Novel hydration induced flexible sulfonated poly(etherketoneketone) foam with super dielectric characteristics

Abstract

High performance thermoplastic polymers, such as poly(etherketoneketone) (PEKK), etc., with excellent mechanical properties and thermo-oxidative stability are in great demand for expanding commercial applications. Transforming these materials into foamed structures through energy efficient approaches can be dramatically significant for various applications in which weight is critical. Due to the rigid aromatic structures, foaming them is normally extremely difficult via blowing agent assisted foaming techniques. In this study, homogeneous sulfonated PEKK (SPEKK) foam was fabricated through a facile and energy efficient hydration reaction induced self-foaming approach, in which, water acted as the blowing agent. The resulting SPEKK foam has a uniform pore size of ca. 5 μm and a cell density of 9.77 × 10⁹cell per cm³, as well as a very low mass density of 0.42 g cm⁻³, suggesting a superiority to other foam structures reported, such as poly(aryl ether ketone) microcellular foams fabricated by conventional blowing agent assisted foaming techniques. The dielectric study demonstrated that the microcellular SPEKK foam possesses great potential for use in energy storage applications. The as prepared SPEKK foam showed a dramatically high permittivity (10⁹ at 0.01 Hz and ca. 10⁶ at 1000 Hz). At the same time, the SPEKK foam has a rather low dielectric loss, between 2 and 10 over the whole frequency range. With the dehydration of SPEKK foam, the relative permittivity dropped, but was still as high as ca. 10⁷ at 0.01 Hz and ca. 10³ at 1000 Hz.