Long shelf life, intrinsically flame retardant, transparent, high-performance one-component epoxy resin based on phosphorus-containing imidazole derivatives

Highly evolving 5G and electronic packaging technologies require one-component epoxy resins with high flame retardancy, long shelf life, and fast curing while maintaining transparency & mechanical properties. However, it's tricky and challenging to meet this requirement simultaneously. Herein, two latent phosphorus-containing imidazole curing agents (PHI-HPP and EMI-HPP) were synthesized from 2-ethyl-4-methylimidazole (EMI) and 2-phenylimidazole (PHI). PHI-HPPx/EP exhibits a superior shelf life than EMI-HPPx/EP. PHI-HPPx/EP allows stable storage at room temperature exceeding 91 days, which is better than previous one-component epoxy resins cured by phosphorus-containing imidazole. PHI-HPP20/EP and EMI-HPP20/EP allow for fast curing at 150 °C and also feature excellent fire safety. In particular, PHI-HPP20/EP features a limiting oxygen index (LOI) of 35.8% and achieves the UL-94 V-0 rating. Its peak heat release rate (PHRR) is reduced by 59.3% compared to PHI/EP. Notably, PHI-HPPx/EP and EMI-HPPx/EP maintain the inherent excellent transparency, mechanical properties and glass transition temperature (Tg) of epoxy resins. Therefore, this research presents a viable approach for preparing one-component epoxy resin with long shelf life, fast curing, flame retardant, transparency and high performance.