Abstract

Two new aromatic diamines with asymmetric structure: 3,5-bis(trifluoromethyl) phenyl-2,4-diaminobenzene (2a) and 3,5-dimethylphenyl-2,4-diaminobenzene (2b), were synthesized by a facile two-step reaction. The resulting polyimides (PI 3a-3c and 4a-4c) containing asymmetric bulky pendant groups were prepared by one-step solution polycondensation through these diamines with three different dianhydride monomers, respectively. The polymers displayed good solubility and film forming ability, and the flexible films could be obtained conveniently by casting their solution. It was worth noting that these films have low dielectric constant and high thermal stability. Their dielectric constants were in the range of 2.68–3.20 (measured at 1 MHz), and their glass transition temperatures (T_g) were in the range of 278–331 °C. The 10% weight loss temperatures of these polyimides in N₂ and air atmosphere were above 543 °C and 585 °C, respectively. Their UV cut-off wavelengths were lower than 358 nm, and their wavelength at 80% light transmittance was between 431–468 nm. Moreover, they also exhibited good mechanical properties with tensile strength, initial modulus, and elongation at break values of 72.6–81.3 MPa, 1.7–2.2 GPa, and 5%–10%, respectively.

摘要

通过简单的两步法合成了两种具有不对称结构的新型芳香族二胺：3,5-双（三氟甲基）苯基-2,4-二氨基苯（2a）和3,5-二甲基苯基-2,4-二氨基苯（2b）反应。所得聚酰亚胺（PI 3a - 3c和4a - 4c) 分别通过这些二胺与三种不同的二酐单体通过一步溶液缩聚反应制备含有不对称庞大侧基的化合物。聚合物表现出良好的溶解性和成膜能力，通过浇铸其溶液可以方便地获得柔性薄膜。值得注意的是，这些薄膜具有低介电常数和高热稳定性。它们的介电常数在 2.68-3.20 的范围内（在 1 MHz 下测量），它们的玻璃化转变温度 ( T _g ) 在 278-331 °C 的范围内。这些聚酰亚胺在 N _{2 中}的 10% 失重温度和空气气氛分别高于 543 °C 和 585 °C。它们的紫外截止波长低于 358 nm，并且它们在 80% 透光率下的波长在 431-468 nm 之间。此外，它们还表现出良好的机械性能，拉伸强度、初始模量和断裂伸长率分别为 72.6-81.3 MPa、1.7-2.2 GPa 和 5%-10%。