Enhancement of CO₂ capture by polyethylene glycol-based polyurethane membranes

Poly (ethylene glycol) (PEG)-based polyurethane (PU) membranes are attractive materials for CO₂ separation from various sources such as flue gas and syngas. However, the strong tendency of PEG chains to crystallize leads to reduced permeability of the membrane. Here, we developed new types of PU chemistries with high PEG content and reduced crystallinity. A series of PUs were synthesized based on mixtures of PEG and poly (propylene glycol) (PPG), and various PEG-PPG triblock copolymers (PEG-b-PPG). The presence of PEG-b-PPG triblock copolymers combines the high selectivity of PEG while the PPG pendant methyl group hinders local crystallization. The resulting membranes showed CO₂ permeability of 144 barrer and high CO₂/N₂ and CO₂/H₂ selectivities up to 54 and 8.3, respectively. Due to the absence of the crystalline soft phase, synthesized PUs with PEG-b-PPG triblock copolymers exhibit higher chain flexibility which is reflected by a decrease in the glass transition temperature of the soft segments. In contrast, the mixture of PEG and PPG showed minimal effects on the crystallinity of PEG domains. This resulted in lower membrane gas separation performance where CO₂ permeability and CO₂/H₂ selectivity decreased to 68 barrer and 4.9, respectively.