Dynamic FT-IR analysis of the crystallization to the planar zigzag form for syndiotactic polypropylene

The polymorph and crystallization process for syndiotactic polypropylene (sPP) formed around at 0 degrees C after quenching from the melt has been dynamically investigated by infrared spectroscopy. The observation is carried out at constant temperatures between -5 and 15 degrees C after quenching into ice-water from the melt. Just after quenching into ice-water from the melt, the specimen is completely in the noncrystalline state with trans-rich sequences. When the samples are kept below 0 degrees C, only the planar zigzag form (form III) is crystallized in a few hours. Above 5 degrees C, in addition to the planar zigzag form, form I with the t(2)g(2) conformation is simultaneously formed. Just above the glass transition temperature (around -5 degrees C), the trans-rich chains are aggregated and developed to form form III. Above 5 degrees C, the trans-gauche transition is accelerated, and then the helical form with t(2)g(2) conformation is crystallized as form I. The total degree of crystallinity is not so high, because further crystallization is promoted in the noncrystalline region when the sample is left at room temperature after reaching the equilibrium state at each crystallization temperature.