/. c?o 0

NBSIR 82-2577

Advances in the SEC Characterization

of Organometallic Copolymers and

Copolymerization: Desorption of

Charged Species by Injected Dilute

Acetic Acid

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Materials Science

Materials Chemistry Division

Washington, DC 20234

August 1 982

Prepared for David Taylor Naval Ship R & D Center

Annapolis Laboratory

Annapolis, MD 21402

NBSIR 82-2577

ADVANCES IN THE SEC CHARACTERIZATION

OF ORGANOMETALLIC COPOLYMERS AND

COPOLYMERIZATION: DESORPTION OF

CHARGED SPECIES BY INJECTED DILUTE

ACETIC ACID

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

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Materials Science

Materials Chemistry Division

Washington, DC 20234

August 1 982

DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED

Prepared for David Taylor Naval Ship R & D Center

Annapolis Laboratory

Annapolis, MD 21402

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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TABLE OF FIGURES (CAPTIONS)

Figure Page

1. Block diagram summarizing the SEC-UV/ARI-GFAA system,

including accessory devices. In the present work, either

the auto-sampler continuously transferred 20 yL eluent

specimens into the graphite furnace at preset 45-60 sec intervals, or batch fractions were collected during elution

for subsequent quantitation of tin. 4

2. The suggested formula of a copolymer prepared by the freeradical addition of TBTM to MMA. The subscripts x and y

represent numbers of monomers, and n represents the number

of repeat units. Neither the numbers x, y, or n, nor the

tacticity of the copolymer is assumed to be constant. 5

3. SEC-GFAA chromatogram of OMP-2. SolvenJ, THF. Column,

yStyragel (one), average pore size 10^ A. Mobile phase,

THF. Flow rate 0.5 mL min”^. SEC detector, Perkin-Elmer

360, equipped with an Sn-specific EDL lamp operating at

224.6 nm. Injected volume 50 yL. Injected concentration:

50 yg/50 yL. 7

4. SEC-GFAA chromatogram of TBTM purified by recrystallization

from petroleum ether. Solvent, THF. Mobile phase, THF.

Columns, yStyragel (three) in series; average pore size

10^ K. Flow rate 1.0 mL min’^ SEC detector, Perkin-Elmer

360. Injected volume, 50 yL. Injected concentration of

TBTM, 50 yg/50 yL. 8

5. SEC-GFAA chromatograms of OMP-2.

(A) Solvent THF. Mobile phase, THF. 50 yL of THF

containing 1.0 percent HOAc (v:v) introduced into

the THF mobile phase 8.0 min (4.0 mL) after injection

of the OMP solution. All other conditions the same

as for figure 3.

(B) All conditions the same as (A), except that 50 yL

of 1.0 percent HOAc in THF was injected 1 min

(0.5 mL) after the solution of OMP-2. 11

6. SEC-GFAA chromatograms of OMP-2.

(A) Solvent, THF containing 1.0 percent HOAc; acid

added 1.0 h prior to injection. All other conditions

same as for figure 3.

(B) Solvent, THF containing 0.1 percent HOAc, acid

added 1.5 h prior to injection. All other conditions

same as for figure 3. 12

1
Figure Page

7. SEC-GFAA chromatogram of OMP-2 undergoing acid hydrolysis.

Mobile phase, THF containing 1.0 percent HOAc. All other

conditions the same as for figure 3. 14

8. Polymerization rate (k) of TBTM. Closed Circles.

Conversion of TBTM during the copolymerization of TBTM

and MMA, determined shortly after the samples were synthesized. Data taken from chromatograms including those

depicted in figure 9.

Open squares. Conversion of TBTM, as calculated from data

obtained after one year of storage at -78 °C, and including

the chromatograms depicted in figure 10. 16

9. SEC-GFAA chromatograms of partially reacted specimens

sampled during the copolymerization of TBTM and MMA.

Solvent, THF. Mobile phase, THF. Flow rate 1.0 m|, min~^.

Columns, yStyragel (three), average pore size 10^ A.

All other conditions same as for figure 3. 17

10. Partially reacted specimens retested after one year of

storage at -78 °C. Histogrammic peak height indicates tin

content of fractions. Solvent, THF. Mobile phase, THF.

Flow rateoO.5 ml min'^. Column, yStyragel (one), pore

size 10^ A. Injected volume, 500 yL. Injected concentration 100 yg/500 yL. 500 yL of 1.0 percent HAc in THF

introduced by injection 8 min (4.0 mL) after the injection

of polymer. 19

11. Mass conversion of low-MW to high-MW materials during the

copolymerization of TBTM and MMA, plotted as a function of

the reaction time. Conversion data were calculated from

chromatograms including those in figure 9. 20

12. SEC-ARI chromatograms of samples taken during the copolymerization of TBTM and MMA and stored one year at -78 °C.

Solvent, flow rate, mobile phase and column the same as for

figure 10. Detector, Knauer dual detector; ARI sensitivity,

6 X 10'® ARI unit = full scale deflection. Injected volume

500 yL. Injected concentration 1000 yg/500 yL. 22
ADVANCES IN THE SEC CHARACTERIZATION OF ORGANOMETALLIC

COPOLYMERS AND COPOLYMERIZATION: DESORPTION OF CHARGED

SPECIES BY INJECTED DILUTE ACETIC ACID

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

Materials Chemistry Division

National Bureau of Standards

Washington, DC 20234

SUMMARY

The chemical characterization of controlled-release, biocidal

triorganotin-containing copolymers (organometall ic polymers, OMPs) is

necessary for predicting the in-service performance of these important

materials. An OMP investigated in the present research was prepared by

the free radical copolymerization of tributyltin methacrylate (TBTM) and

methyl methacrylate (mRa). Size exclusion chromatography (SEC) on uStyragel , coupled with an in-line graphite furnace atomic absorption

detector (GFAA) quantitates the bioactive tin in at least two wel 1 -resol ved

fractions: a polymer fraction, and, probably, unreacted TBTM. However, THF

slowly elutes a third component, now believed to be an adsorbed ionic tincontaining compound.

We now verify that a one percent solution of acetic acid (HOAc),

injected into the THF mobile phase after a measured delay, efficiently

desorbs the third species, without hydrolyzing polymeric TBT-substituted

esters.

Tin-selective SEC-GFAA of a series of partially reacted OMPs indicates

that the TBT-substituted esters partially decompose during one year of

storage at -78 °C, but mass sensitive SEC-aRI indicates that the polymer

backbone remains intact. Comparison of SEC-GFAA and SEC-aRI suggests a convenient chromatographic method for determining reaction kinetics of

both MMA and TBTM simultaneously.

Keywords: Acetic acid, adsorption, differential refractive index.

fractionation, graphite furnace atomic absorption, kinetics,

methyl methacrylate, organometal lie copolymer, SEC, stability,

tributyltin acetate, tributyltin methacrylate.
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1 . INTRODUCTION

A class of experimental biocidal slow release triorganotin compounds

is prepared by the free radical initiated copolymerization of two or

1 2

more monomeric species. ’ The synthesis of an extensively tested

organometal 1 ic polymer (OMP) is depicted in Equation 1 ;

Q Q benzoyl

11 II peroxide

Bu^Sn-O-C-C = CH2 + CH^-O-C-C = CH2 ^^X^Y^N

CH^ CH^ benzene

(reflux)

(A) (B)

The starting materials for this copolymer (OMP- 2 ) are tributyltin esters

of methacrylic acid (A = TBTM) and methyl methacrylate (B = MMA). The

end product includes not only a high polymer tin-bearing species, but

also a species of low MW (TBTM), well resolved in the size exclusion

chromatogram obtained on yStyragel , and a third component that is

retained by an adsorption rather than a size exclusion mode. Thus, the

product is a formulation or mixture rather than a single polymeric

species. This situation is typical of many commercial OMP's tested in

3

our laboratory.. OMP5 are very toxic substances; coated on exposed

marine surfaces, they confer long-term protection against fouling by

4 microorganisms . Initial rapid leaching of tin-bearing species is

followed by a zero-order rate of release that continues for several

years. Consequently, it is of great interest to the U.S. Navy to fully

specify their performance in terms of polymer design, but the protective

mechanism is complex.

I
An urgent need is to characterize the control 1 ed-rel ease mechanism

or mechanisms. What processes are involved in protection and leaching?

What environmental problems might arise from extensive use of OMPs at

sea? To answer these questions and to provide background information for a

Military Specification, the National Bureau of Standards has developed novel

chromatographic methods of molecular characterization for OMPs, based on deter

mination of the distribution of tin in the polymer.

In collaboration with the David Taylor Naval Ship Research and

Development Center, Annapolis, MD, we have applied these methods for the

rapid determination of various parameters of molecular composition: weight

average molecular weight (Mw), number average molecular v/eight (Mn), molecular

weight distribution (MWD), monomer conversion, and reaction kinetics, all

3 5-7

based on the distribution of tin in separated polymer fractions. ’

This report summarizes research undertaken during FY82:

- The size exclusion chromatogram of a typical OMP (OMP-2)

- The ability to force abrupt truncation of tailing by delayed

injection of discrete amounts of dilute acetic acid

- Evidence for the partial decomposition of polymer esters on storage

at -78

- The feasibility of dual methods of detection to aid in the kinetic

analysis of the copolymerization.

This work was presented as a poster session at the VI International

Symposium on Column Liquid Chromatography , Cherry Hill, New Jersey,

June 6-11, 1982, and has been accepted for publication in the Journal of

Chromatography . It concerns characterization by SEC only. Recommendations

for additional research are discussed.

Characterization of OMPs by FT-NMR, with supporting SEC-GFAA will

be the subject of a forthcoming report.

2
2. EXPERIMENTAL

2.1 Apparatus and Chemicals*

In figure 1 is given a block diagram of the chromatographic

analysis system used. Solutions are injected into flowing eluents at

the sample injection port. Analytes separated on the column are detected

by one or more of: ultraviolet absorption, differential refractive

index, or element specific GFAA. The apparatus used has been described

3 5-7

in detail. ’ All chemicals used were reagent grade. The mobile phase

in all of the experiments reported herein consisted of tetrahydrofuran

(THE) with and without addition of pyridine or acetic acid (HOAc).

2.2 Preparation of Copolymer

The OMP-2 copolymer (figure 2) was prepared by the reaction of

TBTM and MMA in 1:1 molar proportions by refluxing in reagent grade

benzene (monomer to solvent ratio 1:2 w:v) as described by Dyckman and

Mcntemarano."' The TBTM was prepared from highly purified tri butyl tin

o oxide and methacrylic acid. MMA was commercially prepared, inhibited

with 25 ppm of hydroquinone, and used as received.

This OMP exhibits the following properties:

- A clear viscous liquid

- Soluble in organic solvents

- Very toxic to humans as well as microorganisms

- A mixture of MW fractions

*Certain commercial materials and equipment are identified in this paper

in order to specify the experimental procedures. In no case does such

identification imply recommendation or endorsement by the National Bureau

of Standards nor does it imply that the material or equipment identified

is necessarily the best available for the purpose.

3
I

I

Figure Block diagram summarizing the SEC-UV/aRI-GFAA system, including

accessory devices. The GFAA spectropliotometer consists of a heated graphite atomizer (HGA) and an atomic absorption spectrophotometer (AA). In the present work, either the auto-sampler

continuously transferred 20 uL eluent specimens into the graphite

furnace at present 45-60 sec intervals, or batch fractions were collected during elution for subsequent quantitation of tin.

4
O-SnBug O CH3

Figure 2. The suggested formula of a copolymer prepared by the freeradical addition of TBTM to MMA. The subscripts x and y

represent numbers of monomers and n represent numbers of

repeat units. Neither the numbers x, y, or n, nor the tacticity

of the copolymer is assumed to be constant.

5
3. 3.1 RESULTS AND DISCUSSION

Chromatograms of OMP-2 (figure 3) and TBTM (figure 4).

Chromatograms of the type depicted in figure 3 yield much

useful information. The scope is indicated in the following paragraphs.

3.1.1 Apparent Molecular Weights

1. The apparent MW of individual chromatographic peaks

3

is based on calibration with polystyrene MW standards.

2. The weight average (M^) and number average M^

molecular weights are given by equations (2) and (3)

^ = V (2)

nE h.

^

( 3 ) Ei = l ^ ^

In these equations h^. is the observed height of the ith peak whose

molecular weight is M^.

3.1.2 Molecular Weight Distribution

The complete molecular weight distribution (MWD) can

only be given by a plot of relative concentrations versus molecular weight.

Nevertheless, a useful shorthand expression defines MWD as M /M .

Defined thus, MWD is exactly 1.0 only for a perfectly homogeneous polymer.

For any real polymer, MWD > 1.0; the magnitude of MWD correlates approximately

with the width of the polymer peak (range of molecular weights) in SEC.

6
OMP - 2

MW

I

1 1 1 1

10® 10“ 10® 10^

T

5

-|

i

1 1 10 15 20

V' , mL

R

Figure 3. SEC-GFAA chromatogram of OMP-2. Solvent, THF. Column,

yStyragel (one), average pore size 10^ A, Mobile phase, THF.

Flow rate 0.5 ml min"^. SEC detector, Perkin-Elmer 360,

equipped with an Sn-specific EDL lamp operating at 224.6 nm. Injected volume 50 yL. Injected concentration 50 yg/50 yL.

7
PURIFIED TBTM

MW

10^ 10^ 10

^

10 20 30

V;,mL

Figure 4. SEC-GFAA chromatogram of TBTM purified by recrystallization

from petroleum ether. Solvent, THF. Mobile phase, THF.

Columns. pStyragel (three) in series; average pore size

10^ K. Flow rate 1.0 ml min"^, SEC detector, Perkin-Elmer 360.

Injected volume, 50 pL. Injected concentration of TBTM,

50 pg/50 pL.

8

I
3.1.3

Extent of Polymerization

The extent of conversion of TBTM to copolymer

is obtained by equation (4)

AP(« = A X 100 (4)

where A = polymer (OMP) peak area

B = monomer (TBTM) peak area

AP(%) = percent conversion

3.1.4 Polymerization Rates

AP is a linear function of the logarithm of the reaction

time, as we shall see. From such data, polymerization reaction rates

have been determined chromatographical ly. Obviously, kinetic analysis

requires accurate measurement of the variables A and B.

3.1.5 Impurities in OMP2

The quantitation of unreacted TBTM in SEC-GFAA chromatograms

is complicated by extensive tailing such as that typically observed

(figure 3). However, figure 4 demonstrates that TBTM is reproducibly

eluted with a narrow Thus we conclude that tailing in figure 3, is

not due to adsorbed TBTM but to new tin-containing impurity species.

To quantitate TBTM, i.e., the value of B, from chromatograms, it is necessary to summarize only those peak heights corresponding

to molecular species of MW 100-500 daltons.

Partially retained or tailing species are eluted by a

mechanism other than size exclusion. This implies that the species

9
retained is of different polarity from neutral TBTM. Its desorption

will be critical for the complete characterization of OMP-2 in support

of the Navy Mil -Spec.

3.2 Desorption of Tailing Organotin Species

In the course of systematic attempts to desorb the tailing

component of OMP-2, we found that a strongly basic mobile phase containing

an electron-donor [5 percent (v:v) pyridine in THF] was not more effective

than the less basic solvent THF alone.

On the other hand, desorption is effected by glacial acetic

acid (HOAc) in THF, as demonstrated by the abrupt termination of tailing

shown in figure 5. To obtain these data, injection of the polymer

solution was followed, after a measured period of time, by injection of

a trace amount of HOAc (1.0 percent in THF, 50 yL). The late-appearing

spike follows elution of TBTM by a period of time (or elution volume,

corresponding to the delay between injections.

These data indicate that HOAc reacts in some manner with the

yStyragel -bound species, resulting in desorption of another tin-bearing

species not subject to adsorption. The release reaction is apparently

not stoichiometric. Figure 6 illustrates that:

(1) When the polymer solution (1.0 percent w:v) contains 1.0 percent

(v:v) glacial acetic acid, the acid is necessarily coinjected

with the polymer. No tailing occurs, but a large low MW

peak bearing the same retention volume as TBTM results.

(2) If the acetic acid concentration is only 0.1 percent (v:v)

and the OMP concentration is 1.0 percent (w:v), the reduced

amount of acid is insufficient to overcome tailing. There I is, nonetheless, a substantial enhancement of the low MW : peak.

I From these results, we conclude that a competitive mechanism

involving acidic ion-exchange sites on yStyragel is involved, causing a

|

shift in retention pattern. '

10
OMP - 2

SEC - GFAA

mSTYRAGEL 10^ A ( ONE )

MW

1 1 1

^ 10^ 10* 10^ 10

^

1

1 r

5 10 15

V’ , mL R

Figure 5. SEC-GFAA chromatograms of OMP-2.

(A) Solvent THF. Mobile phase, THF. 50 yL of THF containing

1.0 percent HOAc (v:v) introduced into the THF mobile

phase 8.0 min (4.0 ml) after injection of the OMP solution.

All other conditions the same as for figure 3.

(B) All conditions the same as (A), except that 50 yL of

1.0 percent HOAc in THF was introduced 1 min (0.5 mL)

after the solution of OMP-2.

i;
OMP • 2

MW

10^ lO'* 10^

T10

2

T

5 10 15 20

V' . mL

R

Figure 6. SEC-GFAA chromatograms of OMP-2.

(A) Solvent, THF containing 1.0 percent HOAc; acid added

1.0 h prior to injection. All other conditions same as for figure 3.

(B) Solvent, THF containing 0.1 percent HOAc, acid added

1.5 h prior to injection. All other conditions same as for figure 3.

12
Adsorbed Desorbed

H Sn- + -species Sri-species

+

H

Ac Co‘ umn 0^\c C

Substrate Substrate

( 5 )

Comparison of the chromatogram depicted In figures 3 and 5

suggest that acetic acid also hydrolyses the OMP-2 polymer itself. This

conclusion was verified by experiments typified by figure 7.

(1) The low MW SEC-GFAA peak is much greater in area than the

high MW peak.

(2) These proportions are consistent with acid hydrolysis of

polymer esters, and co-elution with TBTM, of a derivatized

species

.

(3) Tailing in the chromatogram probably is due to continuing

hydrolysis of the polymer as it is eluted by the THF/1.0%

HOAc solution, with continuing elution of a derivative.

Therefore it is necessary to avoid coinjecting polymer and acids.

3.2.1 Nature of the Desorption Mechanism

A number of questions are suggested by the chromatograms

presented in figures 3-7:

(A) What is the adsorbed species?

(B) What is the desorbed species?

(C) What is the mechanism of desorption?

1. Competition between acid and adsorbed species?

2. On-column derivatization?

Several clues have been noted above:

(1) When HOAc is added at the same time as the dissolved

polymer, the desorbed species co-el utes with TBTM.

(2) This suggests that the desorbed species and TBTM

are of the same polarity.

(3) In turn, the on-column change in polarity suggests

on-column derivatization.

(4) This, in turn, suggests_^that a cation such as tri butyl tin cation (TBT is the adsorbed species.

43
OMP - 2

MW

1 1

i 54321 10 10^ 10 10

^ 1 r

5 10 15

v'^,mL

Figure 7. SEC-GFAA chromatogram of OMP-2 undergoing acid hydrolysis.

Mobile phase, THF containing 1.0 percent HOAc. All

other conditions the same as for figure 3.

14
3.2.2 Future Studies Required

Since conclusive evidence for any definite species is

lacking, future research will include the following chromatographic

experiments:

(1) Spiking OMP-2 with TBTOAc and/or other species

prior to chromatography.

(2) Running TBTOAc with and without HOAc.

(3) Substituting an injected mineral acid for HOAc.

(4) Combining SEC and strong cation exchange chromatography (sex) to isolate cationic species.

3.3 Kinetic Investigation of OMP-2 Copolymerization Combining SECGFAA and SEC-aRI

3.3.1 SEC-GFAA of Partially Reacted Samples

The definition of aP, the degree of polymerization is given

in equation (4), section 3.1.3. We have reported that the copolymerization

of MMA and TBTM under free radical conditions exhibits a high linear

correlation with the logarithm of the time of reaction.

aP = kAlnt + b (6)

where k and b are constants, and t is the time of reaction in minutes.

The published experiment was repeated on a second series

of partially reacted samples. The result shown in figure 8 (closed circles)

shows that the experiment is reproducible in spite of the extent of tailing

in individual chromatograms, e.g., the two chromatograms shown in figure 9

are included in the slope having k = 7.85 and r = 0.985, where "r" is the

coefficient of linear correlation.

Because data collection on these samples was not continued

to the complete extinction of tailing, we decided to reexamine them

15
CONVERSION,

PERCENT

TBTM CONVERSION

AS A FUNCTION OF TIME

Figure 8. Polymerization rate (k) of TBTM. Closed Circles. Conversion

of TBTM during the copolymerization of TBTM and MMA, determined

shortly after the samples were synthesized. Data taken from

chromatograms including those depicted in figure 9.

Open squares. Conversion of TBTM, as calculated from data

obtained after one year of storage at -78 °C, and including

the chromatograms depicted in figure 10.

16
PARTIALLY REACTED SAMPLES

( AS RECEIVED )

MW

I

I I

I 10“ 10^ 10^

1- T"

10

-I r

20 30

. mL

40

Figure 9. SEC-GFAA chromatograms of partially reacted specimens during

the copolymerization of TBTM and MMA. Solvent, THF. Mobile

phase, THF. Flow rate 1.0 ml . Columns, yStyragel

(three), average pore size 10^ A. All other conditions same

as for figure 3.

17
after one year of storage at -78 °C, using desorption by HOAc with

delayed injection.

The results (figure 8, open square, and figure 10) show

that:

(1) The good fit of points has been lost.

(2) Very large quantities of desorbed species are present in the samples reacted either 60 or 360 minutes.

(3) Much more desorption is evident in the 360 minute

sample.

These data are consistent with the decomposition of

polymer esters on prolonged storage in THF, even at -78°.

3.3.2 SEC-aRI of Partially Reacted Samples

SEC-aRI involves use of a mass-sensitive detector.

Hence, conversion plots result from addition of both TBTM and MMA as a

function of time, unlike tin-specific SEC-GFAA. Our objective in obtaining

SEC-aRI characterizations was to determine the difference between the

races of TBTM conversion and mass conversion, and from this difference

ultimately to determine:

(1) the rate of MMA conversion

(2) the relative rates of MMA and TBTM conversion.

Figure 11 demonstrates that:

(1) Mass conversion exhibits a high linear coefficient

of correlation with the log of reaction time, at

least for the first 30-85 percent conversion.

(2) This high coefficient of correlation persists after

one year of storage at -78 °C, suggesting that the

polymer backbone is stable under these conditions.

(3) The rate of conversion appears to slow down between

85 percent and 90 percent conversion, possibly

showing concentration effects.

18
PARTIALLY REACTED SAMPLES

( AFTER STORAGE )

40 -

i-zu

u

cs

lU

a. 30-

>

K

UJ>O

o

UJKz

20 -

10 -

TBTAc

360 MIN

POLYMER

MONOMER

SEC - GFAA

jjSTYRAGEL lO^A ( ONE )

SOLVENT : THE ELUENT : THE

500 mL 1.0 * HAc IN THE

INJECTED AFTER 4.0 mL

OF ELUTION

MW

1 1 1 1 lO® lo“ 10* 10*

10 V . mL

R

T”

15

Figure 10. Partially reacted specimens retested after one year of

storage at -78 °C. Histogrammic peak height indicates tin

content of fractions. Solvent, THF. Mobile phase, THF.

Floworate 0.5 ml min’^. Column, yStyragel (one), pore size

10^ A. Injected volume, 500 pL. Injected concentration

100 pg/500 yL. 500 yL of 1.0 percent HAc in THF introduced

by injection 8 min (4.0 ml) after the injection of polymer.
CONVERSION,

PERCENT

MASS CONVERSION

AS A FUNCTION OF TIME

In t

Figure 11. Mass conversion of low-MW to high-MW materials during the

copolymerization of TBTM and MMA, plotted as a function of

the reaction time. Conversion data were calculated from

chromatograms including those in figure 9.

20
(4) The final point is bad for unknown reasons.

(5) The rate of mass conversion is approximately 1.8

times greater than the rate of TBTM conversion.

Typical chromatograms from which these data were obtained

are illustrated in figure 12. The enclosed darkened areas determined by

planimetry were used in the calculations of conversion. The "negative"

peaks are due to benzene and, probably, preservatives (e.g., hydroquinone,

hydroxyl ated butyl tol uene)

.

3.3.3 Comparative Utility of Combination of GFAA and aRI

Detectors for SEC.

The data presented in figures 8-12 are especially

interesting because they point the way to a novel and convenient method

of discovering the proportions of two monomers in an organometal 1 ic

polymer from the derived equation:

•^MMA " " '^TBTM^

Here is a parameter governing the rate of addition of MMA (on a mass basis)

to the growing chain. is proportional to the difference between the rate

of increase in total mass (Kjv|y^ 33 ) in TBTM(Kygyj^) . If MMA and TBTM contribute equally to observed differences in refractive index, then is

estimated immediately and the ratio of to gives their relative

concentrations in the copolymers. To convert from a mass to a molecule basis

is simple given the molecular v/eights: TBTM = 375 dal tons, and MMA = 100 dal tons.

The essential step is to determine the relative contributions of TBTM and MMA

to the refractive index of a mixture of both substances.

Since the relative rates of conversion depend on the

relative reactivities of the monomers under actual conditions, the composition

of the growing chain would be predictable by equation (4).

This will be useful in engineering the synthesis of OMP's,

since measurement of relative reactivities is both difficult and time

consuming by alternative methods.
PARTIALLY REACTED SAMPLES

SEC -ARI CHROMATOGRAMS

mSTYRAGEL IO’a ( ONE )

1 1 1 r

~

lo' lo' lo' lo"

T 1 1 1 1 5 10 V^.mL

Figure 12. SEC-aRI chromatograms of samples taken during the copolymerization

of TBTM and MMA and stored one year at -78 °C. Solvent,

flow rate, mobile phase and column the same as for figure 10.

Detector, Knauer dual detector; aRI sensitivity,

6 X lO"^ aRI unit = full scale deflection. Injected volume

500 yL. Injected concentration 1000 yg/500 yL. Mote offset

of upper chromatogram to avoid overlap.

22
However, it is still necessary to determine the reproducibil ity

of the mass- and TBTM conversion constants, and the relative weights of

TBTM and MMA in the ARI measurements before the method can be fully

implemented.

4. CONCLUSIONS

The research described in this report was designed to provide basic

information of the type necessary for writing a Mil -Spec for organometal 1 ic

polymers and their synthesis. This work considerably broadens the scope

of the analytical SEC-UV/ARI-GFAA reported in our earlier papers.

4.1 It is now possible to terminate tailing in SEC-GFAA chromatograms.

4.1.1 Thus, it is shown that OMP-2 mixtures include a species,

probably a cation of low MW, that is adsorbed in substantial quantity on

yStyragel

.

4.1.2 Decomposition at -78 °C occurs, involving the pendant

TBT-esters but probably not the polymer backbone.

4.1.3 The combination of SEC-GFAA and SEC-ARI , in line or in

tandem, holds great promise as an analytical and engineering aid in the

design of OMRs.

4.2 Future research must be designed to:

4.2.1 Identify the adsorbed species;

4.2.2 Characterize the measured rate of mass conversion in

terms of the transport of MMA as well as TBTM, on a molecular basis;

4.2.3 Verify the reproducibi 1 ity of results determined in

4.2.1 and 4.2.2 by carrying out model synthesis with kinetic analysis by

SEC-UV/ARI-GFAA.

23
5. ACKNOWLEDGMENTS

The work described in this report was partially supported by the

David Taylor Naval Ship Research and Development Center (DTNSRDC, Annapolis,

MD) to whom we extend our thanks. For valued discussion and suggestions, we

are indebted to C. S. Weiss, D. W. Brown and W. R. Blair, all of NBS;

and to V. J. Castelli, C. E. Mullen, and D. M. Andersen, all of the

DTNSRDC (Annapolis).

6. REFERENCES

[1] Dyckman, E. J.; Montemarano, J. A. Anti fouling Organometal 1 ic

Polymers: Environmental ly Compatible Materials, Naval Ship R&D Center,

Bethesda, MD., Report No. 4186, 1974. 31 p.

[2] Yeager, W. L.; Castelli, V. J. Antifouling Applications of Various

Tin-Containing Organometal 1 ic Polymers, in Organometal 1 ic Polymers , C. E. Carrahar, Jr., J. E. Sheats, and C. U. Pittman, Jr., Eds.,

Academic Press, NY, 1978, pp. 175-180.

[3] 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 and Pharmaceuticals , D. H. Lewis,

Ed., Plenum Press, NY, 1981, pp. 219-238.

[4] Castelli, V. J.; Becka, A. M. Status Report on OMP Materials,

David W. Taylor Research and Development Center DTNSRDC SME 82-39,

Bethesda, MD, 20084; May 1982.

[5] Parks, E.J.; Brinckman, F. E.; Blair, W. R. Application of a graphite furnace atomic absorption detector automatically coupled

to a high performance liquid chromatograph for speciation of metal

containing macromolecules. J. Chroma togr. 185 , 563; 1979.

[6] Parks, E. J.; Brinckman, F. E.; Mull in, C. E. ; Andersen, D. M.; and

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

chromatography of the free radical copolymerization of tri butyl tin

methacrylate and methyl methacrylate. J. Appl . Poly. Sci. 2967;

1981

[7] Parks, E. J.; Johnannesen, R. B.; Brinckman, F. E. Characterization

of Organometal 1 ic Polymers by Chromatographic Methods and Nuclear

Magnetic Resonance, Nat. Bur. Stand. (US) NBSIR81 -2424; December, 1981.

35 p.

24
[8] Montermoso, J. C.; Andrews, T. M.; Marinelli, L.P. Polymers of

tri butyl tin acrylate esters. J. Poly. Sci . 523; 1958.

[9] Jewett, K. L.; Brinckman, F. E. Speciation of trace di- and

triorganotins in water by ion exchange HPLC-GFAA. J. Chromatogr.

Sci. 19, 583; 1981.

25
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BIBLIOGRAPHIC DATA

SHEET (See instruction s)

1. PUBLICATION OR

REPORT NO.

NBSIR 82-2577

2. Performing Organ. Report No. 3. Publication Date

September 1982

4. TITLE AND SUBTITLE

ADVANCES IN THE SEC CHARACTERIZATION OF ORGANOMETALLIC COPOLYMERS AND COPOLYMERIZATION

DESORPTION OF CHARGED SPECIES BY INJECTED DILUTE ACETIC ACID

5. AUTHOR(S)

E. J. Parks, R. B. Johannesen, 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.

8. Type of Report & Period Covered

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

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FI PS 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)

The chemical characterization of control led-rel ease, biocidal triorganotincontaining copolymers (organometal 1 ic polymers, OMPs) is necessary for predicting the

in-service performance of these important materials. An OMP investigated in the

present research was prepared by the free radical copolymerization of tri butyl tin

methacrylate (TBTM) and methylmethacrylate (MMA). Size exclusion chromatography (SEC) on yStyragel , coupled with an in-line graphite furnace atomic absorption detector (GFAA

quantitates the bioactive tin in at least two well -resolved fractions: a polymer

fraction, and, probably, unreacted TBTM. However, THF slowly elutes a third component,

now believed to be an adsorbed ionic tin-containing compound.

We now verify that a one percent solution of acetic acid (HOAc), injected into

the THF mobile phase after a measured delay, efficiently desorbs the third species,

without hydrolyzing polymeric TBT-substituted esters.

Tin-selective SEC-GFAA of a series of partially reacted OMPs indicates that the

TBT-substituted esters partially decompose during one year of storage at -78 °C, but mass sensitive SEC-ARI indicates that the polymer backbone remains intact. Comparison

of SEC-GFAA and SEC-ARI suggests a convenient chromatographic method for determining

reaction kinetics of both MMA and TBTM simultaneously.

12. KEY WORDS (S/x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Acetic acid,; adsorption; differential refractive index; fractionation; graphite

furnace atomic absorption; kinetics; methyl methacrylate; organometal! ic copolyme

SEC I stability^ tri butyl tin acetate; tri butyl tin methacrylate.

r;

13. AVAILABILITY

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

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PRINTED PAGES

30

15. Price

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I

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