Synthesis of polyurethane hot melt adhesive without solvent via Diels-Alder reaction

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 ¹ H 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.