Diphenylmethane diisocyanate-based liquid polyisocyanate mixtures containing urethane groups, process for their preparation and their use for the preparation of flexible polyurethane foams

Claim 1

A liquid, urethane group-containing diphenylmethane diisocyanate-based polyisocyanate mixture having an isocyanate group content of 12 to 30 percent by weight obtained by reaction at a temperature of 0° C. to 100° C. of (a) at least one polyoxypropylene polyoxyethylene polyol having a functionality of 2 to 4, a hydroxyl number of 10 to 65, and 5 to 30 percent by weight of oxyethylene based on total weight of the polyol with (b) a polyisocyanate selected from the group consisting of: (1) a mixture of isomeric diphenylmethane diisocyanates and polyphenyl polymethylene polyisocyanate, containing from 60 to 95 percent by weight of diphenylmethane diisocyanates, and (2) isomeric diphenylmethane diisocyanate containing 50 to 100 percent by weight of the 4,4'-isomer, with the proviso that when the isocyanate mixture (1) is used, the polyol and the isocyanate are reacted in a ratio to provide from 0.001 to 0.19 equivalent hydroxyl group per equivalent of isocyanate group and when the isomeric diphenylmethane diisocyanates (2) are used, the polyol and the isocyanate are reacted in a ratio to provide from 0.001 to 0.19 equivalent hydroxyl group per equivalent isocyanate group followed by dilution of the reaction product with 10 to 60 percent by weight of a diphenylmethane diisocyanate-polyphenyl polymethylene polyisocyanate mixture containing 45 to 80 percent by weight of diphenylmethane diisocyanates.