ELECTRON-SPIN RESONANCE STUDIES ON RADIATION GRAFT COPOLYMERIZATION .1. GRAFTING INITIATED BY ALKYL RADICALS TRAPPED IN IRRADIATED POLYETHYLENE

The behavior of trapped radicals in PE which is irradiated in air at room temperature, under grafting of methyl methacrylate or butadiene has been studied by ESR. Part of the alkyl radicals are converted to allyl radicals by reaction with double bonds and the others disappear by recombination under vacuum. The active species of grafting are alkyl radicals when the vapor pressure of monomers is relatively high, while at low pressure allyl radicals also play a role as well as alkyl radicals. In the grafting at 20C, the grafting yields depend mainly on the decay rate of alkyl radicals which come out of the crystalline regions of PE. The decay rate of alkyl radicals and the rate of grafting at the initial stage increase with decreasing crystallite size of PE.