Patent ID: 8653219

Claim:
Process for preparing a reactive polyurethane composition in the form of a polyurethane hot melt adhesive having a residual monomer content of less than 0.1% by weight, which process comprises: in a first process step, reacting an isocyanate-reactive polymer, or mixture of isocyanate-reactive polymers, said polymer or mixture of polymers having isocyanate reactive end groups and containing at least 90% by weight of linear molecules, with a polyisocyanate having a molecular weight less than 500, wherein the isocyanate groups of the polyisocyanate are present in a molar deficit relative to the isocyanate-reactive end groups of the polymer or mixture of polymers in a molar ratio of 1:1.1 to 1:5, to produce a monomer-free thermoplastic polyurethane which contains isocyanate-reactive end groups as a first product; and in a second process step, reacting the first product with a low-monomer-content, isocyanate-terminal prepolymer, wherein said prepolymer is prepared by reacting polyether polyols with an excess of polyisocyanate followed by removal of monomeric isocyanate by means of a thin film evaporator, wherein the isocyanate-reactive end groups of the thermoplastic polyurethane first product relative to the isocyanate groups of the prepolymer are present in a molar ratio of 1:1.1 to 1:5, to produce the reactive polyurethane composition.