H and ¹³C NMR Study on Local Dynamics of Poly(vinyl alcohol) in Aqueous Solutions

To study the local dynamics of poly(vinyl alcohol) (PVA) in aqueous solutions, several relevant physical models for NMR spin−lattice relaxation in polymers have been tested for 13 C spin−lattice relaxation times, T 1C, nuclear Overhauser enhancement factor, η, determined at 100.6 MHz, and effective 1 H spin−lattice relaxation times, T 1 eff, measured at 80, 300, and 400 MHz over a temperature range 5−87 °C. The fitting parameters of the models were obtained from the 13 C NMR relaxation data, and the their validity was then tested by fitting the parameters to the 1 H relaxation data. The autocorrelation function of Dejean de la Batie et al. ( Macromolecules 1988, 21, 2045) provided the best fit to the data of the PVA−water system studied, showing that the local motion of the polymer could be interpreted by conformational jumps of the backbone and by a fast, anisotropic reorientation movement of the C−H bonds. An AX 2 system was used successfully for the interpretation of the 1 H relaxation data, indicating that dipolar interactions between the hydroxyl group and the protons of the polymer backbone are negligible. An energy barrier associated with the segmental motion of PVA was also estimated (13.4 kJ/mol).