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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. [ABSTRACT FROM AUTHOR]

Linear polyurethane was synthesized by Diels-Alder (DA) reaction between a polyurethane prepolymer end-capped with furan rings (MPF) and bismaleimide (BMI). The polymerization kinetics were studied following a preliminary kinetic study of the DA reaction between furfuryl alcohol (FA) and BMI compounds by attenuated total reflection infrared, ultraviolet-visible and in situ H NMR spectroscopies, where in situ H NMR spectroscopy was selected as the analytical method of choice to study the DA reaction between MPF and BMI. The results showed that the reaction followed second-order kinetics, and the most beneficial experimental conditions to maximize conversion were identified. [ABSTRACT FROM AUTHOR]

Polyurethane hot melt adhesive was synthesized without any solvent via Diels-Alder (DA) reaction between furan terminated prepolymer and bismaleimide (BMI) and was coded as PU-DA-NS. Firstly the DA reaction was inhibited at higher temperature (110 °C) to reduce the viscosity and benefit the contact of furan terminated prepolymer and BMI. Consequently, PU-DA-NS was obtained via DA reaction at lower temperature (70 °C). The structure of PU-DA-NS was investigated via 1H NMR, DSC and TGA. The results showed that the solvent-free preparation cannot reach the reaction degree of solvent preparation, due to the contact of the reactants cannot be as good as preparation in solvent such as DMF, although the higher temperature decreased the viscosity of the reactant. However the heating and pressing procedure during the adhesive process destroyed the looser structure and increased the adhesive tensile strength to 70 % of PU-DA synthesized via solvent preparation. [ABSTRACT FROM AUTHOR]