Preparation, characterization and dielectric properties of 4,4-diphenylmethane diisocyanate (MDI) based cross-linked polyimide films

Flexible Ultrahigh-Temperature Polymer-Based Dielectrics with High Permittivity for Film Capacitor Applications

In this report, flexible cross-linked polyarylene ether nitrile/functionalized barium titanate(CPEN/F-BaTiO₃) dielectrics films with high permittivitywere prepared and characterized. The effects of both the F-BaTiO₃ and matrix curing on the mechanical, thermal and dielectric properties of the CPEN/F-BaTiO₃ dielectric films were investigated in detail. Compared to pristine BaTiO₃, the surface modified BaTiO₃ particles effectively improved their dispersibility and interfacial adhesion in the polymer matrix. Moreover, the introduction of F-BaTiO₃ particles enhanced dielectric properties of the composites, with a relatively high permittivity of 15.2 and a quite low loss tangent of 0.022 (1 kHz) when particle contents of 40 wt % were utilized. In addition, the cyano (⁻CN) groups of functional layer also can serve as potential sites for cross-linking with polyarylene ether nitrile terminated phthalonitrile (PEN-Ph) matrix and make it transform from thermoplastic to thermosetting. Comparing with the pure PEN-ph film, the latter results indicated that the formation of cross-linked network in the polymer-based system resulted in increased tensile strength by ~67%, improved glass transition temperature (Tg) by ~190 °C. More importantly, the CPEN/F-BaTiO₃ composite films filled with 30 wt % F-BaTiO₃ particles showed greater energy density by nearly 190% when compared to pure CPEN film. These findings enable broader applications of PEN-based composites in high-performance electronics and energy storage devices materials used at high temperature.

Instantaneous Pulsed-Light Cross-Linking of a Polymer Gate Dielectric for Flexible Organic Thin-Film Transistors

We report the instantaneous pulsed-light cross-linking of polymer gate dielectrics on a flexible substrate by using intensely pulsed white light (IPWL) irradiation. Irradiation with IPWL for only 1.8 s of a poly(4-vinylphenol) (PVP) thin film with the cross-linking agent poly(melamine-co-formaldehyde) (PMF) deposited on a plastic substrate was found to yield fully cross-linked PVP films. It was confirmed that the IPWL-cross-linked PVP films have smooth pinhole-free surfaces and exhibit a low leakage current density, organic solvent resistance, and good compatibility with organic semiconductor, and that they can be used as replacements for typical PVP dielectrics that are cross-linked with time and energy intensive thermal heating processes. The synchronization of the IPWL irradiation with substrate transfer was found to enable the preparation of cross-linked PVP films on large area substrates with a highly uniform capacitance. Flexible OTFT based on IPWL-cross-linked PVP dielectrics were found to exhibit good electrical performance that is comparable to that of devices with thermally cross-linked PVP dielectric, as well as excellent deformation stability even at a bending radius of 3 mm.

Low-dielectric polyimide nanofoams derived from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride and 2,2′-bis(trifluoromethyl)benzidine

A system is designed to study the properties of nanofoams as well as interactions between the matrix and decomposition products of thermal labile content. With the increase thermal labile content, the dielectric constants of PI nanofoams decrease.

Crosslinked polyarylene ether nitrile film as flexible dielectric materials with ultrahigh thermal stability

Dielectric film with ultrahigh thermal stability based on crosslinked polyarylene ether nitrile is prepared and characterized. The film is obtained by solution-casting of polyarylene ether nitrile terminated phthalonitrile (PEN-Ph) combined with post self-crosslinking at high temperature. The film shows a 5% decomposition temperature over 520 °C and a glass transition temperature (T_g) around 386 °C. Stable dielectric constant and low dielectric loss are observed for this film in the frequency range of 100–200 kHz and in the temperature range of 25–300 °C. The temperature coefficient of dielectric constant is less than 0.001 °C⁻¹ even at 400 °C. By cycling heating and cooling up to ten times or heating at 300 °C for 12 h, the film shows good reversibility and robustness of the dielectric properties. This crosslinked PEN film will be a potential candidate as high performance film capacitor electronic devices materials used at high temperature.

The effect of liquid stabilization on the structures and the conductive properties of polyimide-based graphite fibers

This stabilization method could effectively avoid a sudden jump in temperature and local heat storage during the carbonization, as well as help improve the stability of PI fibers.