Aromatic Polyimide Membranes with tert-Butyl and Carboxylic Side Groups for Gas Separation Applications—Covalent Crosslinking Study

Abstract

A set of aromatic copolyimides was obtained by reaction of 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), and mixtures of the diamines 1,4-bis(4-amino-2-trifluoromethylphenoxy)-2,5-di-tert-butylbenzene (CF3TBAPB) and 3,5-diamino benzoic acid (DABA). These polymers were characterized and compared with the homopolymer derived from 6FDA and CF3TBAPB. All copolyimides showed high molecular weight values and good mechanical properties. The presence of carboxylic groups in these copolymers allowed their chemical crosslinking by reaction with 1,4-butanediol. Glass transition temperatures (Tg) were higher than 260 °C, showing the non-crosslinked copolyimides had the highest Tg values. Degradation temperature of crosslinked copolyimides was lower than their corresponding non-crosslinked ones. Mechanical properties of all polymers were good, and thus, copolyimide (precursor, and crosslinked ones) films could be tested as gas separation membranes. It was observed that CO2 permeability values were around 100 barrer. Finally, the plasticization resistance of the crosslinked material having a large number of carboxylic groups was excellent.

Advanced and sustainable manufacturing methods of polymer-based membranes for gas separation: a review

“…Various methods can be employed to crosslink polymer membranes for gas separation, such as ionic crosslinking (Schmeling et al, 2010), thermal crosslinking Frontiers in Membrane Science and Technology frontiersin.org (Alghunaimi, 2013), and photocrosslinking (Decker and Bianchi, 2003;Decker et al, 2004). However, the choice of approach depends on the polymer functional groups and the expected separation attributes of the membrane (Wind et al, 2002;Bolto et al, 2009;Esteban et al, 2022). Hunger et al, 2012 demonstrated that copolyimide membranes which are crosslinked exhibit increased resistance to plasticization and maintain their selectivity, showing no notable decline compared to non-crosslinked membranes when subjected to CO 2 /CH 4 or toluene/cyclohexane mixtures.…”