Synthesis and studies on some cholesterol containing poly-siloxane based side- chain liquid crystal elastomers

Abstract Siloxane-based side-chain liquid crystal elastomers (SCLCEs) containing cholesteryl 4-(undec-10-en-1-yloxy)benzoate mesogenic unit are described. The cholesteric mesogen was dimesomorphic and displayed a smectic A and nematic phases having a phase range of 69°C and 32°C respectively. Four elastomers (polydomain powders) were synthesized by employing the LC mesogen, polymethylhydrosiloxane (PMHS) backbone and four different cross-linkers (alkyl, phenyl, biphenyl and azo) through hydrosilylation reaction. All the elastomers were found to be stable up to 300°C and exhibited an intercalated lamellar structure. Among the four elastomers studied, a wide phase range was observed for LCE4 with an azo cross-linker and the LCE1 containing an alkyl cross-linker exhibited a low phase range. The photoisomerization of the LCE4 (due to the presence of azo- group) was investigated in toluene and photostationary state for trans-to-cis conversion was observed at 150 s. The polymeric films of the elastomers were also prepared. A noticeable bending response was was observed for a thermal stimulus in elastomers containing alkyl, phenyl and azo cross-linkers which was more pronounced in LCE4 having azo cross-linker.