Studies on different types of hydrogen bonds in poly(vinyl alcohol) films by H-1 CRAMPS and solid-state two-dimensional H-1-C-13 heteronuclear correlation analyses

Different hydrogen-bonded states of OH groups in poly(vinyl alcohol) (PVA) films with different tacticities have been characterized by H-1 combined ro tation and multiple pulse spectroscopy (CRAMPS), solid-state C-13 NMR and t wo-dimensional (2D) H-1-C-13 heteronuclear correlation (HETCOR) analyses. T he newly developed line shape analysis for the H-1 CRAMPS spectra reveals t he existence of three types of OH groups in different hydrogen-bonded state s below T-g intramolecular and intermolecular hydrogen bonded OH (OHintra, OHinter) groups and OH (OHf) groups free from hydrogen banding. Above T-g a nother resonance line which can be assigned Co highly mobile OH (OHr) group s in the noncrystalline region appears as a result of the reduction in mole fractions of the OHintra and OHinter groups, in good accord with the confi rmation of the rubbery component by the solid-state C-13 NMR line shape ana lysis. In contrast, the mole fraction of the OHf groups stays constant at - 60-160 degreesC, indicating that these OH groups are preferentially distrib uted in the crystalline region. In order to examine the correlations of the results obtained by H-1 CRAMPS and solid-state C-13 NMR analyses, 2D H-1-C -13 HETCOR spectra have been also measured at room temperature for atactic and main-chain deuterated atactic PVA films. As a result, evident correlati ons between H-1 OH and C-13 CH constituent lines are observed at a cross po larization (CP) contact time of 120 mus, indicating the validity of the ass ignments for the H-1 OH and C-13 CH resonance lines made previously as well as in this work.