Reverse-Selective Membrane Networks for the Purification of CO2 Gas Mixtures

The selective removal of CO₂ from light gases is an essential process for industry and the nation's long term energy strategy. The objective of this research is the synthesis and characterization of rubbery reverse-selective membranes designed for the preferential transport of CO₂ over light gases such as H₂. Two sets of rubbery membrane networks based on poly (ethylene glycol) diacrylate [PEGDA] crosslinker were prepared via UV photopolymerization. Short-branch networks with varying crosslink density were created by copolymerizing PEGDA with monoacrylate co-monomer, either (i) ethylene glycol methyl ether acrylate, or (ii) 2-hydroxyethyl acrylate. The relaxation characteristics of the resulting networks were investigated using dynamic mechanical analysis, dielectric spectroscopy, and differential scanning calorimetry. The polymerization of PEGDA with acrylate co-monomer led to the insertion of ethylene oxide branch groups along the network backbone and a decrease in overall crosslink density. For the PEGDA/2-hydroxyethyl acrylate copolymers, the presence of the hydroxyl-terminated branches led to a strong increase in T_g and an accompanying decrease in estimated fractional free volume, demonstrating the sensitivity of these materials to relatively small changes in network structure and composition. Current efforts are focused on the characterization of gas transport in the networks and assessment of their potential viability as reverse-selective gas separation membranes.