Graft copolymerization by a preirradiation method

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Abstract
Free radicals as well as peroxides are formed when irradiation of polyethylene is accomplished with the use of cobalt‐60 or a Van de Graaff electron accelerator, as radiation sources, even in the presence of air. The free radicals are able to induce graft copolymerization under low temperatures, in which peroxide grafting cannot occur. When the irradiated polymer is stored in air, the trapped free radicals disappear monomolecularly, probably combining with oxygen. The activation energy for this reaction is 20 kcal./mole. In graft copolymerization by free radicals, the percent grafting is proportional to the square root of the free radical content, and the higher the grafting temperature, the faster the initial rate of graft copolymerization. There occurs, however, a saturation phenomenon of the per cent grafting with a grafting time, especially in high temperatures, and the higher the grafting temperature, the smaller the saturation value. It is believed that the kinetic theory of vinyl polymerization in a homogeneous system is applicable for graft reaction in spite of its apparent heterogeneous character.