CROSS-POLARIZATION BETWEEN H-1 AND C-13 NUCLEI IN ISOTACTIC POLY(PROPYLENE) - EFFECTS OF CRYSTALLINITY AND CRYSTALLOGRAPHIC FORM

C-13 spectra of monoclinic (alpha), hexagonal (beta) and smectic isota ctic poly(propylene) (PP) with different degrees of crystallinity were obtained by the cross polarization/magic angle spinning (CP/MAS) meth od. In order to estimate the effects of cross polarization, an accurat ely weighed poly(oxymethylene) (POM) rod was packed into a rotor toget her with the sample and the ratio of the peak area of PP to that of PO M was measured precisely. Taking the crystallinity into consideration, the cross polarization seems to occur rather effectively in smectic P P. This result indicates that there are constrained chains in the amor phous regions of the smectic PP which contribute effectively to the cr oss polarization. The ratio of the peak area of alpha- and beta-PP is nearly equal, indicating that the cross polarization occurs mainly in the crystalline regions in both samples and not in the amorphous regio ns. The H-1 spin-lattice relaxation time in the rotating frame decreas es with decreasing crystallinity, indicating the presence of imperfect crystallites in the smectic PP.