A novel series membranes based on non-linear all-aromatic polyimides (PIs) was investigated with the aim to understand how the PI backbone geometry and local electrostatics govern gas transport and the ability to separate CO₂/CH₄ mixtures. Non-linear 3-ring aromatic diamines, with exocyclic bond angles varying between 120 and 134°, enable the design of high Tg (>276 °C) PIs. A polar 1,3,4-oxadiazole diamine (ODD) (μ = 3D) monomer and a non-polar m-terphenyl diamine (TPD) reference monomer were synthesized and coupled with 3 dianhydrides, i.e. ODPA, ODDA, and 6FDA. In 6FDA-based membranes CO₂ permeabilities (P_CO2) are the highest of the series. The 6FDA-ODD membrane shows excellent membrane performance with high P_CO2 values at all feed pressures. Up to 12 bar (6 bar CO₂) none of the membranes reached their plasticization pressure. The non-linear backbone geometry promotes CO₂ permeability, whereas the presence of an electrostatic dipole moment associated with the 1,3,4-oxadiazole heterocycle governs CO₂/CH₄ separation selectivity.

研究了基于非线性全芳族聚酰亚胺 (PI) 的新型系列膜，旨在了解 PI 主链几何形状和局部静电如何控制气体传输以及分离 CO ₂ /CH ₄混合物的能力。非线性 3 环芳族二胺，环外键角在 120 和 134° 之间变化，可以设计高 Tg (>276 °C) PI。合成了极性 1,3,4-恶二唑二胺 (ODD) (μ = 3D) 单体和非极性间三联苯二胺 (TPD) 参考单体，并与 3 种二酐偶联，即ODPA、ODDA 和 6FDA。在基于 6FDA 的膜中，CO ₂渗透率 ( P _CO2) 是系列中最高的。6FDA-ODD 膜显示出优异的膜性能，在所有进料压力下均具有高P _CO2值。高达 12 巴（6 巴 CO ₂）的膜都没有达到其塑化压力。非线性主链几何形状促进 CO ₂渗透性，而与 1,3,4-恶二唑杂环相关的静电偶极矩的存在控制 CO ₂ /CH ₄分离选择性。