SYNTHESIS AND CURING OF NOVEL LC TWIN EPOXY MONOMERS FOR LIQUID-CRYSTAL THERMOSETS

This article describes the synthesis and characterization of new liqui d crystalline thermosets having a twin structure. Nematic epoxy-termin ated monomers based on a phenyl benzoate twin mesogen connected by an alkylene spacer were synthesized for these studies. In addition, an ep oxy-terminated monomer based on a 1,4-bis(benzoyloxy)phenylene mesogen was synthesized to determine the effect of the position of the mesoge n on the final network structure. The diepoxy monomer made with phenyl benzoate twin mesogens connected with an alkylene spacer formed a sme ctic-like network when cured with diamines. This smectic organization appeared even though the diepoxy monomer itself showed only a nematic mesophase over a narrow temperature range. The presence of crosslinks at both ends of the mesogens helped to retain a uniform spacing betwee n crosslinking sites during the curing reaction, and aided formation o f the smectic layer arrangement. The epoxy monomer possessing a 1,4-bi s(benzoyloxy)phenylene mesogen and two epoxidized alkylene end groups on both sides of the mesogen formed a stable nematic mesophase. Howeve r, in contrast to the twin epoxies, the latter epoxy when reacted with diamines tended to produce a nematiclike network which was retained a s the crosslinking reaction proceeded. (C) 1996 John Wiley & Sons, Inc .