Kumada Catalyst Transfer Polymerization Research Articles

Correlating Molar Mass, π-Conjugation, and Optical Properties of Narrowly Distributed Anionic Polythiophenes in Aqueous Solutions.

Polythiophene-based conjugated polyelectrolytes (CPE) are attracting increasing attention as sensor or interface materials in chemistry and biology. While cationic polythiophenes are better understood, limited structural information is available on their anionic counterparts. Limited access to well-defined polymers has made the study of structure-property relationships difficult and clear correlations have remained elusive. By combining controlled Kumada catalyst transfer polymerization with a polymer-analog substitution, regioregular and narrowly distributed poly(6-(thiophen-3-yl)hexane-1-sulfonate)s (PTHS) with tailored chain length are prepared. Analysis of their aqueous solution structures by small-angle neutron scattering (SANS) revealed a cylindrical conformation for all polymers tested, with a length close to the contour length of the polymer chains, while the estimated radii remain too small (<1.5nm) for extensive π-stacking of the chains. The latter is particularly interesting as the longest polymer exhibits a concentration-independent structured absorption typical of crystalline polythiophenes. Increasing the ionic strength of the solution diminishes these features as the Coulomb repulsion between the charged repeat units is shielded, allowing the polymer to adopt a more coiled conformation. The extended π-conjugation, therefore, appears to be a key parameter for these unique optical features, which are not present in the corresponding cationic polythiophenes.

Tuning the emission and lighting the circularly polarized luminescence of polyfluorene by incorporating a non-emissive polycarbene

Polyfluorenes carrying a Ni(ii)-terminal were first prepared via Ni(ii)-catalyzed quasi-living Kumada catalyst-transfer polymerization, and poly(fluorene)-b-polycarbene copolymers with high optical activity and CPL were obtained in one pot.

Precision Synthesis of Conjugated Polymers Using the Kumada Methodology

Since the discovery of conductive poly(acetylene), the study of conjugated polymers has remained an active and interdisciplinary frontier between polymer chemistry, polymer physics, computation, and device engineering. One of the ultimate goals of polymer science is to reliably synthesize structures, similar to small molecule synthesis. Kumada catalyst-transfer polymerization (KCTP) is a powerful tool for synthesizing conjugated polymers with predictable molecular weights, narrow dispersities, specific end groups, and complex backbone architectures. However, expanding the monomer scope beyond the well-studied 3-alkylthiophenes to include electron-deficient and complex heterocycles has been difficult. Revisiting the successful applications of KCTP can help us gain new insight into the CTP mechanisms and thus inspire breakthroughs in the controlled polymerization of challenging π-conjugated monomers.In this Account, we highlight our efforts over the past decade to achieve controlled synthesis of homopolymers (p-type and n-type), copolymers (diblock and statistical), and monodisperse high oligomers. We first give a brief introduction of the mechanism and state-of-the-art of KCTP. Since the extent of polymerization control is determined by steric and electronic effects of both the catalyst and monomer, the polymerization can be optimized by modifying monomer and catalyst structures, as well as finding a well-matched monomer-catalyst system. We discuss the effects of side-chain steric hindrance and halogens in the context of heavy atom substituted monomers. By moving the side-chain branch point one carbon atom away from the heterocycle to alleviate steric crowding and stabilize the catalyst resting state, we were able to successfully control the polymerization of new tellurophene monomers. Inspired by innocent role of the sterically encumbered 2-transmetalated 3-alkylthiophene monomer, we introduce the treatment of hygroscopic monomers with a bulky Grignard compound as a water-scavenger for the improved synthesis of water-soluble conjugated polymers. For challenging electron-deficient monomers, we discuss the design of new Ni(II)diimine catalysts with electron-donating character which enhance the stability of the association complex between the catalyst and the growing polymer chain, resulting in the quasi-living synthesis of n-type polymers. Beyond n-type homopolymers, the Ni(II)diimine catalysts are also capable of producing electron-rich and electron-deficient diblock and statistical copolymers. We discuss how density functional theory (DFT) calculations elucidate the role of catalyst steric and electronic effects in controlling the synthesis of π-conjugated polymers. Moreover, we demonstrate the synthesis of monodisperse high oligomers by temperature cycling, which takes full advantage of the unique character of KCTP in that it proceeds through distinct intermediates that are not reactive. The insight we gained thus far leads to the first example of isolated living conjugated polymer chains prepared by a standard KCTP procedure, with general applicability to different monomers and catalytic systems. In summarizing a decade of innovation in KCTP, we hope this Account will inspire future development in the field to overcome key challenges including the controlled synthesis of electron-deficient heterocycles, complex and high-performance systems, and degradable and recyclable materials as well as cutting-edge catalyst design.

A Solution‐Processable Pristine PEDOT Exhibiting Excellent Conductivity, Charge Carrier Mobility, and Thermal Stability in the Doped State

AbstractPEDOT:PSS [poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate] is a widely used insoluble conducting polymer, which is therefore processed from dispersions. In this work, PEDOT homopolymers (PEDOT‐C6C8 1 and 2) highly soluble in common solvents like toluene, tetrahydrofuran, and chloroform are synthesized with a high control of molecular weight and low dispersity using Kumada catalyst transfer polymerization of a newly synthesized EDOT monomer carrying a branched alkyl substituent. Pristine PEDOT‐C6C8 allows the use in accumulation mode transistors with a high charge carrier mobility of 5 × 10−4 cm2 V−1 s−1. Moreover, these polymers can be doped in a controlled fashion, reaching conductivities of 10−3 S cm−1 at 10 mol% of a dopant, Spiro‐MeOTAD(TFSI)2. The doped state is remarkably stable, retaining 80% of the initial value after annealing under nitrogen at 100 °C and being exposed to ambient atmosphere for up to 12 h. During doping, the hole injection barrier decreases and reaches an impressively low value of 130 meV at only 2.5 mol% dopant loading without loss in carrier mobility; as monitored using ultraviolet photoelectron‐ and impedance spectroscopy. This new design concept leading to highly soluble polymers with well‐controlled molecular weights provides solution‐processable PEDOT dopable in a well‐controlled fashion.

Improving the Kumada Catalyst Transfer Polymerization with Water-Scavenging Grignard Reagents.

Conjugated polymers have received widespread interest as optoelectronic materials. Recently, these macromolecules have been adopted for biologically relevant applications, such as sensors, imaging agents, and drug delivery vectors. A major limitation of the chemistry used to prepare these classes of compounds is that the resultant polymers themselves are not tolerant to water or are not inherently water-soluble. For example, the most controlled method of conjugated polymer synthesis, the Kumada catalyst transfer polymerization (KCTP), requires stringent drying of monomers, catalysts, and other reagents. Here, we describe an approach to use a water-scavenging Grignard reagent to alleviate many of the shortcomings that currently hinder the synthesis of water-soluble conjugated polymers. This method shows improved polymerization performance in both traditional conjugated polymer synthesis as well as more challenging syntheses of polar hygroscopic polymers that are of interest for biological applications.

Kinetically Controlled Formation of Semi-crystalline Conjugated Polymer Nanostructures

Conjugated polymer (CP) materials that are considered as an attractive choice for various electronic and optoelectronic applications possess highly heterogeneous complex structures that can span several orders of magnitude in length scale. This is due to the intricate coupling effects of weak secondary interactions and entropic forces that determine molecular organization in bulk polymer materials. Understanding the influence of molecular interactions on the emergence and evolution of nano- and microscale structures is of paramount importance to the guided design and development of condensed CP materials. Such understanding is even more critical for the rational design of hierarchical systems away from equilibrium, where weak molecular interactions can guide the system along competing kinetic pathways toward local energy minima and metastable architectures. In this work, we studied a promising concept for accessing various kinetically stabilized semi-crystalline CP nanostructures that are formed in the process of controlled chain-growth Kumada catalyst-transfer polymerization initiated by a small-molecule catalytic species which can exist in equilibrium between free and aggregated states. Specifically, we chose a small-molecule perylenedicarboximide (PDCI) polymerization catalytic initiator which has a strong tendency toward reversible supramolecular assembly–disassembly that can be controlled by temperature. Addition of a thiophene monomer to a solution of the PDCI initiator starts the chain-growth polymerization process, which produces distinct nanoscale semi-crystalline polythiophene structures formed under predominant kinetic control. We demonstrated that, depending on the reaction temperature (which affects the fine balance between the position of PDCI assembly–disassembly equilibrium, rate of polymerization, and solvent–solute interactions for the growing polythiophene chains), a range of kinetically trapped hierarchically organized semi-crystalline CP systems with substantially varying optoelectronic properties could be obtained. In addition to spectroscopic and electron microscopic studies, in order to better reveal the structural aspects of the generated polymer nanoscale systems, we carried out a series of X-ray diffraction and neutron scattering experiments which indicated complex hierarchical organization in these kinetically stabilized CP assembled materials. We expect that this in situ polymerization-based approach can lead to a general way to expand access to various semi-crystalline CP nanostructured materials with broadly tunable electronic and optical properties.

Cross-coupling polymerization at iodophenyl thin films prepared by spontaneous grafting of a diazonium salt

Cross-coupling at aryl halide thin films has been well-established as a technique for the surface-initiated Kumada catalyst transfer polymerization (SI-KCTP), used to produce covalently bound conjugated polymer thin films. In this work, we report that the spontaneous grafting of 4-iodobenzenediazonium tetrafluoroborate on gold substrates creates a durable iodoarene layer which is effective as a substrate for cross-coupling reactions including SI-KCTP. Using cyclic voltammetry of a surface-coupled ferrocene terminating agent, we have measured initiator surface coverage produced by oxidative addition of Pd(t-Bu3P)2 and estimated the rate constant of the termination reaction in the SI-KCTP system with 2-chloromagnesio-5-bromothiophene and Pd(t-Bu3P)2. We used this system to prepare uniform polythiophene thin films averaging 90 nm in thickness.

Elucidating the Role of Catalyst Steric and Electronic Effects in Controlling the Synthesis of π-Conjugated Polymers

Kumada catalyst transfer polymerization (KCTP) has been widely adopted to synthesize π-conjugated polymers for various electronic and biological applications. However, the scope of monomers that ca...

Investigation of Bimetallic Nickel Catalysts in Catalyst‐Transfer Polymerization of π‐Conjugated Polymers

AbstractA comparative study involving bimetallic nickel catalysts designed from disubstituted N,N,N′,N′‐tetra(diphenylphosphanylmethyl)benzene diamine bridging ligands is reported. Catalyst behavior is explored in the Kumada catalyst‐transfer polymerization (KCTP) using poly(3‐hexylthiophene) (P3HT) as the model system. The success of a controlled polymerization is monitored by analyzing monomer conversion, degree of polymerization, end‐group identity, and molecular weight distribution. The characterization of P3HT obtained from KCTP initiated with the bimetallic catalysts shows chain‐growth behavior; however, the presence of Br/Br end‐groups and broader molecular weight distribution reveals a reduced controlled polymerization compared to the commonly employed Ni(dppp)Cl2. The observed increase in intermolecular chain transfer and termination processes in KCTP initiation with the bimetallic catalysts can be attributed to a weaker Ni(0)‐π‐aryl complex interaction, which is caused by increased steric crowding of the coordination sphere.

Core@Corona Functional Nanoparticle-Driven Rod-Coil Diblock Copolymer Self-Assembly.

Herein, a novel strategy to overcome the influence of π-π stacking on the rod-coil copolymer organization is reported. A diblock copolymer poly(3-hexylthiophene)-block-poly(ethylene glycol methyl ether methacrylate) (P3HT-b-PEGMA) was synthesized by the Huisgen cycloaddition, so-called "click chemistry", combining the PEGMA and P3HT blocks synthesized by atom transfer radical polymerization and Kumada catalyst transfer polymerization, respectively. Using a dip-coating process, we controlled the original film organization of the diblock copolymer by the crystallization of the P3HT block via π-π stacking. The morphology of the P3HT-b-PEGMA films was influenced by the incorporation of gold nanoparticles (GNPs) coated by poly(ethylene glycol) ligands. Indeed, the crystalline structuration of the P3HT sequence was counterbalanced by the addition in the film of gold nanoparticles finely localized within the copolymer PEGMA matrix. Transmission electron microscopy and time-of-flight secondary ion mass spectrometry analysis validated the GNP homogeneous localization into the compatible PEGMA phase. Differential scanning calorimetry showed the rod block crystallization disruption. A morphological transition of the self-assembly is observed by atomic force microscopy from P3HT fibrils into out-of-plane cylinders driven by the nanophase segregation.

Electroactive Composite of FeCl3 -Doped P3HT/PLGA with Adjustable Electrical Conductivity for Potential Application in Neural Tissue Engineering.

Conducting polymers (CPs) is one of intelligent biomaterials with the specific properties of reversible redox states, which have a significant effects on the cell behaviors and nerve tissue regeneration. However, the effects of CPs with different electrical conductivity on the behaviors of nerve cells are rarely reported. Therefore, a kind of Poly(3-hexylthiophene) (P3HT) with certain molecular weight is synthesized by Kumada catalyst transfer polymerization (KCTP) method and employed to prepare bioabsorbable and electroactive intelligent composites of Poly(3-hexylthiophene)/Poly(glycolide-lactide) (P3HT/PLGA). FeCl3 doping electroactive membranes with different electrical conductivities are prepared to investigate the cell behaviors. On the substrate with higher electrical conductivity, the proliferation of rat adrenal pheochromocytoma cells (PC12 cells) is significantly promoted and neurite length is increased obviously. In particular, the most significant improvements are the neuron gene expression of Synapsin 1 and microtubule-associated protein 2 (MAP2) by the composites with high conductivity. These results suggest that P3HT/PLGA with suitable electrical conductivity have a positive role in promoting neural growth and differentiation, which is promising for advancing potential application of nerve repair and regeneration.

Highly Water‐Soluble Rod–Coil Conjugated Block Copolymer for Efficient Humidity Sensor

AbstractIn this report, the preparation of highly water‐soluble rod–coil conjugated block copolymer poly(3‐hexylthiophene)‐b‐polystyrenesulfonic acid (P3HT‐b‐PSSA) is demonstrated using a facile method with its moisture sensing properties. The block copolymer synthesis method comprises Kumada catalyst transfer polymerization and atom transfer radical polymerization from a bifunctional initiator followed by sulfonation of polystyrene using moderate reaction conditions. The polymerization results in the synthesis of well‐defined block copolymers with controllable block length. The successful synthesis of the block copolymer is studied by NMR and FTIR spectroscopy while optical and structural properties of the block copolymer are investigated using UV–vis, photoluminescence spectroscopy, XRD, and FESEM. In water, the block copolymer shows aggregated structure with crystalline core formed by rod‐like P3HT chain with absorption maxima at 558 nm, whereas in solid state the absorption maxima is blue shifted to 548 nm. The proton conductivity of the block copolymer P3HT‐b‐PSSA with ≈91% of PSSA (by weight) is measured from impedance study, and the values for bulk and grain conductivities are 5.25 × 10−4 and 4.66 × 10−6 S cm−1, respectively, at room temperature. The as‐synthesized block copolymer shows a very high water uptake with maximum ≈80% in comparison with its initial weight. The I–V measurement of the device made from block copolymer shows nonlinear, rectifying characteristic and the current increases with increase of relative humidity (RH%). The block copolymer device shows well‐correlated systemic and reversible resistance change with RH both in doped and undoped state. It is believed that the interesting and highly reversible moisture‐sensitive electronic properties of this block copolymer will be useful for the fabrication of moisture‐sensitive polymer‐based flexible electronic devices.

Simple synthesis of end functionalized regioregular poly(3‐hexyl thiophene) by catalytic‐initiated Kumada catalyst transfer polymerization

A simple but efficient route to the preparation of aromatic end‐functionalized regioregular poly(3‐hexyl thiophene) through catalytic initiated Kumada catalyst transfer polymerization from easily accessible reagents is reported here. The introduction of an aromatic moiety at one end of the poly(3‐hexyl‐thiophene) (P3HT) chain was confirmed by NMR, by MALDI‐TOF analysis, and also by successful syntheis of rod–coil‐conjugated block copolymers either from a proper end‐functionalized P3HT or from an end‐functionalized coil polymer.

Modular Synthesis and Structure Analysis of P3HT-b-PPBI Donor–Acceptor Diblock Copolymers

While donor–acceptor block copolymers (BCPs) are widely discussed to be optimal model materials for studying the morphology-dependent processes in organic photovoltaics, the observation of the desired microphase-separated structures is rare. We present a novel modular approach for the synthesis of donor–acceptor block copolymers offering a fast and flexible way for chemical modifications leading to microphase separation accompanied by confined crystallization of the individual blocks. Two donor–acceptor BCPs of poly(3-hexylthiophene)-b-polyperylene bisimide (P3HT-b-PPBI 1 and 2) were synthesized incorporating P3HT as a donor and a polystyrene with two different pendant perylene bisimides (PBI-N3 1 and 2) as acceptor blocks to show the flexibility of the synthetic approach. The synthesis combines Kumada catalyst transfer polymerization (KCTP), controlled radical polymerization, and click chemistry to obtain highly comparable polymers via a modular approach. We synthesized poly(3-hexylthiophene) (P3HT) with...

Silica–Conjugated Polymer Hybrid Fluorescent Nanoparticles: Preparation by Surface-Initiated Polymerization and Spectroscopic Studies

Organic/inorganic hybrid nanoscale materials possess fascinating optical, electronic, magnetic, and catalytic properties that are promising for a variety of practical applications. Such properties can be dramatically affected by the hierarchical structure and molecular organization in the nanomaterials. Herein, we employed surface-initiated Kumada catalyst-transfer polymerization to prepare hybrid materials consisting of shells of conjugated polymers (CPs)—polythiophene or poly(p-phenylene)—and their block copolymers covalently attached to the surface of silica nanoparticles. Because of the controlled chain-growth mechanism of surface-initiated polymerization, we obtained structurally well-defined CP blocks in the diblock copolymer shells, which produced distinct spectroscopic properties related to the intraparticle excitation energy transfer between the nanoscale polymer shell components, as well as the formation of interfacial exciplex states. The spectroscopic phenomena were further understood via time...

Anodic Chlorination of Selenophene‐Containing Polymers: Reaction Efficiency and Selective Reaction of Single Segment in Rod−Rod Diblockcopolymer

AbstractThe post‐polymerization modification of selenophene‐containing (co)polymers is presented based on the electrochemical polymer reaction (ECPR). Selenophene‐ or thiophene‐containing (co)polymers, which are known to be promising materials in optoelectronic devices, were synthesized through Kumada catalyst transfer polymerization to give their homopolymers and block‐ or statistical copolymers with various side chains. Each of the series of polymers was subjected to post‐modification through the ECPR, and the reaction efficiencies were systematically compared. Selenophene‐containing polymers were successfully modified with better ECPR reaction efficiencies than their thiophene analogues. Moreover, the dramatic inhibiting effect of a branched side chain on the ECPR was observed and rationalized, which was very unexpected. Based on the basic tendency observed here, we have finally demonstrated the selective modification of a single segment of a rod−rod block copolymer for the first time.

Facile synthesis of oligo(3-hexylthiophene)s conductive wires with charge-transfer functions

A series of fully conjugated oligo(3-hexylthiophene)s bearing different starting- and end-groups have been synthesized by means of externally initiated Kumada catalyst-transfer polymerization (KCTP) and Grignard Metathesis Polymerization (GRIM).

Evaluation of an external initiating Ni(ii) diimine catalyst for electron-deficient π-conjugated polymers

We have prepared, isolated, and evaluated the first Ni(ii) diimine catalyst able to externally initiate the Kumada catalyst transfer polymerization of an electron-deficient π-conjugated monomer.

Poly(N-alkyl-3,6-carbazole)s via Kumada Catalyst Transfer Polymerization: Impact of Metal–Halogen Exchange

The preparation of poly(3,6-carbazole) via Kumada catalyst transfer polymerization (KCTP) is investigated and analyzed in detail by mass spectrometry to explore the scope of the applied protocols. Namely, common magnesium reagents were screened for the initial Grignard metathesis (GRIM) step and subsequently polymerized using [Ni(dppp)Cl2] (dppp is 1,3-bis(diphenylphosphanyl)propane). The metal–halogen exchange was monitored by GC, while the polymers were characterized by size exclusion chromatography (SEC) and 1H NMR spectroscopy. More importantly, the polymer end groups were investigated by means of mass spectrometry and isotope analysis, which revealed significant deviation from the chain-growth character of related poly(3-hexylthiophene). It was found that standard Grignard reagents led to incomplete GRIM even under extended reaction times and elevated temperatures, while the presence of LiCl greatly accelerated the metal–halogen exchange and also the KCTP. According to end-group analysis of the obtained polymers, side reactions occur that are attributed and explained in terms of catalyst dissociation and/or disproportionation. Namely, the replacement of the bromo-substituents by either alkyl groups via transmetalation or hydrogen via β-hydride elimination was observed. Finally, quantitative metal–halogen exchange was achieved using a magnesiate reagent, which also afforded the corresponding polymer in good isolated yield (66%). The end-group scrambling, dispersity, and observed molar masses support the proposed role of catalyst dissociation and/or disproportionation, even in the absence of excess of residual Grignard reagent.

Precise Synthesis of Block and Miktoarm Star‐Branched Polymers Containing Polythiophene Segments with Low Dispersity by Combination of Living Anionic Polymerization and Catalyst‐Transfer Polycondensation Systems

In this Talent article, the synthesis of well‐defined block and miktoarm star‐branched polymers is described by the combination of living anionic polymerization (LAP) and Kumada catalyst‐transfer polymerization (KCTP), mostly focusing on poly(3‐alkylthiophene) (P3AT)‐based block copolymers and miktoarm star‐branched polymers. The two synthetic methodologies are introduced as follows: (a) a chain‐extension method using chain‐end‐functional polymers via site transformation reaction, and (b) a linking reaction method between two polymer building blocks. The most promising method (b) can further be divided into four different approaches, (b‐1) direct addition reaction of living anionic polymers with chain‐end‐functional P3HT; (b‐2) “Click” reaction between two chain‐end‐functional polymers; (b‐3) direct coupling reaction of living anionic polymers with chain‐end‐functional P3HT; and (b‐4) ionic bond formation of chain‐end‐functional polymers. Based on the recent progresses in synthetic methodologies, versatile block copolymers and miktoarm star‐branched polymers have been successfully produced, well controlling the molecular weights (MW) and dispersities (ÐM). image