Hydration characterization of hydrophobically modified polymers by dielectric measurements in the millimeter range.

Bound water molecules, the fraction of water molecules that are present in the hydration shells of polymers, lose their rotational mobility in the time scale of 10-50 ps, leading to additional ordering compared with unperturbed water. The amount of bound water per number of carbons in the nonpolar groups as measured by the method of waveguide dielectric resonance increased in the following order: hydrophobically modified chitosan < globular protein < hydrophobically modified polyacrylamide. The hydrophobic modification of acrylamide and chitosan polymers gave smaller variation in hydration than did both the coil-to-globule transition of poly(N-isopropylacrylamide) and the masking of nonpolar groups within the protein globule.