Dynamics of concentrated solutions of low molecular weight phenolics and poly(2-vinylpyridine): Role of intermolecular hydrogen bonding

Abstract

The molecular dynamics of solutions of poly(2-vinylpyridine) (P2VPy) and a series of low molecular weight phenols containing from one to six hydroxyl groups were investigated using broadband dielectric spectroscopy (DRS). Dynamic mechanical analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry, small-angle X-ray scattering and wide-angle X-ray diffraction were employed in a complementary role. Segmental relaxation times for the α processes of all solutions follow expectations from T gs derived from DSC experiments. For three of the model mixtures at 30 and 50 mol% [i.e., those containing bis (4-hydroxyphenyl) methane, 2,6 dihydroxynaphthalene, and 2,2-methylenebis[6-(2-hydroxy-5-methylbenzyl)- p-cresol] significantly broadened dielectric α relaxation time distributions were observed, indicating dynamic heterogeneity. On the other hand, 4-ethyphenol–P2VPy solutions display dynamic homogeneity. P2VPy with 10 mol% 2,3,3,4,4,5-hexahydroxybenzophenone behaved differently than all mixtures investigated in this study: it displayed a T g (and T α) significantly higher than that of the neat components, a small SAXS scattering peak, and an additional dielectric relaxation that we propose originates from Maxwell–Wagner–Sillars interfacial polarization. We propose that this behavior is a result of a phase separation of different types of hydrogen-bonded complexes, one rich in P2VPy and the other involving the type of 2,3,3,4,4,5-hexahydroxybenzophenone hydrogen-bonded structures found in the neat state. Intermolecular hydrogen bonding in all of the P2VPy–phenol mixtures suppresses, in some cases completely, the local P2VPy β relaxation by decreasing the mobility of the pyridine side groups.