Synthesis of side-chain liquid crystalline homopolymers and block copolymers with cyanobiphenyl moieties as the mesogen by living anionic polymerization and their thermotropic phase behavior

We performed the anionic living polymerization of 6-[4-(4'-cyanophenyl)phenoxy]hexyl methacrylate. By a selection of suitable initiations, the cyano group was completely stable toward the propagating enolate anion, and the anionic polymerization proceeded with a living nature. The homopolymers could thus be prepared with a wide range of molecular weights from 6000 to 20 000, a narrow molecular weight distribution of less than 1.14, and different tacticities. All the polymers exhibited the smectic A phase in which two mesogenic groups were included within a smectic layer of thickness 36.0 Angstrom. The isotropization temperature of the smectic A phase increased with the increase of the molecular weight and leveled off at around 15 000. No crystallization took place so that the smectic A phase was glassified. Well-controlled block copolymers with methyl methacrylate and styrene were also prepared by living anionic polymerization, and their thermotropic phase behavior and structures are described in a relation to a microphase separation of the two different segments.