Two sequence isomeric poly(amic acid)s (PAAs) are successfully synthesized from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and unsymmetrical 5(6)‐amino‐2‐(4‐aminobenzene) benzimidazole (PABZ). The syntheses are based on the site‐selective reactivity of head/tail amino groups of PABZ and solubility differences of PABZ in good solvent (dimethyl sulfoxide, DMSO) and poor solvent (N‐methyl‐2‐pyrrolidone, NMP). The proton nuclear magnetic resonance (¹H‐NMR) results reveal that the content of head tail–head tail (HTHT) bonding units in PAA‐DMSO (PAA synthesized in DMSO) is 37%, while this content increases to 54% in PAA‐NMP (PAA synthesized in NMP). The wide‐angle X‐ray diffraction (WAXD) results indicate polyimide (PI)‐NMP film with high HTHT content exhibits a semicrystalline structure, while PI‐DMSO film is amorphous. Moreover, PI‐NMP also shows higher in‐plane orientation than PI‐DMSO. The ordered molecular packing and higher in‐plane orientation of PI‐NMP lead to an increase in mechanical properties and a decrease in in‐plane thermal expansion coefficient.

中文翻译：

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聚酰亚胺中头/尾异构结构的控制和异构现象的分子堆积和性质差异

由3,3'，4,4'-联苯四甲酸二酐和不对称5（6）-氨基-2-（4-氨基苯）苯并咪唑（PABZ）成功合成了两个序列的异构聚（酰胺酸）（PAA）。合成基于PABZ头/尾氨基的位点选择性反应性和PABZ在良溶剂（二甲亚砜，DMSO）和不良溶剂（N-甲基-2-吡咯烷酮，NMP）中的溶解度差异。质子核磁共振（¹ H-NMR）结果表明，PAA-DMSO（在DMSO中合成的PAA）中头尾-头尾（HTHT）键合单元的含量为37％，而该含量增加至54％在PAA-NMP中（在NMP中合成的PAA）。广角X射线衍射（WAXD）结果表明具有高HT聚酰亚胺（PI）膜-NMP HT含量显示为半结晶结构，而PI‐DMSO膜为非晶态。此外，PI‐NMP的平面取向也高于PI‐DMSO。PI-NMP的有序分子堆积和较高的面内取向导致机械性能的提高和面内热膨胀系数的降低。