Glass temperature and crystal modification of linear polymethylene

The preparation of high molecular weight linear polymethylene is described at low temperatures. The onset of a polymorphic transformation (triclinic to orthorhombic) is observed on warming this low crystallinity (∼50%) polymer to about −25°C. Relative rates of transformation above this temperature are also given. No significant increase in crystallinity occurs on warming the polymer up to room temperature, where some triclinic phase still persists. Annealing polymethylene at 100°C. leaves only the orthorhombic material which is approximately 80% crystalline. A glass transition temperature around −30°C., is reported for the low crystallinity polymer.