WATER EFFECTS IN POLYURETHANE BLOCK-COPOLYMERS

Equilibrium and dynamic sorption isotherm measurements, differential s canning calorimetry (DSC) measurements, and, mainly, dielectric relaxa tion spectroscopy (DRS) measurements by means of the thermally stimula ted depolarization currents (TSDC) method were used to investigate the hydration properties of linear segmented polyurethane copolymers. Thr ee types of samples were investigated with various fractions of hard a nd soft block segments. They were based on polyethylene adipate (PEA), 4,4'-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO). At 20 degrees C the water content h of the samples at various values of r elative humidity rh increases in proportion to the weight fraction of soft block segments phase. At saturation (rh = 100%) the ratio of sorb ed water molecules to polar carbonyl polyester groups is 0.13. At satu ration at 20 degrees C there is no fraction of freezable water. The gl ass transition temperature, T-g, measured by DSC and by TSDC, shifts t o lower temperature with increasing h by about 8-10 K at saturation at 20 degrees C. A dielectric relaxation mechanism related to interfacia l polarization in the phase-separated morphology is also plasticized b y water in a way similar to that observed for the main (alpha) relaxat ion. (C) 1996 John Wiley & Sons, Inc.