Abstract: Elastic polyurethane moldings having a compact surface and a cellular core are produced by reacting a) modified organic polyisocyanates with b) at least one relatively high molecular weight compound containing at least two reactive hydrogen atoms and, if desired, c) low molecular weight chain extenders in the presence of d) blowing agents, e) catalysts and, if desired, f) customary auxiliaries and/or additives in a closed mold with compaction, wherein the modified organic polyisocyanate used is at least one reaction product of pure MDI and at least one polyether alcohol (polyoxyalkylene polyol), the modified organic polyisocyanate having an NCO content of <15% by weight.

Abstract: In a process for preparing polyisocyanate polyaddition products by reacting isocyanates with compounds which are reactive toward isocyanates, in the presence or absence of blowing agents, catalysts, auxiliaries and/or additives, the reaction is carried out in the presence of (i) particles which have a size of <200 &mgr;m and a melting point in a range from 50 to 300° C., or in the presence of thermoset particles (ii) or in the presence of particles (i) and (ii).

Abstract: In a process for preparing polyisocyanate polyaddition products by reacting isocyanates with compounds which are reactive toward isocyanates, in the presence or absence of blowing agents, catalysts, auxiliaries and/or additives, the reaction is carried out in the presence of (i) particles which have a size of <200 &mgr;m and a melting point in a range from 50 to 300° C., or in the presence of thermoset particles (ii) or in the presence of particles (i) and (ii).

Abstract: The present invention relates to a process for the preparation of CFC-free, flexible polyurethane (molded) foams by reactingA) 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, withB) relatively high-molecular-weight polyhydroxyl compounds and, if desired,C) low-molecular-weight chain extenders and/or crosslinking agents,in the presence ofD) 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.