A study of structural order in various polyethylenes at elevated temperatures

Changes in several structural properties of an ethylene homopolymer have been measured and compared with those of ethylene copolymers with simple and complex branchings over a range of temperature from ambient to above the normal [melting temperature]. In the case of the first two polymeric types, a clear behavioural pattern was observed in which, with rising temperature, a small rotation of the back‐bone chains was followed by melting and recrystallization, the latter two processes occurring in the range from about 110°C to the melting temperature. In the upper temperature range ethyl branches were also rejected from the crystalline lattice. Around the melting temperature, a change from the orthorhombic to the hexagonal phase was suggested as a possibility. The thermal behaviours of the copolymers with the more complex branchings were found to be more complicated with melting and recrystallization occurring over various temperature ranges. No simple relationship appeared to exist between the numbers and shapes of the complex branchings and the structural changes produced in the copolymers by increasing temperature.