THE EFFECTS OF SOFT SEGMENTS ON THE PHYSICAL-PROPERTIES AND WATER-VAPOR PERMEABILITY OF H12MDI-PU CAST FILMS

This research was based on the study of the effects of H12MDI-1, 4BD P U soft segments on the physical properties and water vapor permeabilit y of films cast from solvent evaporation or wet coagulation method. Th e soft segments studied included polyether, polyester, and polycaprola ctone polydiols. The NCO / OH mol ratios of prepolymer were prepared b y 2, 3, 4, 5, and 8, respectively. The chain lengths of the soft segme nts used were: PTMG of molecular weights 650, 1000, 2000, and 2900; PB A of 1000, 2000, and 3000. The results revealed that the polyether-bas ed PU cast films had lower T(g)s than the polyester-based PU films. In general, the polyether-based PU films shows the characters of higher water vapor permeability, lower breaking elongation, and higher breaki ng strength. Films with higher molecular weight soft segments in the p olymer chains exhibited lower T(g)s, lower breaking strength, higher b reaking elongation, and higher water vapor permeability. As the hard s egment contents were increased, the films exhibited higher T(g)s. Film s with higher hard-segment ratios had the highest breaking strength bu t the water vapor permeability, on the other hand, became lower. Films cast from the solvent evaporation method had higher breaking strength and higher breaking elongation but lower water vapor permeability tha n films cast from the wet coagulation method. (C) 1994 John Wiley & So ns, Inc.