One effective route to reduce the dielectric constant is to directly incorporate hollow silica (HoSiO2) microspheres into a polymeric matrix. However, the incompatibility between silica and hydrophobic polymers possibly results in interfacial defects and polarization, and thus a high dielectric loss. In this study, the HoSiO2 microspheres were coated by polystyrene using a surface-initiated ATRP method in order to enhance interfacial property. TGA results indicated that the weight percentage of polystyrene in resulting microspheres (HoSiO2@SI-PS) reached around 33 wt%. OM images showed that the thickness of the polystyrene layer reached around 2 μm. HoSiO2@SI-PS microspheres with a weight percentage of 25% were incorporated into polyethylene (PE) to prepare the composites. The dielectric measurement results indicated that the dielectric constant of the composites was reduced to 2.05, while maintaining low dielectric loss at the level of 10−4. In comparison, when HoSiO2@C-PS microspheres, which were prepared by conventional vinyl-initiated free radical polymerization, were incorporated into polyethylene, the dielectric loss was greatly elevated to 0.007. SEM images and water absorption experiments further revealed that the low dielectric loss of PE/HoSiO2@SI-PS was related to the dense interfacial structure, strong interfacial interaction and low water absorption ability.
