Free radicals in poly(diethylene glycol bis(allyl carbonate)), commercially known as CR-39 resin, cured by radical mechanism with various amounts of diisopropyl peroxydicarbonate were studied by electron paramagnetic resonance (e.p.r.) spectroscopy. It was found that the radicals can survive in the unirradiated polymer network for at least 6 months after polymerization. The dependence of the amplitude of the e.p.r. signal on the dose for CR-39 polymer irradiated by Co-60 gamma rays was found to show a maximum which increased in magnitude and shifted in position to higher doses for samples cured with lower initiator concentration. This behaviour is explained by examining the role of residual allyl groups present in the cured polymer and the scission of the network at the carbonate group. It was found that the refractive index increase observed in the irradiated polymer cannot be directly attributed to the presence of free radicals in the network.