Unusual Chiral Transfer in Radical Copolymerization of Vinyl Monomers Bearing Side‐on p‐Terphenyl Pendants

Abstract

Radical copolymerization of a chiral monomer, (+)-2,5-bis[4'-((S)-2-methylbutoxy)phenyl]styrene and an achiral monomer, 2,5-bis(4'-hexyloxyphenyl)styrene, is carried out in anisole at 90 degrees C with benzoyl peroxide as the initiator. The resultant optically active helical copolymers show an unusual linear relationship between optical activity and composition, in sharp contrast with Green's "sergeants-and-soldiers" and "majority" rules. Analysis of the polarimetry, circular dichroism, and chain extension results suggest that the weak steric interaction between the propagation helical radical and the incoming monomer drove the copolymer chain to grow in a specific direction. Moreover, the helical macroinitiator is successfully used to induce the helix-sense-selective atom transfer radical polymerization of an achiral analogous monomer to yield optically-active block copolymers, which indicate a convenient way to prepare helical polymers with an excess screw sense from an achiral monomer by means of radical polymerization.