| 摘要 |
The present invention relates to a process for the preparation of a hard foam containing urethane groups or urethane and isocyanurate groups by the polyisocyanate polyaddition process, by reacting a) a polyoxypropylene- or polyoxyethylene-polyoxypropylene-polyol containing secondary hydroxyl groups, having a functionality of from 3.5 to 4.3, a hydroxyl number of from 350 to 650 and a viscosity of from 500 to 2,500 mPa 23 .degree.C and prepared by anionic polymerization of 1,2-propylene oxide or ethylene oxide and 1,2-propylene oxide onto an initiator molecule mixture containing, based on the total weight, a1) from 40 to 80% by weight of a hexanetetrol, a2) from 1 to 30% by weight of a hexanetriol, a3) from 0 to 35% by weight of glycerol and a4) from 0 to 15% by weight of sorbitol or mannitol, or a mixture thereof, b) optionally, a low-molecular-weight chain extender and/or crosslinking agent with c) an organic, modified or unmodified polyisocyanate; in the presence of d) a blowing agent, e) a catalyst and, optionally, f) assistants and/or additives, and novel polyoxypropylene-polyols and polyoxyethylenepolyoxypropylene-polyols which can be used for this purpose.
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