The coupling polymerization of 2,6-dimethylphenol to poly(2,6-dimethyl- 1,4-phenylene oxide) was carried out in an aqueous-chloroform biphasic mixture using copper complexes of substituted ethylenediamines as surface-active catalysts. Copper-N,N-dibutylethylenediamine complex gave the highest reaction rate and produced a polymer with an average molecular weight of 48 000 in a 95% yield. The optimum ligand to catalyst ratio and organic to aqueous volume ratio were found to be 3 : 1 and 1 : 1, respectively. The reaction rate also depended strongly on the aqueous ammonia concentration, stirring speed and the emulsifier concentration, The reaction orders with respect to the substrate, catalyst complex and oxygen are 1.0, 1.7 and 0.1, respectively, and the activation energy was approximately 11.7 kcal/mol. A reaction mechanism is proposed which yields a model rate expression in good agreement with the experimental findings.