Increasing Twist Rigidity to Prepare Polyimides with Low Dielectric Constants and Dissipation Factors over a Wide Temperature Range

To ensure the stable performance and extended service life of high-integrity and high-power electronic devices, it is imperative for dielectric materials to consistently exhibit a low dielectric constant (D k) and dissipation factor (D f) across a wide temperature range. Here, we have undertaken the synthesis of two distinct polyimides (PIs), namely, 6FDA-GA and 6FDA-GB, featuring varying biphenyl side groups. These selected side groups have been intentionally incorporated to impede the interchain stacking of PI macromolecules and enhance the twist rigidity of the PI mainchain. It was substantiated that the smaller side-chain groups in 6FDA-GB are notably effective in constraining the rotation of the imide ring within the main chain owing to their closer proximity. This constraint has unequivocally resulted in a substantial increase in the twist rigidity of the main chain. Thus, the resulting film was endowed wtih an expanded free volume and concurrently curtailed dipole motion. These combined effects have led to a reduction in both D k and D f. The 6FDA-GB film exhibits a D k value of 2.70 and a D f value of 0.0022 at 10 kHz and room temperature. Remarkably, even at elevated temperatures up to 200 °C, the D k remains stable, with only a slight increase in D f (0.00386). This contribution holds promise for advancing the comprehensive performance of dielectric PIs and understanding the stability of dielectric properties at high temperatures.