Permeability of hydrated poly(vinyl alcohol): Effect of relaxation behaviors and hydrogen bonds in supramolecular structure

The particular permeability of hydrated poly(vinyl alcohol) (PVA) was investigated from the point of polymeric relaxation behavior, and the more essential effect of hydrogen bonds in supramolecular structure was further analyzed as well. The permeability measurement showed that various hydrated PVA samples all had lower permeability to non-polar solvents, and the permeability was affected by relaxation state, which can be controlled by water content. Dynamic mechanical analysis measurements indicated that, in PVA with lower water content the relaxation motion benefiting permeation almost became frozen in glassy amorphous region, due to high activation energy of conformation transition, which then induced the slower permeation to occur. Solid-state H-1 and C-13 NMR spectra of hydrated PVA samples allowed to analyze the effect of hydrogen bonds. It was found that in PVA with lower water content conformation transition in amorphous region was restricted by more intermolecular and intramolecular hydrogen bonds, especially by the former. Also relatively added crystalline regions, which can affect permeability as physical cross-linking points, were mainly constructed by chain segments with no intramolecular hydrogen bonds. Above results suggest that intermolecular and intramolecular hydrogen bonds via conformation transition control relaxation behavior. Consequently, the relaxation behavior affects the permeability of hydrated PVA, in which water play an important role.