A series of aromatic polyimides were synthesized from three Cardo-based diamines, BAF, DDA, BAP, with different building blocks (ether linkage, dioxane linkage and C–C linkage), and commercially available dianhydride 6FDA. All polyimides were readily soluble in conventional aprotic and protic solvents, which guaranted the fabrication of self-standing membranes for gas separation applications. The Cardo-based polyimides also exhibited excellent thermal stability, with weight loss temperatures (T₅%) of over 538 °C, and good mechanical properties, with tensile strength in the range of 41–64 MPa. Compared to 6FDA-BAF, the substitution of dioxane linkage for ether linkage resulted in increased chain rigidity, looser polymer chain packing, and larger fractional free volume. Consequently, as displayed by single gas permeation tests, 6FDA-DDA showed higher permeability coefficients without significantly sacrificing selectivity. In addition, the CO₂ permeability of 6FDA-BAP was around 2 times as high as that of 6FDA-BAF, while the CO₂/CH₄ selectivity increased by 11%. This can be explained by the lower rotational mobility and the relatively higher imide content caused by the absence of the flexible ether linkage and dioxane linkage in polymer backbone. In short, fundamental insights into structure-property relationships of the Cardo-based polyimides observed in this study provided guidance for the molecular structure design of the gas separation membranes.

由具有不同结构单元（醚键、二恶烷键和 C-C 键）的三种基于 Cardo 的二胺 BAF、DDA、BAP 和市售的二酐 6FDA 合成了一系列芳香族聚酰亚胺。所有聚酰亚胺都容易溶于传统的非质子和质子溶剂，这保证了用于气体分离应用的自支撑膜的制造。Cardo 基聚酰亚胺还表现出优异的热稳定性，失重温度 (T ₅%) 超过 538 °C，具有良好的机械性能，抗拉强度在 41-64 MPa 范围内。与 6FDA-BAF 相比，二恶烷键取代醚键导致链刚性增加，聚合物链堆积更松散，自由体积分数更大。因此，如单一气体渗透测试所示，6FDA-DDA 显示出更高的渗透系数，而不会显着牺牲选择性。此外，6FDA-BAP 的 CO ₂渗透率约为 6FDA-BAF 的 2 倍，而 CO ₂ /CH ₄选择性提高了 11%。这可以通过在聚合物主链中缺乏柔性醚键和二恶烷键导致较低的旋转迁移率和相对较高的酰亚胺含量来解释。简而言之，本研究中观察到的对 Cardo 基聚酰亚胺结构-性能关系的基本见解为气体分离膜的分子结构设计提供了指导。