A study of interaction of water and model compound of poly(vinyl methyl ether)

Poly(vinyl methyl ether) (PVME) aqueous solution possessing specific bimodal phase diagram has been studied on the interaction of water and dimethyl ether (DME) as a model compound of PVME by using ab initio calculation (6-31+G*) and infrared spectroscopy. The most probable interaction configurations of DME with one to five water molecules were intensively searched in the present study. Among the configurations, we found two sorts of interactions appearing as specialties: the hydrogen bond (HB) and the quasi-hydrogen bond (QHB). We further studied the influence of the interactions on infrared band shifts for v(s)(CH3) and v(C-O) as a function of the number of water molecules in statistical average. Comparing with the experiments, the high concentration area and the low concentration area (with two different slopes) suffer from different interaction mechanisms. The former has HB and single-QHB, while the latter double-QHB and triple-QHB, besides the van der Waals and the electrostatic interaction. For understanding PVME hydration in details, we simulated the observation curve of the band shift versus the concentration by using adsorption procedures under three models. The result surprisingly indicates that water adsorption on PVME is not even distributed on each site of the monomer unit even though the polymer hydration is in the homogeneous phase.