The effect of hydrogen bonding on the copolymerization kinetics of 2‐methoxyethyl acrylate with 2‐hydroxyethyl methacrylate in alcohol and aqueous solutions

Abstract

The influence of alcohol and alcohol/water solutions on the radical copolymerization kinetics of 2‐hydroxyethyl methacrylate (HEMA) with 2‐methoxyethyl acrylate (MEA) is studied using pulsed‐laser‐polymerization coupled with size exclusion chromatography. It is found that MEA incorporation into the copolymer is increased in butanol, methanol (MeOH), and MeOH/H2O solutions relative to the bulk system. Copolymer composition can be represented for solvent levels ≥50 vol.% by a single pair of reactivity ratios (rHEMA = 2.39 ± 0.16, rMEA0.25em= 0.28 ± 0.02) that differ from those in bulk (rHEMA = 3.14 ± 0.44, rMEA0.25em= 0.27 ± 0.04). MeOH as solvent slightly reduces the propagation rate coefficient ()kp of HEMA compared to the bulk system, in contrast to the increase in the MEA kp value. Thus, the value of kpcop is higher in MeOH for MEA‐rich systems compared to bulk, with the effect of the solvent reduced as the HEMA content in the comonomer mixture is increased. Adding water as cosolvent significantly increases kp values for both monomers, with kpcop in MeOH/H2O higher than bulk values over the complete composition range. Furthermore, kpcop for 50% monomer in the solvent systems studied can be represented by the implicit penultimate unit model using a single pair of radical reactivity ratios. It is concluded that the strongest influence of hydrogen‐bonding solvents compared to bulk is on the homopropagation kp values, rather than on copolymerization parameters, and that the difference in relative reactivity of non‐functional and functional monomers in bulk and aqueous solution should be accounted for when studying emulsion copolymerization.

Radical copolymerization kinetics of N-tert-butyl acrylamide and methyl acrylate in polar media

“…This opposing behaviour, not seen in aqueous solution, has been explained by the alcohol enhancing the reactivity of the nonfunctional (meth)acrylates through hydrogen-bonding, while the same solvent decreases the reactivity of AA and HEMA through disruption of H-bonding between monomer units (i.e., dimerization). 10,15 As might be expected, the influence of a mixed alcohol/ water solvent on k p values is intermediate to that of water and alcohol, as has been studied for AA, MA, and MEA, 10 and for HEMA and its copolymerization with MEA. 15 However, more studies are required to generalize understanding of these influences, as the chain-growth rates vary with both the weight fraction of monomer in solution and solvent composition.…”

“…However, the influence is significantly lower than that of water, as shown by PLP-SEC studies that directly compared NVP 13 and MA 10 chain growth kinetics in alcohols and water. In contrast to the increase observed for the k p of non-functional (meth)acrylate monomers, dilution of functional monomers (monomers with –OH groups) such as AA 5 and 2-hydroxyethyl methacrylate (HEMA) 14,15 in alcohol lowers k p from the bulk values. This opposing behaviour, not seen in aqueous solution, has been explained by the alcohol enhancing the reactivity of the non-functional (meth)acrylates through hydrogen-bonding, while the same solvent decreases the reactivity of AA and HEMA through disruption of H-bonding between monomer units ( i.e.…”

“…For polymer systems for which M-H parameters are known, agreement between the positions of the maxima (used to estimate k p ) measured by the two detectors is used as a means to validate SEC calibration. 10,12,14,15 The systematic difference in the positions of the features marked in Fig. 1 arise from the use of the poly(STY) calibration to process the RI output.…”

“…While the theoretical premise of the penultimate model remains a matter of debate, 18,19 these extra parameters provide a means to represent experimental k p,cop data when the terminal model fails, as shown in previous studies of acrylate-methacrylate and styrene-(meth)acrylate copolymerizations, 12,17,20 as well as MEA/HEMA copolymerization in alcohol/water mixtures. 15 To the best of our knowledge, this is the first PLP-SEC study of the copolymerization chain-growth kinetics of an acrylamide-acrylate system.…”

“…As might be expected, the influence of a mixed alcohol/water solvent on k p values is intermediate to that of water and alcohol, as has been studied for AA, MA, and MEA, 10 and for HEMA and its copolymerization with MEA. 15 However, more studies are required to generalize understanding of these influences, as the chain-growth rates vary with both the weight fraction of monomer in solution and solvent composition. Thus, this study utilizes the PLP-SEC technique to measure the influence of polar solvents on the homopropagation kinetics of N-tert -butyl acrylamide ( t BuAAm).…”