(663c) Structure and Gas Transport Characteristics of Triethylene Oxide-Grafted Polystyrene-B-Poly(ethylene-co-butylene)-B-Polystyrene (SEBS)

Microphase-separated block polymers have emerged as an interesting material platform for membrane applications, such as gas separation, water purification, proton-exchange membranes, anion-exchange membranes, and polymer electrolytes for battery applications. In these multi-phase systems, one of the phases is continuous and governs the transport of small molecules such as gas, water, and ions, while another phase provides mechanical property support. In this work, SEBS block copolymer is used as a polymer matrix to incorporate triethylene oxide (TEO) functionality. The short ethylene oxide segment is chosen to avoid crystallization, which is confirmed by DSC and wide-angle X-ray scattering. The gas permeability results reveal that CO₂/N₂ selectivity increased with increasing incorporation of TEO functional group. The highest CO₂ permeability (281 Barrer) and CO₂/N₂ selectivity was obtained for the membrane with the highest TEO incorporation (57 mol%). Increasing the TEO content in these copolymers results in an increase in CO₂ solubility and a decrease in C₂H₆ solubility. For example, as the grafted TEO content increased from 0 to 57 mol%, the CO₂ solubility and CO₂/C₂H₆ solubility selectivity increased from 0.72 to 1.3 cm³(STD)/cm³ atm and 0.47 to 1.3 at 35°C, respectively. The polar ether linkage in TEO-grafted SEBS copolymers exhibits favorable interaction with CO₂ and non-favorable interaction with nonpolar C₂H₆, enhancing CO₂/C₂H₆ solubility selectivity. This work demonstrates an effective way of designing polymers with multi-functions with excellent separation performance, mechanical properties, and processability.