Abstract
An in situ nuclear magnetic resonance spectroscopy (NMR) technique is used to monitor the aqueous-phase copolymerization kinetics of methacrylic acid (MAA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) macromonomers. In particular, the study analyses the effect of the number of ethylene glycol (EG) groups along the lateral chains of PEGMA and is carried out under fully ionized conditions of MAA at different initial monomer ratios and initial overall monomer concentrations (5–20 wt % in aqueous solution). The composition drift with conversion indicates that PEGMA macromonomer is more reactive than MAA. Individual monomer consumption rates show that the rates of consumption of both monomers are not first order with respect to overall concentration of the monomer. The reactivity ratios estimated from the copolymerization kinetics reveal, that for the short PEGMA, the reactivity ratios rMAA and rPEGMA increase with the solids content (SC). A totally different trend is obtained for the longer PEGMA, whose reactivity ratio (rPEGMA23) decreases with solids content, whereas the reactivity ratio of MAA remains roughly constant.
Highlights
During the last few years, the use of monomers with a polyethylene glycol (PEG) side chain in the synthesis of polymeric materials [4,5,6,7] has gained increasing attention
This has been reported for the aqueous solution homopolymerization of methacrylic acid (MAA) [19,20,21,25,42]
It has been found that the propagation rate coefficient of MAA was a function of the concentration of the monomer in the aqueous phase and of the ionization degree
Summary
During the last few years, the use of monomers with a polyethylene glycol (PEG) side chain in the synthesis of polymeric materials (as comonomers in aqueous-phase solution copolymerization [1,2,3] or as reactive stabilizers in several heterogeneous polymerization systems) [4,5,6,7] has gained increasing attention. Water-soluble polymers are used in a variety of applications including coatings, cosmetics, antiflocculants, textiles, superabsorbers and water treatment [8,9,10]. These materials are generally produced via free-radical (co)polymerization in aqueous solution [9,11,12]. One major difference found between aqueous and organic solvents is that the propagation rate constant of water-soluble monomers, in addition to temperature, depends on other variables such as monomer concentration, pH and ionic strength of the aqueous medium, which makes the kinetics substantially more complex than in organic systems, especially when dealing with copolymerization processes.
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