Stereocontrol During The Radical Polymerization With Combined Lewis Acids (AlCl₃-FeCl₂)

The radical polymerization of methyl methacrylate (MMA) was carried out in the presence of combined Lewis acids of AlCl3-FeCl2 system. Comparing with the polymerization produced in the presence of single Lewis acids: AlCl3 or FeCl2, the MMA polymerization in the presence of AlCl3-FeCl2 composite in CHCl3 or 1-butanol produced a polymer with a higher isotacticity and in toluene produced a polymer with a much higher isotacticity (mm=50%) . The molecular weight and polydispersity of PMMA in the presence of Lewis acids were similar with that in the absence of Lewis acids, although Lewis acids decelerate the polymerization of MMA. The effects of the Lewis acids were greater in a solvent with a lower polarity. A possible stereocontrol mechanism of the polymerization was proposed. The Lewis acid composite of AlCl3-FeCl2 formed a complex with one or more monomers easily. These monomer complexes possessed apparent bulkiness that changes the direction of monomer addition to the growing radical center.The radical stereospecific polymerization of AM mediated by AlCl3-FeCl2 mixture, AlCl3 and FeCl2 was discussed in this paper. It was found that AlCl3-FeCl2 mixture promoted greatly isotactic-specific propagation of AM. The stereoeffects of solvent polarity and concentration of Lewis acids were also discussed in detail.The radical stereospecific polymerization of DMAA mediated by AlCl3-FeCl2 mixture, AlCl3 and FeCl2 was also discussed in this paper. It was found that AlCl2-FeCl2 mixture promoted greatly isotactic-specific propagation of DMAA.