Pressurized, blowing-agent-containing isocyanate semiprepolymer mixtures based on mixtures of polyhydroxyl compounds and monoalcohols and/or hydroxyketones, the use thereof for the production of polyurethane foams, and a process therefor

A pressurized, blowing-agent-containing, single-component, isocyanate semiprepolymer mixture obtained by reacting

• A) at least one polyhydroxyl compound with
• B) at least one organic polyisocyanate
• in a sealed reactor in the presence of at least one blowing agent or by treating the isocyanate semiprepolymer formed in the absence of blowing agent with at least one blowing agent, wherein the polyhydroxyl compound (A) is used in combination with a .beta.-hydroxyketone (A1ii) of the formula ##STR2## where the radicals R are identical or different and are hydrogen, phenyl, alkyl having 1 to 20 carbon atoms, phenylalkyl having 1 to 14 carbon atoms in the alkylene radical or halogen.