Photopolymerization kinetics and molecular interactions in methacrylate-imidazolium based ionic liquid systems (in English)
Polimery 2014, No 6, 459
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][BF4]) and 1-ethyl-3-methylimidazolium trifluoroacetate ([EMIm][ATF]) was investigated to find the effect of the IL anion on propagation kp and termination rate ktb 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 kp values observed in ILs is higher for polymerization in [EMIm][BF4], 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][BF4] 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].