| 摘要 |
This invention is a liquid polyisocyanate prepolymer comprising the reaction product of an organic polyisocyanate blend and a polyoxyalkylene polyol, where polyisocyanate blend is A) a diphenylmethane diisocyanate comprising from 50 weight percent to 95 weight percent 4,4'-diphenylmethane diisocyanate, from 5 weight percent to 50 weight percent 2,4'-diphenylmethane diisocyanate, and less than 10 weight percent 2,2'-diphenylmethane diisocyanate, said weight percentages based on the total weight of the ingredients in A); B) a polymethylene polyphenyl polyisocyanate comprising from 30 weight percent to 70 weight percent diphenylmethane diisocyanate, the remainder comprising polymethylene polyphenyl polyisocyanates having functionalities greater than two, said weight percentages based on the total weight of the ingredients in B); C) and optionally a uretonimine-carbodiimide modified diisocyanate comprising from 10 weight percent to 35 weight percent uretonimine-carbodiimide species, the remainder comprising essentially pure 4,4'_ diphenylmethane diisocyanate, said weight percentages based on the weight of the ingredients in C); and the polyoxyalkylene polyol has a molecular weight ranging from 700 to 10,000 and an average functionality from 1.6 to about 3 and reacted with the polyisocyanate blend at temperatures less than 80.degree.C. The liquid polyisocyanate prepolymer has an overall NCO content of from 10 weight percent to 31 weight percent. The prepolymer is used to make polyurethane foams advantageously blown only with water. 36
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