Chain-growth condensation polymerization for the synthesis of well-defined condensation polymers and pi-conjugated polymers.

Condensation polymerization is an important method of polymerization that yields not only engineering plastics such as polyamides, polyesters, and polyimides but also π-conjugated polymers, which have recently received considerable attention with the development of the information technology industry. The molecular weight of those polymers is generally difficult to control, and the polydispersity index theoretically approaches 2 at high conversion, which is unlike the behavior of living polymerization. An uncontrolled molecular weight and broad molecular weight distribution do not stem inherently from the reaction type of condensation polymerization, i.e. condensation steps with elimination of a small molecule species but from a polymerization mechanism for step-growth polymerization. Accordingly, if the mechanism of condensation polymerization could be converted from step-growth to chain-growth, living condensation polymerization would be possible. Nature already uses a chain-growth condensation polymerization process to synthesize perfectly monodisperse biopolymers such as polypeptides,1 DNA,2 and RNA.3 For example, in the biosynthesis of polypeptides, the amino group of an aminoacyl-tRNA, monomer, selectively reacts with the terminal ester moiety of polypeptidyl-tRNA in a ribosome to elongate the peptide chain. Even in artificial condensation polymerization of AB monomers, the chain-growth mechanism could be involved in the following two cases. (1) The change of the substituent effect induced by bond formation of the monomer drives the reactivity of the polymer end group to become higher than that of the monomer (Scheme 1A). (2) In condensation polymerization based on a coupling reaction with a transition metal catalyst, the catalyst is intramolecularly transferred to and activates the elongated polymer end group after the coupling reaction of the monomer with the polymer (Scheme * E-mail: yokozt01@kanagawa-u.ac.jp. Tsutomu Yokozawa was born in Chiba in 1957. He received his B.S. (1981), M.S. (1983), and Ph.D. (1987) degrees in Organic Chemistry from Tokyo Institute of Technology under the direction of Professor Nobuo Ishikawa and Professor Takeshi Nakai. In 1985, he had already started an academic career in the Research Laboratory of Resources Utilization, Tokyo Institute of Technology, as a Research Associate, and he was promoted to Assistant Professor in 1988. He joined the Department of Applied Chemistry, Kanagawa University, as a Lecturer in 1991, and he was promoted to Associate Professor in 1993. During 1997-1998, he worked as a visiting scientist at the University of Illinois at Urbana-Champaign with Professor J. S. Moore. He was promoted to Full Professor in 1999. He was also a researcher for PRESTO, JST, during 2001-2005. He received the Award of the Society of Polymer Science, Japan, in 2007. His research interests cover controlled synthesis of polymers, supramolecular chemistry of polymers, as well as synthetic organic chemistry. Chem. Rev. 2009, 109, 5595–5619 5595