Curing kinetics and characterization of dual-curable thiol-acrylate-epoxy thermosets with latent reactivity

A new dual-curing scheme was developed for thiol-acrylate-epoxy mixtures. A photo-initiated latent catalytic system was used to carry out thiol-acrylate Michael addition at 35 °C (Stage 1) followed by thiol-epoxy click reaction (Stage 2) at 80-110 °C. The intermediate materials were shown to have several days of storage stability. The use of a radical inhibitor has suppressed radical mediated acrylate homopolymerization which would otherwise lead to unreacted thiols remaining. Kinetics of Stage 2 was analyzed mathematically using isoconversional differential method and Kamal model regression. Glass transition temperatures (Tg) of samples with varying contents of epoxy and different types of acrylates were measured. Epoxy-rich formulations gave the highest final Tg. Although not as influential as the epoxy content, using higher functional and more rigid acrylate monomers resulted in higher intermediate and final Tg. The proposed curing scheme and the resulting materials could be useful in applications such as adhesives, industrial coatings with high chemical resistance, optical and electronic materials.