Tailored Molecular Fillers Enable High‐Temperature Insulation and Long‐Term Operating Stability in All‐Organic Polymers

A fundamental challenge in the realm of polymer dielectrics is the suppression of charge injection and transport. Here, an application-driven molecular engineering strategy is reported to enhance electrical insulation performance, utilizing the TU3 organic molecule with a benzo[1,2-c:4,5-c']bis([1,2,5]thiadiazole) backbone as a reinforcing filler for epoxy resin (EP), which introduces trap energy levels through the difference in electron affinity. Additionally, thienyls are incorporated to form a zwitterionic structure with high stability. The TU3 molecule can form stable complexes with EP via extensive electrostatic interactions and intermolecular charge transfer, establishing charge traps at the molecular interface that effectively inhibit charge injection and transport in the TU3/EP composites. Furthermore, the cyano and long alkyl groups on both sides of TU3 enhance its solubility and impede the migration of small molecules within the polymer matrix. The results indicate that with only 0.02 wt% TU3, the breakdown strength of the composites increased by 30.75% at room temperature and 52.28% at 120°C. Experimental and computational investigations validate the long-term operating stability of the TU3/EP composites under extreme thermal and electrical stress. This work provides new insights into the design of small organic molecules aimed at enhancing the electrical insulation of polymer dielectrics under extreme conditions.