Effect of chelation of the lithium cation on the anionic polymerization of methyl methacrylate using organolithium initiators

Benzyllithium (BzLi) and 1,1-diphenylhexyllithium (DPHLi) were used to inititate the anionic polymerization of methyl methacrylate (MMA) in the presence of N,N,N',N'-tetramethylethylenediamine (TMEDA) in THF at -78 and -40°C. PMMAs with predetermined molecular weights and narrow polydispersities could be obtained with benzyllithium initiator at -78°C in THF in the absence of TMEDA. Interestingly, even at -40°C, DPHLi in conjunction with TMEDA was able to provide PMMAs with control on molecular weight and polydispersity values of less than 1.2. The results are explained on the basis of the solvation of the Li<SUP>+</SUP> cation by TMEDA resulting in the stabilization of the propagating enolate anion