Zhang Mei, Liu Weili, Gao Xia, Cui Peng, Zou Tao, Hu Guanghui, Tao Liming, Zhai Lei
Beijing Center for Physical and Chemical Analysis, Beijing 100094, China.
Beijing Key Laboratory of Detection Technology and Quality Evaluation of Organic Material, Beijing 100094, China.
Polymers (Basel). 2020 Jul 11;12(7):1532. doi: 10.3390/polym12071532.
Transparent polyimides (PI) films with outstanding overall performance are attractive for next generation optoelectronic and microelectronic applications. Semi-alicyclic PIs derived from alicyclic dianhydrides and aromatic diamines have proved effective to prepare transparent PIs with high transmittance. To optimize the combined properties of semi-alicyclic PIs, incorporating bulky trifluoromethyl groups into the backbones is regarded as a powerful tool. However, the lack of fundamental understanding of structure-property relationships of fluorinated semi-alicyclic PIs constrains the design and engineering of advanced films for such challenging applications. Herein, a series of semi-alicyclic PIs derived from alicyclic dianhydrides and trifluoromethyl-containing aromatic diamines was synthesized by solution polycondensation at high temperature. The effects of alicyclic structures and bulky trifluoromethyl groups on thermal, dielectric and optical properties of PIs were investigated systematically. These PI films had excellent solubility, low water absorption and good mechanical property. They showed high heat resistance with in the range of 294-390 °C. It is noted that tensile strength and thermal stability were greatly affected by the rigid linkages and alicyclic moieties, respectively. These films exhibited obviously low refractive indices and significantly reduced dielectric constants from 2.61 to 2.76, together with low optical birefringence and dielectric anisotropy. Highly transparent films exhibited cutoff wavelength even as low as 298 nm and transmittance at 500 nm over 85%, displaying almost colorless appearance with yellowness index (*) below 4.2. The remarkable optical improvement should be mainly ascribed to both weak electron-accepting alicyclic units and bulky electron-withdrawing trifluoromethyl or sulfone groups. The present work provides an effective strategy to design molecular structures of optically transparent PIs for a trade-off between solution-processability, low water uptake, good toughness, high heat resistance, low dielectric constant and excellent optical transparency.
具有出色综合性能的透明聚酰亚胺（PI）薄膜对下一代光电子和微电子应用具有吸引力。由脂环族二酐和芳香族二胺衍生的半脂环族聚酰亚胺已被证明是制备具有高透光率的透明聚酰亚胺的有效方法。为了优化半脂环族聚酰亚胺的综合性能，将庞大的三氟甲基引入主链被视为一种有力手段。然而，对含氟半脂环族聚酰亚胺结构与性能关系缺乏基本了解，限制了用于此类具有挑战性应用的先进薄膜的设计与工程化。在此，通过高温溶液缩聚合成了一系列由脂环族二酐和含三氟甲基的芳香族二胺衍生的半脂环族聚酰亚胺。系统研究了脂环族结构和庞大的三氟甲基对聚酰亚胺热性能、介电性能和光学性能的影响。这些聚酰亚胺薄膜具有优异的溶解性、低吸水性和良好的机械性能。它们表现出高耐热性，玻璃化转变温度在294 - 390℃范围内。值得注意的是，拉伸强度和热稳定性分别受到刚性连接和脂环族部分的极大影响。这些薄膜表现出明显较低的折射率，介电常数从2.61显著降低到2.76，同时具有低光学双折射和介电各向异性。高度透明的薄膜截止波长甚至低至298nm，在500nm处的透光率超过85%，呈现几乎无色外观，黄度指数（*）低于4.2。显著的光学性能改善主要应归因于弱吸电子的脂环族单元以及庞大的吸电子三氟甲基或砜基。本工作提供了一种有效的策略来设计光学透明聚酰亚胺的分子结构，以在溶液可加工性、低吸水率、良好韧性、高耐热性、低介电常数和优异光学透明度之间进行权衡。
