Nowadays, migration stability is one of the key features for photoinitiators used in radiation curable formulations, especially when the material is in contact with food or the human body. Herein, the synthesis and characterization of statistical copolymers with covalently bound eosin and/or ethyl dimethylamino benzoate units by ring opening metathesis polymerization is presented. The prepared compounds were tested as macroinitiators for the photopolymerization of acrylates aiming at an initiator/coinitiator system which combines good polymerization activity with improved migration stability. An acrylate modified eosin derivative which is incorporated into the polymer network during the photopolymerization reaction and, therefore, less likely to leak from the polymer compound was used as reference. Photoinitiating activities of low and high molecular weight initiators and coinitiators were investigated by photo-DSC. Moreover, leakage studies and viability tests with osteoblast-like cells were performed to proof the suitability of this concept. The use of polymeric eosin in combination with a low molecular weight coinitiator was found to be a good compromise when aiming at a photoinitiating system with sound performance and improved migration stability. (C) 2008 Wiley Periodicals, Inc.