Trapping regions for allyl radicals in irradiated polyethylene

Abstract

Report has examined the anisotropy of ESR spectra using a single-crystal mat of polyethylene. Sample preparation is described. The mat is irradiated at 77/sup 0/K followed by annealing at room temperature. The molecular chains of polyethylene are aligned more regularly in the crystal core than in the crystal surface. It is expected that the spectrum caused by allyl radicals in the crystal core would be sharper than that from the crystal surfaces. When the sample is further annealed by 60/sup 0/C, molecular motion causes the decay of allyl radicals in both regions. Thus the line shape remains unchanged during annealing at 60/sup 0/C. However, when the sample is stored in vacuo for four months at room temperature, molecular motion occurs in the crystal surfaces only. Therefore, allyl radicals trapped at the crystal surface decay. Only allyl radicals in the crystal core survive, and the spectrum becomes sharper. Allyl radicals found in the present work in both the crystal core and the crystal surfaces are presumably produced by the reaction of alkyl radicals and double bonds distributed in both the crystal core and crystal surfaces.