Polymerization of methyl methacrylate with lithium triflate. A kinetic and structural study

Hermosilla, L.; Calle, P.; Tiemblo, P.; García, N.; Garrido, L.; Guzmán, J.
Macromolecules 2013, 46, 5445-5454

The radical photopolymerization of methyl methacrylate in the presence of lithium triflate is investigated by EPR and NMR spectroscopies in order to assess the effect of the ionic medium on the polymerization kinetics. The EPR spectra show a notorious increase in the concentration of propagating radical as result of a dramatic decrease in the average termination rate coefficient. IR spectroscopy experiments and theoretical studies the oxygen atom at the carbonyl position of the ester in the methyl confirm the formation of a complex between the lithium cation and methacrylate. The electrostatic repulsion between the complexed propagating radicals, specifically at the end of the chains, allows explaining the observed low termination rate. This strong interaction would lead to "quasi-living" polymer chains from the first steps of the polymerization.

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