Novel cross-linked urethane/urea polymers with two soft segments, polypropylene oxide and polybutadiene, were prepared by extending polypropylene oxide-based isocyanate-terminated triol prepolymer with polybutadiene diol. Infra-red spectra indicated that with increasing polybutadiene content in the polymers, the hydrogen bonding of urethane/urea groups among hard segments became weaker. This was interpreted as an improvement of freedom of urethane/urea groups and their mixing with polypropylene oxide. The dynamic mechanical thermal analysis indicated that the two soft segments were highly dispersed, and could lead to a molecularly mixed phase. The swelling experiments with ethanol aqueous solutions indicated a preferential sorption of ethanol and a decrease of the swelling degree with increase of polybutadiene content in the polymer films. The preferential permeation of ethanol is confirmed by the pervaporation results.