One component thioxanthone based Type II photoinitiators

Thioxanthone (TX) and their derivatives are bimolecular Type II photoinitiators for free radical polymerization. Photoinitiation by these compounds is based on the reaction of their triplet excited states with a hydrogen donor thereby producing an initiating radical. On the other hand, they suffer from diffusion controlled limitation of reactivity and from deactivation by back electron transfer. In this chapter, we present a very efficient concept to raise the photoinitiator activity by covalent binding of hydrogen donating sites to the TX moiety. Mechanistic details concerning photoinitiated free radical polymerization using two classes of such one-component systems, namely thioxanthone-thiol (TX-SX) and thioxanthone Correspondence/Reprint request: Dr. Yusuf Yagci, Department of Chemistry, Istanbul Technical University, Maslak, Istanbul 34469, Turkey. E-mail: [email protected] Nergis Arsu et al. 18 thio-acetic acid (TX-S-CH2-COOH) are described. The contributions of intraand intermolecular electron transfer processes followed by hydrogen abstraction are discussed. The use of several one-component polymeric photoinitiators is also described. These photoinitiators have additional advantages of overcoming the problems in curing applications associated with low odor and toxicity, and good storage stability.