Liquid crystal polymers copolymers and elastomers containing a laterally attached mesogenic unit

Abstract

The synthesis of a closely-coupled laterally attached side-chain liquid crystal polymer is described. The material exhibits liquid crystalline behaviour over a wide temperature range. Incorporation of non-mesogenic methyl acrylate as a comonomer with the potentially mesogenic monomer results in copolymers which are liquid crystalline, even when the non-mesogenic portion exceeds 60 mol%. Macroscopic alignment can be readily realised in both homopolymer and copolymer samples, either using a magnetic field or by pulling as fibres, and X-ray scattering shows the level of global orientation to be relatively high. Copolymerisation of the mesogenic unit with ca. 10 mol% of hydroxyethyl acrylate results in materials which can be cross-linked by reaction with a diisocyanate. The application of mechanical stress to liquid crystalline elastomers based on this closely coupled unit results in some global orientation of the mesogens, and the stress-strain-orientation behaviour of this cross-linked system is described. Both copolymers and elastomers are compared with liquid crystal polymers in which the mesogen is attached via a terminal linkage.