LIQUID-CRYSTALLINE NETWORKS FROM 1,4-BENZENEDICARBOXYLIC ACID BIS(4-CYANATOMETHYLPHENYL) ESTER

The phase behaviour and curing reaction of 1,4-benzenedicarboxylic aci d bis(4-cyanatomethylphenyl) ester (LC dicyanate) as well as the mecha nical properties of the LC network were examined. The overall reaction kinetics were found to be first order with an activation energy of 67 .5 kJ/mol similar to many conventional dicyanate monomers. Gelation wa s detected by viscoelastic measurements and occurred at a conversion o f approximate to 0.5. These results suggest that the topology of the n etwork formed in the LC dicyanate system was the same as non-LC dicyan ates such as 2,2-bis(cyanatophenyl)propane. The onset of the mesophase was found to start at a conversion of approximate to 0.06 and end at a conversion of approximate to 0.20, independent of the curing tempera ture (180-280 degrees C). This observation indicates that small cluste rs comprising a small oligomer (mainly trimer) surrounded by 6-7 monom ers dominate formation of the mesophase which possesses a clearing tem perature above at least 280 degrees C. Competition between liquid crys talline order and high crosslink density resulted in a large free volu me in the glassy state. This large free volume strongly affects mechan ical behavior as well as the glass transition temperature of the LC ne twork.