| abstract |
The invention relates to a method for producing rigid polyurethane foams by reacting a) polyisocyanates with b) compounds with at least two hydrogen atoms reactive with isocyanate groups in the presence of c) propellants, characterized in that, as compounds with at least two hydrogen atoms reactive with isocyanate groups b) at least a graft polyol b1) is used, that can be produced by in-situ polymerization of olefinically unsaturated monomers in a polyether alcohol b1i), wherein the polyetheralcohol b1i) comprises a functionality of 2 to 4 and a hydroxyl number in a range between 100 and 250 mg KOH/g, the polyether chain of propyleneoxide and up to 20 wt.% is composed, in relation to the polyether alcohol b1i), of ethyleneoxide, and as olefinically unsaturated monomers, acrylnitrile and styrole in a weight ratio of acrylnitril : styrol of > 1 : 1 to 4 : 1, and the reaction in the presence of at least one compound that can be mixed in polyether alcohol b1i) with at least an olefinical double bond b1ii) is used. |