Effect of a Dicycloaliphatic Epoxide on the Thermo-Mechanical Properties of Alkyl, Aryl Epoxide Monomers Cured via UV-Induced Cationic Frontal Polymerization

Radical induced cationic frontal polymerization (RICFP) is a promising route to achieve rapid curing of epoxy-based thermosets, requiring only a localized exposure with UV light. In the presence of a diaryliodonium-based photoinitiator and a thermal radical initiator, a self-sustaining hot front cures epoxide monomer via a cationic mechanism. However, the cationic polymerization of diglycidyl ether derivatives is slow (in comparison with other epoxides with higher reactivity) and, as a consequence, frontal polymerization is sluggish because the heat loss is not compensated by the rate of heat release. Cycloaliphatic epoxies possess a higher ring strain than diglycidyl ether derivatives and can be blended with the latter to increase its rate of frontal polymerization. In the current work, a comprehensive study on the influence of 3,4 epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate (CE) on cure kinetics, viscosity, front velocity, mechanical, and thermo-mechanical properties of frontally cured bisphenol A diglycidyl ether derivatives is presented. The results show a direct relationship between frontal velocity and amount of reactive diluent while an inverse relationship with the storage viscosity is observed. It is found that increasing the content of cycloaliphatic epoxide reduces the glass transition but increases mechanical properties of frontally cured bisphenol A diglycidyl ether derivatives.