Propagation kinetics of free-radical polymerizations in ionic liquids

Propagation rate coefficients, kp, of methyl methacrylate (MMA) and glycidyl methacrylate (GMA) homopolymerizations were measured at ambient pressure in four ionic liquids (ILs): 1-ethyl-3-methylimidazolium ([emim]) ethyl sulfate and [emim] hexyl sulfate as well as butyl-3-methylimidazolium ([bmim]) hexafluorophosphate and [bmim] tetrafluoroborate via the pulsed-laser polymerization size-exclusion chromatography technique. In passing from bulk polymerization at 40°C polymerization in IL solution containing 20 vol % monomer, kp is enhanced by up to a factor of 4 with MMA and by a factor of 2 with GMA. This enhancement of kp primarily results from a lowering of activation energy upon partial replacement of monomer by ionic liquid species.