Design of bi-modal pore structure polyarylene ether nitrile/SiO2 foams with ultralow-k dielectric and wave transparent properties by supercritical carbon dioxide

The introduction of the pores into polymers is an efficient method to prepare the materials with low dielectric constant (ε) and low dielectric loss tangent (tan δ). Herein, low-weight polyarylene ether nitrile (PEN)/SiO2 foams with bi-modal pore structure were prepared via supercritical carbon dioxide batch foaming. The effects of SiO2 as heterogeneous nucleation on the dielectric properties, wave-transparent properties, thermal conductivity properties and mechanical properties of PEN/SiO2 foams have been investigated. Compared with PEN/SiO2 films, PEN/SiO2 foams showed excellent properties, which was most probably due to their uniform bi-modal pore morphology. As cell density and the SiO2 weight content was increased, ε and tan δ of the PEN/SiO2 foams decreased to 1.71 and 0.0047, respectively. The PEN/SiO2 foams exhibited ultra-low dielectric constant, showing low temperature and stabilization dielectric properties from −100 °C to 120 °C. Furthermore, the wave-transparent properties of PEN/SiO2 films and foams, which are required for wave-transparent application, were also investigated. The thermal insulating properties of PEN/SiO2 foams were remarkably improved after the pores and SiO2 fillers were introduced into the PEN polymer, with thermal conductivity reaching as low as 0.073 W/m K. PEN/SiO2 foams showed markedly increased elongation at the break, compared with PEN/SiO2 films, whereas tensile strength ＞50 MPa. The excellent properties of PEN/SiO2 foams indicated their potential as dielectric materials for microelectronics and wave-transparent materials for aerospace technology.