Structural characteristics and gas permeation properties of polydimethylsiloxane/poly(propylene oxide) urethane/urea bi-soft segment membranes

Segmented polyurethane/urea membranes, containing two soft segments, poly(propylene oxide) and polydimethylsiloxane, were prepared by extending a polypropylene oxide-based tri-isocyanated prepolymer (PU) with polydimethylsiloxane bis(hydroxyalkyl) terminated (PDMS). PU/PDMS membranes were characterized by infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and by the gel content. It was concluded that the two soft segments are phase separated and the urethane/urea groups form small aggregates somewhere in these two phases. Gas permeation experiments led to the conclusions that the permeabilities of CO2, O2 and N2 increased with the increase of PDMS membrane content, while the permeability ratios, P(CO2)/P(N2) and P(O2)/P(N2) did not significantly changed. The membrane with highest PDMS content and highest permeabilities is characterized by a lower degree of cross-linking and by a lower contribution of hydrogen bonding between hard segments.