Free Radical Polymerization in Ionic Liquids – Solvent Influence of New Dimension

Abstract

For the free radical polymerization of polar monomers which are soluble in ionic liquids (ILs) an extraordinary strong solvent effect can be observed. The solvent influence of the ILs leads to a strong enhancement of the polymerization rate and extremely high, mostly broadly distributed molecular weights. The experimentally determined very high propagation rate coefficient kp and the reduction of the activation energy of propagation EA can be explained by H‐bonds between both the monomer molecules and the growing radical chains and the cations and anions of the ILs. The high viscosity of the ILs themselves as well as the increase of the viscosity during the polymerization process are responsible for the high molecular weights and the mostly high polydispersities. The systematic variation of the rate constants of propagation kp and termination kt using microwave reactor, IL/conventional organic solvent mixtures and increased reaction temperatures is studied.

Effect of ionic liquid on the thermal decomposition of cyclic organic peroxides

“…Regarding the use of RTILs as solvents in polymerization processes to replace the conventional organic solvents, although their use in free radical polymerization is still limited, they have shown some advantages such as higher polymerization rates and molecular weights than those obtained with traditional solvents such as toluene, tetrahydrofuran, among others. This behavior has been associated to a significant increase in the ratio: propagation rate constant /termination rate constant (k p /k t ), compared to polymerizations carried out in other polar solvents (Benton and Brazel, 2004;Li et al, 2006;Schmidt-Naake et al, 2008;Schmidt-Naake et al, 2009).…”

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 ) .…”

New ionic liquids with hydrolytically stable anions as alternatives to hexafluorophosphate and tetrafluoroborate salts in the free radical polymerization and preparation of ion-conducting composites

“…[1][2][3][4][5][6][7][8] The increasing interest in ILs as reaction media 9 and electrolytes [10][11][12] is due to their unique properties (for example, nonvolatility, nonflammability, high ionic conductivity and good thermal and electrochemical stability) and to the peculiarities of the chemical reactions performed in ILs. 1,9,13 In comparison with common organic solvents, ILs have high polarities and viscosities, 9 and thus they accelerate the free radical polymerization of unsaturated monomers and support the formation of polymers with ultra-high molecular weights.…”

“…[3][4][5][6][14][15][16][17] The influence of ILs on the kinetics of polymerization processes is related to the decrease in the activation energy 5,18,19 and the respective increase in the propagation rate. 4,5,[18][19][20][21][22] At the same time, the rate of termination decreases, 4,5,20,22,23 sometimes even by an order of magnitude, with the increase of IL concentration. 18 The increase in the propagation rate is generally attributed to the increased polarity of the ionic medium in comparison with that of the organic solvents that are traditionally used, whereas the decrease in the termination rate is assumed to be due to the increased viscosity of ILs.…”

“…18 The increase in the propagation rate is generally attributed to the increased polarity of the ionic medium in comparison with that of the organic solvents that are traditionally used, whereas the decrease in the termination rate is assumed to be due to the increased viscosity of ILs. [3][4][5][6]18,20,24,25 Andrzejewska et al 21 detected the phenomenon of viscosity synergism in dimethacrylate monomer/IL mixtures (that is, the viscosity of the mixture is higher than the simple additive combination of the viscosities of the two components); this phenomenon can have an important role in the kinetics of the reaction because the possibility of the gel effect is higher in the IL solution than in the bulk monomer. Schmidt-Naake et al 5 partly explained the reduction of the activation energy of propagation by the specific interaction of ethyl acrylate with ILs and the formation of H-bonds between both the monomer molecules and growing radical chains and the cations and anions of the ILs.…”