Ulrich Oertel

“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).

Dense-shell glycodendrimers: UV/Vis and electron paramagnetic resonance study of metal ion complexation

The development of dendritic metal ion carrier systems for use in a biological environment is a challenging task as the carrier system must possess multiple features (e.g. a protective shell for metal decomplexation, targeting functions, metal–intradendrimer complexes, etc.) to substitute for the function of metal proteins in processes such as copper metabolism. Thus, Cu(II) complexation by a series of poly(propyleneimine) glycodendrimers ranging up to the fifth generation that have either a dense maltose or maltotriose shell was investigated by UV/Vis spectroscopy and electron paramagnetic resonance (EPR). As a necessary step towards potential biological application, we elucidated the complexation capacity, location of the Cu(II)–dendrimer complexes and the Cu(II) coordination sphere in the dendritic environment. A generation-dependent Cu(II) complexation was found. Furthermore, analysis of the EPR spectra revealed that internal and external Cu(II) coordination and the symmetry (axial and rhombic) of the generated complexes depend on the oligosaccharide shell, dendrimer generation and the relative concentrations of Cu(II) and the dendrimers. Both axial and rhombic symmetries are generation dependent, but also distort with increasing generation number. External coordination of Cu(II) is supported by sugar groups and water molecules. Finally, a third-generation dendrimer with a maltose shell was used to explore the general complexation behaviour of the dendritic poly(propyleneimine) scaffold towards different metal ions [Cu(II), Ag(I), VO(IV), Ni(II), Eu(III) and UO2(VI)].

Langmuir-Blodgett layers from polymer-metal complexes: behaviour of monolayers and preparation of multilayers

Amphiphilic polymers with two different alternating functional units along the main chain were synthesized and their monolayer behaviour was investigated. When they have a ligand group adjacent to a carboxylic acid group, two different metal complexes can be introduced into a monolayer: a complex with a free coordination site can be bound via the ligand group, and a cationic complex as counter-ion. These polymer-metal complexes were prepared in an interfacial reaction between the polymer monolayer and the complex dissolved in the aqueous subphase. The resulting monolayers can be transferred onto solid substrates. The presence of the different complexes was proved by means of ultraviolet/visible spectroscopy.

Temperature responsive polymer brushes with clicked rhodamine B: synthesis, characterization and swelling dynamics studied by spectroscopic ellipsometry

Here, we report on a new temperature responsive polymer brush system with a terminal “click” functionality. Bifunctionalized poly(N-isopropylacrylamide) (PNiPAAm) with distinct functional end groups was synthesized by atom transfer radical polymerization (ATRP) and grafted to a modified silicon substrate. The presence of the active terminal alkyne functionality is validated using an azide-modified rhodamine B (N3-RhB) via copper(I) catalyzed alkyne–azide cycloaddition (CuAAC). The optical properties and swelling dynamics of an N3-RhB modified PNiPAAm brush are analyzed in dry state and in situ by VIS-spectroscopic ellipsometry (SE). The best-fit results are obtained using a Gaussian oscillator model and are confirmed by UV/VIS-spectroscopy. We observed evidence of interactions between the aromatic residues of the dye and the PNiPAAm amide groups, which significantly affect the swelling behavior of the modified polymer brush.

Ultrathin Films from Fluorine Containing Polymers: Fabrication and Characterization

Monolayers and ultrathin films of some fluorine containing polymers were prepared by the Langmuir-Blodgett (LB) technique. The polymers were obtained using two main synthetic approaches: firstly, polyamide (PA-1) and polyimide (PI-1) were prepared from direct polycondensation of 4,4′-hexafluoroisopropylidenediphthalic anhydride and 4,4′-hexafluoroisopropylidenedianiline in N-methyl-2-pyrrolidone (NMP). The thermogravimetric analysis (TGA) for PI-1 yielded 580°C by 1% weight loss. They formed stable monolayers with a collapse pressure of 62 mN/m and a collapse area of 0.20 nm2 per repeat unit (R.U.) in the case of PA-1, for PI-1 the collapse pressure was 60 mN/m associated with a collapse area of 0.23 nm2 per R.U. Secondly, poly[(maleic acid perfluorooctylamide-imide)-co-ethylene] (PAPE) with fluorinated side chains was synthesized from poly[(maleic anhydride)-co-ethylene]. They formed stable monolayers too. Multilayer depositions onto various substrates were possible for all the synthesized polymers. LB films were characterized by ultra-violet/visible spectroscopy (UV-Vis), surface plasmon resonance (SPR), dielectric spectroscopy and atomic force microscopy (AFM). Gas phase polymerization of tetrafluoropropyl methacrylate (TFPM) was carried out in the presence of macroinitiator, poly[octadecene-co-(maleic anhydride)] modified with tert-butyl hydroperoxide. Film thickness could be controlled on different hydrophobic substrates varying the reaction time.

Stimulation and binding properties of polyelectrolyte multilayers verified by ATR-FTIR spectroscopy

We report on the deposition and properties of multilayers composed of reactive polymers on planar surfaces. As reactive polymers the polycations poly(ethylene-imine), poly(L-lysine) (PLL), poly(allylamime) (PAA) and the polyanions poly(acrylate) (PAC), poly(vinylsulfate), poly(maleate-co-olefines) were used. ATR-FTIR spectroscopy was adopted to study deposition, binding and stimulation properties of polymer multilayers. The binding of charged species of different molecular size such as rhodanide anions and sodium oleate from solution was examined, whereby binding was found to be dependent on the charge of the outermost layer. For these two analytes a selectivity parameter Q, defined as the ratio between the adsorbed amount obtained at the negatively charged and that at the positively charged surface, respectively, was determined. Furthermore, swelling experiments on multilayer assemblies of PLL and PAC exposed to mixtures of ethanol/water (10 - 70% EtOH content) were carried out. Our experiments gave evidence, that the PLL layers showed a more significant increase in density than the PAC layers. The conformation of PLL incorporated into multilayers could be changed by pH variation.

Adsorption of poly(N-ethyl-4-vinyl pyridinium bromide) onto Langmuir-Blodgett films built up from amphiphilic polymers

The interaction of a strong cationic polyelectrolyte, poly(N-ethyl-4-vinyl pyridinium bromide), with Langmuir-Blodgett (LB) films built up from four monolayers of amphiphilic derivatives of the alternating copolymers of maleic acid and alkenes (one of the monolayers was formed by the amphiphilic copolymer containing pyrenyl groups as fluorescent labels) was examined. Transformations of absorbance spectra and quenching of fluorescence of the LB films were detected after their contact with aqueous solutions of the cationic polyelectrolyte. These changes were attributed to the adsorption of poly(N-ethyl-4-vinyl pyridinium bromide) onto such films. The efficiency of this process was found to be rather sensitive to the variations in pH of the surrounding medium: adsorption of the cationic polyelectrolyte onto the LB films was pronounced in basic media while it became rather weak in acidic media.

Langmuir–Blodgett layers of metal complexes of 4,4′-bis-(1-butyl-pentyl)-[2,2′]bipyridinyl-6,6′-diamine☆

Abstract The amphiphilic ligand 4,4′-bis-(1-butyl-pentyl)-[2,2′]bipyridinyl-6,6′-diamine (BBPBPDA) was synthesized by the Chichibabin reaction. It formed stable monolayers on the water surface which could be transferred onto solid substrates to construct Langmuir–Blodgett (LB) multilayers. The experimental data obtained by monolayer investigations on the water surface and X-ray investigations on multilayers were compared with the results of molecular modeling. In the presence of transition metal ions, BBPBPDA formed metal complexes with 1:1 stoichiometry. Here, the investigations were focused on complex formation with Cu2+ and the construction of LB multilayers thereof. This was possible by transferring a monolayer of the copper complex formed by an interfacial reaction of the ligand monolayer on an aqueous subphase with dissolved Cu2+ ions to solid substrates as well as by exposing an uncomplexed ligand LB layer to a copper ion containing solution.