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

Abstract

Photopolymerization of poly(ethylene glycol) monomethacrylate (PEGMM) in two imidazo- lium based ionic liquids (ILs) differing with the anion size and H-bond accepting ability, i.e. 1-ethyl- -3-methylimidazolium tetrafluoroborate ((EMIm)(BF4)) and 1-ethyl-3-methylimidazolium trifluoroace- tate ((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 indica- ting 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 mono- mer-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 confi- gurations of monomer-IL interactions were proposed: between the monomer carbonyl and C(2)-H hydro- gen of the imidazolium cation in the case of (EMIm)(BF 4 ) and a configuration in which the monomer car- bonyl interacts with the imidazolium cation located on the top of the ring, in the case of (EMIm)(ATF).