Enhanced dielectric properties of sandwich‐structured biaxially oriented polypropylene by grafting hyper‐branched aromatic polyamide as surface layers

Abstract This work represents multilayer films with sandwich structure by grafting hyper‐branched aromatic polyamide (HBP) on both sides of biaxially oriented polypropylene (BOPP) (HBPBOPPHBP). BOPP serves as the middle layer to offer high breakdown strength and HBP acts as surface layers to boost the dielectric constant. As a result, the dielectric constant increases significantly from 2.2 of control BOPP to 5.5 (almost increased 1.5 times) after grafting 2.06 μm HBP surface layers, while the dielectric loss still remains at a very low level (<0.03). In addition, all HBPBOPPHBP sandwich‐structured films show higher charge energy density than that of unmodified BOPP. For instance, the discharge energy density of HBPBOPPHBP (1‐20‐1) film is up to 2.38 J/cm 3 at an applied electric field of 400 kV/mm, which increases about 36% over that of pure BOPP (i.e., 1.75 J/cm 3 ). Meanwhile, charge–discharge efficiency retains about 90%. This work offers a simple strategy to fabricate polymer‐based high performance dielectric composites.