Polymerization Kinetics of Ethylene Oxide Methacrylates in Ionic Media

Abstract

The radical polymerization of ethylene oxide (PEGylated) methacrylates in ionic media has been studied. Lithium salts interact with the monomer causing a significant increase in the propagation rate constant, kp, and also providing an ionic and highly viscous medium that sharply decreases the termination rate coefficient, kt. Both features make the polymerization reactions with lithium salts faster compared to the bulk monomer. The systems are studied by means of FT‐IR spectroscopy to identify the interactions between the monomer and the lithium salt. In addition, an extensive kinetic study by PLP‐SEC has been performed to study the influence of the lithium salt on kp and kt in the polymerization of these monomers. These results are compared to those obtained when ionic liquids are used as polymerization medium. magnified image

Photopolymerization of coordinated ionic liquid monomers: Realizing the benefits of structured media using only common reagents

“…53,54 Indeed, in spectroscopic investigations of vinyl monomers and Li 1 salts, cation complexation has been detected using IR as well as 1 H and 13 C NMR spectroscopy. 55,56,[58][59][60] Based on similar evidence, it can be confirmed that these species are also formed in our study. As displayed in Figure 9, the C@O stretching peaks of MMA undergo shifts to lower wavenumbers following the addition of LiTf 2 N at monomer:salt ratios of 1:1 and 2:1.…”

“…Several previous studies have explored the influence of the addition of small amounts of Lewis acid salts on the free-radical polymerization of polar vinyl monomers. 56,60,62 Addition of ZnCl 2 to reaction mixtures of MMA in N,N-dimethylformamide (DMF) increased the rate of polymerization relative to the control solution 2.43 at a Lewis acid:monomer ratio of 0.15:1, while the presence of AlBr 3 in similar reaction mixtures at a salt:monomer ratio of 0.35:1 improved the rate of reaction approximately 4.23 in comparison to the control mixture. 62 As mentioned previously, multiple studies have found improvements in the reaction kinetics and product properties for radical polymerizations containing LiOTf and LiTf 2 N. [56][57][58][59][60] The improvements in the radical polymerization kinetics in these reactions have been attributed to both electronic and electrostatic factors.…”

“…56,60,62 Addition of ZnCl 2 to reaction mixtures of MMA in N,N-dimethylformamide (DMF) increased the rate of polymerization relative to the control solution 2.43 at a Lewis acid:monomer ratio of 0.15:1, while the presence of AlBr 3 in similar reaction mixtures at a salt:monomer ratio of 0.35:1 improved the rate of reaction approximately 4.23 in comparison to the control mixture. 62 As mentioned previously, multiple studies have found improvements in the reaction kinetics and product properties for radical polymerizations containing LiOTf and LiTf 2 N. [56][57][58][59][60] The improvements in the radical polymerization kinetics in these reactions have been attributed to both electronic and electrostatic factors. [56][57][58][59][60]62 For the ethylene oxide methacrylate polymerizations, the addition of the salt was associated with a corresponding shift in the position of the CAH vinyl stretching peak to higher wavenumbers.…”

“…60 As the presence of similar phenomena in H-bonding systems results in increased monomer reactivity, the increase in the rate of propagation was attributed to favorable electronic redistributions within the vinyl group as a result of interactions between the C@O group and the Li 1 cation. 60,63,64 Likewise, the increase in the rate of polymerization of ACR and MACR monomers in the presence of alkai Tf 2 N salts was partly attributed to the decrease in the difference in the 13 C and 1 H NMR shifts of vinylidene carbon and H atoms that have been previously associated with favorable propagation kinetics. 58,59,65 The presence of these salts also affects the termination kinetics of these reactions, resulting in substantial increases in the radical concentrations of the reaction mixtures as determined by electron paramagnetic spectroscopy.…”

“…[56][57][58][59][60]62 For the ethylene oxide methacrylate polymerizations, the addition of the salt was associated with a corresponding shift in the position of the CAH vinyl stretching peak to higher wavenumbers. 60 As the presence of similar phenomena in H-bonding systems results in increased monomer reactivity, the increase in the rate of propagation was attributed to favorable electronic redistributions within the vinyl group as a result of interactions between the C@O group and the Li 1 cation. 60,63,64 Likewise, the increase in the rate of polymerization of ACR and MACR monomers in the presence of alkai Tf 2 N salts was partly attributed to the decrease in the difference in the 13 C and 1 H NMR shifts of vinylidene carbon and H atoms that have been previously associated with favorable propagation kinetics.…”