Preparation method of flame-retardant chain extender

The invention relates to a preparation method of a flame-retardant chain extender, belonging to the field of chemical synthesis. The flame-retardant chain extender is tris (2-(4-(2-hydroxyethoxy) phenoxy) ethyl phosphate, and the preparation method of the flame-retardant chain extender comprises the following steps: adding hydroquinone, ethylene carbonate and alkali into a solvent under the protection of nitrogen, carrying out heating reaction under a stirring condition, cooling the mixture to room temperature after the reaction is finished, filtering, distilling the filtrate under vacuum to recover the solvent and unreacted ethylene carbonate, and drying to obtain the flame-retardant chain extender. Hydroquinone dihydroxyethyl ether is obtained; the preparation method comprises the following steps: under normal pressure, adding hydroquinone dihydroxyethyl ether, phosphorus oxychloride and a catalyst into a reactor, introducing nitrogen for replacement, and heating for reaction to obtain the flame-retardant c