Polymeric photoinitiators with pendant 2,6-dimethylbenzoyldiphenylphosphinoxide moieties were prepared by reacting the homopolymer of 4-acryloyloxy-2,6-dimethyl benzoic acid, and its copolymers with n-butyl acrylate with thionyl chloride followed by methoxydiphenylphosphine. These polymeric systems were characterized and their photoinitiation activity checked in the UV curing of a standard acrylic mixture, by irradiation both at 330 and over 380 nm, the latter conditions being applied to simulate a TiO2-pigmented coating formulation. The results were compared with those obtained by using the low molecular weight analog 2,4,6-trimethylbenzoyldiphenylphosphinox and previously prepared polymeric systems based on the benzoyldiphenylphosphinoxide moiety. The stability to light and to hydrolytic conditions of the polymeric photoinitiators with respect to the model compound was also tested. The results obtained are discussed and related to the structural requirements of these systems.