Bulky Diamines Modified Crosslinkable Polyimides Hollow Fiber Membranes for Natural Gas Purification

6FDA-based polyimide membranes have received particular attention in natural gas separation. Covalent ester crosslinking is considered as an effective approach to stabilize the membranes against CO₂ plasticization. In the past, it was found that during the crosslinking, collapse of the thin transition layer of asymmetric hollow fibers can occur, thereby causing large losses in permeance. The current work explores partial replacement –CH₃ groups of PDMC (propanediol monoester crosslinkable 6FDA-DAM:DABA 3:2 polyimide) by more bulky –CF₃ groups to inhibit the transition layer collapse responsible for loss in permeance of the standard PDMC fibers during crosslinking. It was found that the introduction of bulky and rigid diamine increases the β-transition temperature of PDMC by increasing the rotational barrier for side group mobility. Low molar fractions (5%) of CF₃-diamine modified PDMC polymer was synthesized and engineered to defect-free hollow fiber membranes by optimizing the dope composition and spinning conditions. The crosslinked PDMC-CF₃ asymmetric hollow fiber membranes, without sacrifice of permeance, exhibited an excellent CO₂ separation performance under aggressive feeds (high pressure, impurities of hydrocarbons), showing great potential in natural gas purification.