CONTROLLED POLYMERIZATION OF METHYL-METHACRYLATE USING LITHIUM ALUMINUM ALKYLS

The important contribution of this paper is to show that certain combinations of lithium and aluminum alkyls enable polymerizations of alkyl methyl methacrylate to be carried out at elevated temperatures. The work also shows that both the lithium and aluminum components must contain alkyl groups which have cross-sectional areas as large as possible. Moreover, these initiators are only effective in hydrocarbon solvents in which they are soluble. Solvents which have previously been preferred for anionic and catalyzed anionic polymerization, such as tetrahydrofuran, dimethoxyethane, etc., inactivate these initiators. In hydrocarbon solvents the separation between the anionic and cationic components are minimized and the high cross-sectional area of the latter "screens" the propagating terminus of the polymer chain from side reactions. Thus we refer to this polymerization of methacrylate monomers as 'screened anionic polymerization". Molecular weights in the range 2000-150 000 have been prepared with dispersions close to that described by the Poisson distribution. A variety of block copolymers have also been prepared. A model has been developed which accounts for the quantitative observations and is based on the known structure of lithium aluminum alkyls.