Anionic living polymerization of styrenes containing electron-withdrawing groups

Six styrene derivatives containing electron-withdrawing groups were synthesized and polymerized with anionic initiators in THF to afford stable anionic living polymers. The electron-withdrawing substituents are N,N-dialkylamide(1), N-alkylimino(2), oxazoline(3), tert-butyl ester(4), N,N-dialkylsulfonamide(5) and cyano(6) moieties. The polymers obtained have predictable molecular weights and narrow molecular weight distributions. The respective postpolymerizations proceeded with quantitative efficiency indicating that each polymer chain end retained the propagating reactivity. However, the resulting living polymers could not initiate the polymerizations of styrene and isoprene. On the other hand, the styrene derivatives(5 and 6) were polymerized with weak nucleophilic initiators, such as living polymer of tert-butyl methacrylate. These results suggest that the electron-withdrawing groups stabilize the living ends and also activate the respective monomers for anionic polymerization. The substitution effect reflects on the ¹³C NMR chemical shift of β-carbon of each vinyl group. The signal of the β-carbon appeared at lower magnetic field than that of styrene indicating electron deficiency on the carbon-carbon double bond of these monomers.