Polyhedral oligomeric silsesquioxane (POSS) constructed stable cross-linking network in polyimide for enhanced flame retardant, mechanical and corona resistance properties

As electrical equipment is progressively advancing towards high-power and large-capacity integration, the electrical insulation components frequently experience severe structural damage and performance degradation when they are exposed to significant voltage impact. Modifying the insulating base materials through filling to enhance their corona resistance is a critical measure to ensure the safe operation of electrical equipment. This article proposes, for the first time, a distinct modification strategy of cage-like octa(aminopropyl) silsesquioxane (8NH₂-POSS) particle toward the molecular structure of polyimide. This particle can form covalent bonds with both the main chains and side chains of polyimide (PI) during polymerization, thereby enhancing the flame retardant, mechanical and corona resistance of the polyimide matrix. Benefiting from the organic-inorganic hybrid structure, the POSS with amino groups provides interfacial compensation for PI at the molecular structural level. The power frequency breakdown strength of the 8NH₂-POSS main-chain grafted PI composite film (8NMP/PI) is increased by 31.5%, and the corona discharge inception voltage is enhanced from 1.93 to 2.13 kV. And the average corona resistance time of 8NMP/PI is prolonged from 305 to 498 s, which is 63.3 % higher than the pure PI film. Meanwhile, its excellent interface effect improves the flexibility of the composite film, with the average tensile strength increased by 17.6% and the elongation at break by 16.2 %. All composite films have reached UL-94 V-0 rating. This work provides valuable reference for developing high-performance polymer composites for applications in large-scale electrical devices.