Abstract: Compact and preferably cellular polyurethane elastomers are prepared by reacting a) relatively high molecular weight polyhydroxyl compounds and if desired, b) low molecular weight chain extenders and/or crosslinkers with c) phenylene 1,4-diisocyanate (p-PDI) and at least one additional aromatic diisocyanate selected from the group consisting of tolylene diisocyanate, diphenylmethane diisocyanate, 3,3′-dimethylbiphenyl diisocyanate, 1,2-diphenylethane diisocyanate and/or aliphatic diisocyanate, having from 4 to 12 carbon atoms and/or cycloaliphatic diisocyanate having from 6 to 18 carbon atoms, where the formative components (a), (c) and, if used, (b) are advantageously reacted by the prepolymer method, in the presence or absence of d) catalysts, e) blowing agents and f) additives. Isocyanate prepolymers suitable for this purpose are described.

Abstract: Polyurethanes are recycled by comminution to particle sizes of from 0.01 to 2 mm and addition to the polyaddition mixture for preparing polyurethanes from(a) polyisocyanates,(b) substances reactive toward isocyanates and having active hydrogens, and, if desired,(c) chain extenders and/or crosslinkers, catalysts, blowing agents and customary additivesin an amount of from 0.1 to 40% by weight, based on the poly-addition mixture.