Process for the preparation of polyester- or polyether-polyester polyol

Abstract From the Canadian patent

Abstract of the Disclosure, In order to prepare polyester or polyetherpolyester polyols, polyols, preferably di- to hexafunctional polyether polyols having hydroxyl numbers from 15 to 250 are esterified with at least one carboxylic acid anhydride preferably phthalic acid anhydride, in the presence of Nmethylimidazole, triethylenediamine, and/or triphenylphosphine as catalysts to form a carboxylic acid half-ester and, said half-ester is then oxyalkylated with at least one alkylene oxide, preferably ethylene oxide in the presence, of N-methylimidazole, triethylenediamine triphenylphos-, phine, thiodialkylene glycol employing a mixture of at, least two of the compounds cited as catalysts.