A novel cycloaliphatic monomer for polyimides (PI), 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride (H′-PMDA) is proposed in this work. H′-PMDA shows high polymerizability with various diamines in contrast to its isomer, i.e., conventional hydrogenated pyromellitic dianhydride (H-PMDA) and leads to highly flexible and colorless PI films with very high T_g's. In particular, the combinations with rigid structures of diamines give rise to PIs with significantly decreased coefficients of thermal expansion (CTE) owing to high extents of in-plane chain orientation induced by thermal imidization, whereas the H-PMDA-based counterparts do not. The decreased CTE reflects structural rigidity/linearity of the H′-PMDA-based diimide units as supported by liquid crystallinity observed in the corresponding model compound. Solution casting of a chemically imidized PI derived from H′-PMDA and 2,2′-bis(trifluoromethyl)benzidine (TFMB) results in a lower CTE than that of the thermally imidized counterpart, suggesting the presence of a self-orientation phenomenon during solvent evaporation. The mechanism is proposed in this work. H′-PMDA/TFMB and its copolymer systems can be useful as plastic substrates in image display devices and/or novel coating-type optical compensation films.

在这项工作中，提出了一种新型的聚酰亚胺（PI）1 S，2 S，4 R，5 R-环己烷四羧酸二酐（H'-PMDA）脂环族单体。与传统的氢化均苯四甲酸二酐（H-PMDA）异构体相比，H'-PMDA与各种二胺显示出高聚合性，并导致具有非常高的T _g的高柔韧性和无色PI膜的。特别地，由于热酰亚胺化引起的高度的面内链取向，具有二胺刚性结构的组合产生具有显着降低的热膨胀系数（CTE）的PI，而基于H-PMDA的对应物却没有。降低的CTE反映了H'-PMDA基二酰亚胺单元的结构刚度/线性，这是在相应的模型化合物中观察到的液晶性所支持的。衍生自H'-PMDA和2,2'-双（三氟甲基）联苯胺（TFMB）的化学酰亚胺化PI的溶液浇铸比热酰亚胺化的PITE的CTE更低，这表明在反应过程中存在自取向现象溶剂蒸发。在这项工作中提出了该机制。