Effect of polymerization temperature on the original morphology of polyethylene prepared by γ‐ray‐induced polymerization

Polyethylene was prepared by γ‐ray‐induced polymerization in the temperature range 0–180°C. The morphology and the physical properties of the polymer as polymerized were studied by electron microscopy, differential scanning calorimetry, and gel permeation chromatography. Aggregates of small lamellar crystals with irregularly growing faces were produced below 55°C. Aggregates of large spherical particles were formed above 60°C together with hemispherical particles which adhered to the substrate. A few lamellar crystals of triangular or amoeba‐like shapes were also found above 55°C. The polymers formed below 55°C showed a sharp single endothermic DSC peak and a bimodal molecular‐weight distribution, while the sample above 60°C had a double endotherm and a unimodal molecular‐weight distribution. These facts suggest that the mechanism of crystallization during polymerization below 55°C is different from that above 60°C. The melting point, however, decreased continuously with increasing polymerization temperature and was much lower than that of extended‐chain crystals. The results show that the polyethylene, as polymerized, is composed of folded‐chain crystals irrespective of the reaction temperature.