A DOPO‐based reactive flame retardant containing benzimidazole groups: Synthesis and its flame‐retardation on epoxy resin

Abstract

DOPO based flame retardants demonstrate exceptional flame retardancy efficiency when applied to epoxy resins. However, the crosslinking degree of epoxy resin may decrease due to the addition of DOPO, leading to a deterioration in flame retardancy and mechanical properties. Herein, a reactive DOPO derivative flame retardant 6‐((1H‐benzo[d]imidazol‐2‐yl) amino) dibenzo oxaphosphinine 6‐oxide (BADO) was successfully synthesized, which contains multiple reactive sites, thus ensuring a higher degree of crosslinking in the system. As a result, the modified epoxy resin exhibits excellent flame retardancy. The limiting oxygen index value of the modified epoxy resins increased from 19.8% to 29.7% by adding 7.5 wt% BADO, and its UL‐94 test passed V‐0. Flame retardancy mechanism analysis reveals that BADO exhibits both gas‐phase and condensed‐phase flame retardant effects. In particular, the formation of a porous inside‐char layer is a significant factor in reducing smoke release. The 7.5% BADO/EP composite exhibited a 43.2% reduction in total smoke production and a 43.6% reduction in total smoke rate compared to neat epoxy resins (EP). Furthermore, the addition of BADO slightly deteriorates the mechanical properties of the modified epoxy resin.

In-Situ Formation of Polynanosiloxane by a Multifunctional Phosphaphenanthrene–Silicone–Epoxy Soybean Oil Flame Retardant Improves the Toughness and Transparency of Epoxy Resin

“…28 Jiang et al produced a FR (BADO) by merging DOPO with aminobenzimidazole. 29 Incorporating 2.5−7.5% FRs, the epoxy composites achieve an increased limiting oxygen index (LOI) value of 25.5−30.7%, satisfying the UL-94 rating. However, the impact strength of the composites decreases by approximately 6−19% due to the excessively rigid molecular structure of FRs.…”

“…Chen et al synthesized a FR curing agent incorporating phosphoric anhydride . Jiang et al produced a FR (BADO) by merging DOPO with aminobenzimidazole . Incorporating 2.5–7.5% FRs, the epoxy composites achieve an increased limiting oxygen index (LOI) value of 25.5–30.7%, satisfying the UL-94 rating.…”

A novel organic-inorganic nanohybrid, DOPO-AS@M (OH)(OCH3) (M = Co, Ni), enhances the flame retardancy and mechanical properties of epoxy resin

“…DOPO contains highly reactive P-H bonds, which can undergo addition reactions with various functional groups such as C = N bonds [12], C = C bonds [13], alkynes [14], carbonyls [15], epoxy groups [16] and so on and prepare a diverse range of DOPO derivatives [17,18], demonstrating the broad potential of DOPO molecules in structural design. However, in the most case, the cross-linking density of EP decreases with the addition of DOPO derivatives increases, which generally deteriorate the mechanical properties of EP [19,20]. For instance, He et al [21] synthesized the DOPO derivative (BMP) for use in EP.…”