Biobased polymer networks by the thiol-ene photopolymerization of allylated p-coumaric and caffeic acids

Diallylated p-coumaric acid (A2CM) and triallylated caffeic acid (A3CF) were synthesized by the reactions of p-coumaric acid and caffeic acid with allyl bromide in the presence of potassium carbonate. The thiol-ene photopolymerization of A2CM and a pentaerythritol-based tetrathiol (S4P) as well as that of A3CF/S4P at allyl/thiol and (allyl + enone)/thiol ratios of 1/1 produced cured products. The FT-IR spectral analysis revealed that the thiol-ene reaction of allyl and thiol groups mainly progressed for the products cured at an allyl/thiol ratio of 1/1, while both allyl and enone groups reacted with thiol groups for the products cured at an (allyl + enone)/thiol ratio of 1/1. The progress of the thiol-ene reaction of the enone and thiol groups caused the lowering of the glass transition and 5% weight loss temperatures (T-g and T-d5). The A3CF/S4P cured at an allyl/thiol ratio of 1/1 exhibited the highest T-g, T-d5, tensile strength, and tensile modulus among all the cured products.