Characteristics of Water in Copoly(methyl methacrylate–N-vinylpyrrolidone) Membranes

Abstract

The characteristics of water in methyl methacrylate–N-vinylpyrrolidone (MMA/NVP) copolymer membranes were studied. The sorption and permeation behavior and differential scanning calorimetric behavior of MMA/NVP copolymer-water systems contained two types of water in the copolymer membranes at relative vapor pressures up to ca. 0.9: water directly bound to polar NVP residues at low relative vapor pressures, i.e., the “tightly bound” water, and water associated in the vicinity of hydrophobic MMA residues forming multimolecular clusters at higher relative vapor pressures, i.e., “hydrophobic hydration” water. The latter was characterized by a rigid structure resulting in an increase in the shear modulus of the copolymer membrane at relative vapor pressure higher than 0.5. It is concluded that the cluster size or clustering tendency in MMA/NVP membranes, i.e., the amount of hydrophobic hydration water in the copolymer, is enhanced by the presence of the proper amount of NVP residues in the copolymers via enhancement of water uptake by the membranes.