Cross polarization between 1H and 13C nuclei in isotactic poly(propylene). Effects of crystallinity and crystallographic form

Abstract

Abstract13C spectra of monoclinic (α), hexagonal (β) and smectic isotactic poly(propylene) (PP) with different degrees of crystallinity were obtained by the cross polarization/magic angle spinning (CP/MAS) method. In order to estimate the effects of cross polarization, an accurately weighed poly(oxymethylene) (POM) rod was packed into a rotor together with the sample and the ratio of the peak area of PP to that of POM was measured precisely. Taking the crystallinity into consideration, the cross polarization seems to occur rather effectively in smectic PP. This result indicates that there are constrained chains in the amorphous regions of the smectic PP, which contribute effectively to the cross polarization. The ratio of the peak are of α‐and β‐PP is nearly equal, indicating that the cross polarization occurs mainly in the crystalline regions in both samples and not in the amorphous regions. The 1 H spin‐lattice relaxation time in the rotating frame decreases with decreasing crystallinity, indicating the presence of imperfect crystallites in the smectic PP.