Free radical induced acceleration of cationic photopolymerization

Two new monomers based on alpha-terpineol were prepared, allyl alpha-terpineol ether epoxide (III) and l-propenyl ether alpha-terpineol epoxide (IV) Th, photoinitiated cationic polymerizations of these two monomers as well as two model compounds, l-propenyl alpha-terpineol ether and methyl alpha-terpineol ether epoxide, were studied using real-time infrared spectroscopy. Surprisingly, the rates of epoxide ring-opening polymerization of both monomers were greatly enhanced as compared to the model compounds. At the same time, the rate of polymerization of the 1-propenyl ether groups in IV was depressed. Two different mechanisms which involve the free radical induced decomposition of the diaryliodonium salt photoinitiator were proposed to explain the rate acceleration effects.