Organometallics 1995, 14, 2225-2231
2225
The 6oCoy-Radiation-InducedPolymerization of Vinylalkoxysilanes Dietmar Seyferth," David Y. Son, and Miklos Tasi Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Received December 8, 1994@ The 6oCo y-radiation-induced polymerization of CH2=CHSi(OEt)3 gave, according to analytical and spectroscopic (IR, lH and 29SiNMR) data, as well as similar data for its L i A l b reduction product, a polymer of composition R-[-CH2-CH(Si(0Et)3)-la-[-C(CH3)(OSi~)-l,-[-CH2-CH(Si(OEt)~)-l~-R, where b >> a and the end groups R = -CH2CH2Si(OEt)a, (Et0)3Si(C-)HCH3, and -CH(OSi=)CH3. A similar polymer was obtained by y-rayinduced polymerization of CHz=CHSi(OMe)s, but less chain transfer involving the alkoxy groups occurred in this case. Similar polymerization of CHz=CHSiCH3(0Et)2 and CH2=CHSi(CH&OEt was less facile, giving polymers of similar composition and of lower molecular weight in much lower yield for a given radiation dose.
Introduction In previous papers we have reported the 6oCoy-radiation-initiated polymerization of vinyltrichlorosilane,l vinylmethyldichlorosilane,2and vinyldimethylchlorosilane2 and the conversion of the resulting vinyl polymers, PVSiCl3, PVSiMeC12, and PVSiMe2C1, to the corresponding silicon hydride polymers, PVSiH3, PVSiMeH2, and PVSiMe2H. To complement this work, we have investigated the 6oCoy-radiation-initiated polymerization of analogous vinylethoxy- and vinylmethoxysilanes. The polymerization of vinylalkoxysilanes has received extensive study by previous workers, the first report being published by Wagner, Bailey, Pines, Dunham, and McIntire in 19533on the di-tert-butyl peroxide-initiated polymerization of vinyltriethoxysilane. It was found that soluble, viscous, liquid polymers of low molecular weight (M, ca. 5000-8000) were produced in high yield when the polymerization was carried out at 130 "C. A later study by Mixer and Bailey4 provided chemical evidence for a polymer composition of R[(EtO)zSiOCH(CH3)lm[CHzCH(Si(OEt)3)1,H(R = vinyl or polymer chain) resulting from chain transfer by a-hydrogen atom abstraction from an ethoxy group (Scheme 1). Such chain transfer t o monomer or polymer would be expected to result in high yields of polymers of low molecular weight, as had been observed. Japanese workers5 polymerized vinyltrimethoxy- and vinyltriethoxysilane using 60Coy-radiation initiation. A 60 -Mrad dose resulted in degrees of polymerization (DP) of 4.3-7.4, respectively, for CH2=CHSi(OMe)3 and CHz=CHSi(OEt)3. The information provided by IR and lH NMR studies was not sufficient to allow any conclusions concerning the composition of the polymers. Andrianov and his co-workers carried out di-tert-butyl peroxide-initiated polymerizations of a number of CH2=CHSi(R)(OR)2compounds, including CHz=CHSiAbstract published in Advance ACS Abstracts, April 15, 1995. (1) Seyferth, D.; Tasi, M.; Woo, H.-G. Chem. Mater. 1995, 7, 236. (2) Seyferth, D.; Son, D. Y. Submitted for publication. (3) Wagner, G. H.; Bailey, D. L.; Pines, A. N.; Dunham, M. L.; McIntire, D. B. Ind. Eng. Chem. 1954, 45, 367. (4) Mixer, R. Y.; Bailey, D. L. J. Polym. Sci. 1955, 18, 573. (5) (a) Hayakawa, K.;Kawase, K.; Yamakita, H.; Inagaki, S.Polym. Lett. 1967, 5,1077. (b) Hayakawa, K.; Kawase, K.; Yamakita, H.; Yumoto, T. J . Polym. Sci., Polym. Chem. Ed. 1981, 19, 3145. @
0276-7333/95/2314-2225$09.00/0
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Scheme 1
+
-CH2CHSi(OC2H5)3
-CH2CH2Si(OC2H5)3
+
R(C2H50)2Si06HCH3
-
CH3CH20Si(OC2H5)2R
CHp2HSi(OC2H5)3
+
CH36HOSi(OC2H&R
R(C2H50)2SiOCHCH26HSi(OC2H&
I
CH3
(R)(OCH3)2(R= n-C3H7, n-C4Hg, n-C5H11, andpC1C&d6 and CH2=CHSi(CH3)(0R)2 ( R = CH3, C2H5, n-C3H,, n-CdHg, and C G H ~ )The . ~ molecular weights of the polymers obtained (M,) were low, ranging from 720 to 2670, depending on the monomer. IR studies indicated that chain transfer of the type shown in Scheme 1 is slight a t the early stages of the polymerization but becomes important a t higher conversions. Later, detailed 13C NMR studies of poly(vinylmethy1diethoxysilane)* and other poly(vinylmethyldialkoxysi1anes)(RO = CH30, n-C3H70, and i-C3H,0)9 prepared by this procedure were reported by Zhdanov and his co-workers. It was concluded that in the case of CH2=CHSi(CH3)(OC2H5)2 polymerization only about 30% of the initial vinyl groups were present as [-CH2CH(Si(CH3)(OCzH&-I units; 3% were present as unchanged CH2=CH groups, 2%as CH2=C(Si(CH3)(0C2H5)2)CHzgroups, and 60% as fragments in which the a-carbon atom had become a CH group by hydrogen atom abstraction from an ethoxy group. It was estimated that some 20% of the OC2H5 groups had in this way been converted into CHdC-)HO and CH3(C> a and the end groups R = -CHzCHzSi(OEt)3, (Et0)3Si(C-)HCH3,and -CH(OSi=)CH3.
backbone. However, the CH to SiH integration ratio was not the expected 1, as it was in PVSiH3 derived from PVSiC13;l rather it was 2.0, which indicates that additional C-H protons were present in the polymer. The 29SiNMR spectrum of y-PVSiH3 was relatively clean, showing two large resonances a t dsi -58.2 and -56.6 and a smaller resonance at -49.9. These resonances are in the region where signals due to RSiH3 compounds usually are observed.ll Further studies using DEPT sequences showed that none of these resonances were due to SiH2 groups, in contrast to the PVSiH3 derived from PVSiCl3 whose 29Si NMR spectrum contained resonances of low intensity due to SiHz gr0ups.l These results may be rationalized as shown in Scheme 2. Single and double H atom abstraction from a-carbon atoms of ethoxy groups on silicon would result in extensive chain branching to give species of types A and B in y-PVSi(OEt)sin addition to the expected [CHzCH Si(OEt)& LiAlH4 reduction of such a branched polymer would reduce branching Si-0-C units, giving, (11)Harris, R. K.; Kennedy, J. D.; McFarlane, W. In NMR and the Periodic Table; Harris, R. K., Mann, B. E., Eds.; Academic: London, 1978; Chapter 10a.3. See also the papers of Schmidbaur and coworkers, e.g.,: Schmidbaur, H.; Dorzbach, C. 2. Naturforsch. 1987, 42B,1088. Schmidbaur, H.; Ebenhoch, J. 2. Naturforsch. 1987,42B, 1543. Schmidbaur, H.; Zech, J. Eur. J.Solid State Inorg. Chem. 1992, 29,5.
after hydrolysis, a less branched polymer with pendant SiH3 groups. The components of y-PVSiH3 resulting from reduction of fragments A and B will have a higher CWSiH ratio and, due to the presence of CH3(C-)HOH and CH3(C
