Core/shell-structured hyperbranched aromatic polyamide functionalized graphene nanosheets-poly(p-phenylene benzobisoxazole) nanocomposite films with improved dielectric properties and thermostability

This study reports the synthesis of core/shell-structured hyperbranched aromatic polyamide functionalized graphene nanosheets-poly(p-phenylene benzobisoxazole) (GNs-HAP-PBO) nanocomposite films with improved dielectric properties and thermostability. PBO precursor polymer chains were grafted onto the ample amino-terminated GNs-HAP via in situ polymerization, and then the reduction of GNs-HAP and the intramolecular cyclization of PBO precursors were achieved through thermal treatment. The unique core/shell-structure is effective to prevent the aggregation of GNs and improves the dispersion of GNs in the GNs-HAP-PBO nanocomposites, forming microcapacitor networks in the matrix. The GNs-HAP-PBO nanocomposite films exhibit lower dielectric loss in comparison with solvothermally reduced graphene oxide/PBO nanocomposite films. At 1 kHz and 200 °C, a dielectric constant of 66.27 and a dielectric loss of 0.045 are observed in the GNs-HAP-PBO nanocomposite films with 2 wt% GNs-HAP. Moreover, the maximum energy density of the GNs-HAP-PBO nanocomposite films is up to 6 J cm−3 owing to the high breakdown strength (132.5 ± 9.3 kV mm−1). The GNs-HAP-PBO nanocomposite films with 2 wt% GNs-HAP also exhibit excellent tensile strength (125 MPa), Young's modulus (6.4 GPa), and high thermal stability (temperature of 5 wt% loss = 643 °C). This work demonstrates a promising strategic approach to fabricating high dielectric materials under extreme environments.