Structure and mass transfer properties of segmented polyurethanes were investigated as a function of hydrophilic segment content in the polymer. For this purpose, polytetramethylene glycol (number average molecular weight 2900 g mol(-1), PTMG 2900) based polyurethane (PU) copolymers with three different polyethyelene glycol (number average molecular weight 3400 g mol(-1), PEG 3400) content viz. 5, 10 and 15 wt.%, and PU without PEG 3400 were synthesized by two steps polymerization process. Experimental results showed that the hydrogen and non-hydrogen bond stretching of carbonyl groups were influences by PEG 3400 content in PU, which was detected by Fourier transform infrared analysis (FTIR). Wide angle X-ray diffraction (WAXD) measurement revealed the presence of microcrystal in the membranes. Heat of fusion, soft segment crystal melting temperature and heat of crystallization as measured by differential scanning calorimetry (DSC) is also dependent on the hydrophilic segment content in PU. Dynamic mechanical thermal analysis showed increase of tan delta value with increasing PEG 3400 content in polymer backbone. PU with delta wt.% of PEG 3400, the tan delta peak becomes unclear due to the increased interaction between the polymer chains. Water vapor permeability (WVP) increases linearly with increasing PEG content in the polymer backbone, and further enhanced at soft segment crystal melting. Equilibrium water sorption of PU, containing different quantities of PEG in their backbone followed a similar trend to that of WVP. However, desorption occurred for PU with 10 and 15 wt.% of PEG 3400 above 25 degrees C. (c) 2005 Elsevier B.V. All rights reserved.