Process for preparing polyoxyalkylene polyester polyols

A process for preparing a polyoxyalkylene polyester polyol having a calculated OH number of 320 mg KOH/g to 530 mg KOH/g by reacting

• an H-functional starter compound (1) having n(1) mol of alcoholic hydroxy groups and/or aminic protons, and
• a fatty acid ester (2) having n(2) mol of fatty acid ester groups
• with an alkylene oxide (3),
• optionally in the presence of a basic catalyst (4) and
• optionally in a solvent (5),
• wherein the H-functional starter compound (1) comprises one or more compounds,
• wherein at least one H-functional starter compound (1) has a melting point of >50.0° C. determined according to the method DIN EN ISO 11357-1:2016,
• wherein the fatty acid ester (2) has an OH number of less than 100 mg KOH/g,
• wherein the fatty acid ester (2) is used in an amount of at least 40% by mass, based on the total mass of the H-functional starter compound (1), the fatty acid ester (2) and the alkylene oxide (3), and
• wherein the process comprises:
• (i) providing a system (i) comprising the H-functional starter compound (1) and optionally the basic catalyst (4) optionally in a solvent (5) in a reaction vessel,
• (ii) adding n(3−1) mol of a first sub-amount of the alkylene oxide (3) to the system (i) over a period t1 to form an intermediate (ii),
• (iii) optionally removing any solvent (5) present from the intermediate (ii) to form an intermediate (iii),
• (iv) adding the fatty acid ester (2) to the intermediate (ii) or to the intermediate (iii) to form an intermediate (iv), wherein n(2) mol of fatty acid ester groups are supplied to the intermediate (ii) or the intermediate (iii),
• (v) adding n(3−2) mol of a second sub-amount of the alkylene oxide (3) to the intermediate (iv) over a period t2 to form the polyoxyalkylene polyester polyol,
• wherein (n(3−2)/n(2))·t2/[h]≥1.0,
• wherein n(2)/n(3−2)≥1.05, and
• wherein n(3−1)/n(1)≥0.43.