Abstract The effect of solution pH on the oxidation of 2-methoxyaniline-5-sulfonic acid (MAS) to form a water-soluble polymer has been investigated. By control of solution pH during polymerisation it was found that both monomer conversion and poly(2-methoxy-5-aniline sulfonate) (PMAS) molecular weight were significantly increased. The electrochemically synthesised PMAS has one sulfonate group attached to each benzene ring along the polymer chain, making this polymer highly soluble in water (30% w/w) and easy to process. The polymer has a DC conductivity of ca. 0.01 S/cm. Gel permeation chromatography analysis indicated the polymer has a bimodal molecular weight distribution, consisting of a high molecular weight fraction (with average molecular weight ∼15,000) and a low molecular weight fraction (with molecular weight ∼2200).