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

To determine the structure-transport properties relations, we synthetized segmented polyether polyurethane with increasing rigidity. The formulation is based on poly(tetramethylene oxide diol) (PTMO) of different molecular weights, diphenylmethane diisocyanate (MDI), and butanediol (BD). The synthesis is effectuated in bulk. The phase-separation degree of the soft segments is determined by DELTAC(p) measurements. The volume fractions and compositions of soft and hard phases are calculated 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 phase-inversion region. The time-lag method is used for determining the permeability, diffusion, and solubility coefficients of gases (He, O2, N2, CO2, Freon 11) in polyurethane at different temperatures. Activation energies of permeation and diffusion and dissolution energy are calculated. The most important factor in diffusion is the chain mobility in the soft phase, which is represented with a good approximation by M(n)BAR, the molecular weight of soft segments. The phase-inversion region where the ratio surface/volume is minimum gave the lowest solubility coefficient. Freon 11 presents a particular interaction with polyurethane; polyurethane membranes are broken when immerged in Freon 11, except the one which has the morphology of the inversion region. (C) 1993 John Wiley & Sons, Inc.