Franz Stelzer

One decade of microwave-assisted polymerizations: quo vadis?

The application of microwave irradiation in polymer syntheses and modifications is of continuously growing interest and has received significant international interest since the beginning of the millennium. Preceded by a review that was published 6 years ago, the present paper summarizes the most recent trends in this research area. Radical as well as step-growth and ring-opening polymerizations will be addressed; furthermore, the evolution from microwave-assisted polymerizations to microwave-assisted material fabrication will be described on the examples of polymeranalogous reactions, polymer/metal composites and bio-based materials.

Anisotropic Optical and Transport Properties of Trans-(Ch)X

Abstract We have produced fully oriented highly crystal 1ine trans-(CH)X films, which exhibit dramatic polarization effects for light polarized parallel or perpendicular to the oriented (CH)X-chains. The polarization behavior in the vicinity of the bandgap and of the characteristic IR-modes, including those which are introduced as a result of doping with ASF5 is presented. DC-conductivity measurements allow to deduce the conductivity anisotropy of δ‖/δ⊥ ∼ 100 for undoped and I2-doped trans-(CH)x at 300 K.

Electroluminescence with Conjugated Polymers and Oligomers

Abstract We report on the optical properties of polymers and oligomers used in light emitting diodes (LEDs) prepared by solution processing or vacuum deposition. Special emphasis is put on the comparison of PPP and its oligomers to planarized forms of PPP.

Blue electroluminescence devices based on parahexaphenyl

Abstract Homogeneous thin films of the organic oligomer parahexaphenyl (PHP) allow the application of this material as a stable emitting layer in blue electroluminescence (EL) devices. We used oligoazomethine (OAM) and diaminoctofluorobiphenyl (DOB) as charge transport layers, which allowed us to achieve excellent EL performance with enhanced EL quantum efficiencies above 1%, improved brightness up to 2000 cd/m2 Luminance and increased rectification ratio in excess of 103 compared to single layer devices.

Self-assembled aromatic oligoazomethines on polar surfaces

The reaction between aromatic dialdehydes and diamines is studied by differential scanning calorimetry-thermal gravimetric analysis (DSC-TGA) measurements. It can be shown that the condensation reaction starts at temperatures below 100 °C. Thus, the high rate and the high conversions of this reaction lead to a new technique of thin-film growth on polar substrates, by successive deposition of monomer layers under high vacuum. Gravimetric measurements show that the first step is a bonding between the organic molecules and the surface. This leads to an oriented prime layer of deposited monomers. In the following steps reactive partners are deposited successively on the surface, layer by layer. Thin films grown by this technique are studied by UV-Vis spectroscopy. These well-ordered films can be applied as interfaces between organic and inorganic layers in solid-state optoelectronic devices.

Studies of the polyparaphenylene/aluminium interface

Abstract The dielectric properties of thin film Al/polyparaphenylene/Al structures have been investigated in the frequency range from 10−2 to 5 × 105 Hz. Experimental data suggest the existence of interfacial layers at the polymer/metal contacts. An equivalent circuit analysis, taking into account the dielectric response of these elements, is presented. To clarify the nature of the contact, X-ray photoelectron spectroscopy (XPS) has been performed on polyparaphenylene (PPP) films covered with Al layers. Displacements of the C(1s), O(1s) and Al(2p) lines lead to the conclusion that a chemical reaction between carbon, oxygen and aluminium occurs at the interface to form a metal-oxygen-polymer complex which is found to be responsible for the electrical a.c. behaviour of Al/PPP/Al structures.

Benchmarking of ruthenium initiators for the ROMP of a norbornenedicarboxylic acid ester

Abstract The kinetic study of ring-opening metathesis polymerization (ROMP) of a diester functionalised norbornene derivative, (±)-exo,endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid diethyl ester, with a series of ruthenium benzylidene complexes revealed the applicability of these initiators for well defined polymerization reactions. Values for the rate of initiation as well as the rate of propagation of the initiators were determined and correlated to the molecular weight and polydispersity of the isolated polymers. As the only initiator providing an entry to virtually monodisperse polymers the classical “first generation Grubbs-catalyst” was identified, while N-heterocyclic carbene based initiators polymerized with a rate of propagation much higher than the rate of initiation yielding polymers with a broader molecular weight distribution.

The aqueous ring-opening metathesis polymerization of 7-oxa-norbornene-2,3-dicarboxylic acid dimethyl ester and norbornene with Ru catalysts

Abstract 7-Oxa-norbornene-2,3-dicarboxylic acid dimethyl ester ( exo , exo -7-oxa-bicyclo[2.2.1]-hept-5-ene-2,3-dicarboxylic acid dimethyl ester) was polymerized by ring-opening methathesis polymerization (ROMP) using various ruthenium catalysts and various aqueous solvents. The influence of solvent on induction time, molecular weight and yield of the product polymer is discussed. Norbornene (bicyclo[2.2.1]hept-2-ene), regarded as quite unreactive in aqueous solvents until now, gave copolymers with this oxa-monomer in good yield.

Ruthenium Catalyzed Homocoupling of Terminal Alkynes

Summary. Several complexes of the type RuTp(L)(L′)Cl (L, L′=P, N, O donors) were tested with respect to their ability of promoting catalytic C–C-coupling reactions of terminal acetylenes. When L=tertiary phosphine, predominantly dimerization occurs, RuTp(PPh3)2H being the most efficient pre-catalyst. In the absence of a phosphine ligand, polymerization takes place with RuTp(COD)Cl as the most effective pre-catalyst. Both product distribution and conversion depend strongly on the substituent of the alkyne and to a lesser extent on the co-ligands of the ruthenium complex. The catalytically active species is the 16e− alkynyl complex RuTp(L)(–C*C–R) which in case of L=PCy3 and R=Bun could be trapped as RuTp(PCy3)(–C*CBun)(CO).Zusammenfassung. Die Fähigkeit einiger Komplexe des Typs RuTp(L)(L′)Cl, C–C-Kupplungsreaktion terminaler Alkine zu katalysieren, wurde getestet. Ist L ein Phosphin und L′ ein labiler Ligand, so dimerisieren die Alkine, während sie in Abwesenheit von Phosphinen polymerisieren. RuTp(PPh3)2H ist der beste Katalysator für die Dimerisierung, RuTp(COD)Cl für die Polymerisation. Produktverteilung und Ausbeute sind in erster Linie vom Substituenten am Alkin abhängig, aber auch von den Liganden am Ruthenium. Die katalytisch aktive Spezies ist der 16e−-Alkinyl-Komplex RuTp(L)(–C*C–R), der im Falle von L=PCy3 und R=Bun als RuTp(PCy3)(–C*C–Bun)(CO) abgefangen werden konnte.

Multicolour electroluminescence diodes using oligophenylene and oligophenylenevinylene multilayers

Abstract We present electroluminescence (EL) characteristics for single-layer and multilayer thin films with oligophenylenevinylenes and oligo-phenylenes. Light-emitting diodes (LEDs) were fabricated by vacuum evaporation techniques of both the oligomer films and the negative electrodes. Depending on the substrate temperature, highly ordered or polycrystalline layers were obtained. Our LEDs emit blue light in the range of 425–460 nm (oligophenylenes) and in a broad visible range of 400–600 nm (oligophenylene/oligophenylenevinylene multilayers). The current-voltage ( I–V ) characteristics of our devices show rectifying behaviour with high rectification ratios. We report I–V characteristics and the respective threshold voltages, quantum efficiencies, photoluminescence (PL), EL and optical absorbance of the thin films and the devices.