The hexagonal phase and melt of low-molecular-weight polyethylene

Phase diagrams of low-molecular-weight polyethylene (M = 1000, 2000, 6500, 16,000) and polyethylene (M ≈ 1,000) after fuming nitric acid treatment have been determined from 20 to 300°C up to pressures of about 10 kbar. The fractions with molecular weights 1000 and 2000 do not exhibit the hexagonal phase, but the others do. Effects of molecular weight and fuming nitric acid treatment on the phase diagrams are discussed in terms of the entropy of the melt.