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.
Yin et al. (Tue,) studied this question.