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Photo-cationic polymerization based on photo-generation of acid from onium salts induced by
UV light and consecutive cationic polymerization initiated by the generated acid was first proposed in 1970's." Since then, photo-cationic curable materials, using cationic polymerizable
monomers such as epoxides and vinyl ether derivatives, have been widely Among them, epoxides are known to give cured coatings with high thermal capability, excellent adhesion and good chemical resistance, however, the curing speed of commercially available epoxides, such as glycidyl ether derivatives, are rather slow. This low reactivity of epoxides has proved to be a considerable drawback to their use in some industrial > Thus, it has been desired to develop novel monomers that have the same performance capabilities as epoxides, while at the same time possess higher reactivity. Three major factors, basicity, the ring strain and steric hindrance, contribute to the reactivity of cyclic ethers in the cationic ring-opening Oxetane, four membered cyclic ether, possesses rather high ring strain energy (lO7kJ/rnol) and basicity (pKa = These
properties of oxetane ring should make the oxetanes more reactive than epoxides. Previously,
photo-cationic polymerization property of oxetanes was investigated and found to possess quite
different polymerization character from > Although the initiation of oxetane polymerization was rather slow, polymerization proceeded smoothly until high conversion of monomer and gave high molecular weight polymer. The slow initiation of oxetane was explained by the high energy barrier for the ring opening of protonated oxetane and high polymerizability was elucidate by the high nucleophilicity of oxygen on the> It is interesting and informative to investigate a cyclic ether monomer possessing high nucleophilicity as oxetanes and the low energy barrier for the first ring opening as well, which should exhibit fast initiation and high polymerizability. to the stable berizyl type structure, introduction of phenyl group on the second position of oxêtane ring might enhance the stability of intermediate in the initiating reaction and contribute to reduce the energy barrier, maintaining the basicity high.
