A Nuclear Magnetic Resonance Study of the Microstructure of Poly (Vinyl Alcohol)

Abstract

The microstructures of Poly (vinyl alcohol) (PVA) and Poly (vinyl alcohol-acetate) copolymers were studied by ID and 2D NMR techniques. The assignments of all CH proton resonances of PVA relating to 1,2-1,4-glycol and terminal 1,2-glycol linkages were made. The concentrations of 1,2-glycol linkages located at inner and terminal positions of a polymer chain were determined to be ca. 1.61 and 0.06mol%. End-groups of PVA, which were arising from chain-transfers to solvent, monomer and initiator or from the termination of hydrogen abstraction, could be readily determined by using α,α,β— trideuterated PVA. The short chain branches consisted of two monomer units (butyl branches) resulting from intramolecular chain-transfer to methine carbons have been also identified. Other structural irregularities, polyene structures which arising from heat treatment, were analyzed by 2D COSY NMR spectroscopy. The sequence distributions of (PVA-Ac) copolymers were studied by 13C-NMR spectroscopy. In the saponification reactions of poly(vinyl acetate), the presence of an irregular bonding could make the rate of saponification more slowly. The relationship between the sequence distribution and a saponification distribution was also discussed and the saponification distribution of (PVA-Ac) copolymers could be evaluated from a block character η which is obtained by 13C-NMR spectroscopy. Combination of 1D and 2D NMR technique provides a powerful method for gaining information on the microstructure of these polymers.