PURPOSE: To obtain the titled copolymer in high efficiency and yield, by contacting an aqueous solution of a dihydric phenol compound and an acid acceptor such as alkali metal hydroxide, with an organic solution containing an organic solvent, a dicarboxylic acid dihalide, and polyphenylene ether.

CONSTITUTION: The objective copolymer is prepared by contacting (A) an aqueous solution containing a dihydric phenol (e.g. hydroquinone) and one or more acid acceptors selected from the hydroxide, carbonate, bicarbonate, phosphate, etc. of alkali metal or alkaline earth metal, with (B) an organic solution containing (i) an organic solvent which is nonsolvent to the above aqueous solution, (ii) a dicarboxylic acid dihalide (e.g. adipoyl dichloride) and (iii) a polyphenylene ether of formula (R1 and R2 are alkyl, aryl, halogen, H, etc.; n is 10W1,500)[e.g. poly(2,6-dimethylphenylene-1,4-ether)]. The molar ratio of the component (iii) to the dihydric phenol is 0.005W2.0 (based on 1mol of the compound having the average molecular weight).