Method for preparing polyphenylene ether oligomer and composite copper foil substrate wherein the polyphenylene ether oligomer is prepared from 2,6-dimethylphenol, a solvent component, a copper halide, and a tertiary amine compound

A method for preparing polyphenylene ether oligomers includes performing an oxidative polymerization reaction on a reactant including 2,6-dimethylphenol, a solvent component, and a catalyst composition formed by a coordination reaction of a copper halide and a tertiary amine compound to obtain a mixture containing a first polyphenylene ether oligomer with a number average molecular weight of 500 to 4000 and a structure shown in formula (I). The molar ratio of copper halide to 2,6-dimethylphenol is 0.001 or more and less than 0.07, and the molar ratio of tertiary amine compound to 2,6-dimethylphenol ranges from 0.01 to 1. R1 to R4 and n in formula (I) are as defined in the specification and claims. The present invention also provides a composite copper foil substrate including a solidified layer formed of the polyphenylene ether oligomer prepared by the above method. The method of the invention can reduce a generation amount of DPQ and a content of copper ions in the mixture, so that the composite copper foil