Thermoplastic elastomers precursors based on urethane: poly(esterurethane) (PU) and polyurethane with lactate segment poly(lactaturethane) (PULS) were synthesized. The lactate segment was added to increase the biocompatibility and biodegradability of PU in order to improve polyurethane applicability to soft tissue replacement and drug delivery systems. Asymmetric porous membranes were prepared by wet phase inversion method, from PULS and PU to compare. The membrane morphology was optimized by controlling the casting parameters. The membrane's morphology and microphase organization were investigated by scanning electronic microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Phase separation in the system PU/DMF/H2O was studied by turbidimetric titration. The molecular structure and organization was investigated by Fourier-transform infrared (FT-IR) spectroscopy techniques: attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and static linear clichroism-infrared (SLDIR). All the used methods confirmed that the membranes material is multiphase, but the PULS is more amorphous as compared with PU due to the lactate segment. It was found that for the studied polyurethane, the order degree of the macromolecular chains secondary structure, investigated by SLDIR, could be controlled by casting parameters and by stretching. For PU, the majority of a-helix structures are parallel to the stretching axis, while a lower order secondary structure was observed in case of PULS as compared with PU. (c) 2005 Elsevier B.V. All rights reserved.