Structural studies of bulk polyethylene using gel permeation chromatography

This paper describes the analysis by gel permeation chromatography (GPC) of the degradation products from a variety of samples of bulk polyethylene degraded with nitric acid. For all samples, except highly oriented linear polyethylene, the GPC traces of the degraded material showed discrete peaks. As in the case of degraded single crystals, it is proposed that these correspond to integral numbers of crystalline traverses by the molecular chains. From a quantitative analysis of the peak intensities, molecular weights, and widths, it has been concluded that the majority of the molecules traversing the crystalline regions fold back into the same crystal, with some tight folding. The fold surface is disordered, with either adjacently reentrant folds at different heights or a distribution in the length of nonadjacently reentrant folds. The results for branched polyethylene suggest that cold drawing does not drastically alter the crystalline lamellae. It was found that, on the contrary, highly oriented linear polyethylene did not show discrete peaks after degradation. This was interpreted in terms of large fluctuations in crystal thickness and suggests that, for liner pholyethylene, the drawing mechanism is in certain respectsconsiderably more complex then for branched polymer.