Novel water-borne macrophotoinitiator containing thioxanthone (TX) end group was successfully synthesized by using Die Is Alder (DA) [4 + 2] click chemistry strategy. For this purpose, thioxanthone-anthracene (TX-A) and maleimide end-functionalized poly(ethylene glycol) (PEG-MI) were reacted in toluene at reflux temperature for 48 h. The final polymer (PEG-TX) and the intermediates were characterized in detail by spectral analysis. PEG-TX possesses absorption characteristics similar to the parent TX. The one-component photoinitiating nature of the photointiator was demonstrated by photopolymeization of several hydrophilic vinyl monomers, such as acrylic acid, acrylamide, 2-hydroxyethyl acrylate, and 1-vinyl-2-pyrrolidone. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2109-2114, 2010