Method of manufacturing esterified substance

A method of manufacturing an esterified substance comprising:

• a process in which a copolymer is obtained by copolymerizing a 1-alkene having 28 to 60 carbon atoms and maleic anhydride;
• a process in which an esterification reaction of the copolymer and an alcohol having 5 to 25 carbon atoms is caused in a presence of trifluoromethanesulfonic acid in order to obtain a reaction mixture containing an esterified substance including at least one repetition unit selected from formulae (c) to (f);
• and
• after the process in which a reaction mixture containing an esterified substance is obtained, a process in which free trifluoromethanesulfonic acid is removed through a depressurization treatment, wherein
• in the formulae (c) to (f), R represents an aliphatic hydrocarbon group having 3 to 78 carbon atoms, R2 represents a hydrocarbon group having 5 to 25 carbon atoms, m represents the copolymerization molar ratio X/Y of the 1-alkene (X) to the maleic anhydride (Y) and is 1/2 to 10/1, and n is an integer of more than or equal to 1: