Polymeric photoinitiators bearing side-chain benzoyldiphenylphosphinoxide moieties have been prepared by reacting poly (4-vinylbenzoic acid) or 4-vinylbenzoic acid/methyl methacrylate copolymers with thionyl chloride followed by methoxydiphenylphosphine. The activity of the above polymeric systems has been checked in the UV curing of the acrylic clear-coating formulation HDDA/BA and compared with that of the low molecular weight model 4-isopropylbenzoyldiphenylphosphinoxide. The stability to light and to hydrolytic conditions of the polymeric photoinitiators with respect to the model has also been tested. The results obtained are discussed in terms of composition and structural features of these systems.