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 liv ing polymers in quantitative yield in tetrahydrofuran with initiators such as oligo(alpha-methylstyryl)dipotassium and 1,1-diphenylhexyllith ium. The substituents included N,N-dialkylamido (1), oxazalinyl (2), t ert-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 demonstra ted by the quantitative efficiency in the postpolymerization. In some cases, taking account of high reactivity of the substituents, strict s election of the polymerization conditions such as initiator, counterca tion, and temperature was required for the successful anionic living p olymerization, 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 met hacrylate. The introduced electron-withdrawing substituents played ver y important roles to enhance the monomer reactivity and to stabilize t he propagating carbanions along with the extended is-conjugation syste m, The anionic polymerizabilities of 1-7 evaluated were ranked between those of 2-vinylpyridine and tert-butyl methacrylate. The reactivitie s of 1-7 were also estimated from the chemical shifts of the vinyl bet a-carbons of these para-substituted styrenes in the C-13 NMR spectra.