Kinetics of the Aqueous-Phase Copolymerization of AA and HPEG Macromonomer in Acidic Media

Abstract

Water-soluble monomers are extensively used in the production of polymeric materials in aqueous media for various applications. Acrylic acid–polyethylene glycol 2-methyl-2-propenyl ether (AA-HPEG) copolymers belong to the class of comb-like polycarboxylate ether (PCE) polymers, employed as superplasticizers for cementitious materials. Due to different reactivity ratios of AA and HPEG, semibatch operations with optimized monomer addition profiles are required to enhance the incorporation of HPEG into the copolymer. The kinetics of this system is complex and, like other water-soluble monomers, depends on monomer concentration, pH, and ionic strength. Despite its high-volume industrial usage, the kinetics of this system have received little attention in the literature. Furthermore, the presence of the HPEG, with 55 ethylene oxide (EO) units in the side chain, complicates the precise determination of individual monomer conversions. To address this, various characterization methods are evaluated, including proton nuclear magnetic resonance (¹H-NMR) and size-exclusion chromatography (SEC). Results show that HPEG conversion is determined more accurately using ¹H-NMR signals from the polymer than unreacted monomer signals or SEC traces. Aqueous semibatch AA-HPEG copolymerization experiments are conducted in acidic media to investigate the effects of comonomer feeding time, initiator and chain-transfer agent concentrations on the copolymerization kinetics, HPEG incorporation, and molar mass.