| Abstract
| - Kinetic and NMR studies of the anionic polymerization of methyl methacrylate usingtetraphenylphosphonium and other phosphorus-containing, metal-free counterions indicated an equilibrium between an active ion pair and a corresponding ylide as a dormant species. We present densityfunctional theory (DFT) calculations of the energy difference between the ion pair and the ylide for theester enolate of methyl isobutyrate with various counterions which support this view. It is possible toestablish a correlation based on the calculated energy difference between the ylide and the ion pair andthe apparent activity of the chain end. The ylide formed after the first polymerization step is extremelystable compared to the ion pair, whereas after addition of one molecule of methyl methacrylate, the ylideof the dimer is destabilized through steric interactions and the polymerization can proceed much faster.This explains the observation of a pronounced induction period when using the ester enolate of methylisobutyrate as an initiator.
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