a 1 1 iol 2 b

o

m m racterization of Organometallic

|

Polymers by Chromatographic

I Methods and Nuclear Magnetic

Resonance. Part II.

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Materials Science

Inorganic Materials Division

Washington, DC 20234

November 1983

Issued February 1984

I’QC

i 100

|.U56

33-2802

1984

Prepared for Naval Ship R & D Center

Annapolis Laboratory

Annapolis, MD 21402

NBSIR 83-2802

CHARACTERIZATION OF ORGANOMETALLIC

POLYMERS BY CHROMATOGRAPHIC

METHODS AND NUCLEAR MAGNETIC

RESONANCE. PART II.

E. J. Parks, W. F. Manders, R. B. Johannesen, and F. E. Brinckman

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Materials Science

Inorganic Materials Division

Washington, DC 20234

November 1983

DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED

Issued February 1984

Prepared for Naval Ship R & D Center

Annapolis Laboratory

Annapolis, MD 21402

l o

) 9

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

CHARACTERIZATION OF ORGANOMETALLIC POLYMERS BY CHROMATOGRAPHIC

METHODS AND NUCLEAR MAGNETIC RESONANCE

E. J. Parks, W. F. Manders, R. B. Johannesen, and F. E. Brinckman

Inorganic Materials Division

National Bureau of Standards

Washington, DC 20234

Abstract

Continuing research into the analytical methodology for

characterization of organometal 1 ic polymers (OMPs) has produced improved

methods of characterization by size exclusion chromatography (SEC) and

Fourier transform nuclear magnetic resonance (FTNMR). Molecular weight

(MW) and MW dispersion (MWD), as well as the amount of tin associated

with fractions of various MW can now be reliably determined by SEC

coupled with various detectors: differential refractive index (ARI),

ultra-violet (UV), and graphite furnace atomic absorption (GFAA)

spectroscopy. Configurational sequencing in terms of both tacticity and

sequencing of monomer units can be determined by FTNMR, as well as certain tin-containing impurities. Removal of tributyltin groups to

produce a metal -free copolymer allows much more informative FTNMR

spectra to be obtained. All of the polymers examined are approximately

80 percent racemic (r) and 20 percent meso (m) in tacticity (i.e.,

predominantly syndiotactic). The growing chain end in the copolymer

adds either of the monomer units approximately in proportion to its

instantaneous concentration in the mixture (i.e., at random).
.

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1.0 Introduction

In previous communications from this laboratory [1,2] we have

described the nature of the problems involved in the characterization of

organometall ic copolymers (OMPs) and the methods of molecular characterization, by size exclusion chromatography (SEC) and Fourier transform

nuclear magnetic resonance (FTNMR), currently under development. The

present report answers several questions arising from our previous

research and provides the basis for using complementary molecular

characterization methods as a part of a Mil-Spec to assure the Navy of

practical criteria for evaluating commercially synthesized OMPs for use

in control led-release coatings on ships.

Earlier reports have dealt with materials prepared by the

free-radical-induced copolymerization of methyl methacrylate (MMA) and

tri butyl tin methacrylate (TBTM) at the temperature of refluxing benzene [3]. We have been primarily concerned with two candidate OMPs:

one, identified as OMP-2, contains a 1:1 mole ratio of MMA to TBTM;

while the second, identified as OMP-8, contains a 2:1 ratio of the

respective monomers. Samples prepared by the David Taylor Naval Ship

Research and Development Center (DTNSRDC) using this method are hereinafter identified as 0MP-2N and 0MP-8N. A new process, proposed

for commercial development, involves preparation of a "pre-polymer" of

MMA and methacrylic acid (MAA) by free-radical -induced copolymerization

followed by esterification of the pendant free acid groups on the

pre-polymer by bis-tri butyl tin oxide (TBTO). We have examined

commercial OMPs of the same nominal composition as above, which are identified in this report as 0MP-2P and 0MP-8P. We have also examined

the pre-polymer before reaction with TBTO.

1. 1 Complementary Nature of SEC and NMR

Size exclusion chromatography (SEC) and nuclear magnetic resonance

(NMR) are complementary techniques involved in organometal 1 ic copolymer

characterization. SEC is coupled with various detectors: graphite

furnace atomic absorption spectroscopy (GFAA), differential refractive

index (ARI), and ultraviolet spectroscopy (UV). SEC-GFAA is capable of

dealing with exceedingly small samples [4], With samples of 5 mg or

less, SEC provides characterization of a copolymer sample according

1
to its molecular weight (MW), molecular weight distribution (MWD), and

the distribution of metal (specifically tin) among fractions of

different MW. SEC, in tandem with the detectors used at NBS, is capable

of detecting solvent impurities and side reaction products. The SEC

method is, however, not at all sensitive to configurational sequencing

of the polymer. The complementary technique of NMR requires

substantially larger samples of (greater than one gram for non-proton

NMR). It provides configurational sequencing information [5] which is

complete at the triad level in the specific case of copolymers of MMA

and TBTM. It also gives information regarding tin-containing

impurities. The NMR method is affected only in the crudest way by MW,

and does not provide a useful way to estimate MW.

1. 2 Limitations

Each of these methods has its own special strengths and

limitations. SEC requires adequate standards to be able to provide

absolute MW information. These are not yet available for the

methacrylate copolymers under consideration here. However, comparative

results are attained and are very useful, so long as suitable reference

material can be made available. NMR is valuable for determining

molecular structures, but it is not a trace method and is not well

suited to determine, or to characterize with certainty, small amounts of

impurities. The smallest amount of an impurity detectable by NMR is

dependent on many factors: (1) whether the impurity signal is well

separated from all other signals; (2) the linewidth of the impurity

signal--smal 1 molecules generally have inherently narrow lines and are consequently easier to see at low concentrations; (3) the amount of time

available for running a spectrum--since the signal-to-noise ratio

increases at best only as the square root of the time, the point of

diminishing returns is usually reached in an overnight scan of about

16 hours. Taking all of these factors into account, it is usually

possible to detect impurities at the 1 percent level if their signals

are well separated from all other peaks and usually not possible to

detect 0.1 percent of impurity except in extraordinarily favorable

cases.

2
2.0 Apparatus and Materials*

2.1 SEC

2. 1. 1 Chemicals

Benzene, tetrahydrofuran (THF), methanol, methyl isoamyl ketone,

acetic acid and other common solvents were all of reagent grade or higher purity. The Stoddard solvent (mineral spirits) serving as a solvent for various OMPs reportedly was of commercial grade.

Tri butyl tin methacrylate (TBTM) used for conditioning chromatographic

columns was of commercial grade originally, but had been stored at -15 °C

for one year before use, with probable degradation. This sample was dissolved in THF without purification.

2.1.2 Instrumental Methods

The SEC-UV/ARI-GFAA including a high pressure pump, has been

described [4]. The eluent consisted of THF. In some of the

experiments, discrete quantities of THF (50 pL or 500 pL) containing

1.0 percent acetic acid (v:v) were injected at measured intervals after

injection of solutions of the polymer dissolved in the THF [6].

GFAA measurements were taken both on-line [7] and off-line. For

off-line measurements, discrete volumes (0.5 to 1.0 mL) of effluent were

collected in vials during a chromatographic run for subsequent tin

quantitation. Individual specimens were diluted with appropriate,

measured volumes of THF to assure that GFAA readings were taken within

the scale of linear response.

Tin recovery was calculated by comparing the amount of signal,

summed over all of the discrete, collected volumes, with that of a sample injected into the sample loop and collected before entering the

SEC column.

*Certain suppliers of chemicals and equipment are identified by name in

order to specify the experimental conditions adequately. This does not

imply endorsement or recommendation by the National Bureau of Standards

nor does it imply that the particular brands of chemicals and equipment

named are necessarily the best for the purpose.

3
Except for one experiment, the SEC columns consisted of pStyragel

(Waters Associates, Milford, MA) having a nominal average pore size of

2

o 2

0 4

° 10 A, 10 A, or 10 A. Columns of these different pore sizes were used

in several combinations.

Several experiments were performed to test the hypothesis that a dissociation mechanism results from exposure of the tributyl ti n-beari ng

polymer to aromatic groups in the solid phase. These experiments

included using one, two, or three columns in series, following their

regeneration by treatment with acetic acid as described above; and two

sets of three columns pretreated individually with a solution of either

OMP or of TBTM in THF. Tables and figures summarizing experimental

results also outline the individual experimental conditions.

For molecular weight (MW) estimation, columns were calibrated with

a series of standard samples of polystyrene in THF (Arro Labs,

Joliet, IL) [4].

2.1.3 Treatment of Data

The determination of number and weight average MW by GFAA has been

described in detail [4]. In the present work we used a manual

procedure [8] for calculating MW from SEC-ARI chromatograms. This

consisted simply of tracing a peak onto graph paper and then cutting

out, at 1/2 cm intervals, and weighing strips of paper subtending the

SEC peak. The MW assigned to each strip was estimated at its center for

the present experiments. For low MW species, usually present in much

smaller amounts, the MWs were estimated from their elution volumes,

determined at the intersection point of lines tangent to the sides of

the peak. Number and weight average MW values were calculated from the same formulae (equations 1 and 2) for both SEC-GFAA and SEC/ARI.

( 1 )

M = —

n Ih./m.

Ih.

i ( 2 )

4
Each h.j represents either the height of a GFAA peak or the weight of a 0.5 cm segment of the peak cut out along its base (ARI).

The extent of polymer conversion was calculated from equation 3:

AP(%) = (p

( ^

H)

X 100 (3)

where AP is the degree of conversion, P is a parameter depending on polymer content, and M is a parameter depending on the content of

monomer or low MW species. In each case, it is assumed that the areas represent actual weight fractions of high or low MW species in the

unfractionated mixture.

2.2 NMR

2.2.1 Instrumentation

Instruments used were Bruker Instruments Inc. superconducting NMR

spectrometers operated in the pulse FT mode at field strengths of

4.7 T and 9.4 T. The respective NMR frequencies for H-l, Sn-119, and 013 are

200, 74.60, 50.31; and 400, 149.20, and 100.62 MHz. Conditions used for

spectral acquisition always included quadrature phase detection and,

when Sn-119 or 013 spectra were run, broad-band proton decoupling with

normal NOE for 013, but with NOE suppressed for Sn-119. Primary

chemical shift references used were internal TMS for protons, external

TMS (concentric tube) for 013, and internal tetramethyl tin for Sn-119;

each of these was assigned a value of 0 ppm. Most of the non-proton

spectra were indirectly referenced to the above standards using the

internal deuterium lock frequency as a secondary reference. All proton

and carbon spectra were run at 9.4 T; tin spectra were run at both 4.7

and 9.4 T. Some spectra run earlier at other field strengths are included for comparison. Normally a pi/2 pulse was used. Table 1 gives

typical operational NMR parameters for the nuclei investigated.

5
Table 1. Typical NMR Parameters

Nucleus

Freguency

MHz

Sample

size

mg/ml

Tube

diam

mm

Spectral

Rangea

ppm

No. of

poi ntsb Hz/poi nt

No. of scans

H-l 400.13 5/. 5 5 -.5 to 4.5 8K .488 64

C-13 100.62 500/3 10 -10 to 60 16K .854 10000

160 to 200 16K .488 10000

Sn-119 74.6 4000/15 20 -20 to 129 8K 2.714 5000

a Both sweep offset and sweep width are adjusted to achieve the desired

spectral range.

b

lK = 1024

2.2.2 Cleavage of Tri butyl tin from OMP

Tin-free polymer was prepared for proton and C-13 NMR spectral

examination as follows: Solvent is removed from polymer by

evaporation, and 5 g of dried polymer is dissolved in 20 mL of

chloroform. To this solution is added 2 mL of 12 N HC1 and the mixture

is shaken. A precipitate of poly (MMA-MAA) appears. The tributyltin

groups remain in solution as tributyltin chloride. The precipitate is

separated from the supernatant by decantion and is then dried. The dried

tin-free polymer is dissolved in pyridine (4 mL pyridine per g of

solid). Proton and C-13 NMR signals from pyridine occur in regions of

the spectrum where there are no polymer signals, so that the pyridine does

not interfere with spectral interpretation.

3.0 Results and Discussion

3.1 SEC

3.1.1 Evidence Supporting a Cleavage Mechanism

Earlier SEC-GFAA results from this laboratory showed a distribution

of tin in OMPs in a high MW fraction, a low MW fraction, and a cationic

6
species that is absorbed on pStyragel [4,9,10]. The latter species is

readily desorbed by trace quantities of acetic acid in THF, with nearly

quantitative tin recovery [6]. Chromatograms of an OMP fractionated on

an acid pretreated column, however, show very little tin associated with

the high polymer fraction, but large proportions of tin-bearing adsorbed

species (table 2, fig. 1).

Table 2. Summary of SEC-GFAA

a for 0MP-2N

Adsorbed

Polymer Monomer Species Recovery

(W b

(%)

b

(%)

b

(%)

c

7.54 0.94 91.5 79.7

5.39 0.86 93.7 80.3

4.36 0.22 95.4 88.2

8.03 0.66 91.3 61.5

4.31 0.52 95.2 69.2

4.48 0.48 95.0 72.8

5.69 0.61 93.7 75.3

1.68 0.26 1.9 9.4

= 6 6 6 6

Column: pStyragel 10

3

°

i A, one. Percent of total tin observed.

Percent of total tin i njected.

Nevertheless, the same OMP shows a much larger proportion of polymer in the

ARI chromatogram and Sn-119 NMR spectra failed to detect the loss of large

quantities of tin from the polymer prior to injection (fig. 2; see detailed

analysis in subsection 3.2.5). This indicates on-column dissociation of the

tin-bearing moieties from the polymer chain. We suggest a mechanism involving

complexation of tin-bearing cationic species formed by dissociation with

7
SEC-ARI GFAA CHROMATOGRAMS OF OMP-2N

ON pSTYRAGEL (io

3 a) WITH DESORPTION

OF TIN-BEARING CATIONS BY DILUTE ACETIC ACID

Desorbed species

I I T r _ I io 5 10 10 10 2

Figure 1. SEC-ARI-GFAA chromatograms of 0MP-2N. Solvent, THF. Column,

O pStyragel (one), average pore size 10 3

A. Mobile phase, THF.

Flow rate, 0.5 mL min -1. Detector Perkin-Elmer 360 equipped

with Sn-specific EDL lamp operating at 224.6 nm. Injected

sample volume 50 pL; concentration 0.38 mg/50 pL. HOAc in THF

(1.0 % v/v) injected (50 pL) 18 min after polymer, and at 5 min

intervals thereafter, ARI sensitivity, 1 X 10 6 ARI for full

scale deflection, decreased to 5 X 10 6 ARI at 15 mL.

8
j i L J I L j

120 100 80 60 40 20 o PPM

Figure 2. Tin-119 at 74,6 MHz of OMPs in chloroform. (A) 0MP-2P*

(B) 0MP-8P.

9
aromatic groups incorporated in the polymer chains of which the packing

material is comprised. In view of our earlier successful experiments in

the SEC-GFAA of OMPs [4,9] the current data indicate that column

conditioning is critical and involves either equilibration of cationic

species with the packing surface or chemical deactivation. A set of

experiments was devised to test this hypothesis.

3.1.2 Demonstration of Cleavage

3. 1.2.1 Varying Length of Column

The data (table 3) clearly demonstrate that the dissociation of

tin-bearing species from the polymer chain occurs mainly on the first

column and is not affected by the number of subsequent individual

columns. A 500 pL solution containing 6.5 mg of OMP in THF was injected

3

° into either one, two, or three 30-cm 10 A pStyragel columns, using a mobile phase of THF, and ARI detection. The polymer fraction and the

monomer fraction were collected consecutively for off-line tin

determination. The adsorbed species were then desorbed with a 1.0 percent solution of acetic acid in THF.

Table 3. Analytical SEC of 0MP-2P

3 with column length (pStyragel) varied.

Column Length

(cm)

Polymer Fraction

(%)

C

Monomer

Fraction

(%)

C

Adsorbed for

Species

(%)

30 7.7 18.1 74.1

60 9.9 2.5 87.7

90 7.9 2.0 90.1

a 500 pL injected solution containing 6.8 mg of unfractionated polymer,

b 3

° 10 A pStyragel, 7.8 mm i.d.

c Fraction of total tin recovered.

Less than 10 percent of the total observed tin is associated with

the polymer fraction eluted from either one, two, or three columns

(table 3); less than 3.0 percent is associated with the low MW species

10
eluted from two or three columns, and a large preponderance of

tin-bearing species is adsorbed on the column packing.

3. 1.2. 2 Varying Sample Size

Injecting relatively large amounts of OMP partially conditions the

SEC packing, reducing the extent of cleavage as an injected sample of

OMP traverses the column. When 50 pL of the same polymer solution,

containing 0.65 mg of OMP, was injected on three columns in tandem, less

than 3.0 percent of the eluted tin was associated with the eluted

polymer, and less than 1.0 percent with the eluted low MW species;

95 percent of the adsorbed tin-bearing species is found on the first

column and about 5 percent on the second and third columns (table 4).

Table 4. Analytical SEC of 0MP-2P on 90 cm of pStyragel (3 columns):

Distribution of Adsorbed Tin Species

Fraction Location Percent

Polymer El uted 2.69

Monomer Eluted 0.67

Adsorbed Species b

Col. #1 95.1

II II Col. #2 0.78

II II Col. #3 0.77

Tin Recovery

0

: 67.0 percent

a Percent of total tin observed.

b Desorbed with aid of 1.0% HOAc

c Percent of total tin injected

in THF.

with 50 pL of solution containing O.i

of polymer.

We infer that a small number of tin-to-polymer bonds (less than three

percent) are exceptionally stable, and that large quantities of sample

promote deactivation of the solid phase. A test of this hypothesis will

include preparatory scale fractionation of an OMP on surface-active SEC

packing, separation of the polymer fraction, and examination of this

11
fraction by FT-NMR for ti n-to-carbon rather than ti n-to-oxygen bonds. A

set of commercial OMPs (0.65 mg per injected specimen) all manifested

similar, small proportions of polymer tin, when elution of adsorbed

species was forced by means of repeated injections of 50 pL volumes of

1.0 percent acetic acid in THF. These data verify the hypothesis that

column conditioning or deactivation by appropriate cationic species is

necessary for successful SEC-GFAA of OMPs. Desorption of such species

by dilute acetic acid in THF regenerates surface activity that cleaves

tin-bearing cations from long-chain OMPs.

3. 1.2. 3 Methylene Chloride As Mobile Phase

To determine whether THF might act as a solvating agent, thereby

promoting dissociation of the tin-polymer bond, methylene chloride was substituted for THF as mobile phase. The result was a single peak

eluted from a single column after 11 mL of eluent (fig. 3A).

Substituting THF as eluent resulted in the appearance of another peak

appearing 11 mL after introduction of THF onto the column (1st peak in

fig. 3B). But a solution of OMP in methylene chloride, injected into a mobile phase of THF, gave polymer and monomer peaks with elution volumes

identical to those obtained with OMP dissolved in THF (2nd and 3rd peaks

in fig. 3B). Thus it is evident that methylene chloride, although a good solvent, is not a satisfactory chromatographic eluent for OMPs.

3. 1.2. 4 Propyl Modified Silica As Solid Phase

This packing material provided a polymer peak and a very long tail

(fig. 4) without evidence of a low molecular weight peak. Since this

tailing indicates a serious absorption problem, no additional

experiments were undertaken using these columns.

3. 1.2. 5 Deactivation of pStyragel

3. 1.2. 5.1 Prior Overloading with OMP

3

° Three selected 10 A pStyragel were conditioned individually by

injecting 5.0 mg of an OMP in 500 pL of THF. Although used extensively

for analysis of oil specimens, these columns had not been previously

exposed to acetic acid. A plate count showed them to be individually

and in tandem, in good condition, with 20,000 theoretical plates per

meter.

A sample of OMP fractionated on these columns gave the SEC-ARI and

the SEC-GFAA chromatograms shown in figure 5, indicating that: (1) the

12
A : METHYLENE CHLORIDE AS SOLVENT AND

ELUENT FOR OMP-2P

MeCI

2 THF

Figure 3. SEC-GFAA of 0MP-2P. (A) solvent, methylene chloride. Mobile

phase CH2 CL2 for the first 25 mL, then THF . Flow rate 0.5 mL

min x. Injected sample 0.45 mg/50 pL. UV sensitivity 0.0125

AUFS. Column the same as for figure 1. (B) Solvent CH 2 C1 2 , eluent THF. Other conditions as above. Acetic acid injected

16 min after the polymer solution and at 2 to 5 min intervals

thereafter.
SEC-GFAA CHROMATOGRAM OF OMP-2P

ON PROPYL-MODIFIED SILICA GEL

10 20 30 40 50 60

V' ,mLs

Figure 4. SEC-GFAA of 0MP-2N. Columns, propyl substituted silica gel

O (two). Average pore size 10 2 and 5 X 10 2 A; dimensions

4.6 mm i.d. X 250 mm. Other conditions the same as for

figure 1, omitting acetic acid.

14
SEC-ARI, GFAA CHROMATOGRAMS

OF OMP-2N, SHOWING

PARTIAL EXCLUSION

_l | |

- -|—

10 5 104 10 3 10 2

Figure 5. SEC-ARI, GFAA chromatograms of 0MP-2N. Columns (jstyragel

O (three), pore size 103 A. Solvent, THF. Eluent THF. Flow

rate 1.0 mL. min-1

. Injected sample volume 5.0 mg/500 pL.

0.5 mL fractions collected for off-line GFAA. ARI sensitivity

1 X 10-6 ARI unit per full scale deflection.

15
triorganotin species indeed is bonded to polymer, and (2) that it

remains so when eluted through a deactivated column.

Asymmetry in the SEC/ARI high polymer peaks indicates total

exclusion of part of this fraction. It is necessary to use SEC columns

of greater pore size for MW determinations. Figure 6 includes

SEC-UV/ARI, SEC-UV, SEC-GFAA chromatograms of 0MP-2P, a commercial

4 3 2

° polymer, using three columns in tandem of pore size 10 , 10 , and 10 A,

respectively. The column calibration is indicated below the

chromatograms. Each column was deactivated with a 500 pL injection

containing 2.0 percent of tributyltin methacrylate (TBTM). The data for

this polymer and four other preparations dissolved in mineral spirits

are all presented in tables 5 and 6.

Table 5. SEC-ARI Chromatography of 0MPs

a

Sample

Number

M

w

(dal tons)

M

n (dal tons) MWD

Mass

Conversion

(%)

0MP-8N 46,000 31,300 1.49 96.7

0MP-8P 50,000 28,400 1.75 96.3

0MP-2N 52,300 32,600 1.56 96.2

0MP-2P 63,700 40,900 1.56 96.6

II 69,700 36,900 1.88 95.7

II 62,800 33,900 1.85 95.8

0MP-2P

Average 65,400 37,200 1.76 96.0

S. D. 3,750 3,500 0.18 0.5

n 3 3 3 3

a 4 ® Columns (pStyragel) 10 A,

0 O 9 O 10

° A, KT A, in series.

Conversion of low to high- MW species.

16
Table 6. SEC, GFAA Chromatography of 0MPs a

Sample

Number

Mw

(daltons)

M

n (daltons) MWD

Conversion^1

(%)

Recovery

0

(%)

0MP-8N 35,300 13,900 2.53 89.9 104.0

0MP-8P 37,800 15,000 2.52 95.9 93.4

0MP-2N 41,600 18,500 2.25 90.0 94.1

0MP-2P 65,000 28,500 2.28 92.5 111.0

II 56,900 24,900 2.29 92.1 97.3

0MP-2P

Average 61,600 26,700 2.28 92.3 104.2

S. D 5,700 2,500 0.01 0.3 9.7

n 2 2 2 2 2

a Col umns (pStyragel

)

10* A, 10'3 A,

2

° HT A. Conversion of low MW ti n-beari ng species to polymer.

c Ratio of eluted to injected tin.

There appears to be little difference between the samples prepared

by DTNSRDC (0MP-2N and 0MP-8N, figs. 8 and 9) and the corresponding

commercial formulations (0MP-2P and 0MP-8P, figs. 6 and 7). It is also

apparent in tables 5 and 6 that the MW determinations are reproducible

within plus or minus 10 percent.

The fact that a UV peak nearly coincides with both the ARI and the

GFAA peaks strongly indicates that chromophoric species are bonded to

the tin-bearing low molecular weight species having a MW of about 650 to

1000 daltons. The molecular weight suggests a compound or complex of

tri butyl tin (or a degradation product) with a chromophoric organic acid

such as benzoic acid, or methacrylic acid.

The explanation suggested is consistent with NMR spectra (fig. 10).

The NMR peak at 101.5 ppm in figure 10 may be due to tri butyl tin

benzoate. A sample of tributyltin benzoate run by itself in chloroform

has the identical chemical shift. Note however that complexation with

benzoic acid is possible only for 0MP-N polymers, since 0MP-P polymers

are made with an aliphatic peroxide as initiator rather than benzoyl

17
RELATIVE

GFAA

SIGNAL

INTENSITY

SEC-UV/ARI.GFAA CHROMATOGRAMS

OF Poly(tri-n-butyltin)Methacrylate

Figure 6. SEC-UV/ARI, GFAA chromatograms of 0MP-2P. Columns, pStyragel

(three), pore size 104

, 10 3

, and 102 A, consecutively.

Solvent THF. Eluent THF. Flow rate 0.5 mL min 1

. Injected

sample 4.2 mg/500 pL. 0.5 mL fractions collected for off-line

GFAA. UV sensitivity 0.1 AUFS. ARI sensitivity 1 X 10"*3 ARI

unit for full scale deflection.

18
Figure 7

SEC-UV/ ARI.GFAA

CHROMATOGRAMS

OF OMP-8P

0MP-8P. All conditions the same as figure 6. Injected sample,

4.9 mg/500 pL.

19
RELATIVE

GFAA

SIGNAL

INTENSITY

SEC-UV/ ARI,GFAA CHROMATOGRAMS

OF Poly (tri-n-butyltin) Methacrylate

~T~ 1 |— \~

in 5 io 4 io 3

10

2

Figure 8. Sample 0MP-2N. All conditions the same as figure 6. Injected

sample, 4.6 mg/500 pL.

20
RELATIVE

GFAA

SIGNAL

INTENSITY

SEC-UV/ARI ,GFAA

CHROMATOGRAMS

OF OMP-8N

io 5 io

4

10 3 10

2

Figure 9. 0MP-8N. All conditions the same as figure 6.

5.8 mg/500 |jL.

Injected sample,

21
PPM

Figure 10. Tin-119 NMR at 74.6 MHz of OMPs in benzene. (A) 0MP-2N;

(B) 0MP-8N. In each spectrum the sharp peak at about 97 ppm

arises from unreacted TBTM.

22
peroxide. An NMR peak at about 97 ppm in OMP-P polymers is attributed

later in this report (subsection 3.2.5) to tributyltin methacrylate (see

fig. 25). However, further work needs to be performed on the

identification of the low MW chromophore--e. g. , collection of fractions

during preparatory scale chromatography for subsequent analysis by

ultraviolet, infrared, and NMR spectroscopy.

Appendix A presents in detail a suggested method for SEC-UV/ARI,

GFAA characterization of OMPs on pStyragel.

3.2 NMR

3.2.1 Introduction

Since the last report [6] was published, we have succeeded in the

complete configurational sequencing, at the triad level, of copolymers

of MMA and TBTM or MMA and MAA. The copolymerization of vinyl monomers

of A and B can give rise to triad sequences which are syndio-(rr),

hetero-(mr), or iso-(mm) tactic. At the same time, compositional

sequences such as AAA, AAB, BAB, ABA, BBA, and BBB may occur. Hereinafter, we will use A to refer to MMA, and B to refer to TBTM or

MAA. With both composition and tacticity taken into account, there are

20 possible triad sequences which may exist [5]. We have examined NMR

spectra of protons, carbon-13, and tin-119.

3.2.2 Solvent Effects

The polymers that we received for examination contained

approximately 33 percent solids, dissolved in either a commercial mixed

hydrocarbon (Stoddard) solvent or in an aliphatic ketone solvent. The

NMR spectra, especially of tin, showed such large differences in

appearance between these two solvents that a study of solvent effects

was undertaken. It is well known that tin, which is nominally

4-coordinate in these polymers, can readily expand its coordination

shell to five or six, and that donor solvents may promote such expansion

[11]. In the absence of coordinating solvents, it appears likely that

tin will expand its coordination number by self-association with ester

groups in other parts of the polymer.

The results of a study of solvent effects in 0MP-2 solutions are given in figure 11. It is clear that for best resolution, chloroform is

the preferred solvent. In subsequent Sn-119 NMR experiments, polymer

solution was diluted with an equal volume of CDCl^, and the spectrometer

23
> « »

jyvi,

i i i i i i i i i i i i 120 100 80 60 40 20 0 PPM

Figure 11. Tin-119 NMR at 74.6 MHz of 0MP-2P in several solvents.

From the top: chloroform, benzene, n-hexane, acetone,

tetrahydrofuran , methanol, and pyridine.

24
was locked to the deuterium signal. This not only improved field

stability for long accumulations, but also provided a frequency

reference so that the signal could be referenced to external tetramethyl

tin. In the discussion that follows, the shape and relative positions

of various tin signals are of considerable significance. However,

because of the large solvent effects and the uncertainties associated

with external referencing, absolute chemical shift values have little

meaning (in these concentrated solutions, the polymer must be regarded

as both solute and a part of the solvent system).

3.2.3 Protons

Proton spectroscopy has been valuable for characterizing the

tin-free polymers (MMA-MAA). These include not only the prepolymers but

also material obtained by cleavage of tri butyl tin groups from OMPs (see

above). In these polymers, proton NMR of the -CH^- units in the polymer

backbone gives an unequivocal determination of tacticity [12]. The

-CH^ - signal, occurring about 1.8 ppm, is diagnostic for dyad sequences

(r or m). In the syndiotactic groups (r), the signal is a single peak

at the chemical shift position. In isotactic groupings (m), however,

the protons are magnetically inequivalent and hence appear as a doublet

approximately equally spaced (by about 0.35 ppm) on either side of the

syndiotactic peak. Because of the inequivalence, each line of the

doublet is split into two by the geminal H-H coupling of about 14 Hz, so that altogether 4 lines are seen. Integrals of the singlet and the

quartet allow the tacticity to be determined quantitatively. Tetrad

splittings (rrr, rrr, rrm,...) have not been observed in these samples.

A sample of poly (MMA) was prepared by butyl 1 ithium-induced

polymerization of MMA at -78 °C [13] and was shown by H-l NMR to be

predominantly isotactic (m) [14]. Figure 12 shows the 400 MHz proton

NMR of isotactic DMMA prepared as described above. The pair of doublets

at 1.55 and 2.20 ppm are diagnostic of the isotactic -CH^ - group. The

small peak at 1.8 ppm in the expanded spectrum represents the residual

syndiotactic groups. The narrow 0-CH

3 signals at 1.2 ppm(mm),

1.0 ppm(mr), and 0.85 ppm(rr) give an indication of triad frequencies

(86.4 : 8.4 : 3.1). These figures are incompatible with Bernoullian

statistics, in agreement with previous reports on anionic polymerization

of MMA [16]. Having only dyad and triad frequencies, we are unable to

test any Markov model.

25
1 i 1 I I 1 I I I I I 1 I I 1 L I 1 I L - . .1- 4 3 2 1 0 PPM

* Figure 12. Proton NMR at 400 MHz of isotactic PMMA dissolved in

CDC1 3

. Upper trace 8X vertical expansion.

26
Figure 13 shows the 400 MHz proton NMR of a commercial 1:1 prepolymer

(MMA-MAA). The -CH^- signals at 1.7 to 1.9 ppm arise from -CH^ - groups

between C00R, C00R; C00H, C00R; and C00H, C00H. All of these groupings

are seen to be syndiotactic since the regions at 1.55 and 2.20 ppm are

free from signal. The p-CH^ region is expected to show two signals,

each split by compositional sequencing as well as tacticity effects.

The complexity of the signals seen indicates that compositional effects

are large; the lines have not been assigned. In tin-containing

polymers, the protons of the butyl groups give strong signals which make

the signals from the rest of the polymer difficult or impossible to

observe and proton NMR is consequently less useful. Figure 14 shows the

400 MHz proton NMR of 0MP-2P. The butyl groups are responsible for

nearly all of the strong signal to high field of 1.7 ppm. The p-methyl

group is completely obscured. However, the signal at 1.8 ppm together

with the absence of signal at 2.20 ppm shows that the polymer is also

predominantly syndiotactic.

3.2.4 Carbon-13

The least sensitive nucleus in these compounds, carbon-13, is also

the most informative. The chemical shift range covered in the C-13

spectrum of the polymer runs from about 10 to 185 ppm (if a ketonic

solvent is present, its carbonyl absorption will occur at about 205 ppm)

(see fig. 15). The final copolymers show such large interferences in

the aliphatic region from the butyl groups (and solvent in the samples

as-received) that only the carbonyl region (around 180 ppm) is useful.

In order to get more exact structural information, we have removed the

tri butyl tin groups from the polymer by treatment with HC1 and extraction

with chloroform, as described above. In the copolymer of MMA and MAA

thus prepared, which is directly comparable with the commercially

prepared pre-polymer, it is possible to distinguish much configurational

information. In the C-13 spectrum of the pre-polymer (see fig. 16

and 17), the NMR signals fall into five distinct regions and are informative to varying degrees. In order of increasing chemical shift,

these are p-methyl (15 to 21 ppm), quaternary carbon (44 to 45 ppm),

methoxyl (50 ppm), methylene (50 to 55 ppm), and carbonyl (177 to 181 ppm).

Comparison of samples derived from 0MP-8 (1:1 vs 2:1 ratio of MMA

to TBTM or MAA) enabled us to distinguish, in the carbonyl region, a

27
4 3 2 1 0 PPM

Figure 13. Proton NMR at 400 MHz of 0MP-2P prepolymer in DMS0-d6

.

28
-1—1 1 t I I L X > I I I llit I t X. JL,- i I I I I 1 PF'M

Figure 14. Proton NMR at 400 MHz of 0MP-2P in CDC1 3

.

29
Figure 15. Carbon-13 NMR at 50.31 MHz of 0MP-2P in methyl isoamyl

ketone, as received. Most of the signal is due to the solvent.
-COOR

180

Figure 16. Carbon-13 NMR at 100.62 MHz of 0MP-2P prepolymer in

pyridine. The major signals are labelled. The weak

signal at 39.5 ppm comes from DMS0-d6 in a concentric

tube. The weak signals between 21 to 35 and at 48 ppm

are not positively assigned; they may be due to small

amounts of the original solvent which was not completely

removed. They are in the wrong position to arise from

residual tri butyl tin groups.

31
J 1 L 180

Figure 17. Carbon~13 NMR at 100.62 MHz of polymer stripped of tin

by treatment with chloroform and HC1 , and dissolved in

pyridine at 360 °K. (A) 0MP-2N; (B) 0MP-8N.

32
correspondence between structure and chemical shift, in the sense that

-COOMe signals appear at higher field than -C00H or -COOSnR^ signals.

Beyond that, we were able to determine from the relative intensity of

signals in the various mul tiplets , which of the multiplets were split by

compositional sequencing effects (quaternary carbon), which by tacticity

(0-methyl), and which by both (carbonyl). The methoxyl signal, although

sharp, is but a single line in all samples studied and conveys no sequencing information. The methylene carbon signal is split into two

broad peaks (r and m) which reflect dyad tacticity, but with poor

precision as the signals are weak. For the three groups to be discussed

below, tacticity effects appear in triads (rr, rm, or mm) and pentads

(rrrr. . . mmmm). The 0-methyl region of the spectrum (15 to 21 ppm) is

relatively unaffected by compositional sequencing but is split into

three wel 1- resol ved peaks according to tacticity (fig. 18). The

material is known from proton NMR to be predominantly syndiotactic , and

the largest peak was thus assigned to the (rr) configuration. The

proportions of the three peaks agree with Bernoulli an statistics, as expected for a free-radical catalyzed polymer [15]. Table 7 lists the

proportions of iso-, hetero-and syndio-tactic configurations for several

polymers derived from analysis of the 0-Me spectrum. The 0MP-2N samples were run after cleaving the tri butyl tin groups.

13 Table 7. Tacticity and Composition Ratios Taken From C FTNMR

Spectra of Poly (MMA-MAA) Copolymers

Copolymer

Designation

COOCH

COOH

Isotactic

(%)

Heterotactic

(%)

Syndiotactic

(%)

p-TBTM — 3.0 32 65

0MP-2N 1.0 4.0 37 59

0MP-8N 2.0 5.0 37 58

0MP-2P 0.9 2.0 35 63

0MP-8P 2.4 2.0 40 58

33
ch 3

f CH- CH- COOR CH

-CH 2 -C-CH 2 -C-CH2 -C-CH2 -C/CH 2 -C-

/

I COOR COOR COOR CH COOR

Figure 18. Carbon-13 NMR at 100.62 MHz of 0MP-2P prepolymer in

pyridine at 360 °K. Expansion of p-Me region. Labelled

according to tacticity.

34
correspondence between structure and chemical shift, in the sense that

-COOMe signals appear at higher field than -C00H or -COOSnR^ signals.

Beyond that, we were able to determine from the relative intensity of

signals in the various multiplets, which of the multiplets were split by

compositional sequencing effects (quaternary carbon), which by tacticity

(p-methyl), and which by both (carbonyl). The methoxyl signal, although

sharp, is but a single line in all samples studied and conveys no sequencing information. The methylene carbon signal is split into two

broad peaks (r and m) which reflect dyad tacticity, but with poor

precision as the signals are weak. For the three groups to be discussed

below, tacticity effects appear in triads (rr, rm, or mm) and pentads

(rrrr. . . mmmm). The p-methyl region of the spectrum (15 to 21 ppm) is

relatively unaffected by compositional sequencing but is split into

three well-resolved peaks according to tacticity (fig. 18). The

material is known from proton NMR to be predominantly syndiotactic, and

the largest peak was thus assigned to the (rr) configuration. The

proportions of the three peaks agree with Bernoulli an statistics, as expected for a free-radical catalyzed polymer [15]. Table 7 lists the

proportions of iso-, hetero-and syndio-tactic configurations for several

polymers derived from analysis of the p-Me spectrum. The 0MP-2N samples were run after cleaving the tri butyl tin groups.

13 Table 7. Tacticity and Composition Ratios Taken From C FTNMR

Spectra of Poly (MMA-MAA) Copolymers

Copolymer

Designation

COOCHCOOHIsotactic

(%)

Heterotactic

(%)

Syndiotactic

(%)

p-TBTM — 3.0 32 65

0MP-2N 1.0 4.0 37 59

0MP-8N 2.0 5.0 37 58

0MP-2P 0.9 2.0 35 63

0MP-8P 2.4 2.0 40 58

33
CHo ch3 ch3 coor ch3

/

I CHj—C—

COOR COOR COOR CH COOR

Figure 18. Carbon-13 NMR at 100.62 MHz of 0MP-2P prepolymer in

pyridine at 360 °K. Expansion of p-Me region. Labelled

according to tacticity.

34
A sample of isotactic PMMA (see above) was about 20 percent

hydrolyzed [15] to a poly (MMA-MAA). The 013 NMR spectrum of

thus-prepared isotactic poly (MMA-MAA) allowed the assignment of the

isotactic (mm) peaks unequivocally. The quaternary carbon region

primarily reflects the effects of composition, and to a lesser degree

tacticity. A quaternary carbon bonded to -COOMe shows a relatively

sharp line with shoulders rather than discrete splittings to indicate a distinction between AAA, AAB, and BAB. A quaternary carbon bonded to

-COOH appears as a broad, structureless peak which is uninformative.

Because the broad and sharp peaks overlap, integrals of the quaternary

region are of little value. The carbonyl region of the spectrum is

split into a great many lines and is consequently informative (figs. 19,

20). The upfield (-COOMe) and downfield (-COOH or -COOSnR^) signals

show'considerable parallelism. Each may consist of a triplet of

triplets. The larger triplet splitting (about 1.2 ppm) is caused by

tacticity. In order of increasing field strength (decreasing chemical

shift) the peaks arise from syndio(rr), hetero(rm), and i so(mm)-tactic

material. In figure 20 the amount of syndio- and heterotactic polymer

is too small to be seen. The smaller triplet splitting (about 0.5 ppm)

is caused by compositional sequencing effects as diagrammed in

figure 20. The additional small splittings in the carbonyl region are probably due to pentad structure; however, they have not been assigned.

Knowing that the 2:1 polymer must have a smaller proportion of B groups,

we can assign the triplets as follows: downfield—AAA;

center--BAA + AAB; upfield—BAB. Correspondingly, the B triplet

sequence is ABA, BBA+ABB, BBB in order of increasing field. It is not

possible by means of C-13 NMR to determine the amount of residual -COOH

in the presence of -COOSnR^, because the chemical shifts of all signals

in these species are virtually coincident. Impurity signals are not

present in large amounts. If present in small amounts, they would be

masked by solvent in the as-received material since the solvent C-13 NMR

spectrum is very rich in signals. The tin-free samples have had the

solvent and solvent impurities replaced by pyridine.

3.2.5 Tin- 119

Tin-119 NMR is useful on two counts: it provides a means of

finding and determining tin-containing impurities, and it also provides

35
Figure 19. Carbon-13 NMR at 100.62 MHz of isotactic poly(MMA-MAA)

in pyridine at 360 °K. Upper trace 2.5X horizontal expansion.

36
CH

I 3 -ch2 -c-ch

COOH

COOH CH3 COOR

I I I 2 -c-ch2 -c-ch2 -c-ch2

I I I CH3 COOH CH3

CH3 COOR CH3 COOR

I • I I —C—CH 2 —C—CH2 —c—ch 2 —c—

I I I I COOH CH3 COOR CH3

Figure 20. Carbon-13 NMR at 100.62 MHz of 0MP-8P prepolymer in

pyridine at 360 °K. The syndiotactic peaks are labelled according

to composition. The weak higher field peaks are caused

by heterotactic polymer; there is too little isotactic

material to be detected.

37
a means of estimating compositional sequencing. By using material of

which a portion has been stripped of tin for C-13 NMR, it was possible

to determine that the Sn-119 NMR signal, which appears as a rather broad

peak at about 90 to 98 ppm in chloroform solution, is but little

affected by tacticity, whereas it shows structure attributable to

compositional sequencing. The additional signals appear as shoulders

rather than as wel 1 -resol ved peaks, and appear in the opposite sense to

the corresponding signals in the C-13 carbonyl region, i.e., the

downfield peak is BBB, the center peak is BBA + ABB, and the upfield

peak is ABA. The proportions found in the several samples examined are

in agreement with the results found from the C-13 spectrum of carbonyl

groups.

Tin-119 NMR is better suited than proton or C-13 NMR to searching

for impurities, inasmuch as common solvents are free from tin compounds.

In general, all samples from whatever source have 96 percent or more of

the tin signal in the region 90 to 98 ppm attributed to -CQOSnBu^ on the

polymer chain. Samples 0MP-2N and 0MP-8N (fig. 10) had additional

signals. The lower field signal, about 105 ppm, is tentatively

attributed to tri butyl tin benzoate, which could arise from decomposition

of the initiator, benzoyl peroxide. The rather sharp signal at 97 ppm

overlapping the polymer signal (see below) arises from TBTM.

Referring again to figure 2 samples 0MP-2P and 0MP-8P have three

impurity peaks. One, found at -12 ppm, is doubled by addition of 20 pL

of tetrabutyl tin (fig. 21), and is therefore attributed to that

substance. A second sharp peak, about 72 ppm, is in the region given in

the literature for a tributytin alkoxide [16] and may be the

4-butyl cyclohexyl oxide of tri butyl tin. This could arise as a decomposition product of the Percadox initiator. The third impurity

peak, about 112 ppm, is much broader than the two peaks at lower field

and coincides with the signal from added tributyltin methoxide. The

result of adding tetrabutyl ti n has been described above. Additions of

TBTM give a fairly sharp signal about 104 ppm (figure 22) which overlaps

the polymer signal to a degree and is therefore not readily quantitated.

Additions of TBT0 were made to sample 0MP-2P in order to learn if it were responsible for the downfield peak. The first three aliquots gave

no appreciable signal anywhere in the spectrum. Finally, a fourth

38
I 1 I 1 I L. J i I i L _i I i I

i 1 iI i I i . / 120 100 80 60 40 20 -20

Figure 21. Same as figure 2(A) plus 20 pi of tetrabutyl ti n , showing

growth of its peak at -12 ppm.

PPM

39
-I I u -J—

u

_l L. _l 1 L- 1 . 1 120 100 80 60 40 20 -20

Figure 22. Same as figure 2(A) plus 15 pL of TBTM, showing growth

of its peak at 104 ppm.

PPM

40
aliquot did increase the signal at 90 ppm (fig. 23). A possible

explanation for this observation is that the polymer sample contains

unreacted pendant free acid groups (which we are not able to detect by

either proton or 013 NMR) and that the first aliquots of TBTO were used

up in reacting with these acid groupings. With the addition of

tri butyl tin methoxide, again no signal was observed until 328 pL had

been added (fig. 24). Two signals were actually observed; one corresponding to the impurity at 100 ppm while the other appeared to be

TBTO at 92 ppm formed by the hydrolysis of the initial aliquots of

tributyltin methoxide added. In figure 25 are shown spectra of early

samples of 0MP-2P(A) and 0MP-2N(B). Despite the fact that preparation

of 0MP-2P uses no TBTM, the signal at 97 ppm in both spectra obtained

from toluene solutions arises from that substance.

4.0 Summary and Conclusions

We have shown that the combination of SEC and FTNMR provides a set

of powerful tools for the characterization of organotin vinyl

copolymers. Direct comparison of samples prepared by esterification of

prepolymer (OMP-P series) and samples prepared by copolymerization of

TBTM and MMA (OMP-N series) shows essentially the same chromatograms

(SEC) and spectra (NMR). There are small differences (below the

1 percent level) in impurity content as measured by Sn-119 NMR. At

present these differences have not been correlated with field

performance of the materials as biocides.

SEC analysis can provide a measure of molecular weight, molecular

weight dispersion, and the distribution of tin among fractions of

different molecular weights. This last is most important since it is

known that there is a strong negative correlation between proportion of

tin in the low MW material and its field performance. The lack of

suitable standards means that it is not possible to determine absolute

molecular weights. Nevertheless, so long as materials of similar

composition are being compared, the relative molecular weights are valid

and are useful for predictive purposes.

Although NMR spectra can be run on polymer solutions as received,

substantially better results are obtainable with a relatively small

amount of pretreatment. In the case of Sn-119 NMR, this pretreatment

41
. I .. . I ... I ... 1 ... 1 ... I ... I .. . . 120 100 80 60 40 20 0 -20 PPM

Figure 23. Same as figure 2(A) with additions of TBTO. (A) 7.8 pL;

(B) 78 pL; (C) 328 pL; (D) 1328 pL.

42
PPM

Figure 24. Same as figure 2(A) with additions of tri butyl tin methoxide.

(A) 20 |jL; (B) 120 \sl; (C) 500 gL; (D) 750 pL.

43
Figure 25. Tin-119 NMR at 74.6 MHz of OMP-2 in toluene. (A) 0MP-2P;

(B) 0MP-2N. The sharp peak at 97 ppm arises from TBTM.

44
Drain

Figure 26. Experimental arrangements for SEC. Solvents degassed by

stirring under partial vacuum. HPLC pumps delivered

eluent at a controlled flow rate of 0.5 or 1.0 mL

min'-1 ± 0.001 mL miri-1

. Sample injection valve equipped with

loops of 50 pL or 500 pL volume. Recommended column set

O includes at least one of pore size 104 A and one of pore

O

size 102 A. Two or more of each size may be desired.

UV/ARI detector: dual detector preferred; two detectors

in tandem may be used, in conjunction with an automatic

dual pen recorder. An autosampler may be used for

on-line GFAA, or fractions may be collected for off-line

GFAA.

45
consists only of diluting the polymer solution with an equal volume of

CDCl^. The usual tin NMR spectrum shows a triplet, not completely

resolved, at about 90 to 98 ppm. The Sn-119 NMR spectrum is little

affected by tacticity, and the triplet splitting is due to compositional

sequencing effects. From lowest to highest field, the three peaks arise

from BBB, (BBA+ABB), and ABA sequences, where B = -COOSnR^ and A = -COOMe.

In addition, Sn-119 NMR will show the presence of tin-containing

impurities. Some which have been identified are tetrabutyl ti n (12 ppm),

TBTO (90 ppm), TBTM (about 97 ppm, overlaps polymer signal), and

tributyltin methoxide (110 ppm). In the absence of extensive field

testing or a fully adequate theory of action of control led-release

polymers, it is not possible to say with certainty that any of these

impurities is either beneficial or harmful to longterm field performance

of the materials. However, the means to measure, and in some cases identify, tin-containing impurities is now available. For proton and

C-13 NMR, it is possible to obtain much improved spectra by working with

tin-free polymer, prepared by stripping the tributyltin groups with HC1

and CHC1

3 as described above. Although proton NMR provides an a priori measure of tacticity in the signal at 1.8 ppm, the same information

can be better obtained from the carbon-13 spectrum. (In a vinyl

copolymer containing a relatively small proportion of isotactic

sequences, such as we have in the OMP series, the triad sequences as seen in C-13 NMR give double the signal for isotactic material compared

to the dyad sequences as seen in proton NMR, for statistical reasons.)

Carbon-13 NMR gives signals from the p-methyl , quaternary,

methoxyl , methylene, and carbonyl carbons which are informative to

varying degrees, as discussed above. If only one signal were to be

observed, it should be carbonyl since this provides (1) the ratio of

-COOMe to -C00H, (2) tacticity, and (3) compositional sequencing

information.

In conclusion, the combination of SEC and FTNMR provides the means

to measure (1) molecular weight, (2) molecular weight dispersion,

(3) percent of tin associated with low MW material, (4) tin-containing

impurities, (5) monomer ratio, (6) tacticity, and (7) compositional

sequenci ng.

46
5.0 Acknowledgments

For valued discussion and suggestions, the authors thank Dr. Bruce Coxon,

of the National Bureau of Standards, and Prof. J. M. Bel lama of the

University of Maryland.

47
6.0 References

[1] Parks, E.J. ; Johannesen, R.B.; Brinckman, F.E. Characterization of

Organometal 1 ic Polymers by Chromatographic Methods and Nuclear

Magnetic Resonance. NBSIR 812424; 1981, 37 p.

[2] Parks, E.J.; Johannesen, R.B.; Brinckman, F. E. Characterization

of Organometal 1 ic Copolymers by Size-Exclusion Chromatography

Coupled with Trace Metal- and Mass-Sensitive Detectors. J. Chromatography 255 , 439-454 (1983).

[3] Dyckman, E.J.; Montemarano, J.R. Antifouling Organometal 1 ic

Polymers: Environmentally Compatible Materials, Report No. 4186,

Naval Ship Research and Development Center, Bethesda, MD (1974).

[4] Parks, E.J.; Brinckman, F.E. Characterization of bioactive

organotin polymers: fractionation and determination of MW by

SEC-GFAA. In controlled release of pesticides and pharmaceuticals,

D.H. Lewis, Ed., Plenum Press, N.Y., 1981, pp. 219-238.

[5] Bovey, Frank A. High Resolution NMR of Macromolecules, Academic

Press, N.Y. , 1972. Chapters 2, 3 and 10.

[6] Parks, E. J. ; Johannesen, R.B.; Brinckman, F.E. Advances in the

SEC Characterization of Organometal 1 ic Copolymers and

Copolymerization: Desorption of Charged Species by Injected Dilute

Acetic Acid. NBSIR 82-2577; 1982, 30 p.

[7] Brinckman, F.E.; Blair, W.R.; Jewett, K. L. ; Iverson, W.P.

Application of a liquid chromatograph couple with a flameless

atomic absorption detector for speciation of trace organometall ic

compounds. J. Chromatogr. Sci. 15, 493-503; 1977.

[8] Yau, W.W. ; Kirkland, J.J.; Bly, D.D. Modern size exclusion liquid

chromatography, practice of gel permeation and gel filtration

chromatography. Wiley-Interscience, N.Y. 1979, pp. 318-322.

[9] Parks, E. J. ; Brinckman, F. E. ; Blair, W.R. Application of a > graphite frunace atomic absorption detects automatically coupled to

a high performance lquid chromatograph for speciation of

metal -contai ni ng macromolecules, J. Chromatography, 185, 563-572

(1979).

[10] Parks, E.J.; Brinckman, F.E.; Mullin, C.E.; Andersen, D.M.;

Castelli, V.J. Characterization by tin-specific size exclusion

chromatography of the free radical copolymerization of tributyltin

methacrylate and methyl methacrylate. J. Appl. Poly. Sci. 26, 2967-2974

(1981).

[11] Okawara, R. ; 0'hara, M. Organotin Compounds with Sn-0 Bonds.

Organotin Compounds, A. K. Swayer, Ed., Marcel Dekker, Inc., N.Y.

,

1971, Vol . 2, Chap. 5.

48
[12]

Reference 5, p. 71ff.

[13] Tsuruta, T. ; Makimoto, T. ; Kanai, H. Stereochemistry in the

Polymerization of Methacrylic Esters. J. Macromolecular Science,

1, 31-60 (1966).

[14] Klesper, E. ; Johnsen, A.; Gronski, W. ; Wehrli, F. Evaluation of

Triads in Methyl Methacryl ate-Methacryl ic Acid Copolymers by 1H-NMR

in Different Solvents and 13C-NMR. Die Makromolekulare Chemie,

176, 1071-1119 (1975).

[15] Reference 4, pp. 74-5.

[16] Smith, P. J. ; Tupciauskas, A. P. Chemical Shifts of 1195 n Nuclei

in Organotin Compounds. Ann. Repts. NMR Spectroscopy, 8, 291-370

(1978).

49
7. 0 Appendix A

7. 1 Procedure for Size Exclusion Chromatography of OMPs

Dissolve in degassed, filtered reagent grade THF (9 ml) 0.1 g of

OMP solids. Let the mixture stand at least overnight (12 hr) to effect

dissolution of the polymer. When solution appears to be complete,

filter through an organic sample clarification apparatus (0.45 pm pore

size), and dilute to exactly 10 mL with THF.

Set up the size exclusion apparatus as diagrammed in figure 26.

Employ an HPLC pump capable of delivering eluent at a flow rate of

0.2 to at least 3.0 mL min ^ with an accuracy of ±0.001 mL min

Install HPLC injection valve capable of accommodating sample loops of

20 pL to 500 pL or greater volume. Install the 500 pL loop. Connect

the injection valve to the inlet end of the conditioned SEC column set.

Connect the outlet to either a ARI/UV dual detector or ARI and UV

detectors in tandem. To the detector outlet, attach a length of

capillary tubing sufficient to transfer effluent into collection

vessels.

Set the ARI and UV detectors at the highest sensitivities

commensurate with recorder sensitivity. Record ARI and UV absorbances

continuously on a dual pen recorder (e.g., Perkin-Elmer Model 156).

With eluent flow rate set at 0.5 mL min \ inject 500 pL of the OMP

solution. Collect as a single fraction all materials eluted prior to

the first ARI peak, in a Teflon stoppered glass vial. Subsequently

collect 0.5 mL fractions (or smaller if desired) similarly to be stored

in Teflon stoppered glass vials. Continue collecting sample until all

ARI and UV activity ceases, including detection of both high-and low-MW

peaks, solvent peaks, and impurities. Because sample collection will

occupy the operator's full attention, repeat ARI and UV chromatograms at

least once without collecting fractions, adjusting the pen location as necessary to keep the ARI record on the chart, without changing the

sensitivity. UV sensitivity may be changed at any time to keep the UV

chromatogram on the chart paper.

Begin measurements of tin by GFAA as soon as possible after

collecting all fractions. In Teflon or polyethylene cups (previously

leached overnight in 10 percent HNO^ at 60 °C), dilute samples of

measured volume with THF to keep GFAA absorbance readings approximately

50
65 percent or less and as nearly equal as possible over the entire

chromatograms. Note the final dilution of each fraction. At the

highest polymer concentrations, dilutions of 200 to 400 may be

necessary. Take three or more replicate measurements on each fraction.

Following all of the measurements on all fractions, disconnect

the injection valve from the column inlet and introduce a capillary tube

leading from the injection valve into a volumetric flask (10 mL). Load

the 500 pL loop with 0MP solution, collect several mL of eluent, and

dilute volumetrical ly. Introduce this diluted sample into a sample cup

and measure the GFAA response, again with sufficient dilution so that

the readings are of an intensity nearly equal to those obtained with the

chromatographic fractions.

7. 2 Calculations

To obtain sample recovery (%), calculate

B/A X 100 = % recovery

i=o

where B = I v.d.s.

• II ')

I] i=n

where A

v. = volume of individual chromatographic fractions

d. = dilution of v^

s. = observed signal intensities

v^ = volume of unfractionated sample (usually 10 mL)

d^ = dilution of vA

s^ = signal intensity observed for A

51
U.S. DEPT. OP COMM. 1. PUBLICATION OR 2. Performing Organ. Report NoJ 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO.

SHEET (See Instructions) NBSIR 83-2802 February 1984

4. TITLE AND SUBTITLE

Characterization of Organometall ic Polymers by Chromatographic Methods and

Nuclear Magnetic Resonance. Part II.

5 . author(S) e.j, parks; W.F. Manders; R.B. Johannessen; and F.E. Brinckman.

6. PERFORMING ORGANIZATION (If joint or other than NBS, see Instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

S. Type of Report & Period Covered

Interagency Report

Oct. 1. 1982-Sept.3Q.19fip

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

Naval Ship R & D Center

Annapolis Laboratory

Annapolis, MD 21402

10.

SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document Includes a significant

bibliography or literature survey, mention it here) Continuing research into the analytical methodology for characterization of

organometallic polymers (OMPs) has produced improved methods of characterization

by size exclusion chromatography (SEC) and Fourier transform nuclear magnetic

resonance (FTNMR) . Molecular weight (MW) and MW dispersion (MWD) , as well as the

amount of tin associated with fractions of various MW can now be reliably determined

by SEC coupled with various detectors: differential refractive index (aRI),

ultra-violet (UV), and graphite furnace atomic absorption (GFAA) spectroscopy.

Configurational sequencing in terms of both tacticity and sequencing of monomer

units can be determined by FTNMR, as well as certain tin-containing impurities.

Removal of tri butyl tin groups to produce a metal -free copolymer allows much more

informative FTNMR spectra to be obtained. All of the polymers examined are approximately 80 percent racemic (r) and 20 percent meso (m) in tacticity (i.e.,

predominantly syndiotactic) . The growing chain end in the copolymer adds either

of the monomer units approximately in proportion to its instantaneous concentration

in the mixture (i.e., at random).

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) C-13 NMR*, differential refractive index; H-l NMR* Mil-spec; molecular weight

organometallic polymer; polydispersity; size exclusion chromatography; Sn-119 NMR

tacticity; tin-specific GFAAt ultraviolet spectroscopy

.

13. AVAILABILITY

Unlimited

| | For Official Distribution. Do Not Release to NTIS

1 Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

QXj Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

55

15. Price

$ 10.00

U S C O MM- D C 8043-P80