Decoding high-frequency dielectric loss of Poly(ester imide)s: Molecular simulation and experiment validation

Polyimides (PIs) are essential materials for electronic and high-frequency communication applications, often face challenges with high dielectric loss. Drawing inspiration from low-dielectric-loss liquid crystal polyesters, ester groups have been introduced into PI backbones to develop poly (ester imide)s (PEsIs). This study delved into various PEsIs, aiming to reduce dielectric loss at high frequencies and to understand the molecular mechanisms behind this improvement. Selection and design of PEsIs were based on four key factors: the number of ester groups, substitution positions, side substituents and intermolecular interactions. The results indicated that the high-frequency dielectric loss of PEsIs, specifically at a frequency of 10 GHz, decreases with an increased number of ester groups. For isomeric PEsIs systems, introducing ester groups into the dianhydride part notably reduced the dielectric loss. The modes of bonding between the phenyl ring and the ester group in PI structures also impacted the dielectric loss. The configuration with an O-linked isomer showed a lower value of dielectric loss. On the other hand, introducing hydrogen bonding into PEsIs were observed to contribute a negative impact on the reduction of dielectric loss. Based on these theoretical findings, two PEsIs structures, which were identified as low-dielectric-loss PEsIs candidates, were successfully synthesized. Their dielectric loss factors at 10 GHz were measured experimentally as 0.00153 and 0.00134, thereby confirming the reliability of the theoretical results.