Influence of Poly(ethylene glycol) Segment Length on CO₂ Permeation and Stability of PolyActive Membranes and Their Nanocomposites with PEG POSS

Three grades of PolyActive block copolymers are investigated for CO₂ separation from light gases. The polymers are composed of 23 wt % poly­(butylene terephthalate) (PBT) and 77 wt % poly­(ethylene glycol terephthalate) (PEGT) having the poly­(ethylene glycol) segments of 1500, 3000, and 4000 g/mol, respectively. A commercial PEG POSS (poly­(ethylene glycol) functionalized polyoctahedral oligomeric silsesquioxanes) is used as a nanofiller for these polymers to prepare nanocomposites via a solvent casting method. Single gas permeabilities of N₂, H₂, CH₄, and CO₂ are measured via the time-lag method in the temperature range from 30 to 70 °C. The thermal transitions of the prepared membranes are studied by differential scanning calorimetry (DSC). It is found that the length of PEG segment has a pronounced influence on the thermal transition of the polymers that regulates the gas separation performance of the membranes. The stability of the nanocomposites is also correlated with the thermal transition of the polyether blocks of the polymer matrices