Photopolymerization kinetics and molecular interactions in methacrylate-imidazolium based ionic liquid systems

Abstract

Photopolymerization of poly(ethylene glycol) monomethacrylate (PEGMM) in two imidazolium based ionic liquids (ILs) differing with the anion size and H-bond accepting ability, i.e. 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF 4 ]) and 1-ethyl-3-methylimidazolium trifluoroacetate ([EMIm][ATF]) was investigated to find the effect of the IL anion on propagation k p and termination rate k t b coefficients (by DSC) as well as molecular interactions in the system (on the basis of viscosity and FT-IR measurements). Polymerizations in bulk and in tricresyl phosphate (TCP) served as references. Both monomer/IL systems show strong viscosity synergism and viscosity deviations are positive indicating that viscosity of associates between the monomer and the ILs is relatively higher than that of pure components. The increase in k p values observed in ILs is higher for polymerization in [EMIm][BF 4 ], which shows stronger Coulomb cation-anion attractions and lower H-bond accepting ability of the anion. The influence of the ionic liquids on the termination rate coefficient results from the viscosity of the monomer-IL system, taking account of viscosity synergism. On the basis of changes of imidazolium ring CH groups vibrations and carbonyl stretching vibrations (both in PEGMM and IL anion) two possible configurations of monomer-IL interactions were proposed: between the monomer carbonyl and C(2)-H hydrogen of the imidazolium cation in the case of [EMIm][BF 4 ] and a configuration in which the monomer carbonyl interacts with the imidazolium cation located on the top of the ring, in the case of [EMIm][ATF].

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

“…As mentioned previously, studies examining the role of ILs as solvents in radical polymerization have shown that ILs are unique, increasing the rate of propagation while decreasing the rate of termination. [39][40][41]72,73 Multiple explanations for this behavior have been proposed, including polarity-associated decreases in the activation energy of polymerization as well as effects resulting from both the inherent viscosity of the solvent as well as specific interactions between the IL media and the monomers. 40,41,72,73 However, several alternative hypotheses have been proposed attributing the improved reaction kinetics of vinyl monomers to the formation of polar and nonpolar domains within the IL solvent.…”

“…[39][40][41]72,73 Multiple explanations for this behavior have been proposed, including polarity-associated decreases in the activation energy of polymerization as well as effects resulting from both the inherent viscosity of the solvent as well as specific interactions between the IL media and the monomers. 40,41,72,73 However, several alternative hypotheses have been proposed attributing the improved reaction kinetics of vinyl monomers to the formation of polar and nonpolar domains within the IL solvent. 42,43,74 Thurecht et al examined the mechanism of radical polymerization of MMA in common IL solvents by determining the effect of several kinetic parameters on the rate of polymerization and polymer molecular weights.…”

Photopolymerization Behavior of Coordinated Ionic Liquids Formed from Organic Monomers with Alkali and Alkaline Earth Metal Bistriflimide Salts

“…Interest in the use of these low‐melting ( T m < 100 °C), primarily organic salts stems from their unique properties such as a negligible vapor pressure and a high degree of thermal stability that have lead them to be proposed as alternatives to conventional solvents in a variety of processes . Thermally initiated radical polymerizations of methyl methacrylate (MMA) were some of the first polymerization reactions studied in IL solvents (e.g., 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C 4 mim][PF 6 ]), and the kinetics of these processes have been extensively investigated for a variety of other monomers and methods of polymerization . Analysis of the rate of propagation ( R p ) using pulsed laser polymerization (PLP) and size exclusion chromatography (SEC) has generally indicated that IL solvation increases propagation rate constants ( k p ) .…”

Polymerization in Ionic Liquids

“…The addition of lithium bistriflimide RTIL to 1-vinylimidazole was used to significantly improve monomer conversion and photopolymerization rate, possibly as a result of coordination between the imidazole and the Li + cation (54). Photopolymerization of poly (ethylene glycol) (PEG)-monomethacrylate was studied in [BMIM]BF 4 and 1-ethyl-3-methylimidazolium trifluoroacetate to determine the effect of RTIL on both propagation and termination rates (55).…”