A comparison of the solution radical propagation kinetics of partially water-miscible non-functional acrylates to acrylic acid

Abstract

There is limited knowledge of the radical polymerization kinetics of partially water-miscible monomers, often used as comonomers in emulsion or solution polymerizations. Herein, the propagation kinetics of 2-methoxyethyl acrylate (MEA) and methyl acrylate (MA) are compared to that of the fully water-miscible monomer acrylic acid (AA) in alcohol/water solutions using the pulsed-laser polymerization–size exclusion chromatography method, with expressions developed to represent the data over the complete range of experimental conditions studied. The propagation rate coefficient (k_p) values for MEA and MA increase by up to a factor of two upon dilution to 5–10 wt% monomer in alcohol, compared to a two-fold reduction in k_p for AA from its bulk value, with the difference in behavior attributed to the influence of hydrogen-bonding on kinetics. The k_p values for all three monomers increase substantially as the fraction of water in alcohol/water mixtures is increased; however, the relative increase is much greater for MEA and MA than for AA. The MEA and MA k_p values exceed that of AA for 5 wt% monomer in water, approaching values of 2 × 10⁵ L mol⁻¹ s⁻¹ at 30 °C, despite having lower values than AA in bulk. Therefore, it is clear that bulk kinetics of sparingly water soluble acrylates cannot be assumed when these monomers polymerize in aqueous or in alcohol solutions.