INTERACTION OF WATER WITH POLYURETHANES CONTAINING HYDROPHILIC BLOCK-COPOLYMER SOFT SEGMENTS

The saturation water uptake and the nonfreezing bound water, determined as a function of temperature in a polyurethane (I) containing the pure polyethylene oxide soft segment are only weakly dependent on temperature from 288 to 333 K. In polyurethanes (II) containing block copolymer polyethylene oxide/polypropylene oxide soft segments with various ratios of the hydrophilic and hydrophobic segments, there is a strong decrease with temperature and a steep drop above 303K. This behavior is interpreted in terms of the temperature dependent phase compatibility of the polyethylene oxide and polypropylene oxide segments of II. The depression of T-g appears to be governed solely by the nonfreezing bound water and is much larger in sample I than in samples of set II. The more limited effect in the samples of set II is attributed to restricted mobility arising from coupling of the short terminal polyethylene oxide segments to rigid hard segment units. The simple Fox mixing equation was judged to provide a more reliable fit to the data from sample I than the available free volume approach, which required unrealistically high values of the thermal expansion coefficient for water.