Publications (13)44.19 Total impact
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Article: Synthesis of a Bifunctional Initiator for Controlled Kumada Catalyst-Transfer Polycondensation/Nitroxide-Mediated Polymerization and Preparation of Poly(3-hexylthiophene)−Polystyrene Block Copolymer Therefrom
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ABSTRACT: Herein, we present a new approach to synthesize rod−coil block copolymers via consecutive Kumada catalyst-transfer polycondensation (KCTP) and nitroxide-mediated free radical polymerization (NMP) performed from a bifunctional initiator, TIPNO−Ph−Ni(dppp)−Br (TIPNO = 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide; dppp = propane-1,3-diylbis(diphenylphosphane). The utility of the method was exemplified in a preparation of a model block copolymer, poly(3-hexylthiophene)-block-polystyrene (P3HT-b-PS) with a relatively narrow molecular weight distribution of 1.33. Synthesis of the bifunctional initiator was accomplished by a reaction of diethylbipyridylnickel with a readily accessible precursor, TIPNO−Ph−Br, followed by in situ replacement of the bipyridyl ligand onto bidentate phosphorus one.12/2009; -
Article: "Hairy" poly(3-hexylthiophene) particles prepared via surface-initiated Kumada catalyst-transfer polycondensation.
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ABSTRACT: 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.Journal of the American Chemical Society 11/2009; 131(45):16445-53. · 9.91 Impact Factor -
Article: Synthesis of Dendronized Diblock Copolymers via Click Chemistry: The Effect of Dendronization on Phase Separation Behaviour.
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ABSTRACT: A novel route towards the synthesis of well-defined linear-dendronized diblock copolymers is reported. Precursor alkyne containing diblock copolymers were modified in a highly efficient cycloaddition reaction with dendritic azides of different generation. The dendronization has been shown to be selective and could be driven to completion under ambient conditions. The phase separation of such dendronized diblock copolymers was investigated in dependence of the generation size being attached. Compared to a linear-linear diblock copolymer as starting material the dendronization yielded in a pronounced phase separation. The nanoscaled features observed in thin films strongly depended on the dendron size and a variety of morphologies could be identified. Hence, the unique combination of controlled radical polymerization and click chemistry allows for the triggering of structured surfaces in the nanometer-regime.Macromolecular Rapid Communications 09/2009; 30(17):1457-62. · 4.60 Impact Factor -
Article: Grafting of Poly(3-hexylthiophene) from Poly(4-bromostyrene) Films by Kumada Catalyst-Transfer Polycondensation: Revealing of the Composite Films Structure
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ABSTRACT: In order to achieve a stable, long-term operation of flexible electronic devices, it is necessary to firmly fix semiconductive conjugated polymers to plastic substrates, thus preventing their damage against delamination or chemical treatments. Surface-initiated Kumada catalyst-transfer polycondensation of 2-bromo-5-chloromagnesio-3-alkylthiophene from photo-cross-linked poly(4-bromostyrene), PS(Br), films leads to covalent grafting of regioregular head-to-tail poly(3-hexylthiophene), P3HT. Herein, we investigate the grafting process in detail and elucidate the structure of the resulting composite films using ellipsometry, X-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, and conductive mode atomic force microscopy techniques. In particular, we found that the grafting process is much more efficient if thick PS(Br) supporting layers are used. The maximal reachable thickness of the P3HT deposits is directly proportional to the thickness of the supporting PS(Br) layers. The obtained data suggest that the grafting process occurs not only at the PS(Br)/polymerization solution interface but also deeply inside the swollen PS(Br) films, penetrable for the catalyst and for the monomer. The process results into a kind of interpenetrated PS(Br)/P3HT network in which relatively short (10 nm) P3HT grafts emanate from long cross-linked PS(Br) chains. The films show good stability against delamination, high electrical conductivity in the doped state, and high swellability that might be exploited for construction of fully “plastic” electronic devices and sensors.09/2008; -
Article: One-dimensional SAMs of (12-pyrrol-1-yl-dodecyl)-phosphonic acid templated by polyelectrolyte molecules.
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ABSTRACT: We present a novel method for the fabrication of one-dimensional (1-D) self-assembled monolayers and multilayers (SAMs) of (12-pyrrol-1-yl-dodecyl)-phosphonic acid (Py-DPA) on various polar surfaces using polyelectrolyte nanostructures as positive templates. Particularly, we demonstrate that (i) patterns of aligned 1-D polycation structures on a poly(dimethylsiloxane) stamp can be prepared by moving a droplet of polycation solution along the surface; (ii) these patterns can be used as templates for the ordered assembly of Py-DPA in water where Py-DPA carries a charge opposite to the charge of the template; and (iii) Py-DPA SAMs can then be transferred onto mica or silicon wafers by a printing process. These nanostructures with a polymerizable pyrrole headgroup might be useful for the creation of electrically conductive patterns of conjugated polymers.Langmuir 09/2007; 23(18):9287-92. · 4.19 Impact Factor -
Article: Ultrathin transparent conductive films of polymer-modified multiwalled carbon nanotubes.
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ABSTRACT: Deposition of multiwalled carbon nanotubes modified by poly(2-vinylpyridine) (CNT-g-P2VP) from aqueous dispersions at low pH is an effective method to prepare homogeneous ultrathin films with a tunable CNTs density. A percolation threshold of 0.25 mug/cm2 and a critical exponent alpha = 1.24 have been found from dc conductivity measurements. The sheet resistance value agrees with the percolation theory for 2D films. According to AFM and electrical measurements, even when only 5% of the surface is covered by CNT-g-P2VPs, the sheet resistance is of the order of 1 MOmega/sq, which indicates that conductivity is imparted by a network of an ultralow density. When the film transmittance decreases down to approximately 70% at 550 nm, the occupied surface area is approximately 15% and sheet resistance falls down to approximately 90 kOmega/sq. These data show that undesired in-plane clustering does not occur upon the dispersion casting of the films and that high-quality networks of CNT-g-P2VPs are built up. The electrosteric stabilization of the CNT-g-P2VP dispersions in water at low pH is at the origin of this desired behavior. Although the multiwalled CNT films prepared in this work are less conductive and less transparent than the SWNTs films, they could find applications, e.g., in touch screens, reflective displays, EMI shielding, and static charge dissipation.The Journal of Physical Chemistry B 09/2006; 110(30):14640-4. · 3.70 Impact Factor -
Article: Simple method for the stretching and alignment of single adsorbed synthetic polycations.
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ABSTRACT: Spin-coating of isolated positively charged macromolecules onto mica in the presence of octylamine was found to be a simple and general method of stretching and aligning the macromolecular chains. The contour length and molar mass for the stretched macromolecules can be directly measured by atomic force microscopy, which makes this method a very useful analytical tool. Moreover, the molecular height is increased by co-deposition with octylamine, which drastically improves the molecular resolution and allows even ultrathin polycations to be visualized. The reason for the key role of the octylamine is found in the formation of an ultrathin liquidlike alkylamine film, which reduces the surface energy of mica and weakens the interactions between the surface and the charged macromolecules.Small 08/2006; 2(7):910-6. · 8.35 Impact Factor -
Chapter: Synthesis and Depositionof Water-Dispersed Prussian Blue Nanocrystals on Polymers and CNTs
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ABSTRACT: Nanoparticles can be used for decoration and functionalization of single polymer molecules that have been adsorbed to asolid substrate. Initial attempts to prepare Prussian Blue nanoclusters by alayer-by-layer deposition technique of hexacyanoferrate anions and ferric cations onto isolated polycation chains in water failed because of the desorption of the first layer upon deposition of the next one. Asimple method for the preparation of charge-stabilized Prussian Blue nanoparticles of readily adjustable size is reported. Prussian Blue nanoparticles have been purified by addition of non-solvents and redispersed in water without aggregation. Thus formed Prussian Blue nanoparticles are crystalline and display along-range ferromagnetic ordering at 5.1K. Prussian Blue nanoparticles were selectively deposited along single polycation molecules to form aone-dimensional array or were attached to the surface of carbon nanotubes (CNTs) functionalized with poly2-vinylpyridine (P2VP). These nanoparticle-based nanostructures might be useful materials for manufacture of electrooptical devices, or mechanically robust ion-sieving membranes.02/2006: pages 161-167; -
Article: Grafting of Conductive Polymers from Poly(glycidyl methacrylate)-Based Macromolecular Anchoring Layer
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ABSTRACT: INTRODUCTION A covalent tethering of polymer chains to solid substrates by one end point is one of the most important immobilization methods leading to the formation of polymer brushes. 1 Conductive polymers (CPs) have been extensively explored for next-generation electronic and optoelectronic applications. 2 In contrast to "usual" non-conductive polymers, CPs can respond to technologically relevant inputs like electrical or optical signals by changing their conductivity, conformation, wetability or color. The optical and electrochemical properties of some substituted CPs can be strongly modified by varying the temperature, the pressure, the solvent, the electrolyte, or upon recognition and binding of some biological objects. In these cases the polymers act as sensors through the detection and transduction of chemical/physical signal into optical or electrical outputs. The observed altering of the optical and electrochemical properties of CPs are due to reversible reconformation of CP chains. Liquid-phase configuration of the CP-based sensors were recently implemented. 3 However, the proper immobilization of CPs onto a solid support with a control over their organization at the mesoscale without loss of their pristine activity and conformational freedom could be very important step toward regenerable sensors. In addition, CP brushes developed on transparent electrodes were recently recognized to be a promising architecture for solar cell applications. 4 In contrast to unsubstituted polymers, anchoring of intrinsically soluble substituted CPs without affecting of their conformational freedom is considerably more complicated task. There are only few examples of surface-tethering of soluble CPs known in the literature. 5 Friend et al have utilized a "grafting from" polymerization of triphenylamine acrylate for the preparation of brushes contained semiconductive oligomer as a side groups attached to the tethered non-conductive backbone. Self-assembled monolayers (SAMs) of specially designed compounds were used as anchors for immobilization of CPs. Thiophene and pyrrole derivatives having thiol-, siloxane-, or phosphonic-end groups were utilized for fabrication of SAMs on gold, silica or metal oxide surfaces (Al, Ti, or indium tin oxide (ITO) coated glass). These SAMs were used for immobilization of various non-conductive and conductive polymers by the "grafting to" and "grafting from" techniques. Collard et. al have reported preparation of SAMs of oligothiophene-substituted alkysilanes on glass surface followed by the chemical and electrochemical grafting of alkylthiophenes from the SAM-modified surfaces. 6 Although the approach utilized SAMs as anchoring layers is a powerful immobilization method, it lacks of universality, since each substrate type and each kind of polymer to be immobilized requires a certain design of the anchoring compound. Recently Luzinov et. al proposed a novel macromolecular anchoring layer of poly(glycidyl methacrylate) (PGMA) for the preparation of non-conductive polymer brushes, as a viable and reasonable alternative to the traditional approach based on silane chemistry. 7 They demonstrated that adsorption of PGMA onto Si-wafers and subsequent annealing results in smooth and robust thin films. The glycidyl methacrylate units serve as reactive sites for the attachment of carboxy-terminated polymers. The high adhesion of PGMA to Si-wafers and films robustness is assumed to be due to multiple bonding of epoxy groups to the hydrophilic substrate and the formation of highly cross-linked network films. Here we report on the extension of this approach and demonstrate the utilization of PGMA as the macromolecular anchor for growing of CP brushes on various surfaces: Si-wafer, glass, ITO-modified glass, and various metals like Al, Ti and Au. Our method relies on the deposition of thin strongly adherent PGMA films, followed by a modification with properly functionalised polymerizable compounds and, finally, chemical or electrochemical growing of CPs. This convenient method has the advantage of the modular approach, allowing easy tuning of head-groups thus optimising the polymerisation process and the properties of resulting CP brushes.Polymeric Materials Science And Engineerinng. 01/2006; -
Article: Polypyrrole nanowires grown from single adsorbed polyelectrolyte molecules.
Angewandte Chemie International Edition 11/2005; 44(39):6391-4. · 13.45 Impact Factor -
Article: Designing Thiophene-Based Azomethine Oligomers with Tailored Properties: Self-assembly and Charge Carrier Mobility
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ABSTRACT: This paper describes synthesis and characterization of two thiophene-based azomethines designed to optimize solubility, self-assembly, and charge carrier mobility. We found that incorporation of azomethine and amide moieties in the α,ω-position, and hexyl chains in the β-position of the quaterthiophene, considerably improves the self-assembly properties without suppression of solubility. Self-assembly of azomethine oligomers with (QT-amide) and without amide moieties (QT-aniline) were monitored by UV−vis, XRD, and AFM. Although no changes in the UV−vis spectrum of QT-aniline is observed upon addition of hexane to the solution in THF, the addition of hexane to QT-amide solution induces a red shift of λmax and appearance of fine structure believed to be vibronic in nature. The concentration dependence of the solvatochromism gives strong support for the intermolecular origin of this effect and clearly indicates that the planarization of the oligomer backbone is forced by the aggregation. Although, no clear signs of the molecular order for various QT-aniline films are observed by AFM, UV−vis, and XRD measurements, the QT-amide film after the annealing at 180 °C displays important molecular and macroscopic orientations. The sum of charge carrier mobilities as determined by pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) technique for QT-aniline was shown to be below the detectable limit; the mobility of QT-amide was determined to be 1 × 10-2 cm2 V-1 s-1, which is comparable with the mobilities of the best organic semiconductors. All these significant differences in properties of related compounds can be attributed to the hydrogen bonding between QT-amide molecules responsible for the observed self-assembly.08/2004; -
Article: Conformation, Molecular Packing, and Field Effect Mobility of Regioregular β,β‘-Dihexylsexithiophene
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ABSTRACT: Improved synthesis, charge carrier mobility, conformation, crystalline structure, and molecular packing of the regiochemically pure 4‘,3‘ ‘‘ ‘-dihexyl-2,2‘;5‘,2‘ ‘;5‘ ‘,2‘ ‘‘;5‘ ‘‘,2‘ ‘‘ ‘;5‘ ‘‘ ‘,2‘ ‘‘ ‘‘-sexithiophene (β,β‘-DH6T) are reported. The sum of charge carrier mobilities of β,β‘-DH6T measured by the pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) technique was found to be ∑μmin = 3.9 × 10-3 cm2 V-1 s-1, which is comparable with the PR-TRMC mobility found for α,ω-DH6T. The field-effect mobility (FEM) of β,β‘-DH6T was found to be on the order of 10-5 cm2 V-1 s-1, which is considerably less than the FEM of α,ω-DH6T. To understand the reason for such poor macroscopic electrical properties, the conformation and the molecular packing of β,β‘-DH6T were systematically studied by means of UV−vis spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray techniques. Absorption spectra of a β,β‘-DH6T spin-cast film indicate the planar conformation of the aromatic backbone. SEM and AFM reveal the formation of an ordered lamellar phase. As a single-crystal X-ray study shows, β,β‘-DH6T exhibits less dense crystalline packing than α,ω-DH6T. In contrast to the almost upright orientation of α,ω-DH6T molecules against the substrate (tilt angle about 68°), the long axis of β,β‘-DH6T molecules and the surface plane form an angle of 20°. Thus, the crystalline structure of α,ω-DH6T “allows” the current to flow along the molecular stacks; the crystalline structure of β,β‘-DH6T suppresses the charge transport.06/2004; -
Article: Conformation, Molecular Packing, and Field Effect Mobility of Regioregular b,b'-Dihexylsexithiophene
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ABSTRACT: Improved synthesis, charge carrier mobility, conformation, cryst. structure, and mol. packing of the regiochem. pure 4',3''''-dihexyl-2,2';5',2'';5'',2''';5''',2'''';5'''',2'''''-sexithiophene (b,b'-DH6T) are reported. The sum of charge carrier mobilities of b,b'-DH6T measured by the pulse-radiolysis time-resolved microwave cond. (PR-TRMC) technique was .sum.mmin = 3.9 * 10-3 cm2 V-1 s-1, which is comparable with the PR-TRMC mobility found for a,w-DH6T. The field-effect mobility (FEM) of b,b'-DH6T was on the order of 10-5 cm2 V-1 s-1, which is considerably less than the FEM of a,w-DH6T. To understand the reason for such poor macroscopic elec. properties, the conformation and the mol. packing of b,b'-DH6T were systematically studied by UV-vis spectroscopy, SEM (SEM), at. force microscopy (AFM), and x-ray techniques. Absorption spectra of a b,b'-DH6T spin-cast film indicate the planar conformation of the arom. backbone. SEM and AFM reveal the formation of an ordered lamellar phase. As a single-crystal x-ray study shows, b,b'-DH6T exhibits less dense cryst. packing than a,w-DH6T. In contrast to the almost upright orientation of a,w-DH6T mols. against the substrate (tilt angle about 68 Deg), the long axis of b,b'-DH6T mols. and the surface plane form an angle of .apprx.20 Deg. Thus, the cryst. structure of a,w-DH6T \"allows\" the current to flow along the mol. stacks; the cryst. structure of b,b'-DH6T suppresses the charge transport. [on SciFinder (R)]Chemistry of Materials. 01/2004; 16:4757-4764.
Top co-authors
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Institutions
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2009
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Technical University of Denmark
- National Laboratory for Sustainable Energy
Copenhagen, Capital Region, Denmark
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2006–2007
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Leibniz-Institut für Polymerforschung Dresden e.V.
Dresden, Saxony, Germany
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