Crystal ordering of α phase isotactic polypropylene

Structural ordering from the α1 to the α2 phase of isotactic polypropylene has been investigated. The DSC studies showed that reorganization or recrystallization occurred in the wide endothermic region. In the high-temperature X-ray experiment of the sample annealed at 135°C, the 2̄31 and 1̄61 reflections ascribed to the α2 phase began to increase from 160°C and to decrease above 172°C. The b-axis length and the angle β of the unit cell increased up to 155°C and decreased afterward. The latter decrease was well correlated with an increase in the α2 phase. The α2 fraction increased in the temperature region where the degree of overall crystallinity decreased. Reorganization or recrystallization into the α2 phase is thus considered to occur with the fusion of the α1 phase, and the growth of the α2 phase in the solid state seems to be difficult.