Polyimides (PI) are considered as one of the most used materials for flexible printed circuit board substrates because of their excellent thermal stabilities, outstanding mechanical properties, and great dielectric properties. Dielectric constants (D_k) of common commercial PIs, however, are still above 3.0 (at 10 GHz), which is still substandard for high-frequency applications. In this study, we develop thermally stable PIs with enhanced dielectric properties by structural design and crosslinking. Stiff aromatic 2,2′-bis(trifluoromethyl)benzidine (TFMB) and soft aliphatic dimer diamines (DDA, priamine), including priamine 1074 (DDA-1) and priamine 1071 (DDA-2), are used as the diamines, and cyclobutanetetracarboxylic dianhydride (CBDA) is used as the dianhydride. By adjusting the ratio of the diamines, a series of PIs (PI-1–PI-5) with high thermal stabilities and low-D_k values are synthesized. Among these PIs, PI-4 synthesized by diamines with the ratio of TFMB:DDA-1:DDA-2 = 85:10:5, possesses relatively good performances. Therefore, PI-4 is further chosen to be thermally crosslinked. By changing the contents of the crosslinker, triallyl isocyanurate (TAIC), crosslinked PIs (CPIs) are synthesized. The resulting CPIs have a significant improvement in thermal properties, dielectric properties, and mechanical strengths. Especially, for the CPI-4-30, in which 30% of TAIC is used, the glass transition temperature (T_g) increases by 20°C, the D_k decreases from 2.62 to 2.41, and the ultimate tensile strength boosts from 91.65 to 115.16 MPa. The CPIs with low D_k and high T_g values may have great potential as substrate materials for broad applications, such as microelectronics and integrated circuit packages.

中文翻译：

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通过交联网络增强介电性能和热稳定性的单体比例控制聚酰亚胺

聚酰亚胺（PI）因其优异的热稳定性、出色的机械性能和良好的介电性能而被认为是柔性印刷电路板基材最常用的材料之一。然而，常见商用 PI 的介电常数 ( D _k ) 仍然高于 3.0（10 GHz 时），这对于高频应用来说仍然不符合标准。在这项研究中，我们通过结构设计和交联开发了具有增强介电性能的热稳定 PI。作为二胺，使用硬质芳香族2，2'-双(三氟甲基)联苯胺(TFMB)和软质脂肪族二聚二胺(DDA、伯胺)，包括伯胺1074(DDA-1)和伯胺1071(DDA-2)，并且作为二酐，使用环丁烷四甲酸二酐(CBDA)。通过调整二胺的比例，合成了一系列具有高热稳定性和低D _{k值的PI（PI-1–PI-5）。}其中，以TFMB:DDA-1:DDA-2 = 85:10:5的二胺合成的PI-4具有较好的性能。因此，进一步选择PI-4进行热交联。通过改变交联剂三烯丙基异氰脲酸酯（TAIC）的含量，合成了交联PI（CPI）。由此产生的 CPI 在热性能、介电性能和机械强度方面都有显着改善。_{特别是对于CPI} -4-30，其中TAIC用量为30%，玻璃化转变温度（Tg）提高了20℃，Dk从2.62降低到2.41，极限拉伸强度从91.65_提高至 115.16 兆帕。具有低D _k和高T _g值的CPI作为基板材料具有巨大的潜力，可用于微电子和集成电路封装等广泛应用。