Mixtures of Liquid-Crystalline and Amorphous Dicyanates: Unusual Curing Behavior and Mechanical Properties

Three series of triazine networks were prepared by a thermal cyclotrimerization reaction between the mesogenic 1,4-benzenedicarboxylic acid bis(4-cyanatomethylphenyl) ester (LC1), 1,4-cyclohexanedicarboxylic acid bis(4-cyanatomethylphenyl) ester (LC2), and either one of two commercial nonmesogenic dicyanates, namely, the (1-methylethylidene)di-4,1-phenylene ester cyanic acid (B) and the [2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]di-4,1-cyanic acid phenylene ester (F). The various mixtures display liquid-crystalline behavior provided that a minimum of 50% of the mesogenic dicyanates LC1 and LC2 are present. Isotropic or nematic networks can be obtained by appropriately adjusting the monomer composition. It can be shown that networks with reproducible properties could be prepared and studied for their thermal and dynamic-mechanical behavior only by additional curing at very high temperatures The observed trend in temperature of the a relaxation in the investigated system with LC1 and LC2 is complex, and substantial deviations from linear behavior are observed The data presented differ from previously reported liquid-crystal thermoset (LCT) systems and demonstrates that mixtures of LC and non-LC thermosets represent a delicate mesomorphic system. A thorough analysis was carried out, and the results will be discussed in detail.