PERMEABILITY AND DIFFUSION OF GASES IN SEGMENTED POLYURETHANES - STRUCTURE PROPERTIES RELATIONS

To determine the structure-transport properties relations, we syntheti zed segmented polyether polyurethane with increasing rigidity. The for mulation is based on poly(tetramethylene oxide diol) (PTMO) of differe nt molecular weights, diphenylmethane diisocyanate (MDI), and butanedi ol (BD). The synthesis is effectuated in bulk. The phase-separation de gree of the soft segments is determined by DELTAC(p) measurements. The volume fractions and compositions of soft and hard phases are calcula ted with the help of T(g) values. The polyurethanes studied correspond to three types of morphology: soft-phase matrix, phase-inversion, and hard-phase matrix. The best phase segregation is observed in the phas e-inversion region. The time-lag method is used for determining the pe rmeability, diffusion, and solubility coefficients of gases (He, O2, N 2, CO2, Freon 11) in polyurethane at different temperatures. Activatio n energies of permeation and diffusion and dissolution energy are calc ulated. The most important factor in diffusion is the chain mobility i n the soft phase, which is represented with a good approximation by M( n)BAR, the molecular weight of soft segments. The phase-inversion regi on where the ratio surface/volume is minimum gave the lowest solubilit y coefficient. Freon 11 presents a particular interaction with polyure thane; polyurethane membranes are broken when immerged in Freon 11, ex cept the one which has the morphology of the inversion region. (C) 199 3 John Wiley & Sons, Inc.