| Summary: | 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<i>H</i>-benzimidazole]-2,2′-diylbis-benzenamine (<b>4-AB</b>) has been reported. However, reports are lacking on homo-polyimides (homo-PIs) containing 3,3′-[5,5′-bi-1<i>H</i>-benzimidazole]-2,2′-diylbis-benzenamine (<b>3-AB</b>), which is one of the isomers of <b>4-AB</b>. 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 <b>4-AB</b> was lower than that of <b>3-AB</b>, resulting in higher reactivity of <b>4-AB</b>. Consequently, PIs containing <b>4-AB</b> displayed better mechanical performance. Molecular simulation confirmed that <b>3-AB</b> and its corresponding PI chain exhibited distorted conformation, leading to the PI films containing <b>3-AB</b> having a lighter color. In addition, the <b>3-AB</b> structure was calculated to have higher rotational energy compared to <b>4-AB</b>, resulting in a higher glass transition temperature (<i>T</i><sub>g</sub>) in PIs prepared from <b>3-AB</b>. On the other hand, PIs containing <b>4-AB</b> exhibited a higher level of molecular linearity, leading to a lower coefficient of thermal expansion (CTE) compared to PIs prepared from <b>3-AB</b>. Furthermore, all PIs showed higher thermal stability with a 5% weight loss temperature above 530 °C and <i>T</i><sub>g</sub> higher than 400 °C.
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