Preparation of triphenylamine polyimides with low dielectric constants with different side group sizes based on β-relaxation theory

Polyimide (PI), as an ideal interlayer dielectric material, is widely used in traditional communication fields. However, with the rapid development of 5G communication, conventional polyimide exhibits disadvantages such as signal delay and missing and is in urgent need of modification. Based on the β-relaxation theory, we designed and prepared three types of triphenylenediamine-containing monomers with different side group sizes (A-AmM, A-AmP, and A-AmBP) and polymerized them with benzene tetracarboxylic dianhydride (PMDA) to obtain three types of polyimides (MPI, PPI, BPPI), to investigate the effect of the relaxation behavior on the dielectric constant (Dk) of the polyimide. It was also polymerized with 4,4′-(hexafluoroisopropyl)diphthalic anhydride (6FDA) to three fluorinated Polyimides (MFPI, PFPI, BFPPI) to investigate the effect of polar groups on Dk and the dielectric loss (Df). In addition, we also calculate the free volume of polyimide molecules under different side groups by materials studio simulation to further verify the effect of side groups on the Dk. The results show that, firstly, with the increase of side group volume, polyimide still maintains excellent thermal stability, and its dielectric constant gradually decreases and mechanical strength gradually increases. Secondly, the dielectric constant of FPIs is significantly lower than that of the PIs due to the low polar group, and the thermal and mechanical properties are almost unchanged. In addition, benefiting from the combined effects of β-relaxation and trifluoromethyl groups, BPFPI exhibits a low Dk (2.64@10 GHz) and Df (0.0092@10 GHz), excellent thermal properties (glass transition temperature (Tg) = 282.3 °C, 5 % decomposition temperature (Td5%) = 537 °C) and excellent mechanical properties (tensile modulus = 1.71 GPa, tensile strength = 134.7 MPa).