Oxidative polymerization of 2,6-dimethylphenol to poly(2,6-dimethyl-1,4-phenylene ether) (PPE) was studied in a high-pressure batch reactor using a copper-diamine catalyst. In the presence of air, the effect of monomer sources, catalyst formulation (copper salts, ligands, surfactant), and reaction conditions (air flow rate and pressure, temperature, agitation, monomer and catalyst concentrations) on the catalyst performance was investigated. The sensitivity of PPE molecular weight and the sensitivity of polymerization rates to these factors were found to be quite different, indicating that little correlation existed between the PPE molecular weight and the 2,6-DMP polymerization rates. Mechanical test showed that the PPE produced with the copper-diamine catalyst had modulus significantly higher than that produced with the copper-dibutylamine catalyst system.