Synthesis and phase behaviour of a class of comb-like cholesteric azobenzene liquid crystalline polymers

Abstract

ABSTRACT In this paper, we designed and synthesised two azo liquid crystal monomers (M1 and M2) and a chiral liquid crystal monomer N, followed by side-chain graft copolymerisation with polymethylhydrosiloxane (PMHS) to synthesize comb-like liquid crystalline polymers PN1 and PN2. The structures of all liquid crystal monomers and polymers conform to the molecular designs by FT-IR and 1H NMR. The liquid crystal properties were tested by DSC and POM, and the results showed that M1 and M2 were thermotropic enantiotropic nematic liquid crystals and N was a thermotropic enantiotropic cholesteric liquid crystal. Both the PN1 and PN2 series were amorphous polymers. The PN1 and PN2 series exhibited a typical Grand-jean texture. The glass transition temperature and isotropic temperature of the PN1 and PN2 series decreased first and then increased with the increase of azo monomer M content. And the glass transition temperature and isotropic temperature of the PN1 series were higher than the PN2 series. Both the PN1 and PN2 series had good thermal stability. The mesophase range of the PN1 series was 173.5°C~181.5°C, and the PN2 series was 162.5°C~172.9°C.