Interactions of Water with Hydrophilic Polyether Polyurethanes

Two series of polyurethanes based on MDI, butanediol and several block copolymer polyethers with varying proportions of poly(ethylene-oxide) PEO and poly(propyleneoxide) PPO have been synthesized. In series 1 the ratio of PEO to PPO is varied at fixed hard segment concentration. In series 2 the hard segment concentration is varied at a feixed 50/50 ratio of PEO to PPO. All of these materials are tough film forming elastomers of approximately the same molecular weight. At constant hard block composition and decreasing amounts of PEO in series 1 polymers, water uptake decreases from approximately 60% in the polymer with pure PEO to approximately 2% for the polymer with pure PPO at 30 degrees C. These amounts of uptake increase as the temperature is decreased. The decrease in water uptake is most marked under immersion conditions or when the sorption isotherm is measured at saturation conditions. However, the trends are the same for both situations. When the hard block composition is varied a similar decrease in water uptake with increase in hard segment composition is seen although the degree of change is not so marked. The sorption isotherms are surprisingly simple concave upward curves which rise very steeply at saturation. Analysis of the data on the basis of moles of water per EO unit provides a picture of the influence of compositional variations on the course of the sorption isotherms and shows that saturation water concentrations are not related in a simple matter to PEO concentration.