Eco-friendly synergistic cross-linking flame-retardant strategy with smoke and melt-dripping suppression for condensation polymers

Conventional methods to improve the flame retardancy of polymeric materials usually involve the use of flame-retardant elements such as Cl, Br and P, however, their use may bring more smoke and toxic gases hazards, and more importantly, cause non-negligible environmental and ecological problems. In this work, we put forward a novel green strategy that eliminates the use of any conventional flame-retardant elements to improve the flame retardancy by incorporating a synergistically cross-linkable structure (named PN) containing phenylacetylene and phenylimide groups. The resulting PN copolymer exhibited an excellent 55% lower smoke release rate and 68% lower heat release rate than the pure polymer, as well as a high LOI value of 32% and UL-94 V-0 rating with excellent anti-dripping performance. TG-DSC, rheological and FTIR results proved the high cross-linking ability of the PN copolymer due to the synergistic cross-linking effect between the “imide-isoimide” rearrangement of phenylimide and the “self-cross-linking” of phenylacetylene. The SEM, Raman and Py-GC/MS results further upheld the condensed phase flame-retardant mechanism. This eco-friendly synergistic cross-linking strategy provided new perspective for the design and synthesis of polymeric materials with excellent flame retardancy, great anti-dripping performance, and low release of heat, smoke, and toxic gas.