Esterification process: before esterification, the product is melted in hot water at 70-80 °C, pumped into a kettle, and an acid catalyst is added below 70 °C to stir for 10 minutes, and then polymerization inhibitor and acrylic acid or methacrylic acid are added for esterification, and the esterification time can be determined according to the esterification rate of the final product. (If the polymerization inhibitor can be dissolved in acrylic acid or methacrylic acid, the polymerization inhibitor can be dissolved in acrylic acid or methacrylic acid after stirring for 10 minutes in MPEG, and then esterified). MPEG2000 and MPEG5000 because they are flakes, can be directly injected in the kettle internalized material, the reactor nitrogen replacement during the material, the material temperature does not exceed 70 °C during the materialization process, otherwise polymer is easy to appear during esterification.