Synthesis and characterization of network liquid crystal elastomers and thermosets

Abstract

A new series of network liquid crystal polymers were synthesized by graft copolymerization of the difunctional mesogenic monomer 4-allyloxy-benzoyloxy-4′-allyloxy-biphenyl (M) upon polymethylhydrosiloxane (PMHS). Monomer M acted not only as a mesogenic unit but also as a crosslinker for the network polymers. The chemical structures of the polymers were confirmed by IR spectroscopy. DSC, TGA, and X-ray scattering were used to measure their thermal properties and mesogenic properties. The glass transition temperature (Tg) of these network liquid crystal polymers was increased when the monomer was increased, and Td (temperature of 5% weight loss) at first went up and reached a maximum at P1, then went down. The slightly crosslinked polymers (P0, P1) show rubber-like elasticity, so it was called liquid-crystal elastomer. Network polymers will lose elasticity property with a highly crosslinked degree, and turn into thermosetting polymers (P4, P5). All polymers exhibited a smectic texture by X-ray scattering. © 2002 Wiley Periodicals, Inc. J. Appl. Polym. Sci.