Catalyst-transfer Condensation Polymerization Research Articles

Scope of controlled synthesis via chain-growth condensation polymerization: from aromatic polyamides to π-conjugated polymers

Conventional condensation polymerization proceeds in a step-growth polymerization manner, in which the generated polymers possess a broad molecular weight distribution, and control over molecular weight and polymer end groups is difficult. However, the mechanism of condensation polymerization of some monomers has been converted from step-growth to chain-growth by means of activation of the polymer end group, either due to the difference in substituent effects between the monomer and the polymer, or due to successive intramolecular transfer of catalyst to the polymer end. In this article, we review recent developments in chain-growth condensation polymerization (CGCP) in these two areas. The former approach has yielded many architectures containing aromatic polyamides and aromatic polyethers, with unique properties. In the latter case, the mechanism, catalysts, and initiators of Ni- and Pd-catalyzed coupling polymerizations leading to poly(alkylthiophene)s and poly(p-phenylene)s have been extensively investigated. Other well-defined π-conjugated polymers, such as polyfluorenes, n-type polymers, and alternating aryl polymers, have also been synthesized by means of catalyst-transfer condensation polymerization. Many π-conjugated polymer architectures prepared by utilizing catalyst-transfer condensation polymerization are not covered in this article.

Catalyst-transfer condensation polymerization for precision synthesis of π-conjugated polymers

Catalyst-transfer condensation polymerization, in which the catalyst activates the polymer end-group, followed by reaction with the monomer and transfer of the catalyst to the elongated polymer end-group, has made it feasible to control the molecular weight, polydispersity, and end-groups of π-conjugated polymers. In this paper, our recent progress of Kumada–Tamao Ni catalyst-transfer coupling polymerization and Suzuki–Miyaura Pd catalyst-transfer coupling polymerization is described. In the former polymerization method, the polymerization of Grignard pyridine monomers was investigated for the synthesis of well-defined n-type π-conjugated polymers.Para-type pyridine monomer, 3-alkoxy-2-bromo-5-chloromagnesiopyridine, afforded poly(pyridine-2,5-diyl) with low solubility in the reaction solvent, whereasmeta-type pyridine monomer, 2-alkoxy-5-bromo-3-chloromagnesio-pyridine, yielded soluble poly(pyridine-3,5-diyl) with controlled molecular weight and low polydispersity. In Suzuki–Miyaura catalyst-transfer coupling polymerization,t-Bu3PPd(Ph)Br was an effective catalyst, and well-defined poly(p-phenylene) and poly(3-hexylthiophene) (P3HT) were obtained by concomitant use of CsF/18-crown-6 as a base in tetrahydrofuran (THF) and a small amount of water.

Precision Synthesis of n-Type π-Conjugated Polymers in Catalyst-Transfer Condensation Polymerization.

Recent developments in catalyst-transfer condensation polymerization, which proceeds in a chain-growth polymerization manner, have made it possible to synthesize well-defined π-conjugated polymers with controlled molecular weight and low polydispersity, as well as block copolymers and gradient copolymers. However, catalyst-transfer condensation polymerization has been limited to the polymerization of donor monomers (such as thiophene) for the synthesis of p-type π-conjugated polymers. Here, we highlight several recent advances in catalyst-transfer condensation polymerization leading to n-type π-conjugated polymers. The Kumada-Tamao coupling polymerization of Grignard pyridine monomers yields well-defined poly(pyridine-3,5-diyl) and poly(pyridine-2,5-diyl) with a broad molecular weight distribution. Monomers consisting of strong acceptor and weak donor moieties also undergo catalyst-transfer polymerization; well-defined poly(fluorene benzothiaziazole) was obtained by Suzuki-Miyaura coupling polymerization and poly(bithiophene naphthalene diimide) was obtained by an unusual Ni-catalyzed coupling polymerization of an anion radical generated from a bromothiophene naphathalene diimide bromothiophene monomer and activated zinc.

Synthesis and Characterization of Fully Conjugated Donor–Acceptor–Donor Triblock Copolymers

A synthetic approach is established to provide a monofunctional telechelic poly(3-octylthiophene) (P3OT) bearing a single bromine-substituted end group that is of potential use in the preparation of well-defined block copolymers. Telechelic P3OT was prepared via a chain growth process by a catalyst-transfer condensation polymerization (CTCP) of 5-bromo-4-octyl-2-thienylmagnesium iodide initiated by a phenylnickel(II) initiator. Optimization of the conditions for quenching the reaction allowed for the installation an α-bromo functionality at the terminus of the polymer. We demonstrate the utility of this well-defined monofunctional polymer, Ph–P3OT–Br, by coupling it to a poly(quinoxaline) (PQ) bearing boronate ester end groups to provided a new class of donor–acceptor–donor (D–A–D) triblock copolymers. The formation of the triblock copolymers was confirmed by gel-permeation chromatography (GPC) and 1H NMR spectroscopy. The optical properties of the polymers were investigated using UV–visible absorption an...

Importance of the Order of Successive Catalyst-transfer Condensation Polymerization in the Synthesis of Block Copolymers of Polythiophene and Poly(p-phenylene)

Abstract Successive catalyst-transfer condensation polymerization of a Grignard-type phenylene monomer and then a thiophene monomer with a Ni catalyst yields well-defined block copolymers of poly(p-phenylene) and polythiophene, but the reverse order of polymerization results in polymers with broad molecular weight distribution.

π共役系高分子アーキテクチャー

π-Conjugated polymers are an attractive class of materials due to their potential applications in electronic devices, but the molecular weight and polymer end groups have not been preciously controlled because most of the polymers have been synthesized by typical step-growth condensation polymerization. However, living polymerization process in the synthesis of π-conjugated polymers has been recently attained by catalyst transfer condensation polymerization, in which the metal catalyst is transferred intramoleculary to the polymer end group of the elongated molecule. This highlight review provides the discovery and development of this polymerization method and its application to the synthesis of π-conjugated polymer architectures such as polymer brush and block copolymers.

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.

Converting Step-Growth to Chain-Growth Condensation Polymerization

The development and applications of chain-growth condensation polymerization are reviewed. Well-defined aromatic polyamides, polyesters, and polyethers have been synthesized via substituent effect-assisted chain-growth condensation polymerization, in which the polymer propagating ends are more reactive than the monomers due to resonance or inductive effects between the functional groups of the terminal monomer units. Chain-growth condensation polymerization for the synthesis of aromatic polyamides has been applied to the construction of well-defined block copolymers and star-shaped polymers. Nickel-catalyzed condensation polymerization of 5-metalated 2-halothiophene has been found to proceed in a chain-growth polymerization manner. Detailed investigations revealed that this polymerization is a catalyst-transfer condensation polymerization, in which the chain-growth nature is attributable to intramolecular catalyst transfer. Phase-transfer polymerization in a solid−solution biphasic system, in which the mo...