Thermal analysis of polyethylene prepared by γ-ray-induced polymerization in various solvents

Thermal properties of polyethylenes prepared by γ-ray-induced polymerization in various solvents were examined by differential scanning calorimetry. The solvents used were ethyl and n-butyl alcohols, tert-butyl alcohol containing 25 vol % of water, 2,2,4-trimethylpentane, 2,2,5-trimethylhexane, and cyclohexane. The dependence of the profiles of the heating curves for the produced polymers on polymerization temperature varies with the solvent type. This difference was discussed in terms of the degree of undercooling in various solvents during polymerization. In all solvent systems, the melting point and heat of fusion of the polymers decrease continuously with polymerization temperature. This decrease is caused by an increase in branches with reaction temperature. The melting point and heat of fusion are 100 to 1240C and 30 to 44 cal/g, respectively, and no superheating is observed. These facts suggest that folded chain crystals are commonly formed in these systems. 5 figures, 6 tables