Currently used hydroxymethyl carboxylic acid hydrophilic chain extenders are mainly DMPA and DMBA two kinds, of which DMPA use time earlier, is currently the most commonly used one. Although it has many advantages, it still has many disadvantages, mainly because its melting point is relatively high (180 °C - 185 °C), it is difficult to heat the melt, which requires the addition of organic solvents such as N-methylpyrrolidone (NMP), NN-II Methyl amide (DMF), acetone, etc., while NMP has a high boiling point, it is difficult to remove after the preparation of APU. Moreover, the solubility of DMPA in acetone is small, and a large amount of acetone needs to be added during the synthesis process. The de-ketoneation process wastes energy and brings security risks. Therefore, using DMPA not only produces high energy consumption, but also causes organic residue in the product. Due to its special molecular structure, DMBA can consume a little solvent during the synthesis process. This not only shortens the reaction time, reduces energy consumption, but also saves energy.