Synthesis of silicone-vinyl block copolymers

Eur. Polym. J. Vol. 26, No. 5, pp. 565-569, 1990 Printed in Great Britain. All rights reserved

0014-3057/90 $3.00 + 0.00 Copyright © 1990 Pergamon Press plc

SYNTHESIS OF SILICONE-VINYL BLOCK COPOLYMERS* CRISTOFOR I. SIMIONESCU,I VALERIA HARABAGIU,2 EUGENIA COM,~,NITA,1 VIORICA HAMCIUC,2 DIANA GIURGIU2 and BOGDAN C. SIMIONESCU1 ~Department of Organic and Macromolecular Chemistry, Polytechnic Institute of Jassy, 6600 Jassy, Romania 2"Petru Poni" Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda, No. 41 A, 6600 Jassy, Romania (Received 19 May 1989; received for publication 24 August 1989)

Abstract--Polycondensation of 4,4'-azobis-4-cyanovaleryl chloride and :t,co-bis(3-hydroxypropyl)polydimethylsiloxane was carried out to yield poly(azo-containing siloxane ester)s. These were used to induce the radical polymerization of various vinyl monomers through the thermal decomposition of the azo groups, resulting in the formation of poly(siloxane-b-vinyl) copolymers.

INTRODUCTION Various methods have been proposed and used for the synthesis of block copolymers but generally they involve the successive polymerization of two or more monomers by the same reaction mechanism. As a consequence, the resulting blocks contain monomers from the same class. The use of two or more reaction mechanisms would diversify the structure and properties of the resulting macromolecular compounds. However, literature approaches in this direction are relatively few. Thus, the synthesis of block copolymers by combination of cationic and radical routes yielded poly(tetrahydrofuran-b-styrene) or poly(tetrahydrofuran-b-methyl methacrylate) copolymers [1], while combination of polycondensation and radical polymerization resulted in polyamide [2-4] or polyester [5] containing block copolymers with vinylic (acrylic, methacrylic) blocks. Incorporation of polysiloxane blocks into conventional vinyl polymers should lead to new thermoplastic elastomers with interesting properties and end uses. Several investigators have already reported synthetic approaches for silicone-vinyl block copolymers. Thus, high block regularity was observed to result from living anionic polymerization of cyclic siloxanes and nonpolar vinyl and diene compounds [6-8], and poly(dimethylsiloxane-b-styrene) multiblock copolymers were synthesized by polycondensation of e,~o-hydrogen terminated polydimethylsiloxane with :t,~o-vinyl terminated polystyrene [9, 10]. This technique of 7,o)-difunctional prepolymers also yielded poly(dimethylsiloxane-b-butadiene) copolymers [11]. Recently, Inoue et aL [12] described the synthesis of silicone-vinyl block copolymers by the use of poly(azo-containing siloxaneamide)s as macroazoinitiators, while Crivello et al. [13, 14] used for the same purpose polydimethylsiloxane macroinitiators containing bis(silyl pinacolate) groups. The incorporation of groups capable of facile thermally scission in the main chain of polysiloxane *Dedicated to Professor J. C. Bevington, in appreciation of his most valuable contributions to polymer science and to the scientific community as a whole.

converts them into potential macroinitiators able to induce the radical polymerization of vinyl monomers to form polysiloxane-vinyl block copolymers. On the basis of this approach, the present paper deals with the synthesis of polydimethylsiloxane with azo linkages capable of facile scission and with its further use for the preparation of block copolymers. EXPERIMENTAL PROCEDURES

Materials 4,4'-azobis-4-cyanovaleryl chloride (ACVC) was synthesized according to the method proposed by Smith [15]. Styrene, acrylonitrile, methyl methacrylate, butyl methacrylate and butyl acrylate were purified by distillation. CHC13, used for the solution polycondensation of ACVC with :t,og-bis-(3-hydroxypropyl)polydimethylsiloxane (BHS), was treated with H2SO4, dried over P205 and distilled. Toluene was distilled over Na wire. Other solvents and reagents were high grade commercial products and used without further purification. Preparation of BHS BHS was prepared through the addition reaction of allyl alcohol to polydimethylsiloxane with Si-H reactive endgroups (HPDMS). The latter was synthesized by the cohydrolysis of (CH3)ESiC12 and (CH3)2SiHCI (40:1 molar ratio), and its molecular weight was determined to be A4n = 7000 (end-group analysis). Yield, 85%. Into a 1 1. flask fitted with motor-driven stirrer, dropping funnel and reflux condenser, 60 g HPDMS (H2% = 0.028) in 60ml dry toluene and H2PtC16 as catalyst (0.6ml, 2% solution in isopropanol, i.e. ca 70 ppm Pt) were introduced. The reaction mixture was heated to ca 110°, and then 4 g (0.07 mol) allyl alcohol was added over one hour. The solution was maintained with stirring for two more hours. The solvent and excess allyl alcohol were removed by distillation at 5~5 mmHg. The resulting product was characterized by i.r. spectroscopy, the disappearance of the 2120 cm ~ absorption band indicating that all Si-H groups were reacted with allyl alcohol. Polycondensation of BHS with ACVC Into a dried 250 ml flask fitted with motor-driven stirrer, thermometer, dropping funnel and reflux condenser having CaCI 2 tube, 22.63 g (3.17 mmol) of BHS, 0.50 g (6.34 mmol) of pyridine and 50 ml of CHC13 were placed. The flask was cooled at 5-10% and then 1.0 g (3.17 mmol) ACVC in 50 ml CHC13 was added with stirring, over 30 min. The solution

565

566

CRISTOFOR I. SIMIONESCUet al.

H3 ICH3 Ct-- i--Ct + CI.-Si--H

I

CH3

H2S04 H20

CH3

CH3

CH3

CH3

CH3

CH3

CH3

i I H-si-o+s~-oF. ~i-. i i t {HPDMS)

HPDMS +

CH2=CH---2--CH OH H2PtCL6

CH3 i CH3 i CH i 3 H0-(-CH2~-Si-O+Si- 0J@TSiq- CH2}3 -OH ~1 I I CH3 CH3 CH3

{BHS) (~H3 B HS +

CtOC--(-CI-'Izl 2

.CH3 {CH2~ COCt

- C - N = N - ~I -

~N c~,

CN

(ACVCI

CH3, CH3

C~

CH3

• -EOffCH2Fd-~ -0-{-~ -O~ttI?i-(CHL~3-0-C0-{-CH2I~-N =N--? q-CH2~- C0-~m--CH3 CH3 CH3 CN CN IPSAE} PSAE +CH2=CR 1R 2 ~

R1 :

-- H,

80%

iH?o (~H3 CH3 R1 i i -(.-}--~nS~-.{CH,,),rO-CO+CH2Iz-C+.OH2_C-~, I "" "~ I I OH3 CH3 CN R2

-OH 3

R2: -C6H5, -CN, --COOCH3, - COO{ CH2)3 CH 3 Scheme 1

viscosity increased slowly as the polycondensation proceeded. The solution was then stirred at room temperature for 3hr and at 30° for 1 hr. The viscous solution was diluted with 200 ml CHC13 and washed with water in a separating funnel. The chloroform layer was dried with sodium sulphate and then the solvent was evaporated at 30° under reduced pressure. A 20.0 g sample of poly(azo-containing siloxane ester) (PSAE) was obtained (yield, 84.6%). Nitrogen content was determined to be 0.5%, i.e. ca 0.01 azo units per cent. Polymerization o f vinyl monomers with P S A E

The polymerization of vinyl monomers initiated by the thermal decomposition of the azo groups in PSAE was performed in toluene (23% total concentration), under N 2, by maintaining the reaction mixture for 9 hr at 80 ° in sealed ampoules. A typical procedure for the synthesis of poly(dimethylsiloxane-b-methyl methacrylate) is as follows. 1.22g (0.122mmol azo groups) of PSAE, 3.35g of methyl methacrylate, and 17.6 ml of toluene were put into a 50 ml polymerization ampoule. Dry N 2 was then introduced into the resulting homogeneous solution. The ampoule was sealed and maintained at 80° for 9 hr. The polymer was separated by purging the contents into a large amount of methanol, and purified by petroleum ether extraction for 24 hr, followed by reprecipitation using benzene/methanol as solvent/nonsolvent system. 2.50 g (54.7% yield) of block copolymer was obtained after filtration and vacuum evaporation of solvents. The whole synthetic route is outlined in Scheme 1, while Table I presents the results of the polymerization of vinyl monomers using PSAE as macromolecular initiator.

Analysis

i.r. Absorption spectra were obtained on a IR-71 Specord spectrophotometer as KBr discs. ~H-NMR analyses were performed on a JEOL C-60 HL spectrometer using CDCI 3 solutions at 55 °, except for polyacrylonitrile-containing block copolymer, where DMSO-d 6 at 90 ° was used. The siloxane/vinyl monomer ratios in block copolymers were calculated from the ratios of the integrals of characteristic proton signals and from elemental microanalyses. The values obtained by the two techniques were in good agreement, within experimental error. Intrinsic viscosities were determined by use of an Ubbelohde viscometer, in toluene solutions, at 25L Average molecular weights were obtained from gel permeation chromatography (Waters Associates chromatograph), calibration being made with polystyrene standards (Pressure Chemicals Co.). Tetrahydrofuran was used as solvent. Each polymerization was accompanied by control experiments, i.e. pure thermal polymerization of vinyl monomer in toluene. No polymer was obtained in the controls. RESULTS AND DISCUSSION Polydimethylsiloxane ( H P D M S ) (3,Stn = 7000) reacts almost quantitatively, in the presence o f H 2PtC16 as catalyst, with allyl alcohol to yield a polydimethylsiloxane with hydroxypropyl reactive end-groups (BHS). This functional polymer undergoes polycondensation with A C V C in equimolecular a m o u n t s to form azo-group-containing polysiloxane esters with the appearance o f a pale yellow very viscous oil. As presented in Table 1, the latter is an effective radical (macro) initiator for the polymerization o f the usual

Synthesis of silicone-vinyl block copolymers

567

3

J

5

7"--'r

- ~ '

8

i

7

6

5

4

3

2

1

~ppm

Fig. 1. tH-NMR spectra of poly(siloxane-b-vinyl) copolymers. (1) PDMS-b-PS2; (2) PDMS-b-PAN; (3) PDMS-b-PMMA2; (4) PDMS-b-PBuMA; (5) PDMS-b-PBuA.

EPJ 2 6 ~ E *

0

568

CRISTOFOR I. SIMIONESCUet al. Table 1. Synthesis of poly(siloxane-b-vinyl)copolymers* Block copolymer Monomer** PSAE Vinyl monomer/azo group g (mmol) g (mmol azo group) molar ratio g Yield(%) Samplecode S 3.33(32) 1.28(0.128) 250 1.83 39.2 PDMS-b-PS~ S 4.42(42.5) 0.21 (0.021) 2000 1.53 33.0 PDMS-b-PS2 AN*** 1.73(32.6) 1.19(0.119) 275 2.40 82.0 PDMS-b-PAN MMA 3.35 (33.5) 1.22 (0.122) 275 2.50 54.7 PDMS-b-PMMAj MMA 3.72 (37.2) 0.37 (0.037) 1000 1.89 46.2 PDMS-b-PMMA: MMA 3.66(36.6) 0.18 (0.018) 2000 1.37 35.7 PDMS-b-PMMA~ BuMA 1.40(9.8) 0.39 (0.039) 250 0.97 54.0 PDMS-b-PBuMA BuA 1.84(14.3) 0.57 (0.057) 250 1.35 56.0 PDMS-b-PBuA *Temperature, 80; duration, 9 hr; total concentration, 23%. **S, styrene; AN, acrylonitrile; MMA, methyl methacrylate; BuMA, butyl methacrylate; BaA, butyl acrylate. ***Polymerization duration, 5 hr.

vinyl monomers. However, its initiating ability is somewhat lower than that of AIBN. Previously, Inoue et al. [12] reported similarly for azo-containing polysiloxaneamides. The formation of polysiloxane ester was proved by the characteristic absorption band in the i.r. spectrum, viz. 1735 cm- i. Cyano stretching vibration band was observed as a trace at 2230 cm -1, while absorption bands for the siloxane polymer appeared at 12571260 cm -1 (Si-CH3) a n d 1000-1100 cm -1 (Si~)--Si asymetric stretching vibration bands). F o r polysiloxane-vinyl block copolymers, i.r. spectra showed also the characteristic a b s o r p t i o n s due to the vinyl blocks. 1 H - N M R spectra o f poly(dimethylsiloxane-b-vinyl m o n o m e r ) copolymers are shown in Fig. 1. They allow estimation of dimethylsiloxane contents in the block copolymers by determining the peak areas of dimethylsiloxy p r o t o n s in siloxane segments as compared to the areas of the p r o t o n s characteristic for vinyl blocks [i.e. the phenyl p r o t o n s in polystyrene, the m e t h o x y p r o t o n s in poly(methyl methacrylate), the methylene p r o t o n s in polyacrylonitrile, poly(butyl acrylate) a n d poly(butyl methacrylate) ( C O O - CH2--)]. The vinyl/Si(CH3)20 m o l a r ratios o b t a i n e d from N M R spectra are in good agreement with those calculated from elemental analyses, within experimental errors. As expected, variation of the m o n o m e r / a z o group feed ratio (Table 1, experiments performed with methyl methacrylate and styrene) results in varying the molecular weights (Table 2) a n d also allows the synthesis o f block copolymers with longer or shorter vinyl blocks. Certainly, slightly modified experimental conditions (e.g. temperature, reaction duration, vinyl m o n o m e r c o n c e n t r a t i o n in feed) would further extend the practical synthetic possibilities of the method.

Sample BHS PSAE PDMS-b-PS~ PDMS-b-PS2 PDMS-b-PAN PDMS-b-PMMAI PDMS-b-PMMA2 PDMS-b-PMMA3 PDMS-b-PBuMA PDMS-b-PBuA

/

\

/

,,,\ ./ /' ~& ./ 3,,. ",',. .......

/

Nx . . . . . . . .

Eluiion volume (ml) ,

I

I

103

104

I

Fig. 2. GPC curves of(I) BHS; (2) PSAE; (3) PDMS-b-PSI ; (4) PDMS-b-PS2; (5) PDMS-b-PMMA~; (6) PDMS-bPMMA2; (7) PDMS-b-PMMA3 (see also Table 1).

Table 2, Characterization of poly(siloxane-b-vinyl)copolymers Vinyl/Si(CH3)20 molar ratio Intrinsic viscosity Mn'10 3 h,l,-10 3 (from IH-NMR) (dl-g i) (GPC) (GPC) k4./k4. 0.17 7.8 21.1 2.71 -0.36 29.3 61.7 2. l 1 0.6 0.55 47.0 98.2 2,09 3.4 -124,4 227.2 1.83 4.8 . . . . 1.6 0.47 86,8 153.9 1.77 5.0 0.58 139.1 304.9 2.19 7.0 0.66 253.4 431.7 1.70 1.2 0.47 ---1.2 0.53 ----

-

I

105 106 MoleculoP weight (PSI

Synthesis of silicone-vinyl block copolymers Gel permeation chromatograms of styrene- and methyl methacrylate-containing block copolymers (Fig. 2) present nearly symmetrical molecular weight distributions, characteristic of radical polymerizations. The molecular weights of the block copolymers are given in Table 2. The synthesized block copolymers, are of ABA or (AB)~ type, depending on the termination reaction of the vinyl m o n o m e r radical polymerization. CONCLUSIONS Poly(azo-containing siloxane ester)s with high initiating ability can be synthesized by the polycondensation of hydroxyl-terminated polysiloxane with ACVC. The facile scission of azo groups included in polymer chain leads to the polymerization of vinyl monomers under suitable conditions with formation of poly(siloxane-b-vinyl) copolymers. The method can be applied to various monomers able to polymerize by the radical mechanism. REFERENCES

1. Y. Yagci. Polym. Commun. 27, 21 (1986).

569

2. A. Ueda, Y. Shiozu, Y. Hidaka and S. Nagai. Kobunshi Ronbunshu 33, 131 (1976). 3. A. Ueda and S. Nagai. J. Polym. Sei.; Polym. Chem. Edn 22, 1611 (1984). 4. A. Ueda and S. Nagai. J. Polym. Sci.; Polym. Chem. Edn 22, 1783 (1984). 5. C. I. Simionescu, E. Com~nit~, V. Harabagiu and B. C. Simionescu. Eur. Polym. J. 23, 921 (1987). 6. M. Morton, A. A. Rembaum and E. E. Bostick. J. Polym. Sei. 8, 2707 (1964). 7. P. Bajaj, S. K. Varshney and A. Misra. J. Polym. Sei.; Polym. Chem. Edn 18, 295 (1980). 8. J. W. Dean. J. Polym. Sci.," Polym. Lett. Edn 8, 677 (1970). 9. P. Chaumont, G. Beinert, J. Herz and P. Rempp. Eur. Polym. J. 15, 459 (1979). 10. P. Chaumont, G. Beinert, J. Herz and P. Rempp. Polymer 22, 663 (1981). 11. W. K. Busfield and J. M. G. Cowie. Polym. Bull. 2, 619 (1980). 12. H. Inoue, A. Ueda and S. Nagai. J. Polym. Sei.; Part A: Polym. Chem. 26, 1077 (1988). 13. J. V. Crivello, D. A. Conlon and J. L. Lee. J. Polym. Sci.; Polym. Chem. Edn 24, 1197 (1986). 14. J. V. Crivello, J. L. Lee and D. A. Conlon. J. Polym. Sci.; Polym. Chem. Edn 24, 1251 (1986). 5. D. A. Smith. Makromolek. Chem. 103, 301 (1967).