Polydimethylsiloxane polyurethane (PDMS-PU), which was synthesized from PDMS as the soft segment, was blended into a variety of ester- or ether-based soft-segment waterborne polyurethanes with different concentrations to investigate the crystallization, thermal, and physical properties of the membrane formations. According to X-ray analysis, the ether-based PUs, synthesized from soft segments of poly(propylene glycol) (PPG1000) or poly(ethylene glycol) (PEG2000), were found to have maximum crystallinity at a 5% blending ratio of PDMS-PU, but the ester-based PU, synthesized from soft segments of polycaprolactone (PCL1250), had decreased crystallinity at a 5% blending ratio. Differential scanning calorimetric analysis revealed that the T values of PUs were highest when the blending ratio of PDMS-pu was 5%-10%, except for PU from PCL1250. Moreover, ether-based PUs showed maximum T-m,T-h values, but the T-m,T-h of the ester-based PU was greatly reduced when PU with PCL1250 was blended with PDMS-PU. In addition, the PU from PEG2000 had the highest melting entropy. Mechanical property analysis showed that the stress of ether-based PUs would be increased when PUs were blended with a small amount of PDMS-PU and that the stress of PU from poly(tetramethylene glycol) (PTMG1000) increased to its greatest value (20-30 MPa). On the other hand, the ester-based PU, from PCL1250 blended with PDMS-PU, would have reduced stress. On the whole, the stress and strain of PU from PEG1000 had excellent balance. (c) 2006 Wiley Periodicals, Inc.