Fabrication of flame retardant poly(methyl methacrylate) with excellent comprehensive properties based on a new phosphorus-silicon-nitrogen-synergistic system

•A new hybrid, polyphosphate-coated silica (SZP), was prepared.•A phosphorus-silicon-nitrogen synergistic flame retardant system was constructed.•The prepared composites have excellent comprehensive properties in addition to high flame retardancy. In general, the addition of phosphate ester flame retardants can improve the flame retardancy of polymethyl methacrylate (PMMA), but the flame retardant efficiency is low when phosphate ester is used alone and the tensile strength and hardness of the material are reduced. It is a challenge to improve the flame retardancy of PMMA while maintaining its inherent mechanical properties. In this study, a polyphosphate-coated silica (SZP) was prepared, which was compounded with dimethyl methylphosphonate (DMMP). At the same time, methacrylamide (MAM), which can be copolymerized with PMMA, was introduced to construct a synergistic phosphorus-nitrogen-silicon flame retardant system. The three components can work together in the gas phase and condensed phase. The results showed that when 12.5% DMMP, 5% MAM and 2.5% SZP were added, the composite material had the best comprehensive performance, its limiting oxygen index (LOI) reached 25.1%, and its total heat release was only 70% of the pure sample. More importantly, the addition of DMMP would significantly reduce the mechanical properties of PMMA. The introduction of SZP and MAM alleviated this problem. Compared with the pure sample, the mechanical properties of PMMA7 did not decrease but increased slightly. The flame retardant mechanism was also analyzed. This study provides a new idea for the industrialization of flame retardant PMMA.