Physical properties and structure of the polyethylene produced by γ‐radiation polymerization

摘要

AbstractPolyethylene produced by γ‐radiation had short‐chain branching to some extent and a small amount of vinylidene unsaturation. An OH group was found in polyethylene produced in the presence of methanol. The properties and structure of the polymer were found to vary widely with changes in the reaction condition, such as ethylene pressure, reaction temperature, time, and dose rate. Polymer density, an important property, varied from 0.88 to 0.96 g./cc. and crystallinity from 40 to 80, depending on the reaction conditions. Polyethylene polymerized at room temperature at a pressure of 300–400 kg./cm.2was shown to have an extremely high molecular weight (up to 300,000) and low methyl content (below 0.5CH3/100C). Density depends solely on the crystallinity of the polymer, which was found to be determined by the degree of short‐chain branching and molecular weight. Quantitative relationships between them were obtained. The use of methanol as a solvent was found to have no effect on short‐chain branching but have a marked effect on molecular weight; hence, high‐density polyethylene could be obtained with the use of methanol solvent. Polyethylenes with a high molecular weight (above 100,000) had a higher melting point than high‐pressure polyethylene. The quantitative correlation between molecular weight and melt index was also determined and found to be similar to that of Sperati. Some mechanical properties were