A series of multiblock poly(benzoxazole-co-imide) (PBOI) membranes were prepared via thermal rearrangement of their corresponding multiblock copolyimide (CPI) precursors based on 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,2′-bis(3-amino-4-hydroxy-phenyl) hexafluoropropane (APAF), and 5-amino-2-(4-aminobenzene) benzimidazole (BIA). For ortho-hydroxy-functionalized CPI precursors, the difference in stacking behavior between the 6FDA–APAF and 6FDA–BIA blocks results in a weak microphase separation in CPI membranes, whereas the random precursor exhibits a homogeneous morphology, which has been identified by dynamic mechanical analysis, small-angle X-ray scattering, and atomic force microscopy analysis. After the subsequent thermal rearrangement at 420 °C, the microphase separation was also observed in the multiblock poly(benzoxazole-co-imide) (TR-PBOI) membranes with an enlarged domain size. The impacts of the sequence structure on the membrane phase-separation behavior and mechanical and gas separation properties were investigated. Comparatively, an obvious increase in the CO₂/CH₄ gas separation property from the random to TR-PBOI membranes was observed. Specially, the resultant multiblock A₄₀B₄₀-TR-420 membrane possesses a CO₂ permeability of 92 Barrer and a CO₂/CH₄ selectivity of 54.7, which is substantially higher than the values of the random-PBOI-420 membrane (CO₂ permeability of 40.2 Barrer and CO₂/CH₄ of 58) and those of recently reported TR-PBOI membranes. The appealing gas separation performance of the multiblock PBOI membranes can be attributed to their microphase-separated morphology, in which continuous percolating microcavities formed in the thermal rearrangement reaction provide transport channels for gas molecules. The present study demonstrates that the modification of the micromorphological structure of membranes can effectively tune their final gas separation properties.

中文翻译：

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在热重排多嵌段聚（苯并恶唑-共酰亚胺）膜中构建气体分子传输通道，以有效分离CO ₂ / CH ₄

通过基于4,4'-（六氟异亚丙基）二邻苯二甲酸酐（6FDA），2,2'的相应多嵌段共聚酰亚胺（CPI）前体的热重排，制备了一系列多嵌段聚（苯并恶唑-共酰亚胺）（PBOI）膜-双（3-氨基-4-羟基-苯基）六氟丙烷（APAF）和5-氨基-2-（4-氨基苯）苯并咪唑（BIA）。对于邻-羟基官能化的CPI前体，6FDA–APAF和6FDA–BIA嵌段之间的堆叠行为差异导致CPI膜的微相分离较弱，而随机前体表现出均一的形态，这已通过动态力学分析确定，小角X射线散射和原子力显微镜分析。在随后于420°C进行热重排后，在具有较大畴尺寸的多嵌段聚苯并恶唑共酰亚胺（TR-PBOI）膜中也观察到微相分离。研究了序列结构对膜相分离行为以及机械和气体分离性能的影响。比较而言，CO ₂ / CH ₄明显增加观察到从随机膜到TR-PBOI膜的气体分离特性。特别地，所得的多嵌段A ₄₀ B ₄₀ -TR-420膜具有92 Barrer的CO ₂渗透率和54.7的CO ₂ / CH ₄选择性，大大高于无规PBOI-420膜（CO ₂渗透率为40.2 Barrer和CO ₂ / CH ₄58）和最近报道的TR-PBOI膜。多嵌段PBOI膜吸引人的气体分离性能可归因于它们的微相分离形态，其中在热重排反应中形成的连续渗流微腔为气体分子提供了输送通道。本研究表明，膜的微观形态结构的改变可以有效地调整其最终的气体分离性能。