New sulfur-centered radicals as photopolymerization initiating species

New thiols and disulfides are proposed as radical polymerization photoinitiators or coinitiators. The drawback of the bad smell is strongly limited for the proposed compounds. Among the systems investigated, the disulfides photosensitized by isopropylthioxanthone and the tetrazole-derived thiols in the presence of benzophenone, camphorquinone, or isopropylthioxanthone have been found to be highly reactive and, in some cases, even better than a reference type I or type II photoinitiator. These thiols can also be incorporated into a combination of chloro-hexaaryl bisimidazole (ClHABI) and a photosensitizer, such as a coumarin or ketocoumarin. Interestingly, a photosensitizer/Cl-HABl/tetrazol( thiol derivative system exhibits a higher reactivity than a commonly used photosensitizer/Cl-HABPN-phenylglycine system. (C) 2007 Wiley Periodicals, Inc.