Stereospecific radical polymerization of alpha-(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-(metho xymethyl)acrylates was performed in the presence of Lewis acids, such as Zn Br2 and Sc(OTf)(3). The stereochemistry of the polymerization was significa ntly affected by the coordination of the Lewis acids to the polar groups of the monomer and polymer. The polymerization systems in the presence of ZnB r2 and Sc(OTf)(3) produced syndiotactic- and isotactic-rich polymers, respe ctively, showing different ESR signals. When amino alcohols were added to t he polymerization system with ZnBr2, heterotactic-rich polymers were obtain ed. Therefore, syndiotactic-, isotactic-, and heterotactic-rich polymers ca n be synthesized by the radical method in the presence of a catalytic amoun t of ZnBr2, Sc(OTf)(3), and the ZnBr2-amino alcohol;complex, respectively, without changing the other polymerization conditions, although an atactic p olymer 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.