A novel, highly efficient, polymerizable sulfur-containing photoinitiator for free radical polymerization, benzophenone thio-acetic acid (BP-S-CH(2)-COOH) was synthesized, characterized, and compared to photoinitiator parameters of the benzophenone (BP) and benzophenone/(phenylthio) acetic acid couple. The photoinitiator possesses a greatly redshifted UV maximal absorption in comparison to BP. Laser flash photolysis studies suggest that photoinitiator radicals are generated by photocleavage of CAS bond. Photopolymerization of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate (TMPTA) demonstrated that one-component system BP-S-CH(2)-COOH is more efficient for polymerization than two-component system. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 2604-2608, 2011