A sulfonic acid-functionalized trimethyl-substituted polyimide was synthesized by reacting 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,5-diamino-2,4,6-trimethylbenzenesulfonic acid (TrMSA). The properties of 6FDA-TrMSA were compared to the related 6FDA-derived polyimide analogues made from 2,4,6-trimethylbenzene-1,3-diamine (6FDA-TrMPD) and 3,5-diamino-2,4,6-trimethylbenzene benzoic acid (6FDA-TrMCA). Compared to 6FDA-TrMPD and 6FDA-TrMCA, sulfonic acid functionalization resulted in significantly lower surface area, reduced fractional free volume, and tighter chain d-spacing. Consequently, 6FDA-TrMSA displayed lower gas permeabilities with a commensurate increase in permeability-based gas-pair selectivities. The enhanced CO₂/CH₄ selectivity of 6FDA-TrMSA was caused exclusively by higher diffusion selectivity, which was promoted by strong hydrogen bonding induced by the SO₃H functionalization. Permeation experiments of 6FDA-TrMSA with a 1:1 CO₂-CH₄ mixture revealed the occurrence of competitive sorption effects (depressing CO₂ gas permeability) and CO₂-induced polymer matrix plasticization, which reduced the polymer selectivity by enhancing CH₄ permeability. At ~20 atm total pressure, 6FDA-TrMSA showed a CO₂ permeability of ~15 Barrer and an equimolar CO₂/CH₄ mixed-gas selectivity of 55, which are ~2-fold higher performance values than those of the state-of-the-art polymer used for industrial scale natural gas sweetening, i.e., cellulose triacetate.

通过使4,4'-（六氟异亚丙基）二邻苯二甲酸酐（6FDA）与3,5-二氨基-2,4,6-三甲基苯磺酸（TrMSA）反应合成磺酸官能化的三甲基取代的聚酰亚胺。将6FDA-TrMSA的性能与相关的6FDA衍生的由2,4,6-三甲基苯-1,3-二胺（6FDA-TrMPD）和3,5-二氨基-2,4,6-三甲基苯制成的聚酰亚胺类似物进行了比较苯甲酸（6FDA-TrMCA）。与6FDA-TrMPD和6FDA-TrMCA相比，磺酸功能化可显着降低表面积，减少自由体积分数和缩短d链间距。因此，6FDA-TrMSA的气体渗透率较低，而基于渗透率的气体对选择性则相应增加。增强型CO ₂ / CH ₄6FDA-TrMSA的选择性完全是由较高的扩散选择性引起的，而较高的扩散选择性是由SO ₃ H官能化诱导的强氢键促进的。6FDA-TrMSA与1：1 CO ₂ -CH ₄混合物的渗透实验显示出竞争吸附作用（降低CO ₂气体渗透性）和CO ₂诱导的聚合物基体增塑的发生，这通过提高CH ₄渗透性而降低了聚合物的选择性。在约20个大气压的总压力下，6FDA-TrMSA的CO ₂渗透性为〜15 Barrer和等摩尔的CO ₂ / CH ₄ 混合气体选择性为55，比用于工业规模天然气脱硫的最新聚合物（三醋酸纤维素）的性能值高约2倍。