Comparison of Homo-Polyimide Films Derived from Two Isomeric Bis-Benzimidazole Diamines.

Heteroaromatic polyimides (PIs) containing benzimidazole have attracted tremendous attention due to their positive impact on the properties of PIs. Some research on PIs containing 4,4'-[5,5'-bi-1-benzimidazole]-2,2'-diylbis-benzenamine () has been reported. However, reports are lacking on homo-polyimides (homo-PIs) containing 3,3'-[5,5'-bi-1-benzimidazole]-2,2'-diylbis-benzenamine (), which is one of the isomers of . In this paper, the influence of amino groups' positions on the performance of homo-PIs was investigated. It was found that the net charge of the amine N group in was lower than that of , resulting in higher reactivity of . Consequently, PIs containing displayed better mechanical performance. Molecular simulation confirmed that and its corresponding PI chain exhibited distorted conformation, leading to the PI films containing having a lighter color. In addition, the structure was calculated to have higher rotational energy compared to , resulting in a higher glass transition temperature () in PIs prepared from . On the other hand, PIs containing exhibited a higher level of molecular linearity, leading to a lower coefficient of thermal expansion (CTE) compared to PIs prepared from . Furthermore, all PIs showed higher thermal stability with a 5% weight loss temperature above 530 °C and higher than 400 °C.