THERMAL REVERSIBILITY OF ORDERED, PHOTOCROSSLINKED LIQUID-CRYSTALLINEPOLY(VINYL ETHER)S

Anisotropic networks were prepared by photoinitiated cationic bulk pol ymerization of aligned liquid crystalline mixtures of mono- and bifunc tional vinyl ethers. The thermal reversibility of the macroscopic orde r of the networks was assessed by infra-red spectroscopy measuring the dichroic ratio of the oriented samples at different temperatures betw een 20 degrees C and 200 degrees C. The order parameter gradually decr eased with increasing temperature and the relative reduction decreased with increasing crosslink density. For systems showing smectic mesoph ase transitions, the decrease in order parameter was concentrated in t he transition temperature ranges. The almost complete recovery of alig nment after cooling to 20 degrees C was due to the network character o f these polymers. A permanent loss in order parameter of about 15% aft er the first heating and cooling cycle was recorded. This was attribut ed to a thermally induced polymerization occurring during the first he ating scan. Copyright (C) 1996 Elsevier Science Ltd.