brass press

described elsewhere.*^ The electrodes and the end plates of the brass press

-99-
were insulated with ceramic material. The cell was suspended in a Pyrex

vessel from a Teflon rod. The leads were brought out through individual

tungsten Pyrex seals, and the electrical connections to external circuit

were arranged through these seals. The conductivity vessel was placed in

a Iewar flask which served to keep the temperature constant. The cell was

heated by an electrical tape wound around the Pyrex vessel. Temperatures

in the vicinity of the sample were monitored by a chromel-alumel thermocouple

attached to a potentiometer. Measurements were carried out in vacuo (10 torr)

and argon atmosphere. Pellets were heated under vacuum to ca. 80 C for 2-3

hours to remove any moisture or volatile matter occluded during Del let

pressing and cooled to room temperature before measurements were made. The

near linear relationship between the applied voltage (12-50 volts for Ag(I)

and Cu(II) complexes and 1.5-6 volts for Cu(I) complexes of thiophenol

and 1 ,4-dimercaptobenzene) and the measured current indicates that the electrodes

provided ohmic contact. No noticeable electrolysis was observed after ;

prolonged passage of current, suggesting that the conductivity was electronic.

RESULTS:

Infrared Spectra. The infrared spectral data are given in Table 2. The

spectra of all complexes are similar and characterized by the occurrence

of a single absorption near 810 cm * due to out-of-plane CH deformations

of the aromatic ring, two absorptions near 1380 and 1460 cm

1 assigned to

C=C skeletal in-plane vibrations, and two absorptions near 1010 and 1090 cm

attributed to C=S stretching vibrations.

16

A comparison with the spectrum of the

-100-
free ligand revealed that these principal absorption bands in the spectra of

'the complexes are also the common features of the ligand. There was no evidence

of a S-H vibration in the spectra of the complexes which for the free ligand

is located at 2560 cm . A slight shift to lower frequency of the principal

absorption bands relative to the ligand was observed as a result of coordination

of the metal to the ligand. A similar observation that the frequency of the

strong dithiene bands does not change much with the metal was made previously

3a

by Schrauzer. Weak to streng-absorptions were found in the spectra of Cu(I)

and Hg(II) complexes in regions where M-S stretching bands are generally

17 observed and are so assigned. The remaining absorptions in the region

490-540 cm * are not readily assigned but are a common feature of all complexes.

A band near 1580 cm of weak to medium intensity, not found in the ligand

spectrum, can be readily assigned to a conjugated aromatic ring.^

X-Ray Diffraction Data . According to X-ray powder diffraction, all M(I) ions

form crystalline complexes. All M(II) complexes reported here are amorphous with

the exception of the Hg(II) complex, which is crystalline. It is interesting

that the X-ray powder diffraction pattern of any one complex regardless of

the method of preparation remains unchanged with no significant variations

in the lattice parameters. It is, therefore, possible that the crystalline

mercaptide complexes prepared in this study are not linear high polymers, but

are small discrete, possibly cyclic, molecules. A final solution to the

structures of these mercaptides should await single-crystal X-ray structural

determination. Thus far, we have been unable to prepare single crystals.

The X-ray powder data for the Cu(I) mercaptides are given in Table 3. As

shown in the table, the data can be indexed based on a simple cubic unit cell.

The density measurements indicate that there are four molecules in the unit

cell of [Cu-S-CJl.-S-Cu] and eight for [C,H c SCu] . 1 6 4 n o 5 n
Table 2

INFRARED SPECTRAL DATA OF THE MERCAPTIDES, CM'

HS-C.H^-SH

6 4 2560(m), 1900(w), 16400*0, 1480(ms), 1400(ms), 1260Cm), U20(vs)

1020CS), 900(ms), 810(vs).

(Cu-S-C

6H

4

- S-Cu)

n 18S5(vw), 1625(w), 1560(m), 1470(vs), 1430(w), 1330(s), 1250Cvw),

1175(vw), 1110(sh), 1092(vs), 1010(vs), 950(w0, 808 (s), 535 (m),

500 Cms), 530(b.3 a).

(Cu-S-C

6

H

4

- 1620(bw), 1570(bw), 1390 (m), 1190(Vw) 3 lllO(s), 1015(s), 810(s),

495 (vs), 535 (sh}.

(Cu-S-C

6

H

5

) n

3060(m), 1920(bwj, 1890(rw), 1860(w), 1800(bvw), 1620(w), 1590(vsj,

1485 0s), 1450(111), 1580(w), 1330(vw), 1310(w), 1270(w), llSO(vw),

1090(s), 1030(s), 1005(vw), 740(vs).

(Pb-S-C

6

H

4

- 1480(vs), 1390(vs), 1260(vw), 1105(vs), 1015 (s) , 815(s).

(Ag-S-C

6

H

4

- S-Ag)

n 1630(vw), 1475 (vs), 1390Cvs), 1350(vw), 1100(vs), 1010(s), 810Cas),

540 (vs), 500 (vs), 490 (s).

CHg-S-C

6H4

- 1930(vw), 1620(bw), 1580(vw), 1485 (vs), 1400(s), 1110(vs), 1020 (s) , 830(ms), S40(s), 500(vs), 350(vs).

(Ni-S-C

6

H

4

- 1900(bw), 1620-700)), 1570'(m), 147S(vs), 1390(s), 1210(vw), llSO(w),

1090(b,n), 1015Cm), 900(w), 810(m).

b = broad

v = very

s = strong

m - medium

w = weak

sh = shoulder

-102-
Table 3

X-RAY DATA FOR THE COPPER(I) COMPLEXES OF 1,4-DIMERCAPTOBENZENE AND THIOPHENOL

•

i Complex r hKl I** d . (X> d . (X) obs. obs. r calc. '

! [Cu-S-C,H -S-Cu] 1 6 4

J n

[C,H 1 c SCu]

6 5

J n

100 80 10.53 10.49

110 7 7.40 7.42

200 7 5.24 5.24

220 7 3.73 3.71

300,221 5 3.48 3.50

310 4 3.30 3.32

311 3 3.18 3.16

400 4 2.61 2.62

410,322 4 2. 54 2.54

100 ^100 12.31 12.20

110 41 8.69 8.63

210 26 5.44 5.55

320 3 3.39 3.38

420 4 2.73 2.73

* The calculated d spacings are based on a cubic unit cell with lattice constant

a = 10.49 A for [Cu-S-C^-S-Cu^ and 12.20 X for [C^SCu^.

** The observed intensities (I ^

) are peak heights of the diffraction lines on

a diffractometer tracing.

-103-
Physical Properties and Chemical Reactivity of the Metal Complexes . Good

thermal stability and resistance to acids and bases marked each of the

complexes prepared in this study. However, with the exception of the silver

complex, concentrated nitric acid reacted vigorously with most mercaptide

complexes. A common feature of all the complexes is their insolubility in

common organic and inorganic solvents. This often is a consequence of the

tendency of coordinated thiolo atoms to form bridges to adjacent metal atoms.

All these properties suggest that the mercaptide complexes reported here

should be coordination polymers involving sulfur bridges. Unfortunately,

we were unable to determine the molecular weights because of the insoluble

nature of these complexes. Contrary to previous experience with the reactions

of S-bridged compounds, we found that several of these mercaptides were

readily cleaved by organic halides under relatively mild conditions in

accordance with reactions CI) and (2):

[-M-C,H.-S-] + RX -y MX + RSC H SR 0=2 for M(_It) ions, but 1 (i) 6 4 n y b 4 for CuCIIll

[M-C

6

H

4 -S-M]

n

+ RX -v MX + RSC^SR (2)

Furthermore, the Cu-S bonds were easily cleaved according to reactions (3)

and (4) when we attempted to incorporate 7,7,8,8-tetracyano-p-quinodimethane

(TCNQ) in the polymeric structure of Cu(I) complexes hoping to increase

their electrical conductivity via the formation of charge transfer complexes.

[C

6

H

5 SCu]

n

+ TCNQ ->• Cu

+TCNQ" + C^SSC^ (3)

[Cu-S-C

6

H

4 -S-Cu]

n

+ 2 TCNQ ^ 2 Cu

+TCNQ~ + [-S-C^-S-^ (4) ,

These reactions suggest that the formation of the charge transfer complex

precedes the breaking of Cu-S bonds. In one experiment, the green reaction

product obtained on heating TCNQ and copper thiophenolate at 45* C in' a

sealed Pyrex tube contained neither diphenyl disulfide nor Cu

+TCNQ . When

-104-
exposed to air, it began to smell strongly of thiophenol. Presumably, the

formation of the charge transfer complex causes weakening of the Cu-S bond,

which is then cleaved hydrolytically to form thiophenol or, in the absence

of moisture, thermally to give diphenyl disulfide. This high reactivity

of the mercaptide complexes towards electrophilic reagents such as organic

halides and TCNQ indicates that the coordinated thiolo atoms still retain

much of their nucleophilic character. The complexes of Cu(I), Cu(II), Pb(II),

and Ni(II) appeared to catalyze the decomposition of hydrogen peroxide, but

only the Cu(II) complex showed some catalytic activity in the decomposition

of hydrazine.

Electrical Properties . The variation of the resistivity with temperature

is displayed in Fig. 3. Table 4 shows values for ^(infinite temperature

limit of the resistivity), E (thermal activation energy for conduction),

a • o together with the resistivity at 25 C. The results show a linear log p vs.

3

10 /T relationship, consistent with a resistivity vs. temperature relationship

E

a/kT

of the form p = pe for the activated conductivity, where E is the

O Si thermal activation energy for conduction. The activation energies determined

from the slopes of the straight line plots fall between 0.054 and 0.23 ev

o in the narrow temperature range of ca. 25-100 C available to us. There is

good consistency between the measurements made on samples from the same batch

in all cases. For example, repeat measurements on analytically pure copper

thiophenolate (entry 8 in Table 1) and (Cu-S-C

6

H

4 -S-Cu)n (entry 3 in Table 1)

reproduced to within + 5 percent. The results, however, differed for samples

of (Cu-S-C H -S-Cu) prepared by different methods. Thus, the sample prepared

-105-
by a solid state reaction (entry 4 in Table 1) had a resistivity of 170 ohm ; cm

at room temperature as compared to 40 ohm- cm for the analytically pure sample

prepared in 2,4-lutidine (entry 3 in Table 1). As the analytical data suggest,

the higher resistivity in the former case is due to foreign impurities, possibly

3 the polymeric sulfide, [-S-C^H -S-]^. As shown in Fig. 3, the logp vs. 10 /T

straight line plots for both samples are parallel and the thermal activation

energy calculated from the observed slope is 0.054 ev in each case. This

suggests that the conductivity is intrinsic to [Cu-S-C^H^-S-Cu]^, and the

higher resistivities of the impure samples are a result of the reduced mobilitie

of the charge carriers caused by the foreign impurity. For the most part

the electrical resistivities of the M(II) complexes, including the Ag(I)

complex, are very high and close to the range ascribed to insulators. Their

9

resistivities are approximately of the same order of magnitude (~10 ohm- cm)

and seem to correlate with the intensity of the band near 1580 cm * in the

infrared spectra, indicative of a conjugated aromatic ring and some degree

of electron derealization. The intensity of the 1580 cm * band is weakest

for the Hg(II) complex, which also has the highest resistivity.

-106-
Table 4

IELECTRICAL RESISTIVITIES OF THE MERCAPTIDES

Entry Complex P2S

(ohm- cm) (ohm-

' E

* a

cm) (ev)

1 [Cu-S-C,H -S-Cu] **

1 6 4

J n

4.0 x 10

1 0.32 0.054

2 [Cu-S-C,H -S-Cu] **

1 6 4

J n

1.7 x 10 1.33 0.054

3

r /-» . e* fy it c l ICu-S-C-H . -S1

1 6 4

J n

T £. mm 1 A^ 3.6 x 10 219 0. 16

4 [C6

H

5 SCu] n

** 5.1 x 10

4 3.39 0.11

5 [Ag-S-C

6

H

4 -S-Ag] n

8.4 x 10

8 0.96 0.23

6

7

[Ni-S-C

6

H

4-S-] n [Hg-S-C

6H4 -S-] n

-109

(at 60 C)

* E

a defined by log p = logp

Q

+ E /kT.

a ** Measured in vacuo. All others were measured under argon.
DISCUSSION: j

In their general properties (good thermal and chemical stability and

insolubility), the metal complexes of 1 ,4-dimercaptobenzene reported here

closely resemble the mercaptide complexes of palladium(II) previously

18

formulated as S-bridged high polymers of general formula [PdfSR^lj^-

This formulation is generally accepted for other mercaptide complexes. *^-2

In view of the well-known tendency of the coordinated thiolo sulfur to form

bridges and the overall similarity to the recently reported Pd(II) complexes

25 of 1,2-ethanedi thiol and 1 , 3-propanedithiol , it would be reasonable to

regard the metal complexes of 1,4-dimercaptobenzene of the type - [M-S-C^H^-S-] n

as coordination polymers with the aggregation shown below:

Similar polymeric structures involving sulfur-bridged metal chains are also

postulated for metal complexes of the type [M-S-C

6

H

4 -S-M] n (M=Cu(I) and Ag(I))

and [C

6H

5SCu]

n

. Although there is a lack of structural evidence, it is

possible that the polymeric chains shown in Figures 1 and 2 are arranged i n the

-103-
solid state so as to allow the formation of metal-metal bonds which would

enhance the ease of intermolecular electron transfer and hence carrier mobilities.

The enormously high electrical conductivities of the Cu(I) complexes relative

to the M(II) complexes would be in accord with this view.

\

S/\s /\s /\s /\

=6H

4 «««4 ^4

f

6

H

4 »* <=6»S

f6

H

5 f

6

H

5 f6

H

5 \

M /\ M /\MM/\ /\ \Cu/\Cu/\Cu/\Cu/\x

Figure 1. . Figure 2

.

The high chemical reactivity of the complexes towards organic halides

and the ready cleavage of the Cu-S bonds by TCNQ under very mild conditions

appear to be consistent with a two-dimensional representation in which

coordinated thiolo sulfur retains much of its nucleophilic character. It

is possible that further cross- linking could lead to a three-dimensional

network. However, we believe that further cross- linking would render the

thiolo sulfur much less reactive towards organic halides. The facile cleavage

of the metal mercaptides by organic halides is a reflection of the appreciable

nucleophilic character of the coordinated thiolo sulfur and, therefore, tends

to discount three-dimensional network structures for the complexes reported here,

The resistivities of compressed powder compacts of the mercaptide complexes

EaAT

in the temperature range of 25-100 C fit the expression p = o^e for the

activated conductivity. There was no apparent relationship between thermal

activation energies for conduction and the band gap of the form 2E = E , as

a g required by the intrinsic band model. As the yellow color of many of these

-109-

I

!
complexes would suggest, the conductivity may be extrinsic and impurity

dominated. The impurity, however, need not be foreign and could arise from

lattice imperfections. The solid state absorption spectra of the copper

complexes in KBr pellets in the range of 3125-14286 cm

1 showed continuous

absorption extending into the visible region with onsets at much higher

energies than the anticipated optical transition energies based on thermal

activation energies for conduction. The onsets, which were neither sharp

nor well-defined, occurred at 5714 cm

1 (0.71 ev) for [Cu-S-C^H^-S-Cu]^

;

4098 cm"

1 (0.51 ev) for [C^SCu^; and 3683 cm"1 (0.46 ev) for [Cu-S-C^-S-^

They do not correlate with the band gap calculated from the thermal activation

energies for conduction.

The Cu(I) complexes of 1,4-dimercaptobenzene and of thiophenol are better

conductors than those of Cu

++ and the other metals studied to date. It is .

interesting to note that both the electrical conductivities and the thermal

activation energies for conduction are markedly influenced by the copper

content of the mercaptide complexes. This is shown for the three copper

complexes reported here. For example, the Cu(II) complex of composition

o [Cu-S-C,H 1 -S-] (wt% Cu, 31.01) has a resistivity of 3.6 x 10 ohm- cm and

6 4 n

E &

= 0.16 ev, whereas the Cu(I) complex of composition [Cu-S-C^H^-S-Cu]^

(wt% Cu, 47.74) has a resistivity of 40 ohm- cm and E = 0.054 ev. The

4 electrical resistivity (5.1 x 10 ohm- cm) and the thermal activation energy

(E a

= 0.11 ev) for [CuSC^]^ (wt% Cu, 36.88) fall between those of the

Cu(I) and Cu(II) complexes of 1 ,4-diraercaptobenzene. This increase in the

conductivity and decrease in the thermal activation energies for conduction

-110-
with increasing copper content indicate that the conductivity mechanism

may involve an interaction of copper 3d-orbitals with the tt* orbitals of

the ligand systems. However, the structural variations due to compositional

differences should be even more important in influencing the electrical

conductivities. As we pointed out earlier, the possible link-up of the

polymeric chain structures of the Cu(I) complexes by the Cu-Cu bonds in the

solid state would greatly facilitate intermolecular electron transfer. It is

therefore likely that the formation of Cu-Cu bonds and the proposed d orbital

overlap , which will influence the probability of electron transfer via a

tunneling process, or the height of the activation energy barrier for electron

26 hopping , play important roles in determining the electrical conductivities

of the copper complexes.

Finally, we mention that the metal mercaptides exhibit visible photoluminescence

o emissions at room temperature after excitation by 3650 A: orange for

[Ag-S-C^-S-Ag] 10 ; red for [Cu-S-C£ H.-S-Cu] ; Durole for [Cu-S-C.H .-S-L and

6 4 n 64 J n ~ ^ 64 n [Hg-S-C

6

H

4 -S-] n

; and pink-red for [C^SCu]^

-111-
ACKNOWLEDGMENTS:

This work was supported by the Office of Naval Research under contract

No. N00014-69A-0200-6035 with the University of California, San Diego (La

Jolla, California 92037). Helpful discussions with Dave Johnston and

A.C. Lawson (IPAPS, La Jolla) on electrical and X-ray measurements are

gratefully acknowledged.

-112-
REFERENCES:

(1) "The Synthesis, Characterization and Electrical Properties of Transition

Metal Mercaptides of 1 ,4-Dimercaptobenzene", G.N. Schrauzer and H, Prakash,

presented as paper No. 26 in the Division of Inorganic Chemistry, 167th

A.C.S. National Meeting,, Los Angeles, April 1-5, 1974.

(2) S.E. Livingstone, Quart. Rev., 19_, 386 (1965).

(3) (a) G.N. Schrauzer, Transition Metal Chem. , 4, 299 (1968)

.

GO Idem, Advan. Chem. Ser. , 110, 73 (1972).

(4) J. A. McCleverty, Progr. Inorg. Chem., 10, 49 (1968).

(S) L.F. Lindoy, Coord. Chem. Rev., £, 53 (1969).

(6) E.J. Rosa and G.N. Schrauzer, J. Phys. Chem., 73, 3132 (1969).

(7) A.P. Terent'ev, V. M. Vozzhennikov, O.V. Kolninov, Z.V. Zvonkova, E.G

Rukhadze, V.P. Glushkova, and V.V. Berezkin, Dokl. Phys. Chem., Proc.

of the Academy of Sciences of the USSR, 160, 60 (1965) (English

Translation from Dokl. Akad. Nauk.SSSR, Vol. 160 , No. 2).

(8) S. Kanda, K. Ito, and T. Nagaito, J. Polym. Sci., Part c, No. 17, 151 (1967)

(9) R. Adams and A. Ferretti, J. Am. Chem. Soc, 8J_, 4939 (1959).

(10) W. Reifschneider, Chem. Abstr. , 63_, 17974b (1965).

(11) Handbook of. Chemistry and Physics, 50th Ed., The Chemical Rubber Co.,

Cleveland, 1969, p.C-273.

(12) L.R. Melby, R.J. Harder, W.R. Hertler, W. Mahler, R.E. Benson, and

W.E. Mochel, J. Am. Chem. Soc, 84, 3374 (1962).

(13) Dictionary of Organic Compounds, Vol. I, 4th Ed., Eyre and Spottiswoode

Publishers Ltd., London, . 1965.

(14) V. Baliah and M. Uma, Tetrahedron, 19, 455 (1963).

(15) P.W.M. Jacobs, J. Sci. Instr. , 30, 204 (1953).

(16) J.R. Dyer, "Applications of Absorption Spectroscopy of Organic

Compounds", Prentice Hall, Englewood Cliffs, N.J., 1965, pp. 33-38.

-113-
(17) G.N. Schrauzer and V.P. Mayweg, J. Am. Chem. Soc, 87_, 1483 (196S) .

(IS) F.G. Mann and D. Purdie, J. Chem. Soc, 1549 (1955).

(19) K. A. Jensen, Z. Anorg. Chem., 2_52, 227 (1944).

(20) R.G. Hayter and F.S. • Humiec, J. Inorg. Nucl. Chem., 26, 807 (1967).

(21) P. Woodward, L.F. Dahl, E.W. Abel, and B.C. Crosse, J. Am. Chem. Soc,

87, 5251 (1965).

(22) R.O. Gould and M.M. Harding, J. Chem. Soc. (A), 875 (1970).

(23) R.S. Nyholm, J.F. Skinner, and M.H.B. Stiddard, J. Chem. Soc, 38 (1968).

(24) D.C. Bradley and C.H. Marsh, Chem. Ind. , 361 (1967).

(25) L. Cattalini, J.S. Coe, S. Degetto, A. Dondoni, and A. Vigato,

Inorg. Chem., 11_, 1519 (1372).

(26) F. Gutmann and L.E. Lyons, "Organic Semiconductors", J. Wiley, New York,

1967, p. 421.

-114-
Figure 3: Temperature dependence of resistivity (p)

q [Cu-S-C^H^-S-Cu]^ (prepared in 2,4-lutidine)

.

A [Cu-S-C^H^-S-Cu]^ (prepared by solid. state reaction)

[C

6

H

5SCu] n (£lAg-S-C

6

H

4 -S-Ag]

n 0[Cu-S-C

6

H

4 -S-]n

-115-
-116-

STATE UNIVERSITY OF NEW YORK

College of Arts and Science

Department of Chemistry

Plattsburgh, New York 12901

(HALOMZIHYLURSINIC CO? 0l?.OS . I. PRIMARY AND

SECONDARY (HALOMETHYL)ARSINES II. PREPARATION AND CHARACTERIZATION 0?

P ENTAKIS ( CHLOROMETHYL) CYCLOPENTAARSINE

By

Arnold L. Rheingold

Department of Chemistry, State University of New Yor

Plattsburgh, NY 12901

A Report Submitted to Dr. M. Broadhurst,

National Bureau of Standards

April 1, 1975

Research Sponsored by the

Office of Naval Research

Under

Contract N00014-73-A-0450-0001

Task Number NR 35 6-5 50

Approved for Public Research; Distribution Unlimited

Reproduction in whole or in part is permitted for any

purpose of the United States Government.

-117-
(HALOMETMYL) ARSEN IC COMPOUNDS . L. PRIMARY AND SECONDARY

(HALOMET11YL) ARSINES

ARNOLD L. RHEINGOLD

Department of Chemistry, State University of New York, Plattsburgh,

New York 12901 (U.S.A.)

and

JON M. BELLAMA

Department of Chemistry, University of Maryland, College Park,

Maryland 20742 (U.S.A.)

SUMMARY

(Chloromcthy 1 ) ars ine , ClCI^AsI^, and bis (chloromethyl )

arsinc, (CICH^) 2ASII , were prepared by the reduction of (chloromethyl) arsonic and bis (chloromethyl) arsinic acids, respectively.

(Bromomethy 1) and (iodomcthyl) analogs of the primary and

secondary arsines could not be prepared because of a facile

rearrangement from C-functional to As-functional halides.

Reactions of ClCH^AsH^ demonstrated a strongly reduced affinity

for proton-proton exchange with hydrogen halide (in comparison

to CH-jAsHj) , a reduction anticipated by group-electronegativity

considerations. Nmr, ir, and mass spectral data are included.
INTRODUCTION

Compounds conLrti nLruj ( h a lonu * t hy 1

). - ubs-t i -L uLed motalfi and

metalloids have long interested organometallic chemists as potential carbene precursors and as intermediates in the preparation of methylene-bridged bimetallics [1]. A recent

investigation of potentially important non-bonded metal-halogen

P_tt - dfT interactions in (halomethyl) silanes and -germanes has

brought further attention to this important group of compounds [2]

Information about primary (halomethyl) derivatives of metals

possessing non-bonding electron pairs (groups V and VI) is limited

to a single substantiated example*: (chloromethy 1) phosphine

,

CIC^P^ [4,5]. The presence of non-bonding electron pairs on the central atom presents additional possibilities (both attractive and repulsive) for "across-space" metal-halogen interactions.

This paper reports the preparation and properties of two new compounds: (chloromethy 1 ) arsine , ClC^Ast^, and bis (chloromethy 1)

arsine, (CICH2 ) 2^ sI1 > an<^ *-he significant failure to prepare

(bromomethyl) and (iodomct^yl) analogs.

RESULTS AND DISCUSSION

Preparation and Characterization of XCH

^ AsH ^ Compounds

ClCt^AsC^, obtained from the diazomethane-AsCl ^ insertion

reaction [6,7], could not be directly reduced to ClCH

2 AsH2

. Reducing agents employed were Zn/HCl, Zn/J^SO^, NaBH^ or LiAlH^;

*A claim has been made for the preparation of (chloromethy 1 ) amine

,

CICH-NH-, but only decomposition products were isolated [3].

-119-
the NaBII^ reactions were conducted in both H

2 0 and n-butyl ether,

and LiAUl^ in n-butyl other. In all cases no more than trace

amounts (less than 1%) of ClCH

2 AsII

2 were obtained. When

ClCH

2 AsCl

2

, however, is first oxidized with 15% ^2°2 tC> t *lc

arsonic acid, ClCh^AsO (OH)

2

, and then reduced by the Zn/H

2 S0

4 couple, a 65% yield of ClCH

2 AsH2 is obtained. Similarly,

oxidation of (ClCH

2

) 2 AsCl produced (C1CH

2

) 2 AsO (OH ) which affords

the corresponding secondary arsine in 10% yield on Zn/H-^SO^

reduction

.

Likewise, BrCH

2AsBr

2 failed to yield BrCH2 AsH2 on direct

reduction, but in this case the cause of failure includes the

inherent instability of the product (see below). Also, attempts

to oxidize BrCH

2 AsBr2 to BrCH2 AsO (Oil) 2 with 15% H2 0

2 were

accompanied by the strong evolution of bromine; no arsonic acid

could be isolated from the reaction products.

In an attempt to prepare (iodomethyl) arsine, ClCH

2 AsH2 was treated with Nal in acetone at 35° [step (1)]. The desired

Nal

(CH-.) _0

ClCH

2AsH

2 rjy-= > ICH2 AsII2 —^*

CH-AsHI , > (CH-.AS) + xHI

3 (3) 3 x

product, ICH

2 AsH

2

, was not obtained; observations during the course

of the reaction suggested that the product spontaneously rearranged

to an arsenic-functional iodide [step (2)], which itself has

previously been shown [10] to disproportionate to polyarsines and

III [step (3)]. This was evidenced by the solution's rapid

-120-
L iiLuiui I I' i <:n L i mi ol yn I low-ni n.ncjo rcrlnr.nl ion n< TCMiiipn.il i cd by n considerable amount of brick-red precipitate analyzed as (CH^As)^. No evidence for free I2 was observed during the

rearrangement. These results also correlate well with thermal

rearrangements observed in ICI^Gell^/ where CH^GeH^ and Gel^

were observed, among other products [8]. Although the germanium

rearrangements could be catalyzed by light, the arsenic reactions

were completely shielded from light.

The rearrangement (step 2) can be conveniently viewed as an elimination/addition of HI through an intermediate of the type

0 © CH2=AsH (which surely would exist primarily as CH^-AsH) ; no evidence for or against its presence was found. Goldwhitc has

suggested CH^^H as an intermediate in the alkaline hydrolysis

of ClCh^Ph^ . [ 4 ] A similar rearrangement of ( chloromethy 1 ) trimethy lsilane , although catalyzed by aluminum chloride,

AlCl^

(CH

3

) 3 SiCH

2 Cl

^

(CH

3

) 2 SiCH

2 CH3 CI

is thought to occur through a doubly-bridged intermediate [9].

(CH

3

) 2

Si'- • • • •'•;CH 2 "CI"

A1C1

3 Since it is known that CH

3AsHI can exist only in equilibrium with

CI^Ast^ and CH

3AsI

2 [10], the formation of polyarsine (step 3),

-121-
may include condensation of CH3AsI.II with either CU

3A ;1I 2 or CII 3AsI

2 in addition to self-condensation.

Proton Magnetic Resonance Spectra

(Chloromethy 1 ) arsine: The 60 Mil?: pmr spectrum of (chloromethyl) arsine is shown in Fig. 1. Spectral parameters tabulated

in Table 1 were obtained from a modified LA0C00N III computergenerated "best-fit" spectra, with the assumption that free

rotation about the C-As bond would allow assignment of the

molecule to the spin system, AA'BB' . [11] . While normal AA'BB'

spectra exist in two mirror-image halves which can lead to

difficulties in assigning the A and B proton sets, the up-field

half of the spectrum in Fig. 1 clearly shows the effects of

75 quadrupolar broadening from As (1=3/2, 100% abundant). The

up-field half is therefore assigned to protons directly bonded

to arsenic. The pmr data for ClCH

2 AsH

2 in Tabic 1 derive from

iteratively converged, observed and calculated, line positions

with a satisfactory resultant RMS error of 0.047.

While the error figure demonstrates that the calculated line

positions produce a good fit, deviations in line intensities of

up to 20% were observed, possibly because of a failure of the

initial assumption of free C-As bond rotation. To test this

possibility the spin system was changed from AA'BB' (free rotation)

to ABCD (restricted rotation) and further calculations performed.

The introduction of anisochronous chemical shifts (±1.0 Hz from

the AA'BB' best fit values) produced, of course, many additional

calculated lines but all new lines were of very weak intensity

-122-
and did not appreciably niter the envelope of observed spectral

lines. The possibility of . restricted rotation was further tested

by examining spectra of ClC^AsI^ in t-buty lbenzene through the

temperature range -100 to 110°. While temperature-dependent

changes in Av (AB) (5 Hz 3-100°; 45 Hz @ 110°) and the effects

of quadrupolar broadening (almost no broadening at -100°) were

found, there was no indication of restricted rotation. The line

intensity discrepancies may be the simple result of unequal (but

small) quadrupolar broadening of the individual lines of the

methylene half of the spectrum [12]. An inherent ambiguity arises

in the assignment of the two geminal coupling constants, J (HAsH)

and J(HCH). Consequently, comparison must be made to known values,

and use made of any additional spectral information before assignment is possible. Although no J(HAsH) values have been previously

reported, several J(HPH) values are available. The seemingly close

relationship between H-N-H couplings and H-P-H couplings (see

below) provides some assurance that trends could, with appropriate

caution, be extended to H-As-H couplings.

The reported values of H-N-H and H-P-H couplings are (in Hz):

NH_, -10.35 [13]; NH

4 +

, -11.67 [14]; CH^NI^, -13.23 (predicted

[15]); PH

3

, -13.45 [16]; CH

3 PH

2

, -12.46 [17]; CF

3 PH

2

, -13.37 [18];

CgH^PH2, -13.11 [17]. It is reasonable, therefore, to assign the

-16.99 Hz geminal coupling to H-As-H. On the basis of the foregoing results the sign assigned to J(HPH) in CICH-^PH- [5] must be

in error. (See Table 1.)

-123-
The other geminal value, -1.28 Hz, is then J(HCII). Experimental evidence suggests that J(HCH) increases algebraically as the II-C-H bond angle widens [19]. Tetrahcdral acyclic carbon

systems generally give rise to geminal couplings in a rather

narrow range from -15 to -10 Hz, with a few values falling just

2 outside this range, and sp_ hybridized carbon generally produces

geminal couplings a little to either side of zero.

1

3

It is also well noted that J( C-H) is quite sensitive to

changes in s-character of the carbon bonding orbitals [20];

increase in s-character leads, in general, to an increase in

13 3 J( C-H). Sp_ carbon normally provides couplings between 125

(methane, cyclohexane) and 175 II z (methylene dihalides). J(^C-H)

for ClCI^AsI^ is 157.8 Hz, which is within the region for electro3 negatively-substituted sp_ carbon, but nonetheless is a rather

1

3

high value. Correlation is then seen between J(HCII) and J( C-H);

each is sensitive to carbon s-character, and in the case of

CICH2ASH2/ both values indicate a high degree of s_ character in

carbon's bonds to hydrogen. The consequently narrowed Cl-C-As

bond angle may be an indication of an attractive As... CI interaction and/or a demonstration of the tendency for p_-character

to concentrate in bonds to electronegative substituents (Bent's

Rule [21]).

In group-V systems a potential exists for both halogen and

group-V element d-orbital involvement in lone-pair delocalization

;

the net result could either increase or decrease the net lonepair electron density, and therefore, either augment or detract

-124-
from the c-electron-withdrawing effect of the (chloromethyl)

group. Both J(H-C-II) and J( 13C-II) for C.lCH

2

AsII

2 support an attractive CI... As interaction, and the strongly reduced

affinity for proton-proton exchange with hydrogen halide of

ClCI^AsH^ (compared to CH^AsH^) suggests that if d-orbital

participation is significant in this interaction, it is chlorine,

not arsenic, that participates.* It is difficult, however, to

account for the apparent absence (from nmr coupling constants)

of similar effects in CICH^PH^.

Bis (chloromethyl) arsine : The 100 MHz pmr spectrum of

(ClCi^^AsH, obtained as a by-product of the preparation of

ClCH^AsH, is shown in Fig. 2. All attempts to perform a complete

analysis of spectral parameters proved futile because of insufficient resolution of individual lives arising from 1) uncertain

assignments of quadrupolar broadened lines, 2) similarity of the

absolute magnitude of chemical shift differences and coupling

constants, and 3) the chemical non-equivalency of the two protons

on each methylene group. Nonetheless,, based on the spin system

assignment AA'BB'C, approximate chemical shifts given in Table I were determined by the bold assumption that the relevant coupling

constants in ClCH_AsH_ remain unchanged in (C1CH- ) ~AsH

.

*M.O. calculations support this conclusion [22], Further, an estimated group electronegativity difference of about 0.2 between

methyl and chloromethyl [23] seems too small to account for the

profound change in basicity.

-125-
Mass Spectrum of ClCH

^ AsI I,, The mass spectrum of C] Cll-Asll., » shown in Table 2, wan obtained at an ionizing voltage of 70 eV and an ionizing chamber

pressure of 2 x 10 ^ mmHg. Some features of the spectra require

special comment. The base peak, m/e 90, suggests a process

involving loss of the elements of HC1 to yield CH-AsH . Since

it is frequently possible to show good agreement between thermal

and electron-impact decompositions, it is noteworthy that the

structural isomer, CH^AsHCl, decomposes thermally with the loss

of HC1. [10] The base peak in the spectrum of CH^AsI^ is also

at m/e 90, but the spectrum of CD-^Asl^ demonstrates that both

arsenic-bonded hydrogens are lost preferentially [24],

The peaks at m/e 110-113 represent rearrangements involving

formation of As-Cl bonds. Identical rearrangements have been

found in a-halosilanes and -germanes [2b]. Dobbie and Cavell

have found similar and extensive rearrangement in the spectra of

CF^-substituted phosphines and arsines [25]. They attribute the

rearrangement process to an initial interaction between the

fluorine p_ orbitals and the unoccupied d orbitals of the metalloid

and they strengthen their argument by citing earlier work which

indicated that CF^-substituted amines did not show these rearrange

ment peaks [ 26] .

Infrared Spectra

(Chloromethyl) arsine is expected to possess symmetry,

the symmetry plane being described by the heavy atoms. It proved
useful in assigning observed absorptional frequencies to the

fundamental modes to examine the rotation-vibration band

contours of vapor-phase spectra [27].

In the spectra for ClCI^AsK,, (see Table 3) , the complex

band at 2900-3000 cm must include both a symmetric and an antisymmetric C-H stretching band. While the resolution in

the infrared spectra is not sufficient to assign the bands on the basis of contour characteristics alone, analogy can be made

to Raman depolarization data from related compounds [28]. Thus,

in methylarsine the antisymmetric mode is found at higher

frequency

.

Two bands are expected for the As-H stretching vibrations

:

one symmetric, giving rise to an A-B hybrid band contour; the

other antisymmetric, giving rise to a C band. The complex band

at 2050-2150 cm ^ surely contains both modes, but again unambiguous assignment of the observed frequencies to expected modes

does not seem possible without Raman corroboration. The veak

band centered at 1410 cm. ^ is characteristic of the methylene

group and is attributed to the CR^ scissors vibration. No rotational character is observed. Other bands characteristic of the

methylene group are observed in the region above 1000 cm ^. The

wagging mode, an A' vibration centered at 118 8 cm , has the

expected A-B hybrid envelope. The twist occurs at 110 8 cm

^

and is weak, but exhibits the type C envelope expected of an

A" vibration.

-127-
The band centered at 96 3 cm bears a strong type C

resemblance (perhaps evidence for the molecule being a nearly

symmetric rotor) , but must be the A-B hybrid expected for the

As-H scissor vibration. This mode is observed at 9 73 cm ^ in

methylarsine [28]. In a number of methylarsine derivatives,

the ASH2 twisting and wagging vibrations show strong interactions and usually appear within 20 cm ^ of each other [28].

The wagging vibration will produce an A-B hybrid envelope, while

the antisymmetric twisting mode is expected to produce a band

of type C. The complex envelope at 760-800 cm ^ is thought to

contain both modes , the absence of adequate resolution again

prevents an unambiguous assignment.

The band centered at 862 cm ^ is of type C and is attributed,

to the antisymmetric AsH^ rocking mode. The C-Cl stretching

vibration displays essentially a B type envelope and is centered

at 727 cm . The antisymmetric CH^ rocking vibration is located

at the shoulder centered at 700 cm ^. This assignment is tentative. The assignments are summarized in Table 3. The C-As

stretching vibration must be incorporated in the group of absorptions in the region from 500-550 cm ^ , but the absence of an obvious contour type prevents the designation of a specific

band origin. The skeletal deformation mode is likely in the region

near 200 cm ^, but could not be observed.

Reaction of ClCH ^ AsH ^ and I_2 Nmr studies of the reactions of CH^AsH^ and I 2 in benzene

followed for considerable periods of time (up to 3 yrs.) show a

-128-
slow, but remarkable, succession of changes in reaction mixture

composition [10,29]. Initially, CII^AsHI, CH^AsIj and HI are rapidly formed on iodine decolorization (immediately following

solution thawing) . When the CH^As^/^ ratio is initially one

or greater, excess CH^Asf^ is also seen. At later times

measurable quantities of H2 are formed, and simultaneous with

the maximum in ^ pressure (3 to 9 mos.) , the concentration of

HI becomes undetectable. At this time a new, broad nmr signal

appears at 8.04 t and is attributed to a family of iodineterminated, benzene-soluble polyarsines, I- (AsCH^ ) -I . At

still longer times, 1.5 to 3 yrs., precipitation of a purpleblack, essentially halogen-free ladder polymer of empirical

formula, CH^As , commences. Suggestions of mechanisms which

satisfactorily explain these observations have appeared elsewhere [29]. It was hoped that the details of these mechanistic

proposals might be tested by comparing the CH-jAs^/^ reactions

with ones utilizing ClCI^AsI^, where the greater electronegativity

of the chloromethyl group would offer predictable quantitative

differences

.

At CICH2ASH2/I2 molar ratios of 3:1 and 3:2 in benzene solution in sealed tubes, I2 was decolorized at a rate too fast to

follow by nmr. Immediately formed are ClCH

2 AsHI, ClCH2 AsI

2

, HI

and, at both molar ratios, excess CICH2ASH2. The proportion of

iodinated products is greater at the smaller molar ratio. Considerable overlap of the complex nmr patterns for CICH2ASH2 (AA'BB 1 ) and

CICH2ASHI (ABC) (see Table 1 for spectral parameters) made difficult

the retrieval of quantitative data from integrated peak-area ratios.

-129-
A striking feature of the spectra from the CH^As^/^

system prior to HI depletion is the spectral appearance of

excess CH^AsI^. Rather than the triplet-quartet pattern

exhibited by CH^AsI^ alone in benzene, the total spectrum for

excess CH^As^ in the iodine systems is a single line coincidental with the central line of the anticipated irethyl triplet.

If CH^AsI^ is rapidly exchanging its arsenic-bonded protons

with another compound far removed in chemical shift from vfAsI^),

then the As^ quartet could broaden sufficiently to merge with

the baseline, and the multiplicity of the CH^ triplet would

collapse to a singlet. Based upon an independent study of the

interaction of HI and CH^AsH2, it is concluded that the distortions in the CH.jAsH2 spectrum in I2 systems result from exchange

with HI [10]

.

H

CH

3AsH

2 + H'l * CH3 As . . . H J CH^AsHH ' + HI (a)

H . . . f

Significantly, the CICH2 spectral system of CICH2ASH2 shows

no indication of the proton-proton exchange broadening or multiplicity collapse found in the CH

3AsH

2 /I2 systems. Thus, the

rate for such exchange must be at least two orders of magnitude

slower on the ClCH

2 As >> moiety, as would be anticipated by the

reduced basicity of ClCH

2AsH2 / assuming that the mechanism for

exchange reflects the availability of the As lone pair. If, as proposed earlier, the exchange intermediate is four-centered (a),

-130-
then the rate-determining step may be proton (from HI) attack

on arsenic as in quaternization mechanisms, and thus related to

lone-pair availability. We have determined activational parameters for HI proton exchange with (CH

3

) 2AsH; roost significant

is AS 7* = -45.1 J mol * deg \ suggestive of an associative,

quaternization-like mechanism [29].

The first appearance of polyarsine* peaks in the CH^AsH.^/^

systems is accompanied by a permanent maximum in H2 pressure and

a disappearance of HI (as evidenced by a return of the complete

quartet-triplet spectrum for CH^AsH-^ ) . This is explicable in

terms of an irreversible consumption of HI through reaction with

CH.jAsH

2

, and requires a different orientation of the HI molecule

with CH^AsH^ than shown in equation b, e.g.,

H

'

I CH

3

AsH

2 + HI -> CH

3 As II * CH3AsHI + H

2

( b)

I H

Since the ability of HX to cleave As-As bonds increases rapidly

with halogen atomic weight, polyarsine formation is inhibited

until all HI is consumed.

If the rate of arsyl-HX proton-proton exchange is greatly

diminished for reasons of decreased lone-pair availability when

ClCH

2 AsH2 replaces CH^AsH,,, then the rate of H

2 production

(therefore also HI consumption and polyarsine formation) would

*Defined herein as meaning a degree of catenation greater than two.

-131-
be anticipated to be greater when R = CICH2 in (b) due to a stronger As ... I interaction. In confirmation of these predictions we find that the rate of H

2 evolution and the onset of

observable polyarsine formation occurs about 40-50 times faster

when R = C1CH

2

; when R = CH^, polyarsine onset does not occur

for up to nine months; whereas, when R = C1CH

2

, in systems of an identical initial As/I ratio, polyarsine onset occurs at 6 days.

In the 3:2 system, the concentrations of ClCH

2 AsH2 and

ClCH

2AsHI decrease slowly, and after 6 days at 60° ClCH

2AsH

2 disappears completely, while the concentration of ClCH

2AsI

2 very gradually increases (very much like the methylarsine reac- tions at similar reactant ratios). At 6 days two new peaks appear

at 6.16 and 9.72 t. The lower-field peak is close to that of

pentakis (chloromethy 1) cyclopentaarsine (av. 6.00 r) [30] and may

possibly be due to a condensed As-As bonded compound of the form

C1CH

2 (I) AsAs (I ) CH

2 C1 , a different diarsine, or a polyarsine of

greater complexity. In the methylarsine systems the open-chain

polyarsine resonance was found 0.35 ppm downfield from that of

(CH^As) t- . [ 10 ] If the assignment of the 6.16 x peak is correct,

explanation of the opposite relationship of linear vs. cyclic

chemical shifts may reflect the steric requirements of the C1CH

2 group in addition to electronegativity effects. Space-filling

models predict a reduction in As-As-As bond angle on shifting from

linear to cyclic forms for the chloromethyl derivatives, and the

reverse for the methyl derivatives.

-132-
The infinite-dilution chemical shift of HC1 in benzene is

9.86 t and moves downfield to about 9.2 t when saturated. HC1

could either derive from a thermal rearrangement of one of the

ClCI^As^ compounds, or from CI abstraction by a kind of intermolecular quaternization , i.e.,

2ClCH„AsH„ -> C1CH„-As-CH 0 -As + HCl.

2 2+ 2 | 2 \

H

H

Recleavage of the starred internal C-As bond by HCl would afford

CICH2ASHCI + CH^AsI^ by a process similar to that described

above for ICI^As^. Regardless of mechanism, the presence of

HCl does not interfere with As-As bond formation as does HI, and

its presence can account for the 9.72 x peak. Pure samples of

CICH2ASH2 in benzene show no tendency to form HCl even on prolonged storage at 60°.

Contrary to CH^As^ systems, the 6.16 x peak shows a slow

decline with time but at 13 days is joined by three new peaks

at 5.32, 6.41, and 6.85 x which may also be polyarsine modifications. The summed intensities of the four peaks attributed to

polyarsines show an increase with time. Whereas in CH^As^

systems (when the halogen is iodine) the polyarsine peak is

alv/ays a somewhat broadened single peak due to intermolecular

exchange of parts, the bromine reactions show polyarsine peaks

resolved into several component resonances from a reduced rate

of exchange [28] . Similarity is seen in the increase in the

electronegativity from iodine to bromine, and CH, to C1CH-:

-133-
both reduce the availability of the non-bonding pair for associative interactions. The rate of intermolecular exchange of

polyarsine parts is, therefore, also an apparent function of

lone-pair density. . •

As a further indication of polyarsine formation, a slight

but increasing amount of orange precipitate is formed during the

course of the reaction. A chemically similar orange solid occurs

as a by-product of all preparative routes to (ClCP^As),- and

likely is related to the red-brown solid frequently found in

association with (CH

3As)5 [30].

EXPERIMENTAL

Volatile, air-sensitive materials were handled in an allglass vacuum system of standard design. Nmr spectra- were recorded

on either a Varian A60A or a Perkin-Elmer R20B in sealed tubes;

chemical shifts and coupling constants were obtained from minimum

sweep-width spectra and represent the average of normally no fewer than five spectra. Mass spectra were recorded on a Varian

M-66 and a duPont 21-492; air-sensitive samples and all gases

were introduced through an unheated inlet system fitted through

the liquid-sample port. The ir spectrum was recorded on a Perkin-Elmer 225 using a 10-cm pathlength gas cell fitted with

CsBr windows. AsCl^ (Fisher Scientific) was distilled before

use; AsBr ^ and C1CH

2 P0C1

2 (both Alfa Inorganics) were used as obtained.

-134-
Chloromethy lar sonic acid and Bis (chloromethyl) arsinic acid

The arsonic acid, CICH-jAsO (OH)

2

/ was obtained from

ClCH

2AsCl [7] by 15% H

2 °2 oxidation [6]. Although elemental

analyses showed consistently correct CI : C: As ratios, variable

H content suggested that this arsonic acid, according to the

details of synthesis and purification (recrystallization) , acquired varying numbers of water molecules of hydration.

0

Similarly, (C1CH

2

) 2

Asfc>Hj was obtained from (ClCH^AsCl by 15%

H

2 0

2 oxidation.

'(Chloromethyl) arsine

A standard preparation of primary arsines (Zn/HCl reduction

of an arsonic acid) [31] was modified by using I^SO^ instead of

HC1 and by minimizing the arsonic acid solution concentration by

slow addition, a technique found important in maximizing arsine

yields in related reductions of As

2 0^ [32 ] . These modifications

are also noteworthy because of the complete absence of As-mirror

or subhydride formation which often accompany Zn/HCl reductions

of As (V) acids

.

Volatile products were removed to the vacuum system over a 30-hr period passing first through a -78° trap then into a -196°

trap. The -196° trap contained small quantities of AsH^ and

C0

2 as identified by their vapor-phase ir spectra. The -78° trap

contained ClCH

2 AsH

2 (61% yield based upon ClCH2 AsCl2

) . Small

quantities of H

2 0 were removed after condensation on P^O^q. Idealgas-law molecular weight of the purified product was 125.5

(calcd. 126.4). The vapor pressure data for ClCH_AsH 9 in the

-135-
temperature range, -47.5 to 13.2 is represented by l°g

1Q

P (mm) =

-1690. Bl 0 ^1 + 7.48407, and yield an extrapolated normal b.p.

of 94.0° and heat of vaporization of -32.31 kJ mol" 1

. The

extrapolated b.p. compares reasonably with C1CH

2 PH

2

, 68° [4],

Because of its tendency to dissolve in mercury, a separate

sample was used for each vapor pressure measurement. (Chloromethyl) arsine is a colorless liquid which shows no thermal

instability after one-year storage at room temperature. The

nmr, ms and ir data are given in Tables 1-3.

Bis (chloromethyl) arsine

(ClCH

2

) 2

AsH was obtained in small quantities as an occasional

Above

by-product of the procedure described tn pagfe e-. Insufficient

quantities were available for vapor pressure measurements. Like

ClCH

2

AsH

2 , (ClCH2

) 2AsH ls a colorless liquid of high thermal

stability. The nmr spectral data are given in Table 1.

(Chloromethyl) phosphine

C1CH

2 PH2 has been prepared by the thermal decomposition of

(chloromethyl) phosphinic acid [4], a not easily accessible starting

material. Although we found that commercially available C1CH

2 P0C1

2 could be reduced with LiAlH^ in butylether to C1CH

2 PH

2 in 15% yield,

we also found that the yield can be tripled if C1CH

2 P0C1

2 is first

converted to C1CH

2 P0 ( OCH3

) 2

. To 10.8 g (0.1 mol) NaOCH

3 suspended in 50 ml butylether was slowly added 16.75 g C1CH

2 P0C12 in 100 ml butylether at 0°. After

warming to room temperature, the solution was filtered and placed

-136-
in a 1000 ml, 3-neck flask attached to the vacuum line. To this

was slowly added 2 g LiALH^ suspended in 150 ml butyLether at

-20 to -30°. Volatile products were removed periodically for

24 hours. 2-ethoxy-ethanol (10 ml) was then added to destroy

excess LiAlH^ and any LiAl (PHCH

2 C1)4 [33] that had formed.

Following fractional condensation purification of the crude

product, 3.7 g C1CH_PH

2 (45% yield based on C1CH

2 P0C12

) , con- firmed by its molecular weight and spectral properties [4] was obtained. Small quantities of PH^ and CH^Cl were removed during

purification. The initial attempt at this reduction was con- ducted at room temperature; the yield was only 10% and a large

quantity of CK^Cl was obtained, presumably the result of C-P

bond cleavage.

Attempted Synthesis of (Iodomethyl) arsir.e

Into a 5 ml tube attached to the vacuum system containing

a 0.5 g of Nal (dried 2 hrs 3 300°) , 1.4 ml of dried acetone and

0.835 mmol ClCH

2AsH

2 were distilled. The mixture was; held at

35° in the absence of air for 8 hrs during which time a progressively heavier coating of an orange-brown solid collected on the tube wall above the acetone level. Both its appearance and

elemental analysis showed this . material to approximate (CH^As) x

, an amorphous, possibly linear, high-molecular-weight polymer.

After complete acetone removal i_n vacuo , a small quantity of a pale yellow liquid (presumed to be ICH-jAsH,,) distilled from the

reaction tube. During its passage to a collection trap, more

-137-
orange-brown solid was deposited. Only HI (identified only by

its molecular weight) was recovered from the trap (see text for

discussion)

.

Reaction of ClCH

^ AsH ^ and I_2 In two separate 5 mm nmr tubes/ each containing thoroughly

degassed and frozen solutions of 0.076 g I

2 (0.30 mmol) in

0.6 ml benzene (freshly distilled from LiAlH^), were condensed

fat -196°) 0.45 or 0.90 mmol ClCH

2AsH

2 to yield final 01CH2AsH

2 /I

2 ratios of 1.5:1 and 3:1. Each ratio was prepared in triplicate

as a check for consistency. Each tube also contained 0.30 mmol

of TMS as both an integration and chemical shift standard.

Iodine was decolorized completely as each tube warmed to the

solution melting pt (about 0°), whereupon the first nmr spectrum

was obtained. Between spectra the tubes were stored at 60° in a

thermostatted oven. Spectra were recorded at intervals sufficiently

often to follow completely all observable chemical events. At a

time dependent upon the initial As/I ratio (see text for details)

varying quantities of orange solid began to deposit on the tube

walls

.

ACKNOWLEDGEMENT

This research project was supported in part by the Office of

Naval Research and in part by the Center of Materials Research of

the University of Maryland.

-138-
REFERENCES

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S.B. Andrews, J. Organome ta 1 . Chem., 30 (1971) 151; (c) D.S. Matteson,

"Organometallic Reaction Mechanisms of the Nontransition Elements,"

Academic Press, New York, 1-974, Chap. 6.

2. (a) V. Chvalovsky, plenary lecture at IVth Int'l. Organosilicon

Conference, Moscow (1975), abstracts p. ; (b) J.M. Bellama and A.G.

MacDiarmid, J. Organometal. Chem., 18 (1969) 275; (c) ibid., 24 (1970)

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11. J.W. Emsley, J. Feeney and L.H. Sutcliffe, "High Resolution Nuclear

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12. E.J. Wells, R.C. Furguson, J.H. Hallett and L.K. Peterson, Can. J. Chem., 46 (1968) 2733.

13. R.A. Bernheinz, J. Chem. Phys., 40 (1964) 3446.

14. G. Fraenkel, J. Chem. Phys., 44 (1966) 4647.

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17. S.L. Manatt, E.A. Cohen and A.H. Cowley, J. Amer. Chem. Soc, 91 (1969)

5919, and references therein.

-139-
18. S.L. Manatt and A.H. Cowley, J. Amer. Chem. Soc, 91 (1969) 1913.

19. A. A. Bothner-By, Advan. Mag. Res., 1 (1965) 195; H.J. Bornstein and

N. Sheppard, J. Chem. Phys., 37 (1962) 3012.

20. M. Barficld and D.H. Grant, Adv. Mag. Res., 1 (1965) 149.

21. H.A. Bent, Chem. Rev., 61 (1961) 275.

22. I.H. Hillicr and V.R. Saunders, J. Chem. Soc, Dalton (1972) 21.

23. J.E. Huheey, J. Phys. Chem., 69 (1965) 3284; J. Hinze, M.A. Whitehead and

H.H. Jaffe", J. Amer. Chem. Soc, 85 (1963) 148.

24. A.L. Rheingold and J.M. Bellama, unpublished results.

25. R.C. Dobbie and R.G. Cavell, Inorg. Chem., 6 (1967) 1450; 7 (1968) 101.

26. D.P. Babb and J.M. Shreeve, Inorg. Chem., 6 (1967) 351; R.C. Dobbie and

H.J. Eme*leus, J. Chem. Soc, A (1966) 933; R.C. Dobbie, J. Chem. Soc,

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27. R.P. Bauman, "Absorption Spectroscopy," Wiley, New York, 1962, p. 529;

A.J. Downs in "Spectroscopic Methods in Organometa 11 ic Chemistry,"

W.O. George (ed.), Butterwor ths , London, 1960, p. 23.

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Chem. Soc. Meeting, Burlington, Vt., 1974, paper 142.

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-140-
TABLE 1 PROTON NMR DATA3

Compound X (CH) t (AsH) J(HCH) b

J (HEH) J (HCEH) b

ClCH

2

AsCl

2

6 . 77

ClCH

2 AsBr

2 6. 32

ClCH

2 AsI2 6.01

ClCH

2AsHI 6.72

6.67

6. 56 c 6.3

4.2

(C1CH

2

) 2 AsH 6.6

6.7

7 0

ClCH

2AsII2 d

6. 84 6. 54 -1.28' -16.99 7.09

4.65

C1CH

2 PH

2 d ' e

6. 38 6.65 9.8^ 10.4- 10.2

4.9

all spectra recorded in benzene except as noted, 10.00 t = TMS

in Hz , E = P or As

;

unavailable from data;

neat; J. ^ = 157 .8 Hz;

probably negative (see text)

.

-141-
TABLE 2 MASS SPECTRUM OF ClCH^AsH

m/e rel. abund. assignment9

150 4.4 As

2 128 7.4 37 + ClCH

2 AsH

2 127 1.0 37 +

'C1CII

2 ASH

126 27.6 ClCH

2 AsH2 (23.3), ClCH

2 As (4

125 4.0 ClCH

2AsH (2.5), CICHAs (1.5)

124 13.3 3 ClCH

2 As (13.0) , CICAs (0.3)

123 4.4 CICHAs

122 1.1 35ClCAs+

113 5.7

37ClAsH+(R)

112 5.0 37ClAs+(R)

111 19. 8 35C1ASH+(R)

110 16.2 35ClAs+(R)

92 27.5 CH

3

AsH

2 +

91 8.7 CH

2 AsH

2 +

90 100.0 CH

2AsH+

89 62.8 CH

2 As

+

88 55.9 CHAs+ (53.4), CH

2 37 ' 37 Cl

2+

(2.5)

87 5.0 CAs

+

86 12.2 c„

2

"'"cl2

+

84 28.9 CH

2 35,35C1

2 +

78 39. 8 AsH

+

-142-
TABLE 2 continued

m/e rel. abund. assignment3

77 16. 2 AsH_

+

2 76 69. 4 AsH

+

75 33.

1

As

+

51 12. 8 37C1CH

2 +

50 2.6 37 + C1CH

49 43.9 35C1CH

2 +

(38. 3) , 37ClC+ (5.6)

48 7.8 35 + C1CH

47 16. 8 35 cic+

37 2.3 37ci+

35 7.1 35 ci+

Parenthetical numbers are the relative abundances of species of same unit m/e value; (R) represents obvious rearrangement peaks,

other fragments may also be the result of rearrangement, e.g.,

ClCH^As; metastable transition data were not available.

-143-
TABLE 3

in SPECTRUM OF ClCil Asll

2

vid. no. Ass ignment Frequency (cm ) Intensity 3

A' Species

VI C-H stretching 2950-2970 m

V2 As-H stretching 2085-2130 vs V3 scissors 1410 vw

v4 wagging 1188 s

v5 ASH2 scissors 963 m

v6 ASH2 wagging 760-800 m

v? C-Cl stretching 727 m

vs • C-As stretching 528 w

vg Cl-As-C deformation

(not observed)

A" Species

250 (est.) -

vlO C-H stretching 2950-2970 m

vll As-H stretching 2085-2130 vs

vl2 CH2 twisting 1108 m

vl3 ASH2 rocking 862 m

vl4 ASH2 twisting 760-800 m

vl5 CH

2 rocking 700 w-sh

av = very strong, s = strong, m = medium, w = weak, sh = shoulder

.

-144-
Figure 1. 60MHz pmr spectrum of CICH2ASH2 (upper) as a 107, solution in benzene

with the "best fit" computer simulation (lower). The up-field half

of the observed spectrum is broadened by residual quadrupolar coupling

to 75^3, Chemical shifts are measured from TMS = 0Hz

.

-145-
J

' » ' I ' » I ' » » 1 I ' ' I 6.5 t 7.0

Figure 2. 100MHz pmr spectrum of (ClCH2)2 A9H as a 10% solution in benzene.

TMS « 10 T".

-146-
(HALOMETHYL) ARSENIC COMPOUNDS

II.* PREPARATION AND CHARACTERIZATION OF PENTAKIS (CHLOROMETHYL)CYCLOPENTAARSINE

ARNOLD L. RHEINGOLD**

Department of Chemistry, State University of New York, Plattsburgh, New York

12901 (U.S.A.)

JON M. BELLAMA

Department of Chemistry, University of Maryland, College Park, Maryland

20742 (U.S.A.)

*For Part I, see previous article.

**To whom correspondence should be addressed.

-147-
SUMMARY

Hypophosphorous acid reduction of chloromethylarsonic acid produces

the novel cyclopolyarsine , pentakis (chloromethyl)cyclopentaarsine (PCCA).

PCCA possesses a greater thermal and oxidative stability than other cyclopolyarsines previously studied. The dynamic pmr properties of PCCA are interpreted as a combination of a low-energy limited pseudorotational motion and

a higher-energy As-atom inversional process. An alternative to ground-state

d-orbital participation in the interpretation of the electronic spectra is

offered

.

INTRODUCTION

It was recognized early in the history of organoarsenic chemistry that

products containing As-As bonds were common terminations of reactions involving

mono- and diorganoarsenic reagents. With diorganoarsenic reagents the terminal

products are simple diarsines, R2ASASR2; but with monoorgano reagents, the

possibility for a great variety of oligomers (usually cyclic) and polymers

(chains and ladders) exist, all characterized by the empirical formula

RAs Jl,23. Cyclic oligomers, (RAs) n where R = alkyl or aryl and n = 4 to 6,

all possess puckered rings of As atoms, and especially when R = alkyl, appear

to have a single, preferred value of n for each R group. All primary alkylsubstituted cyclopolyars ines are pentamers (RAs)5: R = Me (3j , Et{4j , Pr £5] ,

ti-Bu[6j , and _i-Bu{_6}; all secondary and tertiary alkyl-substituted cyclopolyarsines are tetramers (RAs)4: R = cyclohex [6] , £-Br[6j, and £-Bu[6j.

CF3 substitution produces both eye lotetramer and eye lopentamer and is therefore an exception (7,8j.

-148-
This paper describes the preparation and physical characterization of

a new cyclic oligomer , pentakis (chloromethy l)cyclopentaarsine (PCCA),* of

interest because of the presence of both a sterically demanding and electron

withdrawing substituent. Nixon reports £9 J that one of the products of the

decomposition of CICH2PF2 under mild conditions is a not well-characterized

yellow liquid believed to be a cyclic polyphosphine , (ClCH2P) n , with n most

likely five [lCj.

EXPERIMENTAL

PMCA was prepared by the hypophosphorous acid reduction of sodium

methy larsonate [.llj but was not distilled before use. Chloromethy lar sonic

acid, prepared as previously described {12}, was reduced in aqueous solution

by 50% hypophosphorous acid to the cyclic oligomer, (ClCH2As)5 (PCCA). PCCA

separated as an intensely yellow, heavy oil of -undetermined boiling point which

was purified by repeated 5% NaHCC>3 and water washings followed by a 2 hr

degassing at 10"^ mm Hg, but was not distilled. Previous experiences have

shown that PMCA undergoes partial, irreversible and not .well understood

changes on mild heating, e.g., during distillation £4,13^. PCCA is soluble in

both benzene and ether, and insoluble in water. (Found: C, 9.72; H, 1.65;

CI, 28.28. CH2 AsCl calcd.: C, 9.66; H, 1.62; CI, 28.49%)

PCCA's susceptibility to aerobic oxidation is undetectable, as compared

to PMCA, which in thin films is pyrophoric. Additionally, no arsine-like

*PCCA = pentakis (chloromethyl)cyclopentaarsine , (ClCH2As)5; PMCA = pentamethylcyclopentaarsine , (CH3As)5J PFCA = pentakis(trif luoromethyl)cyclopentaarsine ,

(CF3As>5; and PECA = pentaethylcyclopentaarsine, (C^C^As^.

-149-
odor is found surrounding exposed samples. PMCA often forms solid red-brown

modifications on standing which when heated to 180° revert to its original

state £l3j. Purified PCCA, however, showed no tendency to produce solid

forms even after a 20-day exposure to humid air. During its preparation

PCCA did form red-brown solids which could not be thermally reverted to a

liquid state even when heated to 300° in an evacuated tube.

The product's pentameric state was deduced from its nmr spectrum which

according to whether it was measured neat or in solution displayed peaks in

integrated ratios of either 2:3 or 2:2:1, and was confirmed by its osmometric

molecular weight: found, 589, calcd. 612. Considerable difficulty was

experienced in obtaining a satisfactory mass spectrum of PCCA attributable to

its extreme involatility. Samples of PCCA heated to 260° under nitrogen

showed no evidence of thermal decomposition; PMCA decomposes irreversibly

at 205°.

The nmr spectra were recorded on. either a Varian A-60D or a PerkinElmer R20B each equipped with their manufacturer's variable temperature

controller; uv spectra were recorded on a Cary 14.

RESULTS AND DISCUSSION

Structural data on pentameric cyclopolyarsines are limited to the methyl

derivative. Both electron £3] and x-ray diffraction £l3*] studies support the

presence of a puckered f ive-membered ring. The absence of symmetry in the

crystallographic structure (Fig. la) dictates that each methyl group is

unique and that, if the solid-state structure persists in solution, the

nmr spectrum should consist of five equal-intensity lines. All spectra of

cyclopentaarsines show three or fewer lines; even the nmr spectrum of

-150-
PFCA, where chemical shift differences are large and the .likelihood of

accidental degeneracies small, displays only a three-line pattern of

intensity ratio 2:2:1 [l^j . Furthermore, five-line spectra have not been

observed for either PMCA or PFCA even when cooled to -100° . For

PCCA, depending upon solvent, dilution, and temperature, spectra always show

either a 2:2:1 or 2:3 pattern.

One is forced, therefore, to propose a fluxional motion for cyclopentaarsines which generates a time-average plane of symmetry (Fig. lb).

As the symmetry generating notion is still rapid at very low temperatures,

it must be characterized by a low activational free energy. The phenomenon

responsible for these effects is likely one of five possibilities: 1) As

atom inversion, 2) ring opening-closing equilibria in which pentameric forms

are retained, 3) ring opening-closing equilibria involving alteration in

oligomer size, 4) pseudorotation, and 5) that the asymmetrical solid-state

structure results from crystal packing requirements which relax in solution

(a non-f luxional interpretation).

Although Lambert has shown that simultaneous inversion of both As atoms

in diarsines is more rapid than single inversion in monoarsines (due perhaps

to the stabilization of planar intermediates through a maximization of

P77 - d TT interactions) £l5} , reasonable estimates for minimal activational

barriers for As-atom inversion are undoubtedly not less than 80-85 kJmol"-'- ,

a barrier seemingly unsurmountable at -100° especially since a symmetry-generating

motion would be expected to have a negative activational entropy. £G (-100°)

for the observed symmetry generating motion can be approximated from chemical

shift data as being not greater than 25-30 kjmol"^-. In view of this, a

-151-
recently proposed wag-inversion mechanism £l4j must be viewed with skepticism.

Furthermore, Mislow has also demonstrated that inversion barriers in phosphines

(including diphosphines) can be correlated with substituent electronegatives

the greater the electronegativity the higher the barrier £l6,17]. Inversional

processes may, however, be responsible for a different, high-temperature

fluxional behavior described below.

All ring opening-closing equilibria necessitate As-As bond cleavage,

but may be facilitated by impurities introduced either during preparation or

through thermolytic or photolytic decomposition of pure cyclopolyarsine.

Examples of sample-history dependent phenomena are known Again, however,

although possibly relevant at elevated temperatures, ring opening equilibria

whether catalyzed or not, require not only the expenditure of the As-As

bond dissociation energy (ca. 150 kjmol"!), but also the loss of the difficulty estimated stabilization achieved through transannular , non-bonded AsAs interactions.*

Most attractive of the alternatives appears to be pseudorotation, a

rotation of the position of maximum puckering in stepwise, random, or alternate exchange (between two favored positions) patterns resolvable into vertical

motions of As atoms. Pseudorotation of unspecified pattern was first suggested

by West £4] as an explanation for these low-energy fluxional processes.**

*It is difficult to account for the remarkable thermal stability of cyclopolyarsines compared to catenapolyarsines unless additional sources of stabilization,

e.g., transannular attractive interactions, are proposed.

**Wells [l43 has proposed that the high-energy phenomena described elsewhere in

this paper are attributable to a stepwise pseudorotation.

-152-
Unlike inversion, pseudorotation preserves Che non-equivalency of As atoms.

Differences must therefore exist in the barriers for specific pseudorotationa

transitions (both 1,2 and 1,3 exchanges are possible). One concludes that

pseudorotation need not occur at all As atoms with equal frequency, i.e.,

the differences between the bottoms and saddle points on a five-well, freeenergy annulus will differ at each position. The simplest (and therefore

probably least energy) pseudorotational motion capable of generating the

required symmetry would be one that made the (1) and (2) positions equivalent

and transferred the puckered position to (4) (see Fig. 1) followed by a

return of puckering to either position (1) or (2). Note that motion at

position (4) is not a requirement; a simple torsional motion along the

As(l)-As(2) axis suffices.

The general features of the solid-state structure of PMCA also pertain

to those cyclopentaphosphines whose structures have been determined ^18^

•

It is reasonable, therefore, to conclude that the favored ring conformation

in solution phases closely resembles the solid-state structure, a structure

preferred for its minimization of repulsive electronic and steric interaction

and not the result of crystal packing requirements.

The pmr spectrum of PCCA would be expected to be more complex than that

of PMCA. In the absence of a symmetry generating motion, not only are the

chloromethyl groups anisochronous , but so also are the two protons of each

group, producing (in theory) five, distinct AB spin patterns (presuming that

coupling between adjacent chloromethyl groups is negligibly small). In the

presence of the proposed symmetry-generating torsional motion, the spectrum

would reduce to two distinct AB patterns (the protons on C(l) and C(2)

producing degenerate AB patterns, likewise C(3) and C(5)) and a single line

-153-
for the isochronous protons on C(4). As J(AB) /^W(AB) becomes large (>-1.0),

the appearance of an AB pattern collapses to a closely-spaced central doublet

as the outer lines fade in intensity, and as AS)(AB) approaches zero, all

lines collapse to a singlet. It is reasonable to expect that the values of

V (A) and -v> (B) will differ only slightly.

As a 207o (by weight) solution in chlorobenzene, PCCA shows a narrow

line-width (< 1.0Hz at half height) three-line spectra in a 2:2:1 intensity

ratio at 5.91, 6.05 and 6.06 T . The two closely spaced high field peaks

merge at similar dilution in benzene and toluene. Since the line with a

relative intensity of one must represent the C1CH2 group on As(4) and since

the CICH2 environments for positions (3) and (5) resemble (4) more than (1)

or (2), the 5.91T line is assigned to the (1),(2) pair and the 6.05T line

to the (3), (5) pair.

At room temperature and below, spectra of neat PCCA are badly viscosity

broadened as seen also in PMCA, but at 42° show the same three-line spectrum

found in chlorobenzene. (Fig. 2) Two smaller peaks (totaling about 10% of

the intensity of the main peaks) appear upfield at 6.22 and 6.27X. The

presence, position and intensity of the weaker peaks are not a function of

sample history or its method of preparation, and must therefore, be due to

species derived from, and in equilibrium with, PCCA. Similar weak up-field

peaks are found in neat samples of PMCA and similar arguments have been

applied to their origin [4,14,193-

The nmr spectra of PCCA lead, therefore, to the conclusion that the

chemical shift difference between geminal protons at positions (1), (2),

(3) and (5) must be unobservably small, i.e., th'e anticipated AB quartet

patterns have collapsed to singlets. A 100 MHz nmr spectrum of PECA has

-154-
been published by West [4 J. At 120° where all viscosity broadening has

disappeared, he finds a spectrum of high complexity, deriving, he suggests,

from slow pseudorotat ion producing non-equivalency among all ethyl groups.

If West's suggestion is accepted, the conclusion must be that PMCA pseudorotates nmr rapidly at -100° while PECA does so only slowly at +120°; a

220° temperature difference for these essentially isoentropic processes appears

unreasonable. Clearly, however, the methylene portion of the ethyl group

should, at least in theory, also contain anisochronous protons and produce,

in the presence of nmr-fast pseudorotation , one A2B3 and two ABC3 P atterns

(which could be indistinguishable from A2B3 patterns if (AB) is small).

In fact, West's spectrum looks more like overlapping A2B.J patterns where

J (AB ) / (AB ) is about 0.1; the anticipated geminal constant for a freely

rotating ethyl group is about 7Hz and the PECA spectrum appears to have a

about 75Hz. Thus if, as in PCCA, the chemical shift difference

between geminal (CH2) protons is unobservably small, West's spectrum is

reasonable for three overlapping A2B3 patterns, not five triplet-quartet

(first-order ethyl) patterns.

When PMCA is heated above 160° complex, often poorly reproducible, and

sometimes sample history dependent phenomena occur Wells fl4J reports that

the nmr multiline spectra of PMCA and PFCA collapse reversibly to single

lines; above about 170° the lines broaden again continuously to the highest

temperature observed, 200°. In the range of 170-200° the smaller upfield

lines also broaden and eventually disappear. West, however, finds no loss of

triplet structure or alteration in the upfield peaks when fresh samples of

PMCA are heated to 178°, but does find the previously reported broadening and

-155-
collapse of all lines when samples have been preheated at 190° for 2 hrs £4}.

He found that preheated samples of PMCA contained a high mass spectral abundance

of (CIl3)4As2 + tons at m/e 210 that were absent in unheated samples. Tetramethyldiarsine is a product of the pyrolysis of (CH3As)5 and does catalyze

further ring opening; ring opening/closing equilibria are possible explanations

for the high temperature nmr phenomena £l9j

Our own experience with PMCA resembles that of Wells ^143 ; although no

m/e 210 ions were found in our samples, coalescence was achieved at about the

same temperature he observed. Samples of PMCA that were thoroughly degassed

or left undegassed, samples purposely poorly washed to leave residues of

excess hypophosphorous acid or carefully and repeatedly washed, samples

distilled or crude, all showed coalescence at + 3° of Wells' temperature.*

The exposure to normal laboratory fluorescent illumination did, however,

produce significant changes; after one week, exposed samples of highly refined

PMCA showed a coalescence temperature 10° below Wells' temperature. West does

not report if his preheating occurred in light or darkness.

Up to 80° the three-line neat PCCA spectrum sharpens as viscosity effects

lessen. Above 80° the lines again broaden; the two closely spaced lines at

6.05 and 6.05T coalesce at 110° (presumably the result of line broadening

or line position changes but not chemical averaging) and both remaining lines

continue to broaden but do not coalesce up to 160° where heating was discontinued (Fig. 2). If extrapolated, the broadening trend would lead to

coalescence at about 185°, very near the coalescence temperature for PMCA.

*Unrefined samples did show much more rapid formation of polymeric redbrown catena-polymethylpolyarsine than found in refined samples.

-156-
Contrary to the observations for PMCA [j4,14j, however, high-temperature

behavior of PCCA is not rapidly reversible; the broadened, two-line spectrum

of neat PCCA at 160° does not fully revert to its room-temperature spectrum

until 24 to 30 hrs have elapsed. Since all other cyclopentaar9 ines so far

studied rapidly (as fast as samples can be cooled in the spectrometer,

~» 20°/min) equilibrate on cooling, only the steric bulk of the CICHo groups

in PCCA can account for the retarded rates of reequilibration. At these

elevated temperatures, As-atom inversional barriers for PCCA can be realistically surmounted. In this regard, Lambert has found that As-atom inversion

in diarsines becomes nmr-rapid at about 180° ^L5] ; at ISO 0 coalescence of

the methyl resonances for the d,_l and me so forms of 1,2-dimethyl, 1,2-diphenyldiarsine is achieved through inversion (coupled with As-As bond rotation).*

For cyclopentaarsine initially in the crys ta llographic structure,

inversion at three of the five As atoms produces structures possessing up/down

non-bonding electron pair (or substituent) arrangements different from

that of Fig. 1 as suggested by Van Wazer [isQ . In Fig. 3 the various

possibilities are shown. The structures have been arranged intuitively in

order of increasing internal energy by consideration of the number of nearestneighbor electron-pair, electron-pair repulsions. We propose that these higher

energy invertomeric forms become significantly populated at higher temperatures

producing line broadening. On cooling, PMCA rapidly reverts to its thermal

ground state, but PCCA is apparently "frozen out" in thermally excited invertomeric forms, i.e., PCCA readily supercools. The higher barrier to interconversion of invertomeric forms for PCCA must derive from crowding imposed by the

*Mislow £16^ suggests that the coalescence process may be intermolecular . This

suggestion has received recent support from a restudy T20^ of dynamic processes

in diphosphines

.

-157-
sterically demanding chlorine atom. Each Inversion requites a simultaneous

C-As bond rotation to sterically accommodate the CI atom (convincingly seen

from opnce-f 1 LI ing niodeis), but such rotations are restricted by the severe

interaction of the Cl atom with the As atoms three bonds removed. These

steric entanglements prevent rapid return to a thermal ground state. Concentration dependency studies in ^-butyl-benzene indicate that the rate of

return to ground state is an intramolecular process. There is no reason

to believe that the population of excited-state invertomeric forms does not

also satisfactorily explain the high-temperature behavior for all cyclopentaarsines

.

PCCA exhibits several other properties that differentiate it from other

cycloarslnes . It is, for instance, indefinitely stable in contact with

humid air, whereas PMCA is pyrophoric, and PFCA is rapidly hydrolyzed at

room temperature £7]] . Consistent with its stability to oxidation and hydrolysis

is our finding that PCCA possesses the longest wavelength uv absorption of

any cycloarsine reported, A (max) 350nm, as compared to 300nm for PMCA

when measured as 10"^M solutions in benzene. This uv transition is attributed by many to a lone-pair delocalizat ion into an empty _d level or other

orbital of suitable symmetry on an adjacent arsenic atom £2l]. There is

great difficulty, however, in extending this argument to a picture of circumannular derealization in the classical aromatic sense. A molecular orbital

constructed from £ and d orbitals cannot produce conjugation in a non-planar

structure via j>7T — d TT bonding.

An alternative to ground-state d-orbital involvement can be proposed.

Two filled molecular orbitals constructed of £ and £ atomic orbitals, e.g.,

two non-bonding electron pairs on adjacent As atoms, can interact to an extent

determined by their dihedral angle (along the As-As bond axis) reaching a

-158-
maximum at an angle of 0°. Although the total energy of such a system remains

constant with variation in dihedral angle (if secondary effects are neglected),

the HOMO does increase in energy thus lowering the HOM0-LUM0 separation,

Fig. 4. Similar molecular-orbital descriptions have been used effectively

by Weiss [22^ in the analysis of charge-transfer spectra of disulfides and by

Cowley and Dewar Q>3) in a photoelectron-spectroscopy study of CF3~substituted

cyclotetra- and eye lopentaphosphines . Cowley and Dewar find evidence not

only for 1,2 lone-pair interaction but also for transannular interaction.*

Other aspects of their data strongly support the position that ^P" ~ iL*"1

"

bonding is relatively unimportant in phosphorus-phosphorus bonding; one can

safely assume the extendibility of these results to arsenic-arsenic bonding

as well. If, by analogy to cyclopolysilanes |24,25j, the LUMO for cyclopolyarsines is largely ci in character, some excited state derealization appears

likely.

*It should be pointed out that in their study Cowley and Dewar ^23) found

evidence for lone-pair interactions in (CF3P)4 but not (CF3P)^. This they

attribute to the absence of symmetry in the pentamer but give reference only

to a solid-state structural determination. In solution, however, Wells £l4^

has found, as is true also for other cycl,opentamer s , that at least Cs_ symmetry

is achieved permitting symmetry-allowed lone-pair orbital interactions. This

leads to three presently unresolvable interpretations: 1) eye lopentamers

revert to an asymmetric structure in the vapor state (required for photoelectron

spectroscopy), 2) fluxional motions which create the C£ symmetry prevent

orbital association (unlikely considering the vast difference in time scales),

and 3) that Cowley and Dewar's interpretation of their spectra is incorrect.

-159-
It is important to note that the lowest energy absorption in cyclopentaarsinea (and phosph I uos ) la confederal) ly fi»d-Hh I f Led compared to uithiT

that require a time-average structure with a 0° (or near 0°) dihedral angle

between two adjacent lone-pairs.

The steric restrictions imposed by the CICH2 groups may have a dampening

effect on pseudorotat ion (or a limited pseudorotation such as the torsional

motion earlier described) thus restraining the oscillations to a narrower

region either side of a 0° dihedral angle.

In bis fcatena-poly(methylarsenic)j (BCPA), a high-molecular-weight

ladder polymer constructed of CH3~substituted As atoms \_2\, all non-bonding

electron pairs along a ladder upright are constrained to a nearly 0° dihedral

angle relationship. BCPA is intensely purple, X(max ) ca - 450nm and shows

the electrical properties of an intrinsic semiconductor with an energy gap

of about 1.3 ev. Ac conductivity measurements strongly indicate a "hopping"

mechanism for electron mobility ^27^ suggesting that extended excited-state

derealization in this (and perhaps all) polyarsines is unimportant in

confirmation of West's electrochemical results [24}.

ACKNWLEDGmENT

This research project was in part supported by the Dffice of Naval

Research

.

eye Joletra-or eye tohexaaraJ lien [21,26] , and that it la only the eye lopenlamer

s

-160-
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-161-
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.

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J

-162-
m

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-163
-164-
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-166-
A REPORT SUBMITTED

TO

NATIONAL BUREAU OF STANDARDS

TO

DR. MARTIN BROADHURST

JERRY E. WHITE

ORGANIC MATERIALS LABORATORY

ARMY MATERIALS AND MECHANICS RESEARCH CENTER

WATERTOWN , MA. 02172

-167-
SYNTHESIS OF POLY(ARYLAMINOPHOSPHAZENES)

J. E. WHITE,*

R. E. SINGLER,

and

S. A. LEONE**

ARMY MATERIALS 8 MECHANICS RESEARCH CENTER

POLYMER AND CHEMISTRY DIVISION

WATERTOWN , MASSACHUSETTS 02172

Author to whom correspondence shou.ld be addressed.

Present address:

Department of Chemistry

Merrimack College

North Andover, MA. 01845

-168-
SYNOPSIS

The synthesis of a series of poly[bis(arylamino)phosphazenes] is

described. The polymers usually were prepared by treatment of polydichlorophosphazene in benzene-tetrahydrofuran with arylamir.es/triethylamine at reflux for 48-144 hr. The polymers, having viscosities

of 0.3 - 1.4 dl/g, are essentially free of active chlorine sites,

as shown by elemental analysis and their long-term hydrolytic stability.

Thermal analyses revealed glass transition temperatures between 53°

and 105°C and decomposition temperatures between 243° and 266°C.

Analysis by differential scanning calorimetry revealed no first order

endotherr.ri c transitions. For comparison with the arylamino polymers,

poly (diethyl ami nophenyl ami nophosphazene ) , poly [bis (benzyl ami no )phosphazene]

and poly[bis(s -phenethylamino)-phosphazene] were prepared and are

e descri bed.

-169-
INTRODUCTION

The high-temperature melt polymerization of hexachl orocycl otri

phosph'azene (I) is known to lead to high molecular weight, open-chain

1 2a 3 polydichlorophosphazene (II). ' ' The hydrolytically unstable elastomer

II may be converted to hyrolytically stable derivatives by nucleophilic

2a replacement of the active chloro ligands with organo groups. The

properties of the resulting polymers depend greatly on the nucleophile

chosen, a fact which allows polydichlorophosphazene to act as a common

precursor to a large variety of materials.

3 2a Although a large number of poly(aryloxy- ) , poly(alkoxy-) and

4 5 poly(alkylaminophosphazenes) ' have been prepared, only scant attention

has been paid to the synthesis of poly(arylaminophosphazenes)(III)

.

While there are numerous reports describing the reactions of cylic

trimer I and octachlorocyclotetraphosphazene with various aryl amines,

poly[bis (phenylamino)phosphazene] (Ilia) appears to be the only example

of the polymeric class III that has been prepared. Because of the

paucity of information regarding arylamino derivatives of II, and because

3 6 of our continuing general interest in the chemistry of polyphosphazenes""

and their potential appl ications , we undertook the synthesis of a series

of poly(arylaminophosphazenes)

.

-170-
RESULTS AND DISCUSSION

3 Cyclic trimer I was polymerized as described previously, and polydichorophosphazene (II) was isolated in yields of 17 to ^3" (eq. 1).

Although the reaction of polymer II with

ci

2 P<

\, CI NHA

N n (1)

I \ A AMU \ r

cl

Px

P CI, in vacuo » " [ f =N]

n >/ cfr£ C1

" ^"V

2

2 Cl " d

n

E ¥ NHA

r

I II

ammonia and methylamine above room temperature can lead to cross-linked

45 products (eq. 2), ' anilines react cleanly with II to give soluble products

(eq. 1), presumably because steric contraints prohibit the cross-linking

reaction.

Cl

iP=N -

ICl

Cl

I - P = N

i (2) RNH

2 ^ R -

[1 -r

i

/Cl

-171-
In the synthesis of poly(alkylaminophosphazenes) , both excess

alkylamine or a tertiary amine have been employed as hydrohalide ac5 ceptors. We found the use of the latter to be more satisfactory, and

the poly(arylaminophosphazenes) (III) reported here usually were prepared

by the treatment of polymer II in tetrahydrofuran-benzene with aryl amine/

triethyamine (both amines usually were in 4 to 5-fold molar excess) at

reflux temperatures (eq. 1). Poly[bis(phenylamino)phosphazene] (Ilia)

,

prepared using triethylamine as the HC1 acceptor, has a higher intrinsic

viscosity and less residual chlorine than Ilia prepared using aniline alone,

if all other reaction conditions remain equal. Aniline, when added dropwise to a solution of II, appears to react rather slowly at room temperature,

aniline hydrochloride appearing only after heating has commenced. On the

other hand, dropwise addition of a solution of aniline and triethylamine

to II results in almost immediate formation of precipitate (triethylamine

hydrochloride), and the reaction is quite exothermic. Also, the formation

of polymer hydrochloride salt during the reaction 'of II with alkylamines

has been reported, and prolonged treatment of the product with a tertiary

4 amine was required to remove traces of HC1 , a problem that should be

circumvented by the use of triethylamine as the HC1 acceptor during

reaction.

The reactions of aniline, m- and p_- alkyl-, and p_-methoxyphenyl amine

with polydichlorophosphazene are essentially complete afteT 48-56 hr at

reflux (products Illa-g), with yields of purified products ranging from

25% to 73% (Table I). Difficulties were encountered during the

synthesis of poly[bis-(m-methoxypheny1amino)phosphazene], which was isolated

in .pure form in about 5% yield. Also, steric hindrance prohibits complete
reaction of o_-toluidine with II under the conditions discussed above, since

the product can cross-link due to attack of water (used in purification)

2c on the labile P-Cl bonds remaining on the polymer chain. Thus, the

material gave only a gel when dissolution in common solvents was attempted.

This insoluble material .contained 4.85% residual chlorine.

In general, preparations of poly[bis(halophenylamino)phosphazenes]

(Illh-k) required longer reaction- times (up to 144 nr.) compared with

the syntheses of llla-g, probably owing to lesser nucl eophi 1 i ci ty of

the halophenylamines . Yields of the halophenylamino polymers ranged

from 22% to 62% (Table I), with the exception of 1 1 1 h , which was isolated

in 3% yield. Use of higher boiling solvents (diglyme-toluene) to decrease

reaction times resulted in extensive degradation of the polymer backbone.

The reaction of m-aminobenzotrifluoride with polymer II gave a substituted

product in reasonable yield (21%) but with a low inherent viscosity

(0.12 dl/g) and a poor fluorine analysis.

All of the arylamino polymers listed in Table I contain

less than 1% residual chlorine, presumably as P-Cl , except for 1 1 1 k

(1.09%) and the chlorophenylamino polymers 1 1 1 h and Illi, for which

no direct measurement of small amounts of P-Cl is available. Carbon

analyses for those arylamino polymers shown in Table I were from 0.90%

to 3.19% below theory and have no correlation with the amount of residual

chlorine present. Similar behavior has been observed for certain poly(alkyl4 ami nophosphazenes ) and was ascribed to the presence of impurities.

That substitution of chloro ligands is virtually complete is demonstrated

not only by the low chlorine content of polymers III, but also by the

fact that they apparently are stable and remain soluble indefinitely,

-173-
a strong indication that the number of labile P-Cl bonds remaining

in the polymer is small. For example, polymers Ilia, IIIc, and 1 1 1 g

,

which had intrinsic viscosities of 1.4, 1,4, and 1.3 dl/g respectively

immediately after isolation, showed only slight decreases in viscosity

(1.2, 1.02, and 1.2 dl/g respectively) after storage under ambient

laboratory conditions for almost a year.

Although the slightly low carbon analyses for III possibly

4 are due to the presence of trace impurities or incomplete burning

of III during analyses, they may reflect structural variations in the

polymer chain. One possible variation could be the imino intermediate

(III 1 ) shown in eq. 3. After initial substitution of a unit of II

by

MAr ArNH MHAr -HC1 !! ArNH MHAr

(3) II . 2—> -p=N- -P=N- -f=HCl " NHAr

III' -III

an aryl amine. molecule, the imino group might be formed by elimination

of HC1 , as shown. Addition of a second aryl amine molecule to III'

would give structure III. Survival of a few imino groups could account

for the low carbon analyses, and the fact that triethylamine as a hydrohalide

acceptor gives Ilia with less residual chlorine than when aniline,

a weaker base, is used in excess lends some support to this explanation

for the analyses of the arylamino polymers. Also, formation of imino

q intermediates during the reactions of trimer I with ammonia and with

tert-butyl amine ® has been proposed. However, treatment of polydichloro-

-174-
phosphazene (II) with a 20-fold molar excess of aniline or with a 10-

fold molar excess of aniline and a 10-fold molar excess of triethylamine

yields . products for which the carbon analyses are about 2% below theory;

it seems unlikely that the imino structure III

1 would survive such

large excesses of reactants. In addition, one would expect that any

imino groups that survive the reaction would be at least as labile

to attack by water (used in purification) as would P-Cl and therefore

provide a cross-linking site just as effective as P-Cl . Such crosslinking, as mentioned, is not observed for the arylamino polymers.

Even so, a small number of imino groups, as well as other structural

variations, would be difficult to detect and cannot be ruled out completely

The glass transition temperatures (DSC) of polymers III

are rather high (53° to 105°C; Table I) compared with those of poly(aryloxy

phosphazenes ) (-37° to 6°C ). A similar difference exists between

2d

poly(al koxyphosphazenes) (-84° to 14°C ) and poly(alkylaminophosphazenes)

4 5 (-11° to 30°C ' ), suggesting lower torsional mobility of the amino

5 compared with the oxy analogs. Hydrogen bonding has been suggested

as a reason for this decrease in torsional mobility,^ although the

glass transition temperatures of poly[bis(piperidino)phosphazene] (19°C )

and poly[bis(dimethylamino)phosphazene] (-4°C ), polymers in which

there is no opportunity for hydrogen bonding, are in the range of those

of primary alkylamino polymers. The presense of aryl group's" in III also

contributes to their high glass transition temperatures, since the

glass transitions of poly(aryl oxyphosphazenes ) occur at much higher

temperatures than those of the alkoxy polymers. Solution cast films

of some of the arylamino polymers are quite brittle, as one would expect

-175-
for materials having such high glass transition temperatures.

Polymers III gave no indication of having simple first order

endothermic melting points (DSC).

The decomposition temperatures of the poly(arylaminophosphazenes)

range from 243° to 266°C (TGA) in static air (Table I) and are generally

lower than those of the poly(aryloxyphosphazenes) measured under oxygen

3 (250° to 400°C ). The TGA curve of poly[bis(p_-methylphenylamino)phosphazene] (Illb), which is typical for polymers III, is shown in Figure

1 (curve A). The TGA curves of poly[bis(trifluoroethoxy)phosphazene]

(curve B) and poly[bis(p_-methylphenoxy)phosphazene] (curve C) also

are shown. A noteworthy feature of Figure 1 is that 1 1 lb, like its

aryloxy analog, retains appreciable residue at 700°C in contrast to

the trifluoroethoxy polymer, which is completely pyrolyzed at 5C0°C.

For the arylamino polymers III, 13-35% of their original weight remains

at 700°C.

Characteristic infrared absorption, due to PN stretch,

occurs at M200 cm""' (Table I) for the poly(arylaminophosphazenes)

.

Absorption of PN at ^930 cm ' (Table I) also was observed, as was

the iiH stretching frequency at ^3400 cm"''.

Proton nmr spectra of polymers III are, as expected, poorly

resolved (room temperature), but are consistent with the assigned structures.

The solubility characteristics of Illa-g differ'somewhat

from those of Illh-k. All of the polymers are soluble in tetrahydrofuran

and benzene, and 1 1 1 a

- g are soluble in chloroform but insoluble in

methanol. The reverse is true for Illh-k, which are quite soluble

in methanol, but insoluble in chloroform.

-176-
Intrinsic viscosities were obtained for polymers Illa-g

and are shown in Table I. Curiously, poly[bis(halophenylamino)phcsphazenes]

(III h-k ) were found to give anomolous viscosity behavior, and thus

only inherent viscosities were measured (Table I). It is interesting

to note that the viscosities of polymers III are in many cases significantly

lower than those of poly(aryloxyphosphazenes ) (IV) reported earlier,

3 which ranged from 1.6 to 3.2 dl/g. These data probably reflect greater

degradation of the P-N backbone during aminolysis of

polydichlorophosphazene (II) than occurs when II is treated with aryl oxides,

3 although reaction conditions of the latter are far more vigorous.

Chain cleavage also was noted earlier in the reactions of alkyl amines

such as III, to tautomerize to a species more labile to nucleophilic

cleavage (eq. 4) than are poly(aryloxyphosphazenes) (IV)

.

OAr

! V

with II. These observations may indicate an ability of amino polymers

,

NHAr

-P =N- NHAr

NAr NAr

-P - NH- NHAr

-P -NHAr

NHAr +

-177-
Treatment of chloro polymer II with a 20-fold molar' excess of aniline

gave a product having an intrinsic viscosity of 0.2 dl/g vs_. 1.4 dl/g

for Ilia prepared by the usual procedure, supporting the view that

nucleophiles can cleave III possibly by the scheme shown in eq. 4.

However, degradation of polyphosphazenes occurs under a variety of

conditions, including the thermal depolymerization of poly (a] koxy- ) ,

poly(aryloxy-)^ , and poly(alkylaminophosphazenes) Also, the PN backbones

11 12 of cyclooctachlorotetraphosphazene and polydichlorophosphazene

apparently are reductively cleaved by thiolates.

The generally lower viscosities of polymers Illh-k compared

with those of 1 1 1 a - g(c_f. Table I) probably are a consequence of the

longer reaction times required for preparation of III h-k, which result

in increased chain cleavage.

For comparison with the arylamino polymers III, the previously unre

ported copolymer VI and poly(al kylamincphosphazenes.) VII and VIII were

prepared (Table II). Non-geminal ly substituted poly(chlorodiethylaminophosphazene) (V) was prepared by a modification of a procedure reported

earlier (eq. 5). Chloroamino polymer V does not react with aniline

under conditions employed for the preparation of III, presumably because

of steric hindrance by the diethylamino moiety tc attack by aniline.

The reaction did occur in boiling dioxane (eq. 5), but substitution

was accompanied by extensive degradation ([n] = 0.13 dl/g). The proton

nmr spectrum of VI is consistent with the structure shown, although

VI contains 2.18% residual chlorine.

-178-
V VI

Polymers VII and VIII (Table II) were prepared by a method

similar to that for III. Poly[bis (benzylamino)phosphazene] (VII) decomposes

at a lower temperature than do the arylamino polymers III, while poly[bis(3_- •

phenethylamino)phosphazene] (VIII) decomposes at a higher temperature

(Table II). The glass transition temperature of the benzylamino polymer

VII (75°C) is in the same range as those of III. This indicates, as

mentioned above, that the presence of aryl groups in III contributes to

their high glass transition temperatures, since VII is structurally a

poly(al kylaminophosphazene) , polymers which normally have glass transitions

from -11° to 30°C.

4 ' 5

The intrinsic viscosities of VII and VIII (Table II) are comparable

to but somewhat lower than many of the arylamino polymers. Greater

chain degradation during the preparation of VII and VIII may be a consequence

of the stronger nucleophil icity of benzylamine and _3-phenethyl amine

compared with that of the aryl amines.

The P-N stretching frequecies of VII and VIII (Table II)

are consistent with other amino polymers, and their proton'nmr spectra,

though poorly resolved, are consistent with the structures shown.

-179-
EXPERIMENTAL

Material

s

Hexachlorocyclotriphosphazene (I), purchased from El Monte Chemical

was purified by recrystall ization from heptane followed by vacuum distillation

(130-140°C/20 mm), mp 110-112°C. Tetrahydrofuran (THF) was distilled from

lithium aluminum hydride prior to use, and benzene was predried by azeotropic

distillation. Amines generally were distilled shortly before use. Glassware

was oven-dried prior to each experiment, and all reactions were run under

an argon flow. Proton nmr spectra were obtained using a Perkin-Elmer Model

R32 90 MHz spectrometer, and infrared spectra were obtained with a PerkinElmer Model 187 spectrometer. Instruments used for thermal analyses are

described in the footnotes to Table I. Elemental analyses were performed

by Galbraith Labs, Knoxville, Tennessee.

Polymerization of I and Isolation of II

Hexachlorocyclotriphosphazene (I, 50g) was polymerized at

3 240-245°C for 10-56 hr in evacuated sealed tubes. In a dry box, containing

an argon atmosphere, the polymerization mixture was taken up in dry benzene

(MOO ml), and low molecular weight cyclics and oligomers then were separated

from polymer II by coagulation of the polymer with n_-pentane (^400 ml).

Isolated II (17-43%) was immediately redissolved in benzene.

Poly [bis (aryl ami no)phosphazenes] (III)

Poly[bis (phenylamino)phosphazene] (Ilia) A solution of

triethylamine (54.64g, 0.54 mol ) and aniline (33.52g, 0.36 mol ) was added

dropwise to a stirred solution of polydichlorophosphazene (II, 13.85g,

0.12 mol). in 1:1 benzene-tetrahydrofuran (300 ml). Precipitate began

forming almost immediately after addition was begun, the reaction was exothermic,

and the reaction mixture became quite viscous (see below). After addition

-180-
was complete, the mixture was heated to reflux and allowed to stir for

48 hr. After the mixture had cooled to room temperature, it was filtered

to remove triethylamine hydrochloride (23. Og, 70%) and the filtrate was

added dropwise to several liters of methanol to precipitate the product.

The polymer was washed with several portions of 1:1 methanol -water for

several days to remove chloride ion (until the wash solution gave no precipitate

with silver nitrate). The polymer then was taken up in THF, and the resulting

solution was filtered and added dropwise to methanol to give, when dried,

white Ilia (9.7g, 35%), which contained 0.76% residual chlorine.

During the preparation of a number of the arylamino polymers

described in this report, the reaction mixtures became quite viscous after

the addition of the amines. This increase in viscosity may result either

from partially substituted polymer that is only sparingly soluble or from

initial formation of some insoluble polymer hydrochloride salt that is

later neutralized by triethylamine. In any case, frothing and scorching

resulted if reflux temperatures were attained too quickly. Thus, in some

cases (see below), mixtures were allowed to stir for several hours at

room temperature or with gentle warming prior to heating to reflux. As

the reactions proceeded, the viscosities of the mixtures decreased so

that they were easily filtered after the reactions were complete.

Poly [bis fp -methyl phenyl ami no ) ohosphazene] ( 1 1 lb) . In a preparation

similar to that of Ilia, p_-toluidine (125. 37g, 1.17 mol ) in TKF (130 ml)

was added to II (15.10g, 0.13 mol) in 1:1 benzene-THF (200 ml). After

48 hr at reflux, precipitated p_-toluidine hydrochloride (24.60g, 66%) was

-181-
removed by filtration and the filtrate was added to methanol -as before to

precipitate the product. The polymer was purified as described for Ilia

to give white 1 1 lb (12.00g, 36%).

Anal. Calcd. for (C^HjgNgP) : C, 65.35; H, 6.28; CI, 0.00; N, 16.33.

Found: C, 64.43; H, 6.06; CI, 0.90; N, 15.71.

In a similar experiment, a solution of p_-t»luidine (0.45 mol ) and

triethylamine (0.45 mol) was added to II in 2:1 THF-benzene. The mixture

was stirred for 24 hr at room temperature, followed 57 hr at reflux; the

longer reaction time was employed in an attempt to improve the analytical

results for 1 1 1 b . The product was isolated in 65% yield, but, because of

the longer reaction time, gave an intrinsic viscosity of only 0.95 dl/g

(compared with 1.3 dl/g for 1 1 1 b prepared as described above).

Anal. Found: C, 63.49; H, 6.19; CI, 0.66; N , 16.14.

Poly[bi s (m-methyl phenyl ami no )phosphazene] (I He) . In a preparation

similar to that of Ilia, a solution of m-toluidine (66.43g, 0.62 mol) and

triethylamine (62.7^g, .0.62 mol) was added to II (18.07g, 0.16 mol) in

3:2 THF-benzene (250 ml). After 48 hr at reflux, precipitated triethylamine

hydrochloride (24. 4g, 55%) was removed, and the polymer was isolated and

purified as described for Ilia to give white 1 1 1 c (10.49g, 25%).

Anal. Calcd for (C^gf^P) : C, 65.35; H, 6.28; CI, 0.00; N, 16.33.

Found: C, 62.57; H, 6.27; CI, 0.36: N, 16.00.

Poly [bi s (o-methyl phenyl ami no )phosphazene] . In a preparation similar

to that of Ilia a solution of o_-toluidine (68. 5g, 0.64 mol) and triethylamine

(64. 6g, 0.64 mol) was added to II (18.65g, 0.16 mol) in 3:1 THF-benzene

(350 ml). After 48 hr at reflux, precipitated triethylaminehydrochloride

-182-
(24. Og, 54%) was removed and the product was isolated and purified as

described for Ilia to give cross-linked insoluble polymer (2.76g, 7%).

Anal. Calcd for: C, 65.35; H, 6.28; CI, 0.00; N, 16.33.

Found: C, 53.39; H, 5.87; CI, 4.85; N, 5.11.

PolyFbi s(p-ethy! phenylairiino)phosphazene] (II Id) . In a preparation

similar to that of Ilia, a solution of p_-ethylani 1 ine (66. 7g, 0.55 mol)

and triethylamine (55. 5g, 0.55 mol) was added to II (13.00g, 0.11 mol)

in 1.75:1 THF-benzene (275 ml). After 72 hr at reflux, triethylamine

hydrochloride (44. 5g, 147%) was removed, and the polymer was isolated

and purified as described for Ilia to give white 1 1 1 d (22.85g, 73%).

Anal. Calcd for (C^^n^V C, 67.34; H, 7.08; CI, 0.00; N, 14.73.

Found: C, 66.44; H, 6.93; CI, 0.24; N, 14.66.

Poly[bis(m-ethy1 phenyl ami no )phosphazene] (Hie) . Polydichlorophosphazene (II, 6.55g, 0.056 mol) in benzene (60 ml) was added slowly to a

stirred solution of m-ethyl anil ine (27.19g, 0.224 mol) and triethylamine

(22.60g, 0.223 mol) in THF (100 ml). After stirring at room temperature

overnight, the mixture was heated at reflux for 56 hr. After removal of

triethylamine hydrochloride (11.68g, 76%), the polymer was isolated and

purified as before for Ilia to give white 1 1 1 e (7.95g, 50%).

Anal. Calcd for (C-^Hoq^P)^ C, 67.34; H, 7.08; CI, 0.00; N , 14.73.

Found: C, 64.52; H, 7.03; CI, 0.65; N , 14.32.

Poly[bi s (p-n- butyl ami no ) pho.sphazene] ( II If

)

. In a preparation similar

to that of Ilia, a solution of p_- n-butyl anil ine (110. 5g, 0.74 mol) and

triethylamine (74. 8g, 0.74 mol) was added to II (17.20g, 0.15 mol) in

benzene (120 ml) and THF (250 ml). The mixture was heated gently overnight

-183-
and then at reflux for 48 nr. Triethylamine hydroch>oride (33.53g, 93%)

was removed, and the polymer was isolated and purified as described for

Ilia to give white 1 1 1 f (22.33g, 44%).

Anal. Calcd for (C

2 o

H28N

3

P ^n: C ' 70 - 34; H > 8 - 28 "' C1 » °- 00; N > 12 - 31 -

Found: C, 68.97; H, 8.18; CI, 0.32; N , 12.29.

Poly [bi s (p-methoxyphenyl amino)phosphazene] (I I Ig . In a preparation

similar to that of Ilia, a solution of p_-anisidine (61. 8g, 0.50 mol

)

and triethylamine (55. 5g, 0.55 mol) in THF (100 ml) was added to II (16.70g,

0.14 mol) in 2:1 benzene-THF (150 ml). After 48 hr at reflux, triethylamine

hydrochloride (25.28g, 66%) was removed and the polymer was isolated ana

purified as described for Ilia to give light pink 1 1 1 g (16.59g, 41%)

.

Anal. Calcd for (C-^H^^P) : C, 58.12; H, 5.59; CI, 0.00; N , 14.53.

Found: C, 57.18, H, 5.69: CI, 0.15; N, 14.31.

Poly [bi s (m-methoxyphenylanino)phosphazene]

.

In a preparation similar

to that of Ilia, m-anisidine (0.62 mol ) and triethylamine (0.62 mol) were

added to polymer II (0.12 mol). Removal of triethylamine hydrochloride

(21.00g, 64%) after 56 hr of reflux and isolation and purification of the

polymer as described for Ilia gave white product (1.60g, 5%) having an

intrinsic viscosity of 0.55 dl/g; Tg - 78°C; Td = 250°C.

Anal. Calcd for (C-]4 H 15N 302

p ) n

: C, 58.12; H, 5.59; CI, 0.00; N, 14.53.

Found: C, 54.37; H, 5.60; CI, 0.96; N, 14.72.

Po1y[bi s (p-chl pro phenyl ami no)phosphazene] (I I Ih) . A solution of

£-chloroanil ine (95. 5g, 0.75 mol) and triethylamine (75. 5g, 0.75 mol) in

THF (200 ml) was added dropwise to II (21.71g, 0.19 mol) in benzene (125 ml).

-184-
Additional THF (50 ml) was added to the viscous mixture, and the temperature

was raised slowly (over a period of 5 hr) to reflux. After 144 hr at

reflux, triethylamine hydrochloride (24 . 67g , 47%) was removed by filtration

and the filtrate was added dropwise to repentance (^31). The precipitated

product was taken up in THF, and the resulting solution was filtered and

added dropwise to water to again precipitate the polymer, which was washed

several days with several portions of water to remove chloride ion (until

the wash water gave no precipitate with silver nitrate). The polymer again

was taken up in THF and precipitated from water. Drying gave white 1 1 1

h

(1.84g, 3%).

Anal. Calcd for ( C 12H 10C1 2N

3

P V C ' 48 - 34; H > 3 - 39 ' c1 » 23 - 79 >

N , 14.10. Found: C, 46.80; H, 3.20; CI, 21.96: N , 14.07.

In another experiment, reflux was maintained for only 48 hr. The

product, isolated in 20% yield, gave an inherent viscosity of 0.8 dl/g.

Anal. Found: C, 40.44; H, 3.37; CI, 22.54; N , 12.83.

Poly[bis(n-chloroDhenylamino)phosphazene] ( 1 1 1 i

)

. Polydichlorophosphazene (II, 21.00g, 0.18 mol ) in benzene (90 ml) was added slowly to

a stirred solution of m-chloroaniline (130. OOg, 1.02 mol) and triethylamine

(54.00g, 0.53 mol) in THF (300 ml). The mixture was heated at 60°C for 19

hr and then at reflux for 56 hr. Addition of the mixture to 1:1 methanol

water precipitated polymer, which was taken up in THF, filtered, and precipitated from n_-pentane. The polymer was taken up in acetone and again

precipitated from n-pentane, followed by washing for 24 hr with 3:1 watermethanol . Drying gave white II I i (33. OOg, 61%).

Anal. Calcd for ( c -| 2H io

C1

2

N

3 P V C ' 48 - 34 ' H » 3 - 39 '> c1 » 23.79;

N, 14.10. Found: C, 45.69; H, 3.34; CI, 23.30; N, 14.09.

-185-
Poly[bi s (p-f 1 uorophenyl amino)phosphazene] (1 1 1 j

)- . In a preparation

similar to that of 1 1 1 h , a solution of p_-fluoroanil ine (97. 6g, 0.88 mol

)

and triethylamine (88. 8g, 0.88 mol) was added to II (25.12g, 0.22 mol)

in 2.5:1 THF-benzene (250 ml). After 24 hr of gentle heating and then 48

hr at reflux, triethylamine hydrochloride (47. Og, 78%) was removed and the

polymer was isolated and purified as described for 1 1 1 h to give white

1 1 1 j (12.67g, 22%).

Anal. Calcd for (C

]

2

H, r/2

N

3

P )n: C ' 54 - 34; H ' 3 - 81 ' cl » °- 00 ' F »

14.33; N, 15.85. Found: C, 51.15; H, 4.05; Cl , 0.85; F, 12.40; N , 15.20.

Poly[bis (m-fluorophenylamino)phosphazene] (Illk). In a preparation

similar to that of 1 1 1 h , a solution of m-fluoroaniline (62. 4g, 0.56 mol)

and triethylamine (56. 5g, 0.56 mol) was added to II (13.03g, 0.11 mol)

in 2:1 THF-benzene. After 24 hr of gentle hating and 96 hr at vigorous

reflux, triethylamine hydrochloride (21 .6g ,* 71%) was removed, and the

polymer was isolated and purified as described for 1 1 1 h to give 'white 1 1 1

k

(8.09g, 28%).

Anal. Calcd for (C

]

2

H

]

0

F 2 N

3

P ) n

: C ' 54 - 34 ' H » 3 - 81 ; cl » °- 00; F ' 14 - 33 ;

N , 15.85. Found: C, 51.70; H, 3.82; Cl , 1.09; F, 13.08; N, 15.95.

Poly[bi s(m-trifl uoromethyl phenyl amino) phosphazene]

.

In a preparation

similar to that of Illh, m-aminobenzotrifluoride (0.58 mol) and triethylamine (0.58 mol) were added to II (0.12 mol). Removal of triethylamine

\ hydrochloride (19.55g, 59%) and isolation and purification of the product

as described for 1 1 1 h , gave an off-white material (9.26g, 21%), having an

inherent viscosity of 0.12 dl/g; Tg - 75°C; Td - 199°C.

Anal. Calcd for ( c

-]4 H 10

F6N

3

p ) n

: C, 46.03; H, 2.77; Cl , 0.00;

F, 31.21; N, 11.51. Found: C , 42.36; H, 3.44; Cl , 1.31; F, 21.70;

N, 12.88.

-186-
Pol y (al kylaninophosphazer.es) VI, VII, and VIII

Polyfdiethylaminoohenyl aminophosphazene) (VI) . A solution of

diethylamide (65.70g, 0.90.mol) in benzene (100 ml) was added dropwise

to a cooled (ice bath), stirred solution of II (10.66g, 0.09 mol) in

benzene (150 ml). Diethylamide hydrochloride began precipitating almost

immediately. After stirring at room temperature for 72 hr, the salt was

removed by filtraiton, and the filtrate was added quickly (dropwise over

a period of ^30 min) to acetone (^31). The precipitated product was dried

in vacuo at ambient temperature for 24 hr to give poly (diethylaminochlorophosphazene) (V, 8.48g, 62%, 0.06 mol ) , 'which was taken up in benzene

(150 ml). Dioxane was added to the resulting stirred solution, followed

by dropwise addition of aniline (74. 4g, 0.80 mol). The solution was heated

at reflux for 48 hr. As the solution was allowed to cool to room temperature, aniline hydrochloride (3.0g, 39%) precipitated and was removed by

filtration. The dark filtrate was added to methanol to give fine particles

which were washed with methanol and then 1:1 methanol -water for several

days. The product then was taken up in THF and precipitated from 3:1

methanol -water, which gave VI (2.98g, 24« based on V) as a white powder.

The material contained 2.18% residual chlorine.

Poly[bis (benzylarr:ino)phosphazene] (VII) . Polydichlorophosphazene

(9.10g, 0.08 mol) in benzene (100 ml) and THF (75 ml) was added slowly

to a stirred solution of benzylamine (42.00g, 0.39 mol) and triethylamine

(20. 01 g , 0.20 mol) in THF (250 ml). The solution was stirred at room

temperature for 20 hr, followed by gentle heating for 7 hr. After standing overnight at room temperature, the reaction mixture separated into two

layers. The bottom layer ( 60 ml , which contained only hydrochloride salt)

-187-
was discarded, and the top layer was added dropwise to methanol to

precipitate the product, which was taken up in THF and precipitated from

1:1 methanol -water . The product then was washed first with water followed

by methanol and dried to give white VII (15.00g, 73%).

Anal. Calcd for (C 14H 16

N

3 P) : C, 65.35; H, 6.28; CI, 0.00; M , 16.33;

Found: C, 62.96 ; H , 6.20; CI, 0.24; N, 16.09.

Pol y [bi s

( 6-phenethylami no)phosphazene] (VIII) . A solution of polydichlorophosphazene (II, 7.90g, 0.07 mol ) in 1:1 THF-benzene (200 ml) was

added slowly to a stirred solution of _3-phenethyl amine (51. Og, 0.42 mol)

and triethylamine (42. 4g, 0.42 mol) in TKF (100 ml). The resulting viscous

mixture was stirred overnight at room temperature. Additional THF (200 ml)

. was added, and the mixture was heated at 40°C for 4 hr. The product, which

precipitated from the reaction mixture, was, collected by filtration and

washed first with methanol and then with water, and again with -methanol

.

Drying gave VIII (9.4g, 47%) as white powder, which was soluble only in

tetrachloroethane or hot chloroform. For an analytical sample, a portion

of the material was taken up in hot chloroform, filtered by centrifugation

,

precipitated from methanol and dried.

Anal. Calcd for (C-j 6H

2 o

N

3

P

C ' 67 - 34 > H » 7 - 08; C1 • °- 00; N » 14 - 73 -

Found: C, 67.92; H, 7.09; CI, 0.24; N, 14.61.

-188-
REFERENCES

1. H. R. Allcock, R. L. Kugel , and K. J. Valan, Incrg . Chem. , 5_, 1709

(1966).

2. H. R. AUcock, PhosRhorous-Nitrogen Compounds , Academic Press, New

York, 1972 (a) Chap. 16 (b) Chap. 7 (c) Chap. 15 (d) p. 357.

3. R. E. Singler, et. a]

.

, J. POIyn. Sci. , 12, 433 (1974). * S^S

4. H. R. AUcock and R. L. Kugel, Inorq. Chem. 5„ 1716 (1966).

5. H. R. AUcock, N. J. Cook, and D. P. Mack, Inorq. Chem . , 11 , 2584

y\y

(1972).

6. G. L. Hagnauer and N. S. Schneider, J. Polym. Sci A-2 , K), 699 (1972)

7. R. E. Singler, N, S. Schneider, and G. L. Hacnaje**, Pc'y. Er;. Sci. ,

in press.

8. K. A Reynard, A. H. Gerber, and S. H. Rose, U.S. Govt. Res. Rep.,

AD 755-188 (1972).

9. G. R. Feistel and T. Moeller, J. Inorq.m — —N'ucl . Chem., ,_ 20, 2731 (1967).

yss

10. S. K. Das, et. al , J. Chem. Soc , London , 5032 (1965).

11. D. P. Mack, Ph.D. Diss., 1972, page 44.

12. A. D. Carroll, R. A. Shaw, and M. Woods, J. Chem. Soc. , Dal ton Trans.

2736 (1974).

13. J. E. White and R. E. Singler, unpublished results.

-189-
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-190-

Fig. 1. TGA curves for: (A) 1 1 1 b (static air); (B) po1y[bis(trifluoroethoxy)phosphazene[ (static air); (C) poly[bis(p_-rriethylphenoxy)-

phosphazene] (oxygen).

-192-

1 111 >iw>—. w<l^l u „ gXMBBBP"


NBS-114A CREV. 7-73)

U.S. DE B ~ Z- COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLIC ATION OR REPORT NO. NBSIR 75-798

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

NEW POLYMERS

5. Publication Date October 1975

6. Performing Organization Code

7. AUTHOR(S)

Martin G. Broadhurst

8. Performing Organ. Report No. NBSIR 75-798

9. PERFORMING ORGANIZATION NAME AND ADDRESS

rift 1 [UnnL D U r\ C A U Ur J 1 AnUAKUj

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task. Work Una No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address fSrreef, City, State, ZIP)

Office of Naval Research

Arlington, Va. 22044

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.)

This report contains manuscripts of talks that were presented at the

Annual Program Review of the Office of Naval Research. Part of the program

focused on piezoelectric measurements' and applications of polymers and those

papers were compiled in an Interagency Report, NBSIR 75-760. The papers in

this report are concerned with the chemical synthesis and characterization of

potentially useful new polymers. Together these two reports are the final

reports from NBS to ONR as prescribed in contract number NAonr-44-75.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Kalomethyl arsines; metal mercaplides ; polycarboranesiloxanes

;

polyelectrolyte ; polymers; synthesis

18. AVAILABILITY [~| Unlimited

YY For Official Distribution. Do Not Release to NTIS

Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. CI 5 Order From National Technical Information Service (NTIS)

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