Asymmetric anionic polymerization of N-substituted maleimides bearing an azo group with chiral anionic initiators

Abstract

Asymmetric anionic homopolymerizations of N-substituted maleimides bearing an azo group (RMI: R4-(phenylazo)phenyl (PAPMI), 4-(phenylazo)-1-naphthyl (PANMI)) were performed with n-BuLi or Et2 Zn-chiral ligand ((1-ethylpropylidene)bis(4-benzyl-2-oxazoline) (Bnbox) or (-)-sparteine (Sp)) complexes to obtain optically active polymers. The optical activity of poly(RMI) was influenced by N-substituent and polymerization conditions such as organometal type, structure of the chiral ligand, temperature and solvent type. The poly(PANMI) obtained with an n-BuLi-Bnbox complex in tetrahydrofuran showed the highest specific rotation (α D25d=+391.1°). Trans-cis photoisomerizations of poly(PAPMI) and poly(PANMI) caused y ultraviolet (UV) irradiation were observed from UV spectra. The rate of trans-cis photoisomerization for poly(PAPMI) was faster than that for poly(PANMI). The Cotton effects for trans isomers of poly(PAPMI) and poly(PANMI) were relatively small, but those for cis isomers of poly(PAPMI) and poly(PANMI) clearly exhibited a split circular dichroism curve. © The Society of Polymer Science, Japan (SPSJ) All rights reserved.