RAMAN-SPECTROSCOPIC STUDY OF WATER IN AQUEOUS POLYMER-SOLUTIONS

A Raman spectroscopic study of water structure in various aqueous polymer solutions was carried out. Comparing a relative intensity of the peak corresponding to the collective mode of O-H stretching of water molecules in polymer solutions to that of pure water, we evaluated the number of hydrogen bond defects introduced per a monomeric unit of polymer chain (N) in the hydrogen-bonded network structure of water molecules. The polymers used were poly(acrylamide) (PAAm), poly(acrylic acid) (PAA), poly(acrylic acid) sodium salt (NaPAA), poly(ethylene glycol) (PEG), dextran (DEX), poly(allylamine) hydrochloride (PAlA), and poly(N-vinylpyrrolidone) (PVP). The values of N are revealed to increase in the order PVP = PEG < DEX < PAAm = PAA < PAlA < NaPAA, and effects of chemical properties of monomer unit on N are discussed. It is suggested that the N value can be used as an index of relative hydrophilicities of water-soluble polymers. Increase of the N value with molecular weight of polymers examined suggests that more defects exist in compartmentalized water surrounded by pseudonetworks of entangled or hydrogen-bonded polymer chains than in bulk water.