Curing behaviors and kinetics of epoxy resins with a series of biphenyl curing agents having different methylene units

A series of curing agents (LCCAn) bearing biphenyl group and n-methylene units (n = 2, 4 and 6) were synthesized. The curing behaviors of epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) with LCCAn were investigated in comparison with commercial biphenyl type curing agent 4,4′-diaminobiphenyl (DABP) by dynamic DSC. The results indicated that LCCAn curing systems showed higher chemical reactivity and lower glass transition temperatures than DABP system. The kinetics was studied under isothermal and non-isothermal conditions using isoconversional methods, and the isothermal DSC data can be fitted reasonably by an autocatalytic curing model. POM studies revealed that the cured samples of DGEBA/LCCAn systems showed liquid crystalline transitions while DABP curing system displayed an isotropic state, which indicated that methylene units played a key rule for the formation of liquid crystalline phases.