Optical Properties of Chiral Nematic Side-Chain Copolymers Bearing Cholesteryl and Azobenzene Building Blocks

Thermotropic chiral nematic (N*) side-chain copolymers (CPs) bearing cholesteryl and azobenzene units were synthesized to investigate the structure-property relationships of the acrylates of the chiral, achiral, and photochromic monomers of free radical polymerization-derived polymers. The polar effect of chlorine substitution on the benzene ring of the chiral monomer (M3*) widened the mesophase transition temperature only at the monomer level, but no remarkable effect on the mesomorphic, optical or thermochromism of the corresponding CPs was observed. An examination of the CPs prepared using differential scanning calorimetry and hot-stage polarizing microscopy showed that all the CPs exhibited a cholesteric nematic phase (N*), and increasing the content of the cholesteryl units in the CPs displayed only the N* phase over a much wider temperature range. On cooling from the isotropic melt of N* CPs, selective reflections of visible light that changed from short to long wavelengths were observed. The photolysis of CPs revealed that CP1-CP4 undergo reversible photoisomerization and that CP5 and CP6 undergo irreversible photoisomerization. The rate of isomerization depends on the type (-N=N-, -CH=CH-, and both) and content of photochromic units in the CPs. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 770-780, 2011