Engineering Sulfur‐Containing Polymeric Fire‐Retardant Coatings for Fire‐Safe Rigid Polyurethane Foam

Abstract With the advantages of lightweight and low thermal conductivity properties, polymeric foams are widely employed as thermal insulation materials for energy‐saving buildings but suffer from inherent flammability. Flame‐retardant coatings hold great promise for improving the fire safety of these foams without deteriorating the mechanical‐physical properties of the foam. In this work, four kinds of sulfur‐based flame‐retardant copolymers are synthesized via a facile radical copolymerization. The sulfur‐containing monomers serve as flame‐retardant agents including vinyl sulfonic acid sodium (SPS), ethylene sulfonic acid sodium (VS), and sodium p‐styrene sulfonate (VSS). Additionally, 2‐hydroxyethyl acrylate (HEA) and 4‐hydroxybutyl acrylate are employed to enable a strong interface adhesion with polymeric foams through interfacial H‐bonding. By using as‐synthesized waterborne flame‐retardant polymeric coating with a thickness of 600 µm, the coated polyurethane foam (PUF) can achieve a desired V‐0 rating during the vertical burning test with a high limiting oxygen index (LOI) of >31.5 vol%. By comparing these sulfur‐containing polymeric fire‐retardant coatings, poly(VS‐ co ‐HEA) coated PUF demonstrates the best interface adhesion capability and flame‐retardant performance, with the lowest peak heat release rate of 166 kW m −2 and the highest LOI of 36.4 vol%. This work provides new avenues for the design and performance optimization of advanced fire‐retardant polymeric coatings.