Anionic Ring-Opening Polymerization of Octamethylcyclotetrasiloxane

11 Anionic Ring-Opening Polymerization of Octamethylcyclotetrasiloxane in the Presence of 1,3-Bis(aminopropyl)-1,1,3,3-tetramethyldisiloxane 1

Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: August 16, 1985 | doi: 10.1021/bk-1985-0286.ch011

P. M. SORMANI, R. J . MINTON , and J A M E S E. McGRATH Department of Chemistry and Polymer Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Polyorganosiloxanes are probably the most widely used and studied class of "semi-inorganic" polymers. There are a variety of interesting and useful properties exhibited by these materials that make them worthy of study. For example, they exhibit high l u b r i c i t y , low glass t r a n s i t i o n temperatures, good thermal s t a b i l i t y , high gas permeability, unique surface properties, and low t o x i c i t y (1). Cyclic organosiloxanes and s i l a n o l oligomers may be readily prepared by the hydrolysis of chlorosilanes, according to Scheme 1 (1). The predominant c y c l i c s are those corresponding to x=4 or 5, while the strained c y c l i c trimer i s present only i n small quantities. RR'SiCl

2

+ 2H 0 2

-->

[RR'Si(OH) ] + 2HCl 2

Scheme 1. Preparation of c y c l i c organosiloxanes and chlorosilanes.(1) Polydimethylsiloxane oligomers may be easily prepared by the acid or base catalyzed ring opening polymerization of the c y c l i c tetramer, octamethylcyclotetrasiloxane. The molecular weight of the polymer prepared may be controlled by the addition of a linear disiloxane as an endblocker (2,3,4). When the disiloxane i s hexamethyldisiloxane, this i s the well-studied case of the 1

Current address: Thoratec Laboratories, 2023 Eighth Street, Berkeley, C A 94710

0097-6156/ 85/0286-0147506.00/ 0 © 1985 American Chemical Society

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

148

preparation of silicone oil. However, it is the case of functional disiloxanes that has been of interest in our laboratories for quite some time (3,5). Table I shows a l i s t of the various functional disiloxanes that have been used to prepare functionally terminated siloxane oligomers (6). Scheme II shows a general outline for the preparation of these oligomers. It should be noted that in the absence of any endblocker, a high molecular weight silicone gum is formed. Table I


End blockers used to prepare functionally-terminated polysiloxane oligomers CH [H N 2

3

α,ω aminopropyl disiloxane

(-CH )3Si]-0 I 2

2

CH

3

CHo CHo I I (CH ) N-[Si-0]—Si-N(CH ) I I CH CH 0 CH 3

1,3 tetramethyl-

2

3

low molecular weight silylamine end blocker

2

x

3

[ΗΝ

3

3

^K-(CH ) NHC-(CH ) -Si-]-0 ' I 2 CH 2

>

2

2

3

piperazine-terminated disiloxane

3

0

CH

3

α, ω carboxypropyl 1,3 tetramethyldisiloxane

[HOC-(CH ) -Si-]-0 I 2 CH 2

3

3

CH [CH

2

3

CH-CH -0(CH ) -S i ] - 0 2

2

3

CH

α, ω glycidoxypropyl 1,3 tetramethyldisiloxane

3

These ring-opening polymerizations are referred to as e q u i l i b r a t i o n reactions. Since a variety of interchange reactions can take place, a quantitative conversion of the tetramer to high polymer i s not achieved and there i s , at thermodynamic equilibrium, a mixture of linear and c y c l i c species present. Scheme III shows examples of the types of r e d i s t r i b u t i o n reactions thought to be occurring i n these systems. It i s generally convenient to use "D" to refer to a difunctional siloxane unit and "M" to refer to a monofunctional siloxane unit. Thus, D4 represents the c y c l i c siloxane tetramer and MM represents the linear hexamethyldisiloxane.


11.

SORMANI E T A L .

CH CH I I R-Si-O-Si-R I CH3 CH 3

Anionic Polymerization of Octamethylcyclotetrasiloxane

3

CH CH3 1 CH3 | I I • R-Si-0 S1-0--S1-R 3

c a t a l y s t , heat +

D4 argon

CH

3

Scheme I I .

3

+ cyclics

xl

U CH

CH

3

3

Preparation of functional siloxane oligomers. functional group l i s t e d in Table I .

R = any

This terminology normally applies only to dimethylsiloxy u n i t s . I t should be noted that with the exception of using organolithium catalysts i n the anionic polymerization of the D c y c l i c , s i g n i f i c a n t amounts of r e d i s t r i b u t i o n cannot be avoided (7_,8).


3

(1)

-D - + D

(2)

-D - + MM

• MD M

(3)

MD M + MM

• MD _5)M + MD5M

(4)

MD M + MDyM

x

4

— •

x

X

X

-D

( x + 4 )

-

X

(x

• MD

(x+w

) M + MD( _ )M y

w

Scheme I I I . Redistribution reactions occurring during a siloxane equilibration. There are a variety of catalysts that can be used i n the preparation of polysiloxane oligomers by e q u i l i b r a t i o n reactions. The choice of catalyst depends upon the temperature of the e q u i l i b r a t i o n as well as the type of functional disiloxane that i s used. For example, i n preparing an aminopropyl terminated siloxane oligomer, a basic catalyst i s used, rather than an acidic catalyst which would react with the amine end groups. The discussion here w i l l be limited to basic c a t a l y s t s . Bases such as hydroxides, alcoholates, phenolates and siloxanolates of the a l k a l i metals, quaternary ammonium and phosphonium bases and the corresponding siloxanolates and f l u o r i d e s , and organoalkali metal compounds have a l l been found to catalyze the polymerization of c y c l i c siloxanes (1,2,9,10). I t i s believed that a l l catalysts generate the siloxanolate anion i n s i t u , and i t i s t h i s species which breaks the silicon-oxygen bond in either the linear or c y c l i c siloxanes present. However, the r e a c t i v i t i e s of the disiloxane and the various c y c l i c siloxanes d i f f e r . The rate of reaction increases i n the order MM < MDM < MD M < D4 < D , where MM again represents hexamethyldisiloxane, a non-functional endblocker. Catalysts based on the quaternary ammonium and phosphonium bases are referred to as transient catalysts, since they decompose above certain temperatures to products which are not c a t a l y t i c a l l y active toward siloxanes. An example of this i s the tetramethylammonium siloxanolate catalyst, prepared by the reaction of t e t r a methylammonium hydroxide with D4 (11). This catalyst polymerizes D4 at temperatures up to perhaps 120°C. Above this temperature, the catalyst f a i r l y rapidly decomposes to trimethyl amine and methoxyterminated siloxane. 2

3


149

RING-OPENING


150

POLYMERIZATION

However, catalysts such as the potassium siloxanolate catalyst are not transient. Non-transient catalysts must be neutralized or removed by some other method in order to give a thermally stable polymer. If the catalyst i s not removed, i t w i l l cause depolymerization at high temperatures. For example, a s i l i c o n e gum prepared by reacting D4 with 0.01% KOH has been reported to lose over 99% of i t s weight at 250°C i n 24 hours (11). Non-transient catalysts can often be used at much higher temperatures than the transient catalysts, leading, of course, to faster rates of reaction. The kinetics of these processes have been of interest to a number of workers (12). However, there has been no investigation of these e q u i l i b r a t i o n reaction kinetics using functional endblockers. Studies have been done on the kinetics of formation of s i l i c o n e gum or the reaction of D4 with hexamethyldisiloxane. For example, Grubb and Osthoff studied the kinetics of the KOH catalyzed polymerization of D (12). It was found that the ring-opening polymerization of D4 by KOH proceeds according to f i r s t order k i n e t i c s , with a square root dependence on the catalyst concentration. The square root dependence on the catalyst concentration i s believed to be due to the existence of an equilibrium between an active ion pair and a an inactive associated form (-SiOM)2» Rate constants were determined at different catalyst levels and temperatures. An a c t i v a t i o n energy of about 18 kcal/mole was determined by an Arrhenius plot, i n agreement with other workers i n the f i e l d (9). It i s important to consider the effect of solvent on the rate of polymerization as well as on the amount of c y c l i c s that are present. The rate of polymerization can be greatly enhanced by the action of dipolar aprotic solvents such as DMSO. This has been demonstrated by Cooper (13). However, the presence of a solvent w i l l also increase the amount of c y c l i c s present i n a f u l l y equilibrated sample. This can be understood in a qualitative way by considering that the siloxanolate species can attack not only silicon-oxygen bonds i n the c y c l i c s present, but also a phenomenon known as back-biting can occur. Back-biting refers to the attack of the siloxanolate anion on a silicon-oxygen bond along the same chain at least four repeat units away. Scheme IV gives an i l l u s t r a t i o n of this as well as other types of reactions occurring. When the siloxanes present are diluted by the presence of a solvent, the siloxanolate anion w i l l be less l i k e l y to encounter a c y c l i c to attack, and so back-biting w i l l become more prevalent. There i s , i n f a c t , a c r i t i c a l concentration, above which only c y c l i c molecules w i l l e x i s t . Generally therefore, i t i s more desirable to perform these e q u i l i b r a t i o n reactions i n bulk, and so l i m i t the formation of c y c l i c species as much as possible. There have been a variety of a n a l y t i c a l techniques used to study these e q u i l i b r a t i o n reactions. For example, gel permeation chromatography (GPC), or size exclusion chromatography (SEC), and gas-liquid chromatography (GLC) have been useful techniques (5,14). While GPC i s useful for monitoring the overall molecular weight d i s t r i b u t i o n of the polysiloxane, there are some l i m i t a t i o n s . For example, aminopropyl-terminated polysiloxane oligomers cannot be run on styragel based SEC columns due to adsorption of the oligomer on 4


11.

SORMANI ET AL.

Anionic Polymerization ofOctamethylcyclotetrasiloxane

the column. Either a silanized s i l i c a gel-based column must be used, or the oligomer must be derivatized. In addition to these problems, while GPC can be used to monitor the disappearance of D4 as the e q u i l i b r a t i o n proceeds, i t does not address the question of whether or not the functional disiloxane has been quantitatively consumed·

ΘΦ M CH

3


1 -Si-O1 1 CHo

η CH CH I I R-Si-O-Si-R I I CH CH

Terminated

Θ®

Μ

^

0® —0

New Chain

growing chain

3

3

3

3

CH

O-Si-R I CH

M

Catalyst or other growing chain

3

3

CH

3

I ΘΘ + R-Si-0 M I CH

3

I "BACKBITING"

Θ®

0

M

+ Cyclics

Scheme IV.

Possible reactions occurring during a siloxane equilibration.

Gas-liquid chromatography has the potential to discriminate between the different oligomeric species formed. We have found that c a p i l l a r y GC may be used to measure the concentration of α, ω aminopropyl 1,3 tetramethyldisiloxane i n e q u i l i b r a t i o n reactions. Although the presence of catalyst could p o t e n t i a l l y lead to the generation of additional c y c l i c s at the elevated temperatures necessary for GC, there was no effect on the amount of disiloxane present. Of course, to measure the D4 concentration, the samples must be free of c a t a l y s t .


151


152


High-Performance Liquid Chromatography (HPLC) has been used for the analysis of oligomers (15,16). A clear advantage of HPLC i s that the analysis can be done at room temperature, thus eliminating the p o s s i b i l i t y of generating additional reaction products such as c y c l i c s . HPLC has therefore been of use i n measuring the amount of D4 present as the e q u i l i b r a t i o n reaction proceeds, as well as i n observing the appearance of new oligomeric species. This paper w i l l discuss investigations of the polymerization of D4 i n the presence of α, ω aminopropyl 1,3 tetramethyldisiloxane with potassium siloxanolate c a t a l y s t . The effects of temperature and catalyst concentration on the rate of disappearance of both starting materials w i l l be discussed. Demonstration of the u t i l i t y of both non-aqueous reversed-phase HPLC and c a p i l l a r y GC for the investigation of these reactions w i l l be presented. Experimental A.

Catalyst Preparation

The catalyst used i n this work was prepared either i n bulk or using toluene as an azeotroping agent. Octamethylcyclotetrasiloxane, D4, and potassium hydroxide (KOH) were used as received. The KOH was crushed into a fine powder and added to enough D4 to make a mixture with a molar r a t i o of D4 to KOH of 10/1 i n the case of the bulk c a t a l y s t . This corresponds to 2 wt% KOH. The mixture was then put into a flask equipped with an argon i n l e t , an overhead s t i r r e r , an attached Dean-Stark trap, with a condenser attached to the Dean-Stark trap. Argon was bubbled through the mixture with s t i r r i n g , and the mixture was heated to 120°C. The high temperature and argon stream were necessary to eliminate water present i n the base as well as any water formed during the reaction. As the KOH reacted with the D4, the mixture gradually became more viscous. After a l l the KOH had dissolved, the mixture was s t i l l transparent and c o l o r l e s s . In general, within 12 hours, the mixture was a milky white, viscous material. After approximately 24 hours, the mixture was clear and colorless and able to be removed by pipet. T i t r a t i o n s of the catalysts were performed on a Fischer automatic t i t r a t o r . Isopropanol (100 mis.) and 20 mis. water were used as the solvent media. Alcoholic HC1 (0.0995 N.) was used as the t i t r a n t . The calculated amount of KOH present was between 1.9 and 2.7%, which compared favorably with the theoretical value of 2.0 wt%. The procedure for the preparation of catalyst using toluene as an azeotroping agent i s s i m i l a r . The same r e l a t i v e amounts of potassium hydroxide and D4 were used and enough toluene was added to make a 50% solution. The reaction mixture was heated for about 12 hours at 95°C and then at 120°C for an additional 12 hours. In each case, the catalyst was stored under argon i n v i a l s sealed with teflon tape and placed i n a dessicator u n t i l use. To remove catalyst for use i n reactions, the v i a l was warmed s l i g h t l y , i f necessary, to reduce the v i s c o s i t y , and the desired amount of catalyst removed by pipette. Argon was then flushed through the catalyst remaining i n the v i a l , which was then resealed and returned to the dessicator.


11. B.

SORMANI ET AL.

Anionic Polymerization of Octamethylcyclotetrasiloxane 153

E q u i l i b r a t i o n Reactions


Octamethylcyclotetrasiloxane and the α, ω aminopropyl 1,3 tetramethyldisiloxane were put into a three neck flask, f i t t e d with a reflux condenser, an argon i n l e t , and a magnetic s t i r r i n g bar. One neck of the flask was covered with a septum for the removal of samples by a syringe equipped with a stopcock. Potassium siloxanolate catalyst was pipetted into the f l a s k . The flask was then immediately f i t t e d with the argon i n l e t and heated by a s i l i c o n e o i l bath. Samples were removed at various times and put into sample v i a l s which were capped with septums. These were stored i n a refrigerator u n t i l analysis by HPLC. Some samples were analyzed immediately by c a p i l l a r y gas chromatography. C.

High Performance Liquid Chromatography

Quantitative analysis of D4 i n e q u i l i b r a t i o n samples was carried out using a Waters Model 450 solvent delivery system. The columns employed were ODS columns, either Dupont Zorbax columns obtained from Fischer, or the Regis L i t t l e Giant. The L i t t l e Giant i s a 5 cm. long, 10 mm. i . d . column packed with 3 micron p a r t i c l e size ODSII packing. The Dupont Zorbax columns were 25 cm. long with a 10 mm. i . d . and a 10 micron p a r t i c l e size ODS packing. A d i f f e r e n t i a l refractometer and a fixed wavelength infrared detector were used. Samples were made up i n one ml. volumetric flasks i n toluene. Typical concentrations were i n the range of 10-17%. The mobile phase was composed of 35% acetone and 65% a c e t o n i t i r l e i n the case of the Dupont columns with a flow rate of 1.5 ml./min. The L i t t l e Giant column used a mobile phase of 20% acetone and 80% a c e t o n i t i r l e at a flow rate of 0.8 ml./min. The change i n mobile phase and flow rate was necessary to restore s u f f i c i e n t resolution for quantitative analysis while s t i l l maintaining fast analysis times. A l l solvents were HPLC grade solvents and were used as received with no further purification. A c a l i b r a t i o n curve was prepared for D4 by plotting peak height i n millimeters vs. micrograms injected. A 20 m i c r o l i t e r sample loop was used with the DuPont columns to ensure reproducible sample s i z e . A 35 m i c r o l i t e r sample loop was used with the short column. Larger sample volumes could be used i n this case due to a lower operating pressure. A t y p i c a l c a l i b r a t i o n curve for D4 i s shown i n Figure 1. D4 c a l i b r a t i o n curves were prepared using both the refractive index and the infrared detector. The ug of D4 corresponding to the measured D4 peak height of an e q u i l i b r a t i o n sample can be read from the c a l i b r a t i o n curve. Knowing the ul injected and the t o t a l sample weight, the D4 concentration can be determined. D.

Capillary Gas Chromatography

C a p i l l a r y gas chromatography was used to measure the amount of aminopropyl disiloxane present i n the samples. An 11 m. column with an internal diameter of 0.2 mm. coated with a dimethylsiloxane stationary phase was used. A s p l i t t e r injector was employed with a



154


s p l i t ratio of 100/1, at a temperature of 310°C. Samples were dissolved i n methylene chloride and one m i c r o l i t e r of solution injected. A flame ionization detector was employed, at a temperature of 275°C. Temperature programming was necessary to give good resolution and reasonable analysis times. The program followed was as follows: 80°C to 170°C at 5°C/min., 170°C to 225°C at 30°C/min. The c a r r i e r gas flow rate (He) was 1.7 ml/min at 80°C. Peak areas were calculated using a Perkin Elmer 3600 data station. Tetradecane (C^^) was used as an internal standard, and added from a stock solution to disiloxane or e q u i l i b r a t i o n sample solutions. Shown i n Figure 2 i s a t y p i c a l c a l i b r a t i o n curve, where the disiloxane/Ci4 area ratio i s plotted against the disiloxane/Ci4 weight r a t i o . Knowing the experimentally determined disiloxane/Ci4 area r a t i o , and the weight of added (^4 and e q u i l i b r a t i o n sample, the amount of disiloxane present i n any sample may be determined. The amount of disiloxane found i s approximately plus or minus 1%. Results and Discussion A set of control experiments was f i r s t performed, where no aminopropyldisiloxane "end blocker" was used i n the reaction. Reactions were done at 82°C, 111°C, 117°C and 140°C using s u f f i c i e n t catalyst to make 0.02 wt% KOH (0.034 m o l e / l i t e r ) . Samples were removed at convenient intervals by syringe. In the case of the reaction done at 140°C, after only 15 minutes the reaction mixture was too viscous to be removed by syringe. At 111°C i t took 120 minutes for the mixture to become too viscous for removal by syringe, while at 82°C i t took 8.5 hours to reach this point. The observed increase i n v i s c o s i t y i s expected i n the absence of endblocker and corresponds to the appearance of high molecular weight species. This presents a d i f f i c u l t y i n the k i n e t i c analysis of this data. Shown i n Figure 3 i s a plot of In [D4] vs. time for a l l four reaction temperatures. If the reaction i s f i r s t order with respect to D4 concentration, plotting In [D4] vs. time should give straight lines where the slope - -rate constant, k. However, the concentration of D4 should be monitored to at least 75% conversion to d i f f e r e n t i a t e between f i r s t and second order k i n e t i c s . In fact, in this concentration range, a second order plot - [D4] vs. [D4] time - also gives straight l i n e s . However, i t i s known that this reaction i s f i r s t order i n D4 concentration (11). In fact, a second order plot of Grubb and Osthoff's data (11) gives a plot that i s indeed linear i n the same concentration range as we have studied, but that then curves at higher concentrations. Therefore, the s i m i l a r i t y between our f i r s t and second order k i n e t i c plots i s expected i n the concentration range studied. Assuming f i r s t order k i n e t i c s , a plot of In k vs. 1/T (°K) was made (Figure 4), and the activation energy calculated to be 18.1 kcal/mole, i n good agreement with previous values calculated by other workers (9). Reactions which used either the bulk catalyst or the catalyst prepared using toluene as an azeotroping agent gave rate constants which f e l l on the same l i n e i n the Arrhenius plot, indicating that the e f f i c i e n c y of each method of catalyst preparation i s roughly the same. The next set of experiments involved the determination of the


Anionic Polymerization of Octamethylcyclotetrasiloxane


1. SORMANI ET AL.


156


-0.6

An[D l


4

o.o

e0

50

100

150

200

250

300

350

400

450

500

time (minutes) Figure 3. Disappearance of D4 at various temperatures. • = 140°C, • = 117°C, 0 = 111°C, •= 82°C.

£n (rate constant) -6

0.0024

0.0025

0.0026 1/T

Figure 4 .

0.0027

0.0020

(°K)

Arrhenius plot f o r the reaction of D4 with potassium siloxanolate catalyst at 0.02 Wt. % KOH.


0.0029


11.

SORMANI ET AL.

Anionic Polymerization ofOctamethylcyclotetrasiloxane 157

rate of disappearance of D4 i n the presence of disiloxane. Shown i n Figure 5 i s a plot of D4 concentration vs. time a£ 0.02 wt% KOH. In each case, the D4 concentration decreases from 75 wt% to under 10 wt% i n approximately 30 minutes. The r a t i o of D4 to disolxane i n this case should give an oligomer with = 1000. Similar results were obtained at 0.12 wt% KOH and 91 °C, 111°C, and 131 °C, shown i n Figure 6. No huge increase i n v i s c o s i t y was observed in any of these cases, i n contrast to the reactions done i n the absence of endblocker. In these reactions, the aminopropyl disiloxane i s functioning analogously to a chain transfer agent to control the molecular weight. There i s no large buildup i n v i s c o s i t y because the growing chains react with the aminopropyl disiloxane and are terminated. I t i s also interesting to note that i n the absence of disiloxane at 140°C the amount of D4 has decreased from 99 wt% to about 65 wt% at 20 minutes, which i s much more than the amount that i s remaining at the same time in the presence of disiloxane. One possible explanation of this i s that since the reaction mixture i s much less viscous i n the presence of disiloxane, the D4 can more e a s i l y react with the siloxanolate species. In other words, since this i s a d i f f u s i o n - c o n t r o l l e d process, the lower v i s c o s i t y has a dramatic effect on the rate of reaction of D4 with potassium siloxanolate c a t a l y s t . Lastly, the rate of reaction of the aminopropyl disiloxane was investigated. On the basis of electronegativity differences, i t would be expected that the aminopropyl disiloxane would react more slowly than D4 with the potassium siloxanolate c a t a l y s t . This was indeed found to be the case. At levels of 0.02 wt% KOH, the reaction was rather slow. However, at 0.12 wt% KOH, the reaction proceeded at convenient rates. Shown in Figure 7 i s a plot of disiloxane concentration vs. time at 0.12 wt% KOH and temperatures of 90°C, 105°C, 129°C, 140°C. For example, at a temperature of 129°C, after approximately 6.5 hours, the disiloxane concentration has decreased from 19 wt% to 2.7 wt%. (In these reactions, the i n i t i a l D4 concentration was 80 wt%. This r a t i o of D4 to disiloxane should y i e l d a 1200 oligomer.) This corresponds to an 85% decrease in the amount of disiloxane present. In contrast, at 131°C and the same catalyst l e v e l , the amount of D4 present has decreased by over 90% after only 60 minutes. Conclusions It has been found that the attack of potassium siloxanolate catalyst on octamethylcyclotetrasiloxane i s greatly accelerated in the presence of α, ω aminopropyl 1,3 tetramethyldisiloxane. The disiloxane functions analogously to a chain transfer agent and serves to prevent a large increase in v i s c o s i t y , leading to a faster rate of reaction of D4 with c a t a l y s t . The rate of reaction of aminopropyl disiloxane with potassium siloxanolate catalyst was s i g n i f i c a n t l y slower than the rate of reaction of D 4 . Temperatures above 100°C appear to most e f f i c i e n t l y incorporate the functional disiloxane at the catalyst levels studied. The studies described herein have been most useful (6,17,18,19) i n establishing reaction conditions for the synthesis of well




158

0.8

j

0.7

Î

time (minutes) Figure 5.

Disappearance of D4 i n the presence of aminopropyl disiloxane at 115°C (O) and 140°C (•), 0.02 Wt% KOH.

time (minutes) Figure 6.

Disappearance of D, i n the presence of aminopropyl disiloxane with 0.12 wt% KOH at temperatures of 91°C (•), 111°C (O), and 131°C (•).


SORMANI ET AL.

Anionic Polymerization of Octamethylcyclotetrasiloxane 159


11.


160


defined amino a l k y l functional oligomers, which i n turn have been employed to produce novel segmented copolymers. Acknowledgment s The authors would l i k e to thank Mr. M. Ogden for assistance with the c a p i l l a r y GC work and the Army Research Office for supporting this research under Grant DAAG-29-85-G-0019. They also thank the Exxon Educational Foundation for p a r t i a l support.

Literature Cited


1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Wright, P. V., in Ring-Opening Polymerizations, K. J. Ivin and T. Saegaser, Editors, Elesevier Press (1984). Noll, W., Chemistry and Technology of Siloxanes, Academic Press, New York (1968). McGrath, J. E., Riffle, J. S., Banthia, A. K., Yilgor, I., Wilkes, G. L., in "Initiation of Polymerization", ACS Symposium Series No. 212, F. E. Bailey Jr., Editor, 1983, p. 145-172. Kantor, S. W., Grubb, W. T., Osthoff, R. C., J. Amer. Chem. Soc. 76, 5190 (1954). Riffle, J. S., Yilgor, I., Banthia, Α. Κ., Wilkes, G. L., McGrath, J. E., in Epoxy Resins II, R. S. Bauer, Editor, ACS Symposium Series No. 221 (1983). Yilgor, I., Riffle, J. S., McGrath, J. E., in "Reactive Oligomers", F. Harris, Editor, ACS Symposium Series, in press (1985). Saam, J. C., Gordon, D. J., and Lindsay, S., Macromolecules 3, 4 (1970). Bostick, Ε. E., in Block Polymers, edited by S. L. Aggarwal, Plenum Press (1970). Voronkov, M. G., Mileshkevich, V. P., Yuzhelevskii, Υ. Α., The Siloxane Bond, Consultants Bureau, New York and London (1978). Stark, F. O., Falender, J. R., Wright, A. P., in Comprehesive Organometallic Chemistry, Sir Geoffrey Wilkinson, FRS, Editor, Pergamon Press (1983). Gilbert, A. R., Kantor, S. W., J. Polym. Sci. 11, 35 (1959). Grubb, W. T., Osthoff, R. C., J. Am. Chem. Soc. 77, 1405 (1955). Cooper, G. D., J. Polym. Sci. A-1, 4, 603 (1966). Carmichael, J. B., Heffel, J., J. Phys. Chem., 69, 2213 (1964). Andrews, G., Macromolecules, 14 (5), 1603 (1981). Andrews, G., Macromolecules, 15 (6), 1580 (1982). Johnson, B. C., Ph.D Thesis, VPI and SU, June 1984, and forthcoming publications. Tran, C., Ph.D Thesis, VPI and SU, November 1984, and forthcoming publications. Yorkgitis, E., Tran, C., Eiss, N. S., Yu, Τ. Υ., Yilgor, I., Wilkes, G. L., McGrath, J. E., Siloxane Modifiers for Epoxy Resins, in "Rubber-Modified Thermoset Resins," C. K. Reiw and J. K. Gillham Editors, Adv. Chem. Series No. 208 (1984).

RECEIVED April 1, 1985


Anionic Ring-Opening Polymerization of Octamethylcyclotetrasiloxane

Recommend Documents