An investigation of the photoinitiated cationic ring-opening polymerizations of various epoxy monomers was conducted using real-time infrared spectroscopy and optical pyrometry. Several types of behavior were observed and interpreted on the basis of the relative stabilities of the secondary and tertiary oxonium ion intermediates that are generated during the ring-opening polymerization of these monomers. Based on the mechanistic interpretations proposed, attempts were made to accelerate the photopolymerizations of epoxy monomers that undergo overall slow reaction as a result of the presence of an induction period. Three general methods were effective for the acceleration of the photopolymerizations of these and other epoxy monomers:  (1) carrying out the photopolymerizations at higher temperatures, (2) copolymerization with more reactive monomers, and (3) the use of free radical photoinitiators.

Curcumin, a naturally occurring, intensely yellow dye extracted from the spice turmeric, is an efficient photosensitizer for diaryliodonium salt photoinitiators at wavelengths ranging from 340 to 535 nm. With curcumin as a photosensitizer, it is possible to carry out the cationic photopolymerization of a wide variety of epoxide, oxetane, and vinyl monomers with long-wavelength UV and visible light. An example of the photopolymerization of an epoxide monomer with ambient solar irradiation is provided. Several other curcumin analogues were synthesized, and their use as photosensitizers is examined. With such photosensitizers, the range of spectral sensitivity can be extended well into the visible region of the electromagnetic spectrum. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5217-5231, 2005

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

Summary: Curcumin, an intensely yellow dye isolated from Indian turmeric is an excellent electron-transfer photosensitizer for cationic vinyl and ring-opening polymerizations. Especially attractive features of curcumin are its strong absorption, broad spectral sensitivity, efficient electron-transfer, low toxicity and low cost. Using curcumin as a photosensitizer, the cationic photopolymerizations of a variety of monomers were carried out including such naturally derived monomers as epoxidized terpenes and epoxidized vegetable oils. The impact of this technology on applications such as housing, boat-building and water distribution is discussed.

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This article reports the use of a quinoxaline derivative as a photosensitizer for diaryliodonium salt photoinitiators. 2,3‐bis(3,4‐bis(decyloxy)phenyl)‐5,8‐bis(2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl)quinoxaline (DOPEQ), is a highly conjugated compound with strong absorption bands at wavelengths ranging from 300 to 550 nm and is shown to facilitate photoinitiated cationic polymerization of heterocyclic monomers such as oxiranes and oxetanes. The polymerizations are initiated at room temperature by using long wavelength UV light in the presence of diphenyliodonium hexafluorophosphate (Ph2I+PF 6−). The polymerizations are monitored by optical pyrometry (OP). It is also possible to initiate photopolymerizations with ambient solar irradiation in the presence of this photosensitizer dye. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 209–213, 2010

The photoinitiated cationic ring-opening polymerizations of 3,3-disubstituted oxetanes display a characteristic induction period followed by very rapid thermally accelerated polymerization. When a thin-film sample of such a monomer is irradiated for a time within the induction period and then allowed to stand at room temperature, no appreciable further conversion of monomer to polymer takes place. However, when heat is applied to a small portion of the films rapid polymerization takes place as a front, which propagates rapidly throughout the entire reaction mass. To characterize these frontal polymerizations, a new monitoring technique, employing optical pyrometry has been instituted. This method provides a simple, rapid means of following these polymerizations and quantitatively determining their frontal velocities.

Selective inhibition of the photoinitiated cationic ring‐opening polymerization of epoxides by dialkyl sulfides has provided dual systems that can be “activated” by UV irradiation and then subsequently be polymerized by the application of heat. It is proposed that dialkyl sulfides terminate the initial or growing polyether chains at an early stage to form stable trialkylsulfonium salts. These systems are dormant at room temperature but on thermolysis, the sulfonium salts are capable of reinitiating ring‐opening polymerization. These dual photo‐ and thermal cure systems have potential applications in adhesives, potting resins, and composites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6750–6764, 2006