Preparation of high‐efficient flame retardant PA6 via DOPO‐ITA initiated ring‐opening polymerization of caprolactam

Abstract It has been a long‐term challenge to synthesize intrinsically flame retardant polyamide 6 (FRPA6) with high‐molecular weight. In this work, through the ring‐opening polymerization of caprolactam initiated by 9,10‐dihydro‐10‐[2,3‐di(hydroxycarbonyl)propyl]‐10 phosphaphenanthrene‐10‐oxide (DOPO‐ITA), intrinsically flame retardant PA6 with high‐molecular weight was successfully prepared. Its chemical structure, thermal stability, mechanical and combustion properties, as well as the retarding mechanism were thoroughly characterized in detail. The FRPA6 containing 3.0% retardant could achieve a V‐0 rating with an LOI value of 31.2%. An interesting phenomenon was observed during V‐0 tests. The melt drip slowly extended downward to form a long strip after moving fire, which was in favor of its heat release in a short time, thereby effectively prevented it from igniting the cotton. That is, a facile method to prepare intrinsically high‐efficiency fire retardant polymer via ring opening and polycondensation was proposed.