Structure and molecular mobility of nascent isotactic polypropylene powders

The detailed structure and molecular mobility of nascent isotactic polypropylene (iPP) powder was investigated using differential scanning calorimetry, transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR). The crystallinity of the nascent iPP powder is approximately 33%, which is much lower than that of melt-quenched or isothermally crystallized iPP. Peaks from the variable temperature-cross-polarization and magic-angle spinning spectra at high temperature for the noncrystalline component of nascent powder (POW) were enhanced over those of the melt-crystallized samples. Pulse NMR experiments indicated that the mobility of the rigid component of the POW was easily activated with temperature. No lamellar structures were observed in the TEMs of the POW. The annealing treatment of the POW induced the development of a lamellar structure and temperature independence in the rigid component mobility. From these results, one can conclude that the crystalline size of the POW is extremely small and that the intermediate component is easily affected by the surrounded noncrystalline component.