End-Functionalization with Alcohols in Metal-Catalyzed Living Radical Polymerization through Umpolung of Growing Carbon-Halogen Bond

A novel method is described for the synthesis of end-functionalized polymers [-C-OR; R = CH2CH2OH, (CH2)(3)CH=CH2; CH2C(O)C6H5] via sequential terminal umpolung and alkoxy end-capping in metal-catalyzed living radical polymerizations of methyl acrylate and methacrylate with Ru(II) catalysts. The first umpolung step involved the single-unit addition of a modifier monomer [CH2=C(OCH3)C6H5; alpha MOS] onto the growing carbon halogen end (similar to similar to C-X; X = Cl, Br) to modify it from neutral (radical) into more nucleophilic (carbocationic). Subsequently, the modified terminal was quantitatively end-capped into an alkoxy with a functionalized alcohol (ROH). Systematic evaluation indicated that the modifier monomer be bulky (geminally disubstituted) and thus incapable of homopropagation and be electron-rich and conjugated for promoting the subsequent electrophilic substitution of alcohols. Thus, alpha-methoxystyrene (alpha MOS) was better suited than its alpha-monosubstituted p-methoxy and alpha-methyl-p-methoxy versions, with which respectively homopropagation overrode the single addition and HX elimination over the alcoholic substitution. For the second step a variety of functionalized alcohols are available; the simple methoxy from methanol may further be reduced into a more versatile ketone functionality. Similarly, telechelic polymers were also obtained from alpha,omega-bifunctional polymers.