Semiaromatic Poly(ester imide) Copolymers with Alicyclic Diamines for Low-K Properties at a High Frequency of 10–40 GHz

Abstract

High Resolution Image Download MS PowerPoint Slide Polyimide, a highly promising insulating material for high-frequency applications, has recently been the focus of attention. In particular, poly(ester imide) (PEI) has garnered significant interest due to its remarkably low dissipation factor ( D f < 0.002 @ 10 GHz) and coefficient of thermal expansion (CTE < 20 ppm K –1 ). However, its relatively high dielectric constant ( D k > 3.0 @ 10 GHz) has posed a challenge for its use in high-frequency flexible circuit boards. This study presents the approach by introducing a series of alicyclic diamines with varying steric hindrances into the PEI backbone to disrupt the molecular chain stacking and reduce PEI’s D k . The copolymerization of PEIs with a series of alicyclic diamines, including 1,4-cyclohexane diamine, 1,4-bis(aminomethyl) cyclohexane, 4,4′-methylenebis (cyclohexylamine), bis(aminomethyl)norbornane, tricyclodecane diamines (TCDDA), has yielded promising results. Notably, TCDDA, a value-added chemical derived from a well-known petroleum waste of dicyclopentadiene, has shown significant potential. The results demonstrate that introducing flexible methyl linkers, bicyclic rings, bridged rings, or fused rings effectively reduces D k by increasing the steric hindrance. Importantly, PEIs can maintain low D f and decent thermal and mechanical properties. Among them, PEI with 10 mol % TCDDA demonstrates excellent properties, including a glass transition temperature higher than 380 °C, low CTE of 15.7 ppm K –1, high ultimate tensile strength of 132.4 MPa, high elongation at break of 8.5%, and low D k (2.88/2.67) and D f (0.0019/0.0025) at 10/38 GHz. The steric hindrance generated by TCDDA achieves an optimal balance in thermal, mechanical, and dielectric properties, making it a promising low-dielectric insulating layer for next-generation communication.

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