This is a first comprehensive study on the photoinitiating capability of a vinyl polyperoxide. Polymerization of methyl methacrylate photoinitiated by poly(styrene peroxide) (PSP) at 30 degrees C has been shown to follow the usual kinetic behaviour with respect to the initiator, monomer and light intensity for a PSP concentration of 0.0021-0.034 mol-equiv 1(-1). At higher concentrations of PSP (0.046-0.31 mol-equiv 1(-1)) although kinetic order with respect to the monomer and light intensity follows usual kinetics the order with respect to PSP was found to be very low (0.21), which has been attributed to the occurrence of primary radical termination which has been quantified in terms of the primary radical termination parameter (delta/Sigma). The initiator efficiency was found to be very low (0.06-0.07), it has been attributed to the competing unimolecular decomposition of alkoxy radicals with primary radical initiation. The presence of PSP segments in the poly(methyl methacrylate) backbone was confirmed by H-1 nuclear magnetic resonance.