Simultaneously enhanced CO2 permeability and CO2/N2 selectivity of styrene–butadiene–styrene membrane by modulating internal structure with various dopants

Styrene-butadiene-styrene triblock copolymer (SBS) has attracted increasing research attention due to its low cost, excellent mechanical properties, and superior gas permeability performance. In this work, a series of novel SBS doped membranes were prepared by introducing polyphosphoric acid (PPA), lithium 2,2,2- trifluoroacetate (TFALi), and 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane (Siloxane-Cl) into SBS as dopants. The results indicated that the addition of dopants into SBS membranes simultaneously enhanced the CO2 permeability and CO2/N2 selectivity of SBS membranes. Specially, doping Siloxane-Cl expanded the d-spacing, introduced flexible siloxane (Si-O) groups to enlarge molecular spaces, and formed more crosslinked network structure. Therefore, the SBS/Siloxane-20 membrane showed an approximately 4-fold increase CO2 permeability compared to the pristine SBS membranes (from 203.3 to 842.9 barrer), accompanied by an increase in CO2/N2 selectivity from 15.8 to 22.0. The obtained membranes also exhibited attractive anti-plasticization and anti-physical aging properties, no obvious decline in CO2 permeability and/or CO2/N2 selectivity can be observed after 1-week continuous permeation test, making them promising candidates for CO2/N2 separation.