Carborane-Modified Polyetherimide Films for High-Temperature Dielectric Applications

Abstract

While polyetherimide (PEI) is widely used in electrical insulation, aerospace components, its high-temperature performance remains limited due to thermal degradation and dielectric loss at elevated temperatures. To address these limitations, a series of PEI composite films (xBACB/PEI, x = 5, 10, 15, 20 wt%) was synthesized by copolymerizing the rigid monomer 1,2-Dibenzylamino-o-carborane (BACB) with 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA) and pphenylenediamine (PDA). Incorporation of the three-dimensional carborane cage effectively enhanced thermomechanical and dielectric properties. The composites exhibited good thermal stability, with 5% weight loss temperatures (Td5%) reaching up to 509 °C in argon and exceeding 500 °C in air, alongside elevated glass transition temperatures (Tg =240 °C). Additionally, the carborane units reduced the dielectric constant (ɛr) and dielectric loss tangent (tanδ) by enlarging free volume and suppressing dipole polarization. The 10BACB/PEI achieved the lowest ɛr (3.31 at 20 °C) and the smallest tan δ increase (Δtanδ = 0.68) from 20 °C to 200 °C. Furthermore, breakdown strength increased from 9.33 kV/mm (neat PEI) to 75.5 kV/mm (15BACB/PEI), demonstrating good dielectric reliability. This work presents a viable molecular design strategy for developing high-performance insulating materials that are operable under extreme conditions.