Mixed‐crystal infrared studies of chain folding in polyethylene single crystals: Effect of crystallization temperature

Abstract

AbstractMixed crystals of polyethylene (PEH) and various‐molecular‐weight perdeuterated polyethylenes (PEDs) have been prepared at 80°C and their infrared spectra compared with those of samples grown at 55°C. Concentrations of 80 PEH/1 PED were required in the former case to eliminate segregation effects whereas 40 PEH/1 PED sufficed in the latter. Resolution of the observed CD2 bend contour was most reasonably achieved with a crystalline singlet and two crystalline doublets, in addition to a contribution (ca. 15%) from the noncrystalline component. The singlet, comprising about 20% of the crystalline area, contains contributions from both isolated stems and (200) adjacent reentry folding. Random reentry folding is therefore not a predominant mode of chain organization in polyethylene single crystals. The inner of the two doublets arises from adjacent reentry folding along single (110) planes, and is present for all PED molecular weights. For low‐molecular‐weight fractions this splitting is consistent with the number of stems of one PED molecule allowed in the crystal. The outer doublet arises from multiple (110) plane adjacency, and is present for intermediate and high molecular weights. An analysis of both doublets suggests that at high molecular weights a single molecule can crystallize with noncontiguous regions of adjacent stem domains.