Liquid crystalline cyanurate thermosets through cyclotrimerisation of novel triaromatic dicyanates

Abstract

Three novel triaromatic dicyanates, hydroquinone bis(4-cyanatobenzoate) (1), methylhydroquinone bis(4-cyanatobenzoate) (2), and trimethylhydroquinone bis(4-cyanatobenzoate) (3) were synthesized and cyclotrimerised to form s-triazine thermoset networks. All monomers have a nematic mesophase. Networks with frozen nematic textures were obtained from 2 and 3 while 1 underwent a transition from the nematic melt to a smectic thermoset. The curing reactions were monitored by infrared spectroscopy and calorimetry. The final conversion of the rigid monomers was approximately 95% from dynamic DSC experiments. The nematic-isotropic transition and the glass transition temperature of 2 was measured as a function of conversion. The final glass transition temperature of the thermosets from the triaromatic dicyanates is 100°C and more below that of a diaromatic dicyanate, indicating that flexibility is increased with the number of ester groups between the branch points.