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

• Published in: RSC advances Vol. 5; no. 119; pp. 98419 - 98428
• Main Authors: Kim, Seongku, Ando, Shinji, Wang, Xiaogong
• Format: Journal Article
• Language: English
• Published: 01.11.2015
• Subjects: Crosslinking; Dielectric constant; Dispersion; Electronics; Hybrid composites; Networks; Polyimide resins; Silicon dioxide
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/c5ra20722c

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 HBPI BPADA-TAP(Si) . This method involves modifying the polymer termini by coupling (3-isocyanatopropyl)triethoxysilane to HBPI BPADA-TAP(OH) via the hydroxyl (-OH) groups at peripheral positions of the polymer chain. Then, based on the HBPI BPADA-TAP(Si) with silane-modified termini, linear PI 6FDA-APB(Si) and tetraethoxysilane cross-linking agent were used to prepare ternary composites, PI 6FDA-APB(Si) _HBPI BPADA-TAP(Si) _SiO 2 , by sol-gel cross-linking reaction. The dielectric constant ( D k ) of PI 6FDA-APB(Si) _HBPI BPADA-TAP(Si) -30%_SiO 2 -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 HBPI BPADA-TAP(Si) and PI 6FDA-APB(Si) that improves phase dispersion. The highest transparency, 95% at 450 nm, was obtained for PI 6FDA-APB(Si) _HBPI BPADA-TAP(Si) -30%_SiO 2 -20%, a significant improvement from that (87%) of the binary composite of PI 6FDA-APB(Si) _SiO 2 -20%. The glass transition temperature ( T g ) of PI 6FDA-APB(Si) _HBPI BPADA-TAP(Si) -30%_SiO 2 -20% is 212.6 °C, which is the highest in the ternary composite series. PI 6FDA-APB(Si) _HBPI BPADA-TAP(Si) -40%_SiO 2 -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 HBPI BPADA-TAP(Si) content. The ternary hybrid composites with densely cross-linked SiO 2 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. Flexible insulating materials that are both thermally and mechanically stable, highly transparent, and have low dielectric constants are highly desirable for electronic applications.