A high degree of conversion can be obtained for the solid phase polymerization ofp-vinylbenzamide when initiated thermally or by a post-irradiation technique. The Arrhenius activation energy for the radiation-induced polmerization is 20.3 kcal/mole while the value for the thermally initiated polymerization is 25.8 kcal/mole. EPR data of the polycrystalline sample shows a broad line spectrum which changes shape as the sample is heated from -196° (the irradiation temperature) to 105° (the polymerization temperature). The latter spectrum, is consistent with a radical of the type: