A,polymeric photoinitiator (PTXP) containing in-chain thioxanthone (TX) and coinitiator amines was synthesized by step-growth polymerization, as well as low-molecular-weight model compounds. Photopolymerizations of methyl methacrylate (MMA) initiated by these photoinitiator systems were studied. Compared with corresponding low-molecular-weight model compounds, PTXP has a similar UV-vis spectrum with a red-shifted maximum absorption, and weaker fluorescence emission, and can photoinitiate the polymerization of MMA more effectively.