Palladium-catalyzed chain-growth polycondensation of AB-type monomers: high catalyst turnover and polymerization rates.

Chain-growth catalyst-transfer polycondensations of AB-type monomers is a new and rapidly developing tool for the preparation of well-defined π-conjugated (semiconducting) polymers for various optoelectronic applications. Herein, we report the Pd/PtBu3-catalyzed Negishi chain-growth polycondensation of AB-type monomers, which proceeds with unprecedented TONs of above 100,000 and TOFs of up to 280 s(-1). In contrast, related AA/BB-type step-growth polycondensation proceeds with two orders of magnitude lower TONs and TOFs. A similar trend was observed in Suzuki-type polycondensation. The key impact of the intramolecular (vs. intermolecular) catalyst-transfer process on both polymerization kinetics and catalyst lifetime has been revealed.

On the role of single regiodefects and polydispersity in regioregular poly(3-hexylthiophene): defect distribution, synthesis of defect-free chains, and a simple model for the determination of crystallinity.

Identifying structure formation in semicrystalline conjugated polymers is the fundamental basis to understand electronic processes in these materials. Although correlations between physical properties, structure formation, and device parameters of regioregular, semicrystalline poly(3-hexylthiophene) (P3HT) have been established, it has remained difficult to disentangle the influence of regioregularity, polydispersity, and molecular weight. Here we show that the most commonly used synthetic protocol for the synthesis of P3HT, the living Kumada catalyst transfer polycondensation (KCTP) with Ni(dppp)Cl(2) as the catalyst, leads to regioregular chains with one single tail-to-tail (TT) defect distributed over the whole chain, in contrast to the hitherto assumed exclusive location at the chain end. NMR end-group analysis and simulations are used to quantify this effect. A series of entirely defect-free P3HT materials with different molecular weights is synthesized via new, soluble nickel initiators. Data on structure formation in defect-free P3HT, as elucidated by various calorimetric and scattering experiments, allow the development of a simple model for estimating the degree of crystallinity. We find very good agreement for predicted and experimentally determined degrees of crystallinities as high as ∼70%. For Ni(dppp)Cl(2)-initiated chains comprising one distributed TT unit, the comparison of simulated crystallinities with calorimetric and optical measurements strongly suggests incorporation of the TT unit into the crystal lattice, which is accompanied by an increase in backbone torsion. Polydispersity is identified as a major parameter determining crystallinity within the molecular weight range investigated. We believe that the presented approach and results not only contribute to understanding structure formation in P3HT but are generally applicable to other semicrystalline conjugated polymers as well.

Chain-growth polymerization of unusual anion-radical monomers based on naphthalene diimide: a new route to well-defined n-type conjugated copolymers.

Strongly electron-deficient (n-type) main-chain π-conjugated polymers are commonly prepared via well-established step-growth polycondensation protocols which enable limited control over polymerization. Here we demonstrate that activated Zn and electron-deficient brominated thiophene-naphthalene diimide oligomers form anion-radical complexes instead of conventional Zn-organic derivatives. These highly unusual zinc complexes undergo Ni-catalyzed chain-growth polymerization leading to n-type conjugated polymers with controlled molecular weight, relatively narrow polydispersities, and specific end-functions.

Kumada Catalyst-Transfer Polycondensation: Mechanism, Opportunities, and Challenges.

Kumada catalyst-transfer polycondensation (KCTP) is a new but rapidly developing method with great potential for the preparation of well-defined conjugated polymers (CPs). The recently discovered chain-growth mechanism is unique among the various transition metal-catalyzed polycondensations, and has thus attracted much attention among researchers. Most progress is found in the areas of mechanism and external initiation via new initiators, but also the number of monomers other than thiophene that can be polymerized is steadily increasing. Accordingly, the variety of CP chain architectures is increasing as well, and a considerable contribution of KCTP toward more efficient materials can be expected in the future. This review critically focuses on very recent progress in the synthesis of CPs and the mechanism of KCTP, and is finally aimed at providing a comprehensive picture of this exciting polymerization method.

Random catalyst walking along polymerized poly(3-hexylthiophene) chains in Kumada catalyst-transfer polycondensation.

A "walking" process of Ni catalysts during Kumada catalyst-transfer polycondensation along polymerizing poly(3-hexylthiophene), P3HT, chains was investigated. To simplify polymer end group identifications, a compound Br-C(6)H(4)-Ni(dppe)-Br was prepared and used as an externally addable initiator. Normally, aryl moieties present in initiators incorporate into the structure of the resulting P3HT as the starting groups. We demonstrate that due to the presence of the C-Br group located in the para-position to the Ni substituent of the initiator, two different polymeric products are formed. One of them is the "normal" product, that is, P3HT with a para-bromophenyl end group, whereas another one has the phenyl ring inside the P3HT chain. The content of the product with the internal phenyl ring increases with the increase of the polymerization degree. Control experiments demonstrated that no intermolecular catalyst transfer takes place in the conditions used. Such results suggest that catalytic Ni(0) species are able to walk along the polymerizing chain containing many tens of thienyl rings up to the opposite end and can initiate polymerization there. Numerical analysis of a random hopping model was undertaken, which revealed that a combination of a random catalyst walking along the chain and a "sticking effect" at the end groups is operative in Kumada catalyst-transfer polycondensation.

Microparticle-supported conjugated polyelectrolyte brushes prepared by surface-initiated kumada catalyst transfer polycondensation for sensor applications.

A 'grafting-from' approach to synthesize microparticle-supported conjugated polyelectrolyte brushes is presented. Poly(3-bromohexylthiophene) is selectively grown from monodisperse organosilica microparticles by surface-initiated Kumada catalyst-transfer polycondensation (SI-KCTP) and then ionizable amino groups are introduced by a two-step polymer analogous transformation. Optical properties of the resulting microparticle-supported conjugated polyelectrolyte brushes were found to be dependent on the surrounding chemical environment and thus the particles are promising materials for sensor applications.

Surface engineering using Kumada catalyst-transfer polycondensation (KCTP): preparation and structuring of poly(3-hexylthiophene)-based graft copolymer brushes.

Poly(4-vinylpyridine)-block-poly(4-iodo-styrene), P4VP-b-PS(I), block copolymers obtained by iodination of readily available P4VP-b-PS block copolymers strongly adhere to variety of polar substrates including Si wafers, glasses, or metal oxide surfaces by a polar P4VP block, forming polymer brushes of moderately stretched PS(I) chains. Kumada catalyst-transfer polycondensation (KCTP) from the P4VP-b-PS(I) brushes results into planar brushes of the graft copolymer in which relatively short ( approximately 10 nm) poly(3-hexylthiophene), P3HT, grafts emanate from the surface-tethered PS(I) chains. Grafting of the P3HT leads to significant stretching of the PS(I) backbone as a result of increased excluded volume interactions. Specific adsorption of the P4VP block to polar surfaces was utilized in this work to pattern the P4VP(25)-b-PS(I)(350) brush. The microscopically structured P4VP(25)-b-PS(I)(350) brush was converted into the respectively patterned P4VP-PS(I)-g-P3HT one using KCTP. We also demonstrated that KCTP from functional block copolymers is an attractive option for nanostructuring with polymer brushes. P4VP(75)-b-PS(I)(313) micelles obtained in selective solvent for the PS(I) block form a quasi-ordered hexagonal array on Si wafer. The P4VP(75)-b-PS(I)(313) monolayer preserves the characteristic quasi-regular arrangement of the micelles even after extensive rinsing with various solvents. Although the grafting of P3HT from the nanopatterned P4VP(75)-b-PS(I)(313) brush destroys the initial order, the particulate morphology in the resulting film is preserved. We believe that the developed method to structured brushes of conductive polymers can be further exploited in novel stimuli-responsive materials, optoectronic devices, and sensors.

"Hairy" poly(3-hexylthiophene) particles prepared via surface-initiated Kumada catalyst-transfer polycondensation.

Herein, we present a new paradigm in the engineering of nanostructured hybrids between conjugated polymer and inorganic materials via a chain-growth surface-initiated Kumada catalyst-transfer polycondensation (SI-KCTP) from particles. Poly(3-hexylthiophene), P3HT, a benchmark material for organic electronics, was selectively grown by SI-KCTP from (nano)particles bearing surface-immobilized Ni catalysts supported by bidentate phosphorus ligands, that resulted in hairy (nano)particles with end-tethered P3HT chains. Densely grafted P3HT chains exhibit strongly altered optical properties compared to the untethered counterparts (red shift and vibronic fine structure in absorption and fluorescence spectra), as a result of efficient planarization and chain-aggregation. These effects are observed in solvents that are normally recognized as good solvents for P3HT (e.g., tetrahydrofurane). We attribute this to strong interchain interactions within densely grafted P3HT chains, which can be tuned by changing the surface curvature (or size) of the supporting particle. The hairy P3HT nanoparticles were successfully applied in bulk heterojunction solar cells.

Grafting of polyfluorene by surface-initiated Suzuki polycondensation.

Graft work: The first surface-initiated and site-specific palladium-catalyzed Suzuki polycondensation that allows selective grafting and patterning of semiconducting and emissive poly[9,9-bis(2-ethylhexyl)fluorene] (1) at room temperature is developed (see scheme). The patterning is demonstrated by AFM (see image).

Surface-Initiated Synthesis of Conjugated Microporous Polymers: Chain-Growth Kumada Catalyst-Transfer Polycondensation at Work.

Most of conjugated microporous polymers (CMPs) prepared to date are poorly processable, intractable solids. The immobilization of CMPs onto various surfaces is strongly desirable for many applications, such as for gas storage and separation, heterogeneous catalysis, and so forth. However, the preparation of thin porous films remains a challenging task. This Letter reports Ni-catalyzed surface-initiated Kumada catalyst-transfer polycondensation of a tetrafunctional thiophene-based (AB) 2-monomer from organosilica microparticles leading to microparticles covered by thin-film (∼30 nm) layers of the CMP. A sample of unbound CMP was also prepared by a bulk polymerization of the same monomer. Thus-obtained CMP possesses a relatively high specific surface area of 463 m2 g-1. The porosity of the immobilized polymer is somewhat lower with a specific surface area of 123 m2 g-1.

Zr(IV) and Hf(IV) based metal-organic frameworks with reo-topology.

Zr and Hf based MOFs with enhanced pore accessibility for large molecules and good hydrothermal stability were obtained using a bent dithienothiophene dicarboxylate and Zr(4+) or Hf(4+) source. A modulator (benzoic acid) facilitates formation of an eight-connecting cluster leading to a new framework which adopts reo topology.

Surface-initiated Kumada catalyst-transfer polycondensation of poly(9,9-dioctylfluorene) from organosilica particles: chain-confinement promoted beta-phase formation.

Surface-initiated Kumada catalyst-transfer polycondensation of poly(9,9-dioctylfluorene) (PFO) was performed from organosilica microparticles that resulted in PFO brushes with densely grafted PFO chains with a significantly enhanced propensity to adopt planar and ordered conformations (beta-phase).

Conductive polymer brushes of regioregular head-to-tail poly(3-alkylthiophenes) via catalyst-transfer surface-initiated polycondensation.

We describe a new method to grow conductive polymer (CP) brushes of regioregular head-to-tail poly(3-alkylthiophenes) (P3AT) via surface-initiated polycondensation of 2-bromo-5-chloromagnesio-3-alkylthiophene. A simple procedure for the preparation of the Ni(II) macroinitiator by the reaction of Ni(PPh3)4 with photocross-linked poly-4-bromostyrene films was developed. Exposure of the initiator layers to the monomer solution leads to selective chain growth polycondensation of the monomer from the surface, resulting in P3AT brushes in a very economical way. In contrast to the P3AT films prepared by traditional solvent casting methods, our approach leads to mechanically robust CP films, stable against delamination. We believe that our approach will be helpful in the fabrication of all-plastic devices.