Patent ID: 8592497
Filing Date: 2013-11-26
Classification: C08G,C08J,C08L

Abstract:
1. A process for the preparation of a polyurethane, the process comprising: (A) removing uretonimines from a mixture comprising diphenylmethane diisocyanate and polyphenylenepolymethylene polyisocyanates ai) until a content of the uretonimines is not more than 4% by weight, thereby obtaining a polyisocyanate a); and (C) reacting the polyisocyanate a) with one or more compounds having at least two hydrogen atoms reactive with an isocyanate group b), wherein the polyisocyanate a) is at least one mixture of diphenylmethane diisocyanate and polyphenylenepolymethylene polyisocyanates ai) having an average functionality of from 2.2 to 5.2, a content of dinuclear MDI of not more than 2% by weight, a content of trinuclear MDI of from 25 to 65% by weight, a content of tetranuclear MDI of from 5 to 45% by weight, a content of ≧pentanuclear MDI of from 1 to 17.5% by weight, and a content of uretonimines of not more than 4% by weight, based in each case on a weight of the polyisocyanate ai), and wherein the polyisocyanate a) has a viscosity of 1258 to 7000 mPa·s at 25° C.