Controlled Radical Polymerization of Methacrylic Monomers in the Presence of a Bis(ortho-chelated) Arylnickel(II) Complex and Different Activated Alkyl Halides

Abstract

A novel class of homogeneous nickel(II) catalysts, i.e [Ni{ o, o ‘(CH 2 NMe 2 ) 2 C 6 H 3 }Br], denoted as Ni(NCN‘)Br, is reported to mediate in the presence of activated alkyl halides, e.g., CCl 4 or α-halocarbonyl compounds, a well-controlled radical polymerization of methacrylic monomers [methyl and n-butyl methacrylate), (MMA, n-BuMA)] at rather low temperatures (<100 °C). The number-average molecular weight of the polymer gradually increased with the monomer conversion and was inversely proportional to the initiator concentration of alkyl halides. The molecular weight distribution (MWD) remained very narrow during the whole course of the polymerization (MWD < 1.3). All the experimental data including a successful block copolymerization ( n -BuMA- b -MMA) experiment were in agreement with a living polymerization process, and remarkably enough, poly(methyl methacrylate) (PMMA) with molecular weight up to at least 10 5 g/mol was synthesized in a controlled fashion. Increased thermal stability of the PMMA is a further indication of the high regioselectivity and the virtually absence of termination reactions. Owing to the compatibility of the Ni(II) complexes toward water, extension to aqueous suspension polymerization was attempted successfully as attested by the promising preliminary results. Indications on the mechanism let us suggest that the reactive alkyl halide or the corresponding growing chain end is reversibly activated/deactivated by single electron transfer together with the halogen transfer.