| Abstract: | Information on molecular conformations inside polyethylene lamellas following high pressure treatments is obtained by comparing observed and predicted length distributions of nitrated samples. Three types of conformation are inferred. The commonest is that molecules are folded with chain ends included in lamellas, except that ends are not turned in by less than ～600 Å from a surface. This situation accounts in detail for the previously observed agreement between the number fracture-surface distribution of crystal thicknesses and the gel permeation chromatography (GPC) weight distribution following nitration. The second conformation, found especially for samples of low polydispersity, is also of folded molecules but with chain ends excluded from lamellas. This particular case justifies rigorously the initial assumption of folding. Finally there are examples where the molecular length distribution is substantially lower than the crystal thickness distribution, implying that molecular length is not the upper limit of crystal thickness and that molecules can be fully extended inside lamellas. |
