Living anionic polymerization of styrenes substituted with electron-withdrawing groups

Anionic polymerizations of seven styrene derivatives para-substituted with electron-withdrawing groups were carried out to afford stable living polymers in quantitative yield in tetrahydrofuran with initiators such as oligo(alpha-methylstyryl)dipotassium and 1,1-diphenylhexyllithium. The substituents included N,N-dialkylamido (1), oxazalinyl (2), tert-butyl ester(3), (trimethylsilyl)ethynyl (4), N-alkylimino (5), N,N-dialkylsulfonamido (6), and cyano (7) groups. The resulting polymers possessed the predicted molecular weights based on the molar ratios of monomers to initiators and narrow molecular weight distributions (M-w/M-n 1.1). The persistency of each propagating carbanion was demonstrated by the quantitative efficiency in the postpolymerization. In some cases, taking account of high reactivity of the substituents, strict selection of the polymerization conditions such as initiator, countercation, and temperature was required for the successful anionic living polymerization, The enhanced anionic polymerizability of these monomers and the reduced nucleophilicity of the active chain end of the living polymers were clarified by the sequential block copolymerization of 1-7 with the conventional comonomers such as styrene and tert-butyl methacrylate. The introduced electron-withdrawing substituents played very important roles to enhance the monomer reactivity and to stabilize the propagating carbanions along with the extended is-conjugation system, The anionic polymerizabilities of 1-7 evaluated were ranked between those of 2-vinylpyridine and tert-butyl methacrylate. The reactivities of 1-7 were also estimated from the chemical shifts of the vinyl beta-carbons of these para-substituted styrenes in the C-13 NMR spectra.