Investigation of the Dual Polymerization of Rapid Curing Organophosphorous Modified Epoxy/Amine Resins and Subsequent Flame Retardancy

In this work, two rapid curing, low viscosity phosphorous modified epoxy amine resin systems are simultaneously cured via chain growth and step growth mechanisms. Anionic chain growth polymerization is catalyzed by a Lewis base using 2‐ethyl‐4‐methylimidazole (2E4MI), while cationic chain growth polymerization is catalyzed using a Lewis acid boron trifluoride ethyl amine (BF3). The effects of these catalysts and increasing chemical incorporation of 9,10‐dihydro‐9‐oxy‐10‐phosphaphenanthrene‐10‐oxide (DOPO) on the cure reaction, chemorheology, and flame retardancy are investigated. The 2E4MI catalyst accelerates the onset of cure, but retards cure at higher DOPO concentrations. The addition of BF3 also accelerates the onset of reaction further, but does not significantly retard cure with increasing DOPO. Increasing DOPO reduces the glass transition temperature regardless of catalyst but the imidazole displays a larger reduction. These contrasting effects are discussed in terms of the increased concentration of hydroxyl groups from DOPO retarding anionic polymerization, while establishing a secondary propagating reaction mechanism in the case of cationic polymerization. Rheological studies show that these formulations remain ideal for liquid molding fabrication technologies, while the cured resins maintain a V0 fire rating according to the UL‐94 test and are promising candidates for the rapid manufacture of fire resistant composites.