Significant process improvements, additional kinetic findings, and a proposed mechanism are presented for a previously reported biphasic synthesis of poly(2,6-dimethyl-1,4-phenylene oxide) that avoids the need for a toxic organic solvent. A switch from magnetic stirring to the more vigorous mechanical stirring coupled with the use of an emulsifier increases the rate of formation and molecular weight of the polymer product each by more than 500%. New data indicate that the reaction has an activation energy of 14.7 kcal/mol and a first-, second-, and 0.15-order dependence on the monomer, catalyst; and oxygen concentrations, respectively. The optimal phase ratio for a fast reaction is around 1:1, and the optimal aqueous ammonia concentration is around 0.26 M. The reaction profile shows an unusual accelerating-rate feature that suggests a shifting balance between chain-growth and emulsion stabilization effects on one hand and a site competition effect at the catalyst on the other hand. A mechanism is proposed which gives a rate law in good agreement with the experimental rate law. A successful extension of the biphasic technique to several carbonylation and autoxidation reactions suggests a general utility of the technique for chemical synthesis.