| 摘要 |
ACCELERATED PREPARATION OF ISOCYANATE TERMINATED POLYURETHANE PREPOLYMERS In accordance with the invention, an accelerated method for preparing moisture curable, isocyanate terminated polyurethane prepolymers is taught. Whereas prior art prepolymer formation techniques require ssveral hours or more, ours takes only minutes. The subject process yields thermally stable polyurethane prepolymers particularly suited for sealant applications. In accordance with the method, about one equivalent of a diisocyanate is combined with from about 0.37 to 0.60 equivalents of a polyoxypropylene diol, about 0.05 to 0.27 equivalents of a polyoxypropylene triol, and about 5 to 15 weight percent, based on the total composition, of a plasticizer such that an excess of from about 0.5 to 10% isocyanate, by weight of the composition, is achieved. Thereafter, the mixture is catalyzed with from about 0.05 to 0.4 weight parts of a tin based urethane polymerization catalyst dissolved in about 5 to 15 weight percent, based on the total composition, additional plasticizer, and stirred until the concentration of free isocyanate levels off. |
