Reactivity of oxetane monomers in photoinitiated cationic polymerization

• Published in: Journal of polymer science. Part A, Polymer chemistry Polymer chemistry, 2005-08, Vol.43 (15), p.3205-3220
• Main Authors: Bulut, Umut, Crivello, James V.
• Format: Article
• Language: English
• Subjects: Applied sciences; cationic polymerization; Exact sciences and technology; frontal polymerization; oxetanes; photopolymerization; Physicochemistry of polymers; Polymerization; Polymers and radiations; ring-opening polymerization
• ISSN: 0887-624X; 1099-0518
• DOI: 10.1002/pola.20723

Studies of the onium salt photoinitiated cationic ring‐opening polymerizations of various 3,3‐disubstituted oxetane monomers have been conducted with real‐time infrared spectroscopy and optical pyrometry. The polymerizations of these monomers are typified by an extended induction period that has been attributed to the presence of a long‐lived tertiary oxonium ion intermediate formed by the reaction of the initially formed secondary oxonium ion with the cyclic ether monomer. Because the extended induction period in the photopolymerization of these monomers renders oxetane monomers of limited value for many applications, methods have been sought for its minimization or elimination. Three general methods have been found effective in markedly shortening the induction period: (1) carrying out the photopolymerizations at higher temperatures, (2) copolymerizing with more reactive epoxide monomers, and (3) using free‐radical photoinitiators as synergists. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3205–3220, 2005 3,3‐Disubstituted oxetanes display long induction periods during their photoinitiated cationic ring‐opening polymerizations with strong Brønsted acid generating photoinitiators. Investigations have shown that the induction periods are due to the formation of long‐lived tertiary oxonium ions. The further reaction of these species with the monomer is the slowest step in the reaction sequence shown. Several methods for shortening the induction period have been explored.