Molecular Dynamics Study of Polymer−Water Interaction in Hydrogels. 1. Hydrogen-Bond Structure

Molecular dynamics simulations have been performed for hydrogel models of poly(vinyl alcohol) (PVA), poly(vinyl methyl ether) (PVME), and poly(N-isopropylacrylamide) (PNiPAM). The spatial distributions and stability of hydrogen bonds in the vicinity of polymer segments are analyzed to investigate the properties of water which is highly cooperative with the surrounding polymer chains. Water−water hydrogen bonds are enhanced around hydrophobic groups especially for PVME and PNiPAM by the hydrophobic hydration. Hydrogen bonds are also stabilized around hydrophilic groups for PVME and PNiPAM. The stabilization is accounted for by a severe constraint of the mutual orientation between water and polar group.