Synthesis and characterization of nonaromatic polyimides with a polyalicyclic structure

从理论上讲，芳香聚酰亚胺中的着色是由模型化合物的半经验分子轨道计算得出的分子内电荷转移引起的。通过Diels-Alder反应和pd催化的二甲氧基羰基化反应合成了几种新的脂环结构的四羧酸二酐。以二酐和芳香族或脂环二胺为原料，采用两步缩聚法制备了半芳香族或全脂环聚酰亚胺薄膜。这些胶片为无色，可见光区的透明度在85%以上。在空气中加热至300℃，在氮气中加热至400℃，薄膜保持无色。半芳香族聚酰亚胺的平均折射率为1.599 ~ 1.617，双折射率小于0.017。全脂环聚酰亚胺薄膜的截止波长短于235 nm。PI（BHDA-BBH）聚酰亚胺薄膜的平均折射率为1.522，双折射近似为零。由折射率估算出的介电常数为2.55。

It has become theoretically apparent that the coloration in aromatic polyimides is attributable to a intramolecular charge transfer from the semi-empirical molecular orbital calculations for the model compounds. Several new tetracarboxylic dianhydrides bearing an alicyclic structure were synthesized by a Diels-Alder reaction and the Pd-catalyzed dimethoxycarbonylation reaction. Semi-aromatic or fully alicyclic polyimide films were prepared from the dianhydrides and aromatic or alicyclic diamines by two step polycondensation method. These films were colorless, and the transparencies in the visible region were over 85%. The films remained colorless up to 300℃ when heated in air, and 400℃ in N_2. The semi-aromatic polyimides had an average refractive index range of 1.599 to 1.617, and the birefringencies were lower than 0.017. The fully alicyclic polyimide films showed a cut-off wavelength shorter than 235 nm. The average refractive index of the PI(BHDA-BBH) polyimide film was 1.522, and the birefringence was nearly zero. The dielectric constant estimated from the refractive index was 2.55.