Flame retardancy of linear polyurethane with Diels–Alder adducts

Flame retardant polyurethane was synthesized via introducing thermally reversible covalent Diels–Alder (DA) adducts into the polyurethane main chain. Firstly, furan-terminated polyurethane prepolymer(PU-Furan) was synthesized from the reaction between isocyanate-terminated prepolymer with or without DOPO-based polyester polyols and furfuryl amine. Secondly, polyurethane with DA adducts (PU-DA) was obtained via Diels–Alder reaction between PU-Furan and commercial 1,1′-(methylenedi-1,4-phenylene) bismaleimide. PU-Furan and PU-DA were characterized by DSC, TGA and 1H NMR, confirming the introduction of the DA adducts into the polyurethane chain. The results of the limiting oxygen index test, Underwriter Laboratory 94 vertical burning (UL-94) test and cone calorimeter test demonstrated that the introduction of the DA adducts improved the flame retardancy of the polyurethane significantly, especially when the polyurethane with flame-retardant element P, due to the synergism flame-resistant effect between flame-retardant element P and thermally reversible DA adducts.