where he obtained his M.S. degree in Organic Chemistry on asymmetric synthesis from Professor Dennis Liotta. He earned his Ph.D. degree in Polymer Chemistry in 1999 on controlled/"living" radical polymerization at Carnegie Mellon University under the direction of Professor Krzysztof Matyjaszewski. His current research interests include the controlled synthesis of novel polymeric materials.

The homogeneous atom transfer radical polymerization (ATRP) of styrene using solubilizing 4,4‘-dialkyl substituted 2,2‘-bipyridines yielded well-defined polymers with M w/M n ≤ 1.10. The polymerizations exhibited an increase in molecular weight in direct proportion to the ratio of the monomer consumed to the initial initiator concentration and also exhibited internal first-order kinetics with respect to monomer concentration. The optimum ratio of ligand-to-copper(I) halide for these polymerizations was found to be 2:1, which tentatively indicates that the coordination sphere of the active copper(I) center contains two bipyridine ligands. The exclusive role for this copper(I) complex in ATRP is atom transfer, since at typical concentrations that occur for these polymerizations (≈10-7−10-8 M), polymeric radicals were found not to react with the copper(I) center in any manner that enhanced or detracted from the observed control. ATRP also exhibited first-order kinetics with respect to both initiator and copper(I) halide concentration; however, the polymerization kinetics were not simple inverse first-order with respect to the initial copper(II) halide concentration. The latter observation was found to be due to the persistent radical effect, which resulted in an increase in copper(II) concentration during the initial stages of the polymerization. This phenomenon also has the effect of regulating the polymerization by ensuring that the rate of radical combination and/or disproportionation is sufficiently less than the rate of propagation.

A radical polymerization process that yields well-defined polymers normally obtained only through anionic polymerizations is reported. Atom transfer radical polymerizations of styrene were conducted with several solubilizing ligands for the copper(I) halides: 4,4'-di-tert-butyl, 4,4'-di-n-heptyl, and 4,4'-di-(5-nonyl)-2,2'-dipyridyl. The resulting polymerizations have all of the characteristics of a living polymerization and displayed linear semilogarithmic kinetic plots, a linear correlation between the number-average molecular weight and the monomer conversion, and low polydispersities (ratio of the weight-average to number-average molecular weights of 1.04 to 1.05). Similar results were obtained for the polymerization of acrylates.

Three multidentate amines, tetramethylethylenediamine (TMEDA), N,N,N‘,N‘,N‘‘-pentamethyldiethylenetriamine (PMDETA) and 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) have been successfully used as new ligands in the copper mediated atom transfer radical polymerization (ATRP) of styrene, methyl acrylate and methyl methacrylate. All the polymerizations were well controlled with a linear increase of molecular weights (M n) with conversion and relatively low polydispersities throughout the reactions. Compared to the 2,2‘-bipyridine (bipy) based ligands, most multidentate amines are less expensive and the polymerization mixtures are less colored. In particular, the use of the tridentate PMDETA and the tetradentate HMTETA as the ligands resulted in faster polymerization rates for styrene and methyl acrylate than those using bipy as the ligand. This may be in part attributed to the fact that the coordination complexes between copper and the simple amines have lower redox potentials than the copper−bipy complex, resulting in higher rates of activation of the dormant halides. Additional rate effects may originate from the solubilities of the copper(I) and copper(II) complexes. The new ligands are very attractive alternatives to bipy and its derivatives as ligands.

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