Extruder-Polymerisation von Polyurethanen

Bulk polymerization process for making radiation curable polyurethanes which comprises: A) providing the following raw materials: 1) diisocyanate; 2) oligomeric diol >/= 400 molecular weight; and 3) >/= 1 chain extending monomer; B) reacting the raw materials in a twin screw extruder under the following conditions: 1) molar ratio of isocyanate to hydroxy moieties of about 1; 2) ratio of chain extending monomer to other monomers sufficient to yield a polymer having chain extender incorporated at 0.1 to 10 weight percent; 3) extruder temperature sufficient to initiate and maintain reaction; and 4) residence time sufficient to obtain substantially complete reaction of diisocyanate; C) cooling product polymer. Polyurethane product has weight average molecular weight greater than 80,000 and acrylate or methacrylate functionality. Process permits continuous production of radiation curable polyurethanes having narrow molecular weight distribution and high tensile strength.