Liquid crystalline side-chain triblock copolymers consisting of a nematic central subblock edged by photochromic azobenzene-containing fragments: their synthesis, structure and photooptical behaviour

Abstract

For the first time, symmetrical photosensitive fully liquid crystalline side chain triblock copolymers (pAzo-b-pPhM-b-pAzo) and random copolymers (pAzo-ran-pPhM) with nematogenic phenyl benzoate (PhM) and photosensitive smectogenic azobenzene containing groups (Azo) were synthesized by the combination of RAFT polymerization and subsequent chemical modification. The central block of synthesized photochromic block copolymers contains 80 PhM groups, while the length of “peripheral” blocks includes 4 or 10 Azo units. The microphase separation structure is observed in the block copolymer when the length of a subblock with Azo groups reaches ten monomeric units. The influence of photochromic polymers’ molecular architecture (homopolymer, block copolymer and random copolymer) on the photochemical and photoorientation processes induced by light in their amorphous films has been revealed. The optical anisotropy induced in block copolymer films by illumination with linearly polarized 546 nm light was studied and the results were compared with those of the Azo homopolymer and of a random copolymer with a similar composition. It was found that practically only Azo groups are included in the process of photoinduced orientation in films of block copolymers, whereas the orientational cooperative effect of both azobenzene chromophore and phenyl benzoate mesogenic groups is observed in the case of a random copolymer.