Differential thermal analysis of polyethylene obtained by radiation-induced polymerization

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Abstract
The fine structure of polyethylene prepared by radiation-induced polymerization of ethylene at room temperature is investigated by differential thermal analysis (DTA). This polyethylene is difficult to affect by annealing, but does show a tendency to reorganize during heating. A double endotherm on the DTA heating curve is observed in samples annealed at temperatures between 121 and 125°C. The structure represented by the endotherm at the lower temperature shows a strong tendency to reorganize, but that represented by the endotherm at the higher temperature does not. These double endotherms do not disappear from the heating curve of a sample oxidized by fuming nitric acid. It is proposed that polyethylene prepared by radiation-induced polymerization has a large crystalline fraction but small crystallite size and a small amorphous part; the polymer molecules, in both parts, may be strained with some hindrance to thermal movement, for example, by the existence of long-chain branches.