Cross polarization/magic angle spinning 13C n.m.r. study of solid structure and hydrogen bonding of poly(vinyl alcohol) films with different tacticities

Abstract

Cross polarization/magic angle spinning (CP/MAS) 13C n.m.r. measurements have been performed at room temperature for poly(vinyl alcohol) (PVA) films with different tacticities to obtain information about the structure and hydrogen bonding in the crystalline and non-crystalline regions. 13C spin-lattice relaxation analyses have revealed that three components exist for each sample, with different spin-lattice relaxation times T 1C, which are assignable to the crystalline, less disordered non-crystalline and amorphous components. Using such differences in T 1C, we separately recorded the spectra of the crystalline and non-crystalline components, and then analysed the triplets of the CH resonance lines appearing in both spectra in terms of three Gaussians which should be ascribed to CH carbons associated with two, one and no intramolecular hydrogen bond(s) in the mm, mr and rr sequences. As a result, it has been found that the relative intensities of the triplets are not in accord with the contents of the triad sequences, suggesting the formation of intramolecular and intermolecular hydrogen bonds in the meso sequences at almost equal probability. The effects of water on hydrogen bonding have also been examined for the almost atactic PVA sample.