EFFECT OF SILOXANE SPACER ON PHOTOCHEMICAL PHASE-TRANSITION BEHAVIOR OF POLYMER LIQUID-CRYSTALS WITH AZOBENZENE MOIETIES IN THE SIDE-CHAIN

The effect of flexible siloxane spacers on photochemical phase transit ion behavior was investigated for polymer liquid crystals (PLCs) with an azobenzene group as a photoresponsive moiety in which mesogens (azo benzene and cyanobiphenyl moieties) are attached to the polymer main c hain through different types of spacers (siloxane and alkyl chains). T he PLC possessing the siloxane spacer and the non-photoresponsive moie ty in the same side chain showed a slower response in the photochemica l liquid-crystalline (LC) to isotropic (I) phase transition than the a nalog having the siloxane spacer and the photoresponsive moiety in the side chain. The result indicates that the flexible siloxane spacer st abilizes the phase structure of the LC phase and depresses the propaga tion of the perturbation due to trans-cis isomerization of the azobenz ene in the LC phase. Furthermore, it was also confirmed that the space r structure did not affect the photoisomerization behavior of the azob enzene moieties.