Stereospecific radical polymerization of α-(alkoxymethyl)acrylates controlled by Lewis acid catalysts:: Mechanistic study and effect of amino alcohols as ligand for zinc bromide

The stereospecific radical polymerization of methyl and benzyl alpha-(methoxymethyl)acrylates was performed in the presence of Lewis acids, such as ZnBr2 and Sc(OTf)(3). The stereochemistry of the polymerization was significantly affected by the coordination of the Lewis acids to the polar groups of the monomer and polymer. The polymerization systems in the presence of ZnBr2 and Sc(OTf)(3) produced syndiotactic- and isotactic-rich polymers, respectively, showing different ESR signals. When amino alcohols were added to the polymerization system with ZnBr2, heterotactic-rich polymers were obtained. Therefore, syndiotactic-, isotactic-, and heterotactic-rich polymers can be synthesized by the radical method in the presence of a catalytic amount of ZnBr2, Sc(OTf)(3), and the ZnBr2-amino alcohol;complex, respectively, without changing the other polymerization conditions, although an atactic polymer was produced in the absence of a Lewis acid. The detailed tacticity (tetrad) of the obtained polymer was estimated by C-13 NMR analysis of the main-chain methylene carbon.