Preparation of novel aramid film with ultra-high breakdown strength via constructing three-dimensional covalent crosslinked structure

Electrical insulation materials with excellent thermal resistance and high breakdown strength have great application potential in energy storage devices. Herein, poly(benzimidazole-terephthalamide) (PABI) film with ultra-high breakdown strength was prepared by introducing three-dimensional covalent crosslinked structure, which was constructed by reactive PABI oligomers (PABI-O) and nano-SiO 2 derivate (SiO 2 -Ac). PABI-O was end-capped with acryloyl chloride, and crosslinking reaction of C C groups from acryloyl chloride could take place above 300 °C. Then, SiO 2 -Ac grafted with large amounts of C C groups on its surface was prepared, and it was blended with PABI-O, which was followed by processing into films and annealing at 360 °C. Due to steric structure of SiO 2 -Ac and large amounts of C C groups on its surface, three-dimensional crosslinking can be attained in the composite film by radical addition reaction of SiO 2 -Ac and PABI-O. It is found that the three-dimensional crosslinked structure can increase path tortuosity in the electrical treeing breakdown, which endows the film with breakdown strength up to 624 kV mm −1 and shows 70% enhancement compared with that of Kapton film (a famous polyimide film). Moreover, the film exhibits excellent mechanical properties and dimensional stability. Tensile strength of the film is nearly 340 MPa, and the coefficient of thermal expansion (CTE) is only 5.06 ppm/°C at 20–250 °C.