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Flexible insulating materials that are both thermally and mechanically stable, highly transparent, and have low dielectric constants are highly desirable for electronic applications. With these technical needs, a highly disperse inorganic matrix is the most important factor in polyimide–inorganic composites. We report an optimised method for the preparation of a hyperbranched polyimide using HBPIBPADA-TAP(Si). This method involves modifying the polymer termini by coupling (3-isocyanatopropyl)triethoxysilane to HBPIBPADA-TAP(OH) via the hydroxyl (–OH) groups at peripheral positions of the polymer chain. Then, based on the HBPIBPADA-TAP(Si) with silane-modified termini, linear PI6FDA-APB(Si) and tetraethoxysilane cross-linking agent were used to prepare ternary composites, PI6FDA-APB(Si)_HBPIBPADA-TAP(Si)_SiO2, by sol–gel cross-linking reaction. The dielectric constant (Dk) of PI6FDA-APB(Si)_HBPIBPADA-TAP(Si)-30%_SiO2-20% was very low, 2.04, and the optical transparencies of the ternary hybrid composite films also improved over those of similar composites due to the synergistic interactions between HBPIBPADA-TAP(Si) and PI6FDA-APB(Si) that improves phase dispersion. The highest transparency, 95% at 450 nm, was obtained for PI6FDA-APB(Si)_HBPIBPADA-TAP(Si)-30%_SiO2-20%, a significant improvement from that (87%) of the binary composite of PI6FDA-APB(Si)_SiO2-20%. The glass transition temperature (Tg) of PI6FDA-APB(Si)_HBPIBPADA-TAP(Si)-30%_SiO2-20% is 212.6 °C, which is the highest in the ternary composite series. PI6FDA-APB(Si)_HBPIBPADA-TAP(Si)-40%_SiO2-20% has the largest storage modulus, 2952.0 MPa at 180 °C. The tan δ values of the composite films decreased from 0.96 to 0.73 with increasing HBPIBPADA-TAP(Si) content. The ternary hybrid composites with densely cross-linked SiO2 covalent networks developed in this study have improved dielectric, optical, thermal, and mechanical properties. Our fabrication method paves the way to the facile production of high-performance flexible and transparent electronic circuits that could be used in a broad range of applications in future electronics.

rsc advances

Highly dispersible ternary composites with high transparency and ultra low dielectric constants based on hyperbranched polyimide with organosilane termini and cross-linked polyimide with silica