The microscopic orientational order in a variety of transcrystalline films of isotactic poly(propylene) was investigated by means of two‐dimensional solid‐state NMR. From the experimental results the orientation distribution function of the microcrystallites relative to the macroscopic growth direction was determined. The NMR measurements were performed at room temperature on samples that had been crystallized at conditions at which the morphology of spherulitic crystallization changes as a function of temperature or composition. For transcrystalline samples of isotactic poly(propylene) crystallized in the α‐modification a drastic breakdown of molecular order was observed at a crystallization temperature of 137°C, with the absolute degree of order depending on the molecular mass of the polymer. For samples crystallized in the β‐modification a small stepwise decrease of molecular order was observed at a crystallization temperature of 128°C. A continuous decrease of the orientational order of the isotactic part was observed by blending isotactic poly(propylene) with atactic poly(propylene).

SUMMARY: The microscopic orientational order in a variety of transcrystalline films of isotactic poly(propylene) was investigated by means of two-dimensional solid-state NMR. From the experimental results the orientation distribution function of the microcrystallites relative to the macroscopic growth direction was determined. The NMR measurements were performed at room temperature on samples that had been crystallized at conditions at which the morphology of spherulitic crystallization changes as a function of temperature or composition. For transcrystalline samples of isotactic poly(propylene) crystallized in the a-modification a drastic breakdown of molecular order was observed at a crystallization temperature of 137 8C, with the absolute degree of order depending on the molecular mass of the polymer. For samples crystallized in the bmodification a small stepwise decrease of molecular order was observed at a crystallization temperature of 128 8C. A continuous decrease of the orientational order of the isotactic part was observed by blending isotactic poly(propylene) with atactic poly(propylene).