UV Cross-Linked Poly(ethylene glycol)-Based Membranes with Different Fractional Free Volumes for CO2 Capture: Synthesis, Characterization, and Thiol-ene Modification Evaluation

CO2 separation is of paramount importance in CO2 capture from flue gas and natural gas sweetening. In this paper, the thiol-ene UV photopolymerization technique was employed to synthesize improved UV cross-linked amorphous poly­(ethylene glycol) (PEG)-based membranes using poly­(ethylene glycol) diacrylate (PEGDA) and poly­(ethylene glycol) methyl ether acrylate (PEGMEA) oligomers. To increase the fractional free volume (FFV) and consequently decrease the network cross-link density of PEGDA network, PEGMEA was incorporated to prepare the PEGDA-PEGMEA copolymer network. A tetrathiol cross-linker, namely, pentaerythritol tetrakis­(3-mercaptopropionate) (PETMP), was also utilized to alter the polymerization route from the chain-growth acrylate photopolymerization to step-growth free radical thiol-ene photopolymerization. The membranes were characterized by SEM, ATR-FTIR, DSC, TGA, and tensile analyses. Permeation measurements were carried out for CO2, CH4, N2, and H2 over wide ranges of temperature (308–348 K) and pressure (2–16 bar). It was revealed that a thiol-modified copolymer membrane, i.e., PEGDA-PEGMEA-PETMP, offers promising CO2 separation performance, more conspicuously at high temperatures.