Hybrid ternary composites of hyperbranched and linear polyimides with SiO2: a research for low dielectric constant and optimized properties

Abstract

Based on a hydroxyl-terminated hyperbranched polyimide (HBPI_{BPADA-TAP(OH)}), two series of hybrid ternary composites composed of a linear polyimide (PI_6FDA-APB), HBPI_{BPADA-TAP(OH)} (10% and 20%), and various concentrations of SiO₂ were fabricated by sol–gel method. Research showed that properties of the composites are closely related with the ratio of HBPI_{BPADA-TAP(OH)} to SiO₂, which can be optimized by proper choice of the compositions. Under optimized conditions, the hybrid ternary composites show properties complementary to the drawbacks of unary or binary systems. The dielectric constant (D_k) of the PI_6FDA-APB_HBPI_{BPADA-TAP(OH)}-10%_SiO₂-10% composite reaches the lowest value of 2.26. The silica loading and reinforcement binding with PI_6FDA-APB_HBPI_{BPADA-TAP(OH)} matrix are confirmed by the SEM morphology of the hybrid ternary composite films. When a suitable amount (20%) of HBPI_{BPADA-TAP(OH)} is added into the PI_6FDA-APB_SiO₂-10% composite, the optical transmittance is significantly improved to be 63% at the wavelength of 450 nm. With increase in the content of SiO₂, the thermal expansion is obviously reduced. For the PI_6FDA-APB_HBPI_{BPADA-TAP(OH)}-10%_SiO₂-30% composite, the coefficient of thermal expansion (CTE) of the film is reduced to 15.9 ppm °C⁻¹ compared to 37.1 ppm °C⁻¹ for the PI_6FDA-APB film (reducing about 59%). Due to these optimized properties, hybrid ternary composite films are expected to have potential applications in micro-electronic insulator fields such as interlayer dielectric of advanced electronic devices.