Positron studies of the temperature-dependence of free volumes in Polydimethylsiloxane/poly(propylene oxide) urethane/urea membranes

Free-volume parameters in polyurethane/urea membranes have been studied by positron annihilation lifetime and Doppler broadening measurements. The bi-soft segment membranes were obtained by varying the ratio of the structural constituents, polypropylene oxide and polydimethylsiloxane (PU/PDMS), with PDMS content from 25 to 75 wt%. The free-volume holes determined by PALS are correlated with gas permeation features. The phase separation of the various soft and hard segments in the membranes is mirrored in both lifetime and Doppler results.