Polysiloxane dizwitterionomers. III. Water sorption

The interaction of water with the various polysiloxane dizwitterionomers and the model compound 4,7‐diazaheptyl‐4,7‐di(3‐propane‐sulfonate) heptamethyltrisiloxane was studied. The model compound is soluble in water but the polymers swell inhomogeneously when soaked in water. The initial sorption kinetics of these zwitterionomers indicate similar mechanisms of water uptake which is independent of ion concentration (D = 4.7 × 10−7 cm2/sec). The sorption isotherms reveal the high sorptive capacity of these ionomers. Furthermore, the linear relationship between the water uptake and the concentration of ions over a large relative humidity range (0.22 ≤ P/P0 ≤ 0.93) allowed us to treat each phase separately. It has been found that most of the absorbed water molecules are immobilized in the ionic domains. Their concentration in this phase is nearly identical to the sorptive capacity of the model compound.