Thermal reversibility of ordered, photocrosslinked liquid crystalline poly(vinyl ether)s

Anisotropic networks were prepared by photoinitiated cationic bulk polymerization of aligned liquid crystalline mixtures of mono- and bifunctional vinyl ethers. The thermal reversibility of the macroscopic order of the networks was assessed by infra-red spectroscopy measuring the dichroic ratio of the oriented samples at different temperatures between 20 degrees C and 200 degrees C. The order parameter gradually decreased with increasing temperature and the relative reduction decreased with increasing crosslink density. For systems showing smectic mesophase transitions, the decrease in order parameter was concentrated in the transition temperature ranges. The almost complete recovery of alignment after cooling to 20 degrees C was due to the network character of these polymers. A permanent loss in order parameter of about 15% after the first heating and cooling cycle was recorded. This was attributed to a thermally induced polymerization occurring during the first heating scan. Copyright (C) 1996 Elsevier Science Ltd.