1,3,4-Oxadiazole epoxy resin-based liquid crystalline thermosets and their cure kinetics

摘要

Liquid crystalline thermosets were synthesized based on a difunctional liquid-crystal (LC) epoxy resin monomer, namely 2,5-bis(4-glycidyloxyphenyl)-1, 3,4-oxadiazole with various tetrafunctional crosslinkers such as diaminodiphenyl methane, diaminodiphenyl sulfone, and diaminodiphenyl ether. The epoxy monomer was characterized by infrared and nuclear magnetic resonance spectroscopy. Cure kinetics of a stoichiometric mixture of epoxy monomer and diaminodiphenyl methane was investigated by differential scanning calorimetry (DSC) for specimens cured under various cure conditions. The nematic LC texture for the cured specimen was identified by polarized microscopy and confirmed by X-ray diffractometry. Phase diagram of cure time versus transition temperature was constructed based on the DSC data for epoxy/DDM system. The diagram displayed the changes of melting transition, isotropic transition, and glass transition temperatures as curing proceeds.