Water sorption in poly(zwitterions) of the ammonioalkoxydicyanoethenolate type

Abstract

AbstractWater sorption by amorphous (meth)acrylic poly(zwitterions)‐bearing quaternary ammonioalkoxydicyanoethenolate side groups , dipole moment μ(D) = 25.9 and 30.8 for p = 2 and 3, respectively was studied at 23°C over a broad range of water activity a (0.14–0.98). Water diffusion is nearly Fickian (Ds = 5.9 10−7 cm2.s−1 for a = 0.63) and the sorption isotherms may be quantitatively analyzed according to the Guggenheim‐Anderson‐De Boer equation for a multilayer process characterized by a number of site‐bound water molecules per monomeric unit, nm ⋑ 0.7. The Flory χ interaction parameter is a strongly increasing function of the water content in the glassy hydrated systems and it always remains higher than 0.75. Clustering of water molecules (Zimm‐Lundberg theory) is never observed. Differential scanning calorimetry allows to quantify nonfreezable bound water (type I) of strong plasticization efficiency, n(I) = 2.8 mol. of water per monomeric unit, and it points out the quasisimultaneous emergence of low amounts of freezable bound water (type II) crystallizing at −40°C and melting at −1°C and of bulkfree water (type III, n(II)/n(III) ⋑ 0.1). All these typical features distinguish these rather hydrophobic poly(zwitterions) from their hydrophilic homologues of the quaternary ammoniopropanesulfonate type . © 1995 John Wiley & Sons, Inc.