Effect of nitrile-functionalization and thermal cross-linking on the dielectric and mechanical properties of PEN/CNTs–CN composites

In this study, a novel series of composite films consisting of nitrile-functionalized carbon nanotubes (CNTs–CN) and poly(arylene ether nitriles) (PEN) were successfully fabricated by the tape-casting method. The –CN groups in PEN chains and the phthalonitrile groups on CNTs–CN formed the thermally stable triazine rings by thermal cross-linking reaction in the presence of diamino diphenyl sulfone, which was characterized by Fourier transform infrared spectroscopy. The result indicated that the chemical cross-linking reaction occurred accompanied by the emergence of a new absorption peak at 1,361 cm⁻¹. Besides, the effect of cross-linking on the morphology, thermal stability, mechanical and dielectric properties of the PEN/CNTs–CN was investigated. The SEM images showed that the phase interface between surface modified CNTs and PEN matrix was indistinct, and the surface modified CNTs presented a better dispersion behavior in PEN matrix. The mechanical properties of the processed films were improved substantially compared with the unprocessed films. Furthermore, the glass-transition temperature (T _g ) of composite films processed at 320 °C for 4 h (about 245 °C) was higher than that of composite films before thermal treatment (about 205 °C). The 5 % weight loss temperature of the composite films (processed at 320 °C for 4 h) increased by about 110 °C compared with the composite films (unprocessed). More importantly, by thermal cross-linking, the dielectric constant (ε) of composite films with 8 wt% CNTs–CN loading was increased from 31.8 to 33.9, and dielectric loss (tan δ) was decreased from 0.90 to 0.61 at 1 kHz.