Synthesis and properties of poly(ester imide) copolymers from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride, 2,2′‐bis(trifluoromethyl)benzidine, and 4‐aminophenyl‐4′‐aminobenzoate

Abstract A series of poly(ester imide) (PEsI) copolymers were synthesized using 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (4,4′‐BPDA), 2,2′‐bis(trifluoromethyl)benzidine (TFMB), and 4‐aminophenyl‐4′‐aminobenzoate (APAB) as the monomers. Wide‐angle x ‐ray diffraction results revealed that the average interchain distances of these polymers ranged from 4.6 to 5.7 Å, increasing with the increase of TFMB contents. PEsI‐0.3 and PEsI‐0.4 exhibited a glass transition temperature ( T g ) of 445 and 455°C, respectively, while no distinctive T g was observed for the PEsI copolymers when the APAB content was >50 mol%. The coefficients of thermal expansion (CTE) of these PEsI copolymers ranged from 3.8 to 24.2 ppm K −1 , increasing with the increase of TFMB contents. The PEsI copolymers exhibited a modulus of 5.7–7.8 GPa, a tensile strength of 282–332 MPa, and an elongation‐at‐break of 10.2%–23.3%. Furthermore, these copolymers exhibited a dielectric constant of 2.53–2.76, and a low dissipation factor ( D f ) of 0.0026–0.0032 at 10 GHz in dry state. Because of their excellent combined properties, these PEsI copolymers are promising candidates as dielectric substrate materials for the applications in next generation flexible printed circuit boards operating at high frequencies.