Olefin separation performances and coordination behaviors of facilitated transport membranes based on poly(styrene-b-isoprene-b-styrene)/silver salt complexes

Solid-state facilitated, olefin transport membranes were prepared by complexation of poly(styrene-b-isoprene-b-styrene) (SIS) block copolymer and silver salt. Facilitated olefin transport was not observed up to a silver mole fraction of 0.14, representing a threshold concentration, above which transport increased almost linearly with increasing silver salt concentration. This was because firstly the silver ions were selectively coordinated with the C=C bonds of PI blocks up to a silver mole fraction of 0.20, and secondly the coordinative interaction of the silver ions with the aliphatic C=C bond was stronger than that with the aromatic C=C bond, as confirmed by FT-Raman spectroscopy. Small angle X-ray scattering (SAXS) analysis showed that the cylindrical morphology of the neat SIS block copolymer was changed to a disordered structure at low silver concentrations (0.01-0.02). However, at intermediate silver concentrations (0.15-0.20), disordered-ordered structural changes occurred and finally returned to a disordered structure again at higher silver concentrations (>0.33). These results demonstrated that the facilitated olefin transport of SIS/silver salt complex membranes was significantly affected by their coordinative interactions and nano-structural morphology.