Tsutomu Yokozawa

Chain-Growth Condensation Polymerization for the Synthesis of Well-Defined Condensation Polymers and π-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

Precision synthesis of poly(3-hexylthiophene) from catalyst-transfer Suzuki-Miyaura coupling polymerization.

(t)Bu(3) PPd(Ph)Br (1)-catalyzed Suzuki-Miyaura coupling polymerization of 2-(4-hexyl-5-iodo-2-thienyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (2) was investigated. Monomer 2 was polymerized with 1 at 0 °C in the presence of CsF and 18-crown-6 in THF containing a small amount of water to yield P3HT with a narrow molecular weight distribution and almost perfect head-to-tail regioregularity. The M(n) values increased up to 11,400 g · mol(-1) in proportion to the feed ratio of 2 to 1. The MALDI-TOF mass spectra showed that P3HT with moderate molecular weight uniformly had a phenyl group at one end and a hydrogen atom at the other, indicating involvement of a catalyst-transfer mechanism. Successive 1-catalyzed polymerization of fluorene monomer 3 and then 2 yielded a well-defined block copolymer of polyfluorene and P3HT.

Catalyst-Transfer Condensation Polymerization for the Synthesis of Well-Defined Polythiophene with Hydrophilic Side Chain and of Diblock Copolythiophene with Hydrophilic and Hydrophobic Side Chains

Chain-growth condensation polymerization of 2-bromo-5-chloromagnesio-3-[2-(2-metho-xyethoxy)ethoxy]methylthiophene (2) with Ni catalysts was studied, and the block copolymer of poly2 and poly(3-hexylthiophene) was synthesized by this polymerization method. The polymerization of 2 depended on the ligands of the Ni catalyst, and poly2 with the lowest polydispersity was obtained when 1,2-bis(diphenylphosphino)ethane (dppe) was used as the ligand. The linear relationships between the conversion of 2 and Mn of the polymer and between the feed ratio of 2 to the Ni catalyst and Mn of the polymer indicate that this polymerization proceeds in a chain-growth polymerization manner via a catalyst-transfer condensation polymerization mechanism. The block copolymerization of 2 and 2-bromo-5-chloromagnesio-3-hexylthiophene (1) was then carried out in four ways by changing the order of polymerization of the two monomers and the catalysts. It turned out that the block copolymer was obtained without the formation of the homopolymers by the polymerization of 1 with Ni(dppe)Cl2 or Ni(dppp)Cl2 (dppp = 1,2-bis(diphenylphosphino)propane), followed by the postpolymerization of 2. Of the two catalysts, Ni(dppe)Cl2 resulted in narrower polydispersity of the block copolymer.

Chain-Growth Polycondensation: Living Polymerization Nature in Polycondensation and Approach to Condensation Polymer Architecture

In this review article, polycondensation that proceeds in a chain-growth polymerization manner (“chain-growth polycondensation”) for well-defined condensation polymers are described. Our approach to chain-growth polycondensation is (1) activation of polymer end group by substituent effects changed between monomer and polymer and (2) phase-transfer polymerization in biphase composed of monomer store phase and polymerization phase. In the approach (1), a variety of condensation polymers such as aromatic polyamides, aromatic polyesters, aromatic polyethers, poly(ether sulfone), and polythiophene with defined molecular weights and low polydispersities were obtained. Their polycondensations had all of the characteristics of living polymerization: a linear correlation between molecular weights and monomer conversion maintaining low polydispersities, and control over molecular weights by the feed ratio of monomer to initiator. Taking advantage of the nature of living polymerization in this polycondensation, we synthesized diblock copolymers of different kinds of aromatic polyamides and of aromatic polyamide and conventional polymers such as poly(ethylene glycol), polystyrene, and poly(tetrahydrofuran), as well as triblock copolymers and star polymers containing aromatic polyamide units. Some copolymers were arranged in a supramolecular self-assembly. In the approach (2), the polycondensation of solid monomer dispersed in organic solvent with a phase transfer catalyst (PTC) was carried out, where solid monomer did not react with each other, and the monomer transferred to organic solvent with PTC reacted with an initiator and the polymer end group selectively in organic solvent, to yield well-defined polyesters.

Lewis acid-catalyzed three-component condensation reactions of aldehydes, N-silylcarbamates, and allylsilane: synthesis of N-homoallylcarbamates

Abstract For simultaneous construction of the polyurethane backbone and the allyl side chains, Lewis acid-catalyzed three-component condensation reactions of carbonyl compounds, N -trimethylsilylcarbamates, and allyltrimethylsilane are studied. The reaction of these three compounds took place in the presence of a catalytic amount of TrClO 4 at 0°C to yield the corresponding N -homoallylcarbamates in good yields. This reaction was also applied to the synthesis of a polyurethane having the allyl side chains.

Structural Requirements for Palladium Catalyst Transfer on a Carbon–Carbon Double Bond

Intramolecular transfer of (t)Bu3PPd(0) on a carbon-carbon double bond (C═C) was investigated by using Suzuki-Miyaura coupling reaction of dibromostilbenes with aryl boronic acid or boronic acid esters in the presence of various additives containing C═C as a model. Substituent groups at the ortho position of C═C of stilbenes are critical for selective intramolecular catalyst transfer and may serve to suppress formation of the bimolecular C═C-Pd-C═C complex that leads to intermolecular transfer of (t)Bu3PPd(0).

Influence of the Boron Moiety and Water on Suzuki–Miyaura Catalyst-Transfer Condensation Polymerization

Although water promotes Suzuki-Miyaura coupling reaction, it also induces side reactions such as deboronation and dehalogenation. Therefore, Suzuki-Miyaura polymerization of triolborate halothiophene monomer 1 with (t) Bu3 PPd(o-tolyl)Br (2) in dry tetrahydrofuran (THF) is investigated. However, the resultant poly(3-hexylthiophene) (P3HT) shows a broad molecular weight distribution and uncontrolled polymer ends. Model reactions of a number of boron reagents 3 with 2,5-dibromothiophene (4) in the presence or absence of water indicate that intramolecular transfer of the catalyst is hardly affected by the boron moiety of 3, whereas it is hindered in the absence of water. Indeed, polymerization of 1 with 2 in H2 O/THF affords P3HT with a narrower molecular weight distribution and controlled tolyl/H ends, as compared to the reaction in dry THF.

Condensative chain polymerization. II. Preferential esterification of propagating end group in Pd‐catalyzed CO‐insertion polycondensation of 4‐bromophenol derivatives

For a development of condensative chain polymerization where polycondensation proceeds from an initiator in a chain polymerization manner to yield polymer with a defined molecular weight and a narrow molecular weight distribution, the Pd-catalyzed polycondensation of 4-bromophenol derivatives with CO is studied. Model reactions showed that monomer reacted the polymer terminal Br preferentially compared to the monomer Br, but that the ester exchange reaction of polymer backbone with monomer phenoxide occurred in some extent. In the polymerization of 4-bromo-2-n-octylphenol with CO using 4-bromo-2,6-dimethylphenyl benzoate as an initiator, the molecular weight of polymer increased in proportion to time up to 30 min. The GPC elution curves showed that oligomers were produced from the initiator.

Lewis acid-catalyzed coupling reactions of allyl trimethylsilyl ethers with allysilanes

Abstract For the simultaneous preparation of molecules having both the nucleophilic and electrophilic sites, allyl trimethylsilyl ethers as eletrophilic allylating reagents are studied. Allyl trimethylsilyl ethers react with allyl trimethylsilanes in the pressence of a catalytic amount of ZnCl2 at room temperature to afford the corresponding 1,5-dienes in good yields.

Chain-growth polycondensation in solid-liquid phase with ammonium salts for well-defined polyesters

Polycondensation of a potassium 4-bromo-methylbenzoate derivative dispersed in organic solvent was carried out with tetrabutylammonium iodide as a phase transfer catalyst (PTC) and a reactive benzyl bromide as an initiator to yield polyesters having a defined molecular weight and a narrow molecular weight distribution (M w /M n <1.3). Polymerization involves the transfer of monomer to organic solvent layer with the PTC and the reaction of monomer with the initiator and the polymer end benzyl bromide moiety in a chain polymerization manner, as evidenced by polymerization behavior; increase of the molecular weight in proportion to monomer conversion and equal amount of the initiator unit and the end group in polymer irrespective of monomer conversion. Furthermore, the molecular weight increased in proportion to feed ratio ([monomer] 0 /[initiator] 0 ), and the polydispersity index M w /M n stayed less than 1.3 over the whole range of feed ratio.