Overcoming the Trade-Off between Electrical Insulation and Mechanical Robustness of Polymers by Inorganic Ionic Molecular Segments

Compositing insulated inorganic nanoparticles in bulk polymers is widely applied to improve electrical insulation and mechanical properties. However, the use of inorganic nanoparticles always faces a trade-off in the coenhancement of both properties, limiting the performance from reaching an ideal state. This study reveals that "molecularization" of inorganic ionic compounds into a polymer network can overcome the trade-off between electrical insulation and mechanical robustness due to the molecular-size effect of inorganics. By using epoxy and calcium phosphate oligomers as examples, chemically functionalized calcium phosphate molecular segments are successfully copolymerized into epoxy to create a hybrid resin. The calcium phosphate molecular segments show increased bandgap and high interfacial fraction in epoxy, directing to a high alternating current (AC) breakdown strength (116.7 kV/mm). Meanwhile, the calcium phosphate molecular segments enhance the strength of the polymer network, increasing the flexural strength and bending toughness to 136.9 MPa and 8.85 MJ/m3, respectively. The overall electrical insulation and mechanical properties are superior to those of all reported and commercial bulk epoxy-based composites we have consulted. This work demonstrates that an inorganic ionic compound with a molecular-size effect is a promising unit for high-performance electrical insulation materials, supporting the development of advanced power equipment in the future.