PROCESS FOR PRODUCING BORIC ACID ESTER COMPOUND

A process for producing a boric acid ester compound which comprises esterifying a compound represented by the formula (1): X - ÄO(AO)n - HÜa wherein X represents a group independently selected from a residue of a compound having 1 to 6 hydroxyl groups, an acryloyl group and a methacryloyl group with a boron-containing compound represented by the formula (2): (RO)3 - B wherein R represents an alkyl group having 1 to 4 carbon atoms. The present invention can provide a boric acid ester compound which has a high ion conductivity, which is useful as a material for an electrochemical device, such as a secondary battery or a capacitor, having excellent safety and which is low in water and impurity contents, a polymer electrolyte containing the boric acid ester compound, and a secondary battery using the polymer electrolyte.