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Blend membranes of synthesized polyurethane (PU) based on toluene diisocyanate (TDI), polydimethylsiloxane (PDMS) and polytetramethylene glycol (PTMG) with polyamide 12-b-polytetramethylene glycol (PA12-b-PTMG) were prepared by a solution casting technique. The heterogeneous microstructures of the blend membranes (PU /PA12-b-PTMG) were characterized by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Gas transport properties were determined for O 2 , N 2 , CH 4 , and CO 2 gases and the obtained permeabilities were correlated with polymer properties and morphology of the membranes. Comparison of the results with that of the pure PU membrane indicates that the blend membranes had higher permeability to CO 2 , but lower permeability to O 2 , N 2 and CH 4 gases, and, therefore, had higher values of CO 2 /N 2 and CO 2 /CH 4 ideal gas pair selectivities. The blend membrane with 20 % (wt) PA12-b-PTMG showed the highest CO 2 permeability (≈105 Barrer) compared to the PU and other blend membranes. In the blend membranes with 5-20 % (wt) PA12-b-PTMG contents an enhancement of CO 2 /CH 4 (≈ 10) and CO 2 /N 2 (≈ 52) selectivities was observed. The experimental permeabilities of the blend membranes were compared with the calculated permeabilities based on a modified additive logarithmic model.

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