Iron-catalyzed radical polymerization of acrylamides in the presence of Lewis acid for simultaneous control of molecular weight and tacticity

This work is directed to the stereospecific living radical polymerization of acrylamides such as N,N-dimethylacrylamide and N-isopropylacrylamide with an iron complex and a Lewis acid. DMAM was polymerized with [FeCp(CO)(2)](2) in conjunction with an alkyl iodide [(CH3)(2)C(CO2Et)I] as an initiator in the presence of Y(OTf)(3) in toluene/methanol (1/1) at 60 degrees C to be converted almost quantitatively to the polymers with controlled molecular weights and high isotacticity (m > 80%), wherein the Fe-complex generates radical species from a covalent C-I bond of the dormant species and the Lewis acid controls the stereochemistry of the polymerization via coordination with the amide groups of the polymer terminal and the monomer. A series of Lewis acids were also used for the iron(I)-catalyzed DMAM polymerization, and Yb(OTf)(3) and Yb(NTf2)(3) proved effective in giving isotactic polymers without deteriorating the molecular weight control similar to Y(OTf)(3). Furthermore, a slight enhancement of isospecificity was observed for the iron-catalyzed system in comparison with the alpha,alpha-Azobisisobutyronitrile-initiated, when coupled with Y(OTf)(3). Stereoblock polymerization of DMAM via a one-pot reaction was also achieved by just adding the Y(OTf)3 methanol solution in the course of the polymerization to give atactic-b-isotactic poly(DMAM). A similar but slightly lower control in the molecular weight and tacticity was achieved in the polymerization of NIPAM with [FeCP(CO)(2)](2)/Y(OTf)(3), (c) 2006 Wiley Periodicals, Inc.