Abstract Thermal rearrangement of α-functional polyimide membranes into poly(benzoxazole) improves the permselectivity performance compared to the precursor polymer. This is due to the bimodal cavity size distribution generated through the TR process. The cavity volume can be further increased by including segments within the polyimide that undergo degradation at a lower temperature than the TR process. The loss of these segments leaves behind cavity space that can be used to increase gas permeability. This is achieved here for copolymers based on 4,4′-hexafluoroisopropylidene diphthalic anhydride (6FDA) and 3,3′-dihydroxy-4,4’-diamino-biphenyl (HAB) with poly (ethylene glycol) segments, where the PEG segments undergo thermal degradation below the PI to PBO transition temperature. HAB-6FDA-PEG copolymer membranes, with different weight % PEG, had poor permselectivity for CO 2 -N 2 and CO 2 -CH 4 separation. Undertaking thermal treatment to degrade the PEG segments but retaining the PI polymer resulted in an increased fractional free volume of the resulting membrane and higher gas permeability, but a corresponding loss of CO 2 selectivity. Producing TR-PBO from the copolymers through thermal rearrangement at 450 °C, improved the gas permeability of the resulting membranes by over an order of magnitude, as well as improving the CO 2 selectivity. This was attributed to the degradation of the PEG segments increasing the FFV of the membranes, resulting in over a third of the polymers' morphology being free volume. The resulting TR-PBO membranes formed from copolymers with PEG segment had enhanced permselectivity performance compared to TR-PBO formed from the polyimide homopolymer.

中文翻译：

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用于气体分离的热重排聚（酰亚胺-共-乙二醇）膜

摘要 与前体聚合物相比，将 α 功能聚酰亚胺膜热重排为聚（苯并恶唑）可提高选择性渗透性能。这是由于通过 TR 工艺产生的双峰腔尺寸分布。通过在聚酰亚胺中包含在比 TR 工艺更低的温度下降解的片段，可以进一步增加腔体体积。这些段的损失留下了可用于增加气体渗透性的空腔空间。这是基于 4,4'-六氟异亚丙基二邻苯二甲酸酐 (6FDA) 和 3,3'-二羟基-4,4'-二氨基-联苯 (HAB) 与聚（乙二醇）链段的共聚物实现的，其中 PEG 链段在 PI 到 PBO 转变温度以下经历热降解。HAB-6FDA-PEG 共聚物膜，具有不同重量百分比的 PEG，CO 2 -N 2 和CO 2 -CH 4 的分离选择性较差。进行热处理以降解 PEG 链段但保留 PI 聚合物导致所得膜的自由体积分数增加和气体渗透率更高，但相应地降低了 CO 2 选择性。在 450 °C 下通过热重排从共聚物中生产 TR-PBO，将所得膜的气体渗透性提高了一个数量级，并提高了 CO 2 选择性。这归因于 PEG 片段的降解增加了膜的 FFV，导致超过三分之一的聚合物形态为自由体积。与由聚酰亚胺均聚物形成的TR-PBO相比，由具有PEG链段的共聚物形成的所得TR-PBO膜具有增强的选择性渗透性能。