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)...
The
decisive role of counterions on the propagation mechanism in
the radical polymerization of ionized monomers is comprehensively
studied. Propagation rate coefficients, k
p, were obtained for cationic monomers [2-(methacryloyloxyethyl)]trimethylammonium
chloride (TMAEMC) and [3-(methacryloylaminopropyl)]trimethylammonium
chloride (MAPTAC) in aqueous solution by pulsed-laser polymerization
combined with size-exclusion chromatography over broad ranges of monomer
concentration (1–40 wt %), temperature (5–90 °C),
pH (2–12), and salts selected to provide a molar counterion
concentration, c
counterion, between 0.05
and 3 mol·L–1. Both monomers behave similarly
under conditions at which repulsive electrostatic interactions between
a polymer chain and a reacting monomer dominate (c
counterion < 0.2 mol·L–1). The k
p values increase linearly with c
counterion above this value due to screening of the repulsive
interactions and follow the family behavior of nonionized methacrylate
and methacrylamide monomers manifested by a higher k
p for TMAEMC than for MAPTAC. The hydration of the polyelectrolyte
chain is considered as an additional factor contributing to higher k
p values for cationic TMAEMC at high c
counterion values compared to its nonionized
analogue 2-dimethylaminoethyl methacrylate. The extensive set of k
p data can be represented using average activation
energies of 14.4 ± 2.7 and 14.7 ± 2.0 kJ·mol–1 for TMAEMC and MAPTAC, respectively, and a preexponential factor
that increases with c
counterion. The batch
polymerization of MAPTAC compared to that of TMAEMC reflects the differences
in k
p behavior for these monomers.
Multi‐functional polymers used for personal care products can be synthesized by radical polymerization of acrylic acid (AA) in alcohol/water solutions with non‐functional monomers such as methyl acrylate (MA) and N‐tert‐butylacrylamide (t‐BuAAm). However, solvents capable of forming or disrupting hydrogen bonds cause the polymerization kinetics of these monomers to deviate from their polymerization behaviour in bulk and non‐polar solvents. In this work, a previous mechanistic model developed for MA/t‐BuAAm copolymerization is extended to represent the terpolymerization system MA/t‐BuAAm/AA. The additional kinetic coefficients required for the system are estimated from fitting to AA homopolymerizations and AA/MA and AA/t‐BuAAm copolymerizations conducted in an ethanol/water solution. In‐situ nuclear magnetic resonance (NMR) spectroscopy is used to follow monomer conversions and composition drift behaviour, with the molar mass distributions of the polymer products characterized by size‐exclusion chromatography. Although AA is more reactive than MA in non‐polar solvents, the reactivities of the two monomers equalize under the experimental conditions examined. Thus, the batch and semi‐batch terpolymerization data collected are represented equally well by a reduced acrylate/t‐BuAAm copolymerization model and the full terpolymerization implementation.
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