Prediction of the Ionic Liquid Influence on Propagation Rate Coefficients in Methyl Methacrylate Radical Polymerizations Based on Kamlet-Taft Solvatochromic Parameters

Pulsed laser initiated polymerizations of methyl methacrylate (MMA) in the presence of ionic liquids (ILs) resulted in a strong enhancement of the propagation rate coefficient, k(p), compared to the bulk system. To correlate the IL influence on MMA k(p) with IL solvent properties, the Kamlet-Taft parameters alpha, beta, and pi* of the ILs were derived. A correlation in the form of In(k(p)/k(p,bulk)) = ln(k(p)/k(p,bulk))(0) + s pi*+ a alpha + b beta was obtained from a linear solvation energy relationship (LSER) analysis of a data set consisting of polymerizations in 11 ILs, as well as in DMSO, in THF, and in bulk.. The coefficients are s = 1.72, a = 0.63, b = 0.37, and In(k(p)/k(p,bulk))(0) = -1.27. The data indicate that dipolarity, polarizability, and electron pair accepting ability of the IL, associated with the pi* parameter, contribute to a large extent to the variation in k(p), whereas electron pair donating and hydrogen bond accepting ability, accounted for by beta, are of lesser importance. The hydrogen bond donating ability, related to alpha, of the IL has no significant influence on k(p).