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.Highlights► In this study we synthesized curing agents (LCCAn) with similar structures. The isothermal kinetics of DGEBA/LCCAn systems was studied. ► DGEBA/LCCAn systems showed higher chemical reactivity and Ea than DGEBA/DABP system. DGEBA/LCCAn systems showed liquid crystalline transitions. ► We found the formation of LC phase of epoxy networks can be decided by curing agents.

A series of chain-extended ureas (U-TPBn) containing hydroxyl-terminated polybutadiene spacer were synthesized and used to modify epoxy resin based on a diglycidyl ether of bisphenol A and dicyanodiamide. The ultimate aim of the study was to enhance the curing reactivity and improve the toughness characteristics of the brittle epoxy matrix. The curing behavior, viscoelastic properties, impact response and fracture surface morphology of the curing systems were systematically investigated. DSC analysis reveals that the curing reactions of the epoxy systems are greatly accelerated with the addition of U-TPBn. Impact tests show that the modifiers are very effective in toughening the epoxy resin.

A new homologous series of curing agents (LCECAn) containing 4,4′-biphenyl and n-methylene units (n = 2, 4, 6) were successfully synthesized. The curing behaviors of a commercial diglycidyl ether of bisphenol-A epoxy (E-51) and 4,4′-bis(2,3-epoxypropoxy)biphenyl (LCE) by using LCECAn as the curing agent have been investigated by differential scanning calorimetry (DSC), respectively. The Ozawa equation was applied to the curing kinetics based upon the dynamic DSC data, and the isothermal DSC data were fitted using an autocatalytic curing model. The glass transition temperatures (Tg) of the cured epoxy systems were determined by DSC upon the second heating, and the thermal decomposition temperatures (Td) were obtained by thermogravimetric (TG) analyses. The results show that the number of methylene units in LCECAn has little influence on the curing temperatures of E-51/LCECAn and LCE/LCECAn systems. In addition, the activation energies obtained by the dynamic method proved to be larger than those by the isothermal method. Furthermore, both the Tg and Td of the cured E-51/LCECAn systems and LCE/LCECAn systems decreased with the increase in the number of methylene units in LCECAn.