Some Problems Concerning the Mechanism of the Isotactic Polymerization of Methyl Methacrylate Initiated by Organomagnesium Compounds in Toluene Solution—Application of Modified Dilatometer and NMR Methods

A dilatometer capable of being rapidly filled with monomer and initiator solutions mixed under carefully controlled conditions and a modification of an NMR T₁ program, adapted to store and display on recall the results of frequent sweeps at 30-s intervals of relevant proton resonances of a polymerizing mixture, are reported. These techniques have been applied to the identification of the optimum conditions for efficient, initiation of isotactic polymerization and investigation of the mechanism of propagation. It is shown that heat treatment does not remove the coordinated THF (1 molecule per RMg group) when toluene-soluble “tBuMgBr” or “PhMgBr” initiators are prepared and that the optimum THF concentration is slightly in excess of this. The nature of the solute in the toluene-soluble initiator solutions is discussed. The kinetics of the polymerization change from internal zero order to internal order of one with respect to monomer as the temperature increases from 225–275 K. This is consistent with a previously proposed mechanism in which propagation proceeds through a complex between monomer and the active center.