Abstract Four spirobichroman-based polyimides (6FDA-F, 6FDA-O, 6FDA-P, and 6FDA-M) were successfully obtained via polyreaction between diamines of different substituents (-H, -OCH3, -N, and -CH3) and 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA). The molecular weights, thermophysical, dihedral angle of the molecules, fractional free volume, d-spacing, Brunauer–Emmett–Teller surface area, and gas separation performance were studied through a combination of experiments and molecular dynamics simulations. These polymers show high molecular weights, with number-average molecular weights (Mn) in the range of 5.0–15.3 × 104, and excellent thermal stability, with weight loss temperatures (T5%) of over 420 °C. The pure-gas (O2, N2, CO2, and CH4) permeation results indicated that the four polymers selectivity of CO2/CH4 over 31 and that 6FDA-F had the highest gas permeability among the four tested gases. Importantly, the dihedral angle from molecular simulation was used to clarify the phenomenon wherein the 6FDA-P gas permeability lower than 6FDA-F. A detailed analysis indicates that -CH3 increased the gas permeability of the polyimides, while the turnstile-like rotary thermal motion of -OCH3 formed channel obstacles and improved the gas selectivity. The polymers containing pyridine ring and those containing benzene ring follows different gas separation mechanisms, based on the gas solution-diffusion behaviour.

中文翻译：

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螺双色满基聚酰亚胺结构与性能关系的洞察：取代基对分子结构和气体分离的影响

摘要 通过不同取代基（-H、-OCH3、-N 和-CH3）与 4 ,4'-(六氟异亚丙基)-二邻苯二甲酸酐 (6FDA)。通过实验和分子动力学模拟的结合，研究了分子的分子量、热物理、二面角、自由体积分数、d 间距、Brunauer-Emmett-Teller 表面积和气体分离性能。这些聚合物显示出高分子量，数均分子量 (Mn) 在 5.0–15.3 × 104 范围内，并且具有出色的热稳定性，失重温度 (T5%) 超过 420 °C。纯气体（O2、N2、CO2、和 CH4) 渗透结果表明，四种聚合物的 CO2/CH4 选择性超过 31，6FDA-F 在四种测试气体中具有最高的透气性。重要的是，使用分子模拟的二面角来阐明 6FDA-P 气体渗透率低于 6FDA-F 的现象。详细分析表明，-CH3 增加了聚酰亚胺的透气性，而-OCH3 类似旋转门的旋转热运动形成了通道障碍，提高了气体选择性。基于气体溶液扩散行为，含吡啶环聚合物和含苯环聚合物遵循不同的气体分离机制。利用分子模拟的二面角来阐明6FDA-P气体渗透率低于6FDA-F的现象。详细分析表明，-CH3 增加了聚酰亚胺的透气性，而-OCH3 类似旋转门的旋转热运动形成了通道障碍，提高了气体选择性。基于气体溶液扩散行为，含吡啶环聚合物和含苯环聚合物遵循不同的气体分离机制。利用分子模拟的二面角来阐明6FDA-P气体渗透率低于6FDA-F的现象。详细分析表明，-CH3 增加了聚酰亚胺的透气性，而-OCH3 类似旋转门的旋转热运动形成了通道障碍，提高了气体选择性。基于气体溶液扩散行为，含吡啶环聚合物和含苯环聚合物遵循不同的气体分离机制。