Phthalic anhydride based polyester-ether polyos and double metal cyanide catalyst system for preparing same

Disclosed are polyester-ether polyols and their use in foams, in particular rigid or flexible foams. Methods for producing such polyester-ether polyols using potassium hydroxide or double metal cyanide catalysts are disclosed, along with methods for producing urethane prepolymers. The polyester-ether polyols of the instant invention are preferably the reaction product of phthalic anhydride, diethylene glycol, and propylene oxide. These polyester-ether polyols are useful as either the primary polyol in urethane compositions or in combination with conventional auxiliary polyester- and/or polyether-based polyols. The polyester-ether polyols impart greatly improved solubility and compatibility to mixtures of either polyether and/or polyester polyols. The polyester-ether polyols of the instant invention are desirably of lower viscosity than their precursor intermediate polyester polyols and are generally soluble in either polyester- and/or polyether-based polyols.