A Systematic Investigation of Copolymerization Reactivity Ratios of (Meth)acrylic Acid and MPEG Macromonomers for the Controlled Synthesis of PCE Superplasticizers

Abstract Polycarboxylate ether superplasticizers (PCEs) are typically produced by aqueous free-radical copolymerization of an acid monomer (methacrylic acid (MAA) or acrylic acid (AA)) with a macromonomer (poly(ethylene glycol) methyl ether methacrylate (MPEG)), yet the reactivity ratios that govern their microstructure remain scattered and contradictory. Here, we determine accurate reactivity ratios for MAA/AA–MPEG systems under intrinsic acidic conditions at 70 °C using the IUPAC-recommended, error-aware f0–X–F method with quantitative 1H NMR, systematically varying (i) acid monomer, (ii) MPEG molar mass, and (iii) solid content. Increasing MPEG molar mass leads to a decrease in MPEG reactivity ratios under acidic conditions, conceivably caused by a reduced homopropagation rate coefficient. Solid content has negligible influence at low pH. This study provides more accurate reactivity ratios that replace inaccurate values from previous reports, enabling predictive drift simulations and practical process design rules for controlling PCE homogeneity, backbone composition, and side chain spacing.