pi-Complexes consisting of silver salts such as AgBF4 and AgCF3 SO3 dissolved in poly(styrene-b-butadiene-b-styrene) (SBS) block copolymers have been prepared for use as facilitated olefin transport membranes. Facilitated olefin transport is not observable up to the silver mole fraction of 0.14, a threshold concentration, above which it increases almost linearly with the silver salt concentration. FT-IR spectra of these complexes show that silver ions selectively coordinate with the C=C bonds of P13 blocks up to the silver mole fraction of 0.14, and that the coordinative interaction of the silver ion with aliphatic C=C is stronger than that with aromatic C=C. Interestingly, the bicontinuous morphology of the neat SBS block copolymer prepared from THF solution persists in the SBS complex with the salt concentrations less than 0.14. At high silver salt concentrations, the PS domains are additionally coordinated by silver ions and thus the morphology transition occurs from bicontinuous to lamellar. The threshold silver concentration of 0.14 for the facilitated olefin transport is nearly coincident with the composition at which the silver ions start coordinating with the aromatic C=C bonds of the PS blocks, suggesting their important role in determining overall transport properties. Therefore, we have shown that the transport properties of the SBS complex membranes are significantly affected by the coordinative interaction of the block copolymers with the silver ions and their membrane morphology. (c) 2006 Elsevier B.V. All rights reserved.