Method for preparing polyester polyol

A method for preparing a polyester polyol comprising performing transesterification of an inorganic oxyacid ester and a polyhydric alcohol as raw materials to obtain the polyester polyol;

• wherein the method comprises the following steps:
• a) mixing the inorganic oxyacid ester, the polyhydric alcohol and a transesterification catalyst, and then performing a transesterification reaction under stirring conditions and in an inert atmosphere, wherein the reaction temperature ranges from 80 to 180° C., and the reaction time ranges from 2 to 10 hours;
• b) after the reaction in step a), performing vacuum distillation during which the vacuum degree ranges from 0.01 to 5 kPa, the reaction temperature ranges from 170 to 230° C., and the reaction time ranges from 0.5 to 5 hours;
• wherein a molar ratio of inorganic oxyacid ester, polyhydric alcohol and transesterification catalyst satisfies:
• inorganic oxyacid ester:polyhydric alcohol=(0.8˜1.2)n3/x,
• wherein x is the number of moles of alkoxyl groups contained in each mole of inorganic oxyacid ester, and n3 is the number of moles of hydroxyl groups contained in each mole of polyhydric alcohol.