Effect of annealing on the structure of quenched isotactic polypropylene

Smectic isotactic polypropylene films were annealed at different temperatures for different times. Density, wide-angle x-ray scattering (WAXS), differential scanning calorimetry, and the transport properties of methylene chloride vapor were used to follow the transformation of the smectic phase into the monoclinic phase. The results of WAXS diffractograms indicate different saturation levels of crystallization with the maximum order attained progressively more quickly at higher temperatures. Density measurements, however, show that, after a first saturation level, a further increase of this parameter occurs after long annealing times; and this second step is lower, the higher the temperature. Sorption and diffusion, analyzed to investigate the amorphous component, show that annealing the smectic phase at 50°C results in a decrease of amorphous fraction without transformation of the smectic phase. The transition from smectic to monoclinic phase occurs at temperatures higher than 60°C. During the annealing at 80°C there is first a decrease of amorphous fraction corresponding to the first saturation level of the density, and then a further decrease of amorphouse phase corresponding to the final increase of density after 24 hr of annealing.