Free radicals and new end groups resulting from chain scission: 2. Mechanical degradation of polyethylene

Abstract

The number of chain scissions accompanying mechanical degradation of polyethylene has been estimated from i.r. analysis of new end group concentrations. Polyethylene specimens fractured in tensile deformation and ground under liquid nitrogen were examined. The results are compared to the number of free radicals generated during mechanical degradation and measured by e.s.r. In comparison with previous results in the literature our results are lower by 1–2 orders of magnitude and in better agreement with estimates of the number of chain scissions from viscosity measurements. An ultra high molecular weight polyethylene was examined as a control specimen containing few end groups. The change in the number of vinyl groups resulting from grinding of this specimen were estimated to be at least an order of magnitude lower than that found for lower molecular weight polyethylenes. This finding suggests that large errors may be introduced into the determination of concentrations of end groups through subtraction of relatively intense absorption bands.