Using recently introduced Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP), the kinetics of acrylic acid polymerization was studied, ACOMP yields the absolute weight-averaged mass (M-w), monomer conversion, and other quantities, As the initiator concentration increased, it was shown that the rate increased and the M-w decreased as in regular free-radical polymerization. The effect of salt on acrylic acid polymerization in an aqueous solution was investigated. The polymerization rate and M-w both decreased with an increasing salt concentration, ACOMP molecular weights were also compared with size exclusion chromatography on aliquots periodically withdrawn during the reaction, and good agreement was found. The effect of the pH on the rate and investigated, and when the medium pH was changed from 2 to 5 with sodium hydroxide, the rate and M-w both decreased as the pH increased. Light-scattering results of reaction en products in the reference solvent showed that molecules synthesized at higher pH were in a more expanded form: When equimolar sodium hydroxide was added to the acrylic acid (pH = 5) and sodium acrylate formed, adding salt did not effect the reaction kinetics of the poly(sodium acrylate); its effect on the products was a relatively minor decrease of M-w. (C) 2003 Wiley Periodicals, Inc.