Variation of esterfication conditions to optimize solid-state crosslinking reaction of DABA-containing copolyimide membranes for gas separations

In membrane based gas separation, crosslinking of membrane materials was shown to be an effective method to stabilize the polymer structure against undesirable plasticization effects. In this study a crosslinkable copolyimide was synthesized by using the dianhydride 6FDA (4,4′-(hexafluoroisopropylidene)diphthalic anhydride) and the diamines ODA (4,4′-oxydianiline), 4MPD (2,3,5,6-tetramethyl-1,4-phenylene diamine) and DABA (3,5-diamino benzoic acid). The last mentioned diamine contains a free carboxylic acid group where crosslinking of the polymer chains is possible by esterfication reaction with a diol. In the current work EG (ethylene glycol) was chosen as crosslinker. The esterfication conditions were varied to optimize the solid-state crosslinking reaction. To investigate the influence of crosslinking conditions on the separation properties of the membranes pure gas permeation experiments were performed with non-crosslinked and the different EG-crosslinked films at 35°C for the gases CO2 using feed pressures up to 40 bar and CH4 at pressures up to 10 bar.