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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]

ABSTRACT Diels-Alder (DA) reactions between furan and maleimide have been widely applied in thermally remendable polymeric materials. Crosslinked polyurethane with DA adducts exhibited much better mechanical properties than linear polyurethane with DA adducts. However, the highly crosslinked polyurethane needs a higher temperature and a longer healing time. This will increase the possibility of side reactions proceeding during the healing procedure. In this paper, slightly crosslinked polyurethane with DA adducts was synthesized by incorporating trimethylolpropane into linear polyurethane with DA adducts. The structure of the intermediate and final products was characterized by Fourier transform infrared spectroscopy, 1H-NMR, and differential scanning calorimetry, confirming that the synthesizing process proceeded successfully. The images from the polarizing optical microscope demonstrated that the final product with slight crosslinking needed less time and a lower healing temperature to complete the healing procedure. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43971. [ABSTRACT FROM AUTHOR]

ABSTRACT The Diels-Alder (DA) reaction is particularly desirable for the preparation of heat-stimuli self-healing polymeric materials because of its thermal reversibility, high yield, and minimal side reactions. Some attempts were conducted to synthesize polyether-maleimide-based crosslinked self-healing polyurethane with DA bonds (C-PEMIPU-DA) through the reactions of the prepolymer (polymeric MDI/PBA-1000) functionalized by furfuryl amine and polyether-maleimide without benzene in this study. The structures of intermediates and C-PEMIPU-DA were first confirmed by 1H-NMR, Fourier transform infrared spectroscopy, and differential scanning calorimetry. Next, the thermal reversibility and the self-healing performance of C-PEMIPU-DA were studied by 1H-NMR, polarizing optical microscopy, tensile testing, and a sol-gel process. The results show that C-PEMIPU-DA exhibited interesting properties of thermal reversibility and self-healing. The polymers could be applied to self-healing materials or recyclable materials in the fields of the repair of composite structures and aging parts because of their thermosetting properties at room temperature and thermoplasticity at higher temperatures. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41944. [ABSTRACT FROM AUTHOR]

ABSTRACT Crosslinked self-healing polyurethane/urea based on a Diels-Alder reaction (C-PMPU-DA) was synthesized from a multiple-furan monomer and a commercial bismaleimide. The multiple-furan monomer (PMPU-furan) was obtained from a functionalized prepolymer (polymeric MDI: PBA-2000 = 2:1) by furfuryl amine. The structures of both the PMPU-furan and C-PMPU-DA were characterized by attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and 1H-NMR. The Diels-Alder bonds enabled C-PMPU-DA thermal reversibility, which was investigated by ATR-FTIR spectroscopy, 1H-NMR, gel-solution-gel experiments, and viscosity tests. Meanwhile, the self-healing properties of C-PMPU-DA were also investigated by the recovery of the mechanical properties. The results showed that C-PMPU-DA exhibited good thermal reversibility and self-healing properties. C-PMPU-DA exhibited thermosetting properties at room temperature, although it exhibited thermoplastic properties at higher temperatures and may find applications in self-healing materials, recyclable materials, or removable materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40234. [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]

Pendant cross-linked polyurethane hot melt adhesive was synthesized without any solvents via Diels-Alder reaction (DA reaction) and was coded as DAPU. Firstly, a chain extender containing furan ring was synthesized via Michale addition reaction between hydroxyethyl acrylate (HEA) and furfuryl amine (FA). Secondly, the polyurethane prepolymer with pendant furan rings was synthesized from the reaction between the chain extender and isocyanate-terminated polyurethane prepolymer. Finally, the hot melt adhesive was cross-linked via DA reaction between furan rings and bismaleimide (BMI) without organic solvents due to the viscosity inhibition at higher temperature. DAPU exhibited a higher bonding performance (11.2 MPa) than the commercial reactive polyurethane hot melt adhesive (PUR-Ausbond 3550) and can reach 10.2 MPa after three times break as thermoplastic polyurethane hot melt adhesive (TPU-XJU83), due to the higher cross-linked density and the thermal reversibility of DA adducts. This confirmed that DAPU combined the merits of the two kinds of polyurethane hot melt adhesives successfully without involving solvents. [ABSTRACT FROM AUTHOR]

Traditional hot melt adhesives are thermoplastic resins with non-covalent hydrogen bonds. In this letter, a polyurethane hot melt adhesive (CDI-PUR-DA) was synthesized via introducing thermally reversible covalent Diels-Alder adducts into the polyurethane main chain. Results from hydrogen nuclear magnetic resonance (NMR) analysis and an assessment of rheological properties demonstrated that CDI-PUR-DA exhibited a much lower viscosity than a traditional hot melt adhesive. The viscosity of the polyurethane decreased to 4 Pa s at 110 °C due to rupture of Diels-Alder adducts. However, the viscosity returned to its initial value on cooling due to the regeneration of the Diels-Alder adducts. This approach provides a new method for preparing hot melt adhesives. [ABSTRACT FROM AUTHOR]