A DOPO-based anhydride as co-hardener for cycloaliphatic epoxy resins with enhanced flame-retardant, thermal and dielectric property

Cycloaliphatic epoxy resins are widely used in electronic packaging owing to their excellent dielectric properties and weather resistance. However, their inherent flammability and the trade-off between flame retardancy and low dielectric properties limit practical applications. To address these issues, a phosphaphenanthrene-based anhydride (DPIA) was employed as a co-hardener for cyclosiloxane cycloaliphatic epoxy resins. The flame retardancy was gradually enhanced with increasing DPIA content, leading to a limiting oxygen index (LOI) up to 29.2% and achieving a UL-94 V-0 rating. Heat release was also significantly suppressed, with a 45% reduction in both peak heat release rate and total heat release. Meanwhile, the chemical incorporation of DPIA improved the thermal stability of the epoxy resins, as evidenced by increased thermal decomposition temperature, char residue, and glass transition temperature. The DPIA-modified epoxy resins also exhibited superior tensile strength compared to the control sample, attributable to good compatibility and the rigid structure of DPIA. Importantly, the chemical introduction of an appropriate amount of DPIA effectively enhanced the dielectric performance of the epoxy resins owning to the increment of free volume suppressing polarity. In summary, the chemical incorporation of DPIA simultaneously enhances the flame retardancy, thermal stability, dielectric properties, and mechanical performance of epoxy resins. Thus, this work provides a facile strategy for fabricating high-performance epoxy resins for applications in the electronic packaging field.