Hybrid ternary composites of hyperbranched and linear polyimides with SiO 2 : a research for low dielectric constant and optimized properties

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 SiO 2 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 SiO 2 , 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%_SiO 2 -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 _SiO 2 -10% composite, the optical transmittance is significantly improved to be 63% at the wavelength of 450 nm. With increase in the content of SiO 2 , the thermal expansion is obviously reduced. For the PI 6FDA-APB _HBPI BPADA-TAP(OH) -10%_SiO 2 -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.