| Abstract: | Graft copolymerization of gaseous styrene was carried out onto polypropylene preirradiated in the presence of oxygen at ?78°C and at room temperature, respectively. The origin of the graft initiation activities of these polymers was investigated by means of electron spin resonance (ESR) of trapped radicals. More grafting was found for the polymers irradiated at ?78°C than for those irradiated at room temperature. The difference of grafting between polymers irradiated at ?78°C and those irradiated at room temperature was not explained by the total amounts of trapped radicals, and it was found that all radicals are not effective in the grafting reaction. ESR measurements showed that there exist two kinds of peroxy radicals, one has more effective ability of abstracting hydrogen atoms from the surrounding polymer chains to form carbon radicals, and another is less effective at the temperature of grafting reaction (40°C). Although the samples irradiated at ?78°C contain the both types of radicals, those irradiated at room temperature do not contain the former type of radicals. It was shown that the carbon radicals produced by such a hydrogen abstraction reaction are actually the effective centers in the grafting reaction of polymers irradiated in the presence of oxygen. |
