CP/MAS 13C NMR analyses of hydrogen bonding and the chain conformation in the crystalline and noncrystalline regions for poly(vinyl alcohol) films

Abstract

The chain conformation and hydrogen bonding in the crystalline and noncrystalline regions have been characterized for atactic poly(vinyl alcohol) (PVA) films prepared under different conditions by CP/MAS 13C NMR analyses developed recently. The CH resonance lines of the crystalline and noncrystalline components split in different ways, depending significantly on casting solvents and annealing. These lines are found to be successfully resolved into 3–7 constituent lines by the least-squares curve fitting. In this analysis, nine lines with different chemical shifts are prepared as elementary lines for the curve fitting by assuming the upfield shifts due to the γ-gauche effect and the downfield shifts due to the formation of the intramolecular hydrogen bonds. The integrated intensities of the constituent lines thus obtained are also interpreted in terms of statistical calculations, assuming the random distribution of the trans and gauche conformations along PVA chains and the statistical distribution of the intramolecular and intermolecular hydrogen bonds between appropriate adjacent OH groups. On the basis of probabilities ft and fa for the trans conformation and the intramolecular hydrogen bond obtained through these analyses, the effects of casting solvents and annealing are discussed for both crystalline and noncrystalline components. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1–9, 2000