SIDE-CHAIN LIQUID-CRYSTALLINE POLYMERS CONTAINING A SILOXANE SPACER .2. EFFECTS OF MESOGENIC GROUPS ON THE THERMAL-PROPERTIES OF SIDE-CHAINLIQUID-CRYSTALLINE POLYMERS CONTAINING A DISILOXANE UNIT IN THE SPACER

A series of side-chain liquid-crystalline polymers was prepared contai ning disiloxane units in the spacer. The polymers consist of a polymet hacrylate backbone and several kinds of mesogenic side groups. For the synthesis of the desired monomers, silanol compounds carrying a mesog enic group were prepared as the intermediates. The polymers were obtai ned by ordinary free-radical polymerization. As the mesogenic groups, linear-type p- or p'-substituted phenyl and biphenylyl benzoates, p- o r m-substituted benzoyloxybiphenyl groups and laterally attached biphe nylyl benzoate-type mesogens were chosen, and the structural effects o n the thermal properties of the polymers were investigated. In the cas e of linear-type mesogens, only when triple-core mesogens were introdu ced a stable smectic mesophase was observed with a wide range of phase stability, while no mesophase was observed for the linear double-core and the laterally attached mesogens. On the other hand, a highly orde red smectic phase was observed for polymers having linear-type triple- core mesogens with p-alkoxy and m-cyano end groups. Furthermore, it wa s revealed that the introduction of a disiloxane unit in the spacer lo wered the temperature range of the mesophase, in comparison with polym ers having an alkylene spacer with the same backbone component and mes ogens.