| abstract |
The present invention relates to a process for the preparation of CFC-free, flexible polyurethane (molded) foams by reacting A) liquid polyisocyanate mixtures containing bonded urethane groups having a content of NCO groups of from 22 to 30% by weight which are themselves prepared by reacting a mixture of diphenylmethane diisocyanates and polyphenyl-polymethylene polyisocyanates having a content of diphenylmethane diisocyanate isomers of from 55 to 99% by weight, based on the total weight, with at least one trifunctional polyoxypropylene-polyol having a hydroxyl number of from 20 to 60, with B) relatively high-molecular-weight polyhydroxyl compounds and, if desired, C) low-molecular-weight chain extenders and/or crosslinking agents, in the presence of D) blowing agents, E) catalysts and, if desired, F) auxiliaries and/or additives, and to the polyisocyanate mixtures (A) modified by means of urethane groups which can be used according to the invention. |