Atom transfer radical polymerization.

Chemical Reviews is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 “Green” Atom Transfer Radical Polymerization: From Process Design to Preparation of Well-Defined Environmentally Friendly Polymeric Materials Nicolay V. Tsarevsky, and Krzysztof Matyjaszewski Chem. Rev., 2007, 107 (6), 2270-2299• DOI: 10.1021/cr050947p • Publication Date (Web): 27 May 2007 Downloaded from http://pubs.acs.org on April 2, 2009

"Green" atom transfer radical polymerization: from process design to preparation of well-defined environmentally friendly polymeric materials.

Transition metal catalysts for controlled radical polymerization

Reversible addition-fragmentation chain transfer (RAFT) chemistry can be effectively employed to construct macromolecular architectures of varying topologies. The present article explores the principle design routes to star, block, and comb polymers in the context of theoretical design criteria for the so-called Z- and R-group approaches. The specific advantages and disadvantages of each approach are underpinned by selected examples generated in the CAMD laboratories. In particular, we demonstrate how the modeling of full molecular weight distributions can be employed to guide the synthetic effort. We further explore the theory and practice of generating amphiphilic block copolymer structures and their self-assembly. In addition, the article foreshadows how modern synthetic techniques that combine RAFT chemistry with highly orthogonal click chemistry can be employed as a powerful tool that furthers the enhancement of macromolecular design possibilities to generate block (star) copolymers of monomers with extremely disparate reactivities. Finally, the ability of RAFT chemistry to modify the surface of well-defined nano- and microspheres as devices in biomedical application is detailed.

Complex Macromolecular Architectures by Reversible Addition Fragmentation Chain Transfer Chemistry: Theory and Practice

The reversible addition fragmentation chain transfer (RAFT) bulk polymerization of a fast propagating monomer (methyl acrylate, MA) has been studied using 1-phenylethyl dithiobenzoate (1-PEDB) and 2-(2-cyanopropyl) dithiobenzoate (CPDB) as RAFT agents at 60 °C. Rate retardation with increasing initial RAFT agent concentrations is common to both 1-PEDB- and CPDB-mediated MA polymerizations and occurs in comparable magnitude. A pronounced inhibition period is observed in 1-PEDB-mediated MA polymerizations, whereas the corresponding CPDB-mediated polymerizations show considerably less inhibition. The cause for this inhibition may either be associated with the leaving group of the initial RAFT agent or with the slow fragmentation of the initial intermediate macroRAFT radical. The present experimental data suggest that slow fragmentation is the probable cause for inhibition. We conclude that the radical intermediate formed by addition of radicals to the initial RAFT agent is different in stability than the macroRAFT radical formed analogously from macroRAFT agent. The inhibition period is effectively reduced by the use of CPDB as the initial RAFT agent in methyl acrylate polymerizations.

Origin of Inhibition Effects in the Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization of Methyl Acrylate

Schiff bases of types 1, 2, and 3, easily prepared by the condensation of primary amines with pyridine-2-carboxaldehyde, glyoxal, or 2-acetylpyridine, respectively, are described as ligands for a copper(I) catalyst in the atom transfer polymerization of a range of methacrylates in toluene and xylene solution. Increasing the length of the alkyl group on ligands of type 1 increases the solubility of the catalyst in nonpolar solvents. The rate of polymerization increases on going from R = ethyl to propyl; however, on increasing the length of R further, we see no effect on the rate. The molecular weight distribution is narrow for all ligands where R = n-alkyl, and the number-average molecular weight (Mn) increases linearly with conversion. A decrease in rate and a loss of control are observed when branching is introduced in the α-position of the side chain. The polymerization is approximately first order in initiator, 0.90 ± 0.22, CuBr, 0.90 ± 0.13, and methyl methacrylate, 0.93 ± 0.01. Polymerization with Cu...

Atom Transfer Polymerization of Methyl Methacrylate Mediated by Alkylpyridylmethanimine Type Ligands, Copper(I) Bromide, and Alkyl Halides in Hydrocarbon Solution

Bogdan H. Dana

Papers

Atom Transfer Polymerization of Methyl Methacrylate Mediated by Alkylpyridylmethanimine Type Ligands, Copper(I) Bromide, and Alkyl Halides in Hydrocarbon Solution