Carborane-modified polyetherimide films for high-temperature dielectric applications

Abstract

While polyetherimide (PEI) is widely used in electrical insulation and 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, and 20 wt%) were synthesized by copolymerizing the rigid monomer 1,2-dibenzylamino-o-carborane (BACB) with 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA) and p-phenylenediamine (PDA). Incorporation of the three-dimensional carborane cage effectively enhanced the thermomechanical and dielectric properties. The composites exhibited good thermal stability, with 5% weight loss temperatures (T_d5%) reaching up to 509 °C in argon and exceeding 500 °C in air, alongside elevated glass transition temperatures (T_g = 240 °C). Additionally, the carborane units reduced the dielectric constant (ε_r) and the dielectric loss tangent (tan δ) by enlarging free volume and suppressing dipole polarization. 10BACB/PEI achieved the lowest ε_r (3.31 at 20 °C) and the smallest tan δ increase (Δtan δ = 0.68) from 20 °C to 200 °C. Furthermore, the breakdown strength increased from 9.33 kV mm⁻¹ (neat PEI) to 75.5 kV mm⁻¹ (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.