Polymeric photoinitiators bearing benzophenone triphenylbutyl berate salt as the side chain have been synthesized and characterized and their activity measured in the photoinitiated polymerization of a bifunctional monomer, diethylene glycol diacrylate. The results were compared with a low-molecular weight model compound. At lower concentrations of the requisite benzophenone moiety, the highest activity was observed for the model compound, while at higher concentrations the homopolymer was superior. For both cases, the lowest photoinitiation activity was observed with significant induction period for copolymers with methyl methacrylate when compared to the homopolymer. The results are discussed in light of the microenvironment of the initiator fragments in the polymeric systems.