Abstract: The present invention relates to a process for the production of polyether alcohols by catalytic addition of alkylene oxides to H-functional initiators using amines as catalysts, wherein the addition of the amines to the reaction mixture is effected prior to or at the commencement of the chemical addition of the alkylene oxides and also at least once during the reaction, said additional addition of the catalyst being carried out at the point of the reaction at which there is an increased occurrence of side reactions and/or when the alkylene oxides undergo a change in the polyether chain.

Abstract: Flexible foams based on polyisocyanate polyaddition products are produced by reacting polyisocyanates with compounds which are reactive toward isocyanates in the presence of catalysts, blowing agents and, if desired, flame retardants, auxiliaries and/or additives, wherein polyether polyalcohols (c) which are obtainable by addition of alkylene oxides onto substances containing active hydrogens are used as substances which are reactive toward isocyanates, where, in a first stage, at least one substance (a) containing 2 or 3 active hydrogens is reacted with at least one alkylene oxide in the presence or absence of catalysts, subsequently at least one substance (b) which contains at least four active hydrogens and, if desired, further catalyst is added to the reaction mixture from the first stage and this mixture is then reacted in a second stage with at least one alkylene oxide.