Solid-state C-13 NMR of microscopic order in transcrystalline films of isotactic poly(propylene)

The microscopic orientational order in a variety of transcrystalline films of isotactic poly(propylene) was investigated by means of two-dimensional s olid-state NMR. From the experimental results the orientation distribution function of the microcrystallites relative to the macroscopic growth direct ion was determined. The NMR measurements were performed at room temperature on samples that had been crystallized at conditions at which the morpholog y of spherulitic crystallization changes as a function of temperature or co mposition. For transcrystalline samples of isotactic poly(propylene) crysta llized in the alpha-modification a drastic breakdown of molecular order was observed at a crystallization temperature of 137 degrees C, with the absol ute degree of order depending on the molecular mass of the polymer. For sam ples crystallized in the beta-modification a small stepwise decrease of mol ecular order was observed at a crystallization temperature of 128 degrees C . A continuous decrease of the orientational order of the isotactic part wa s observed by blending isotactic poly(propylene) with atactic poly(propylen e).