In Leuchtdioden wird Licht durch die Rekombination von injizierten Ladungsträgern erzeugt. Das kann einerseits in anorganischen Materialien geschehen. In diesem Fall ist es notwendig, hochgeordnete Kristallstrukturen herzustellen, die die Eigenschaften der Leuchtdioden bestimmen. Ein anderer Ansatz ist die Verwendung von organischen Molekülen und Polymeren. Auf Grund der Vielseitigkeit der organischen Chemie können die Eigenschaften der verwendeten halbleitenden Polymere schon während der Synthese beeinflusst werden. Außerdem weisen auch diese Polymere die bekannte mechanische Flexibilität auf. Die Herstellung von flexiblen, großflächigen Beleuchtungsquellen und Anzeigelementen ist so möglich.<br> Die erste Leuchtdiode mit einem halbleitenden Polymer als Emitter wurde 1990 hergestellt. Seither hat das Forschungsgebiet eine rasante Entwicklung genommen. Auch erste kommerzielle Produkte sind erhältlich. Im Zuge dieser Entwicklung wurde deutlich, dass die Eigenschaften von polymeren Leuchtdioden – beispielsweise Farbe und Effizienz – durch die Verwendung mehrerer Komponenten in der aktiven Schicht deutlich verbessert werden können. Gleichzeitig ergeben sich neue Herausforderungen durch die Wechselwirkungen der verschiedenen Filmbestandteile. Während die Komponenten oft entweder zur Verbesserung des Ladungstransportes oder zur Beeinflussung der Emission zugegeben werden, muss darauf geachtet werden, dass die anderen Prozesse nicht negativ beeinflusst werden. In dieser Arbeit werden einige dieser Wechselwirkungen untersucht und mit einfachen physikalischen Modellen erklärt.<br> So werden zunächst blau emittierende Leuchtdioden auf der Basis von Polyfluoren untersucht. Dieses Material ist zwar ein sehr effizienter blauer Emitter, jedoch ist es anfällig für chemische Defekte, diese sich nicht vollständig verhindern lassen. Die Defekte bilden Fallenzustände für Elektronen, ihr Einfluss lässt sich durch die Zugabe von Lochfallen unterdrücken. Der zugrunde liegende Prozess, die Beeinflussung der Ladungsträgerbalance, wird erklärt. Im Folgenden werden Mischsystemen mit dendronisierten Emittern, die gleichzeitig eine Falle für Elektronen bilden, untersucht. Hier wird die unterschiedliche Wirkung der isolierenden Hülle auf die Ladungs- und Energieübertragung zwischen Matrix und Farbstoffkern der Dendrimere untersucht. In Mischsystemen haben die Natur der angeregten Zustände sowie die Art und Weise des Ladungsträgertransportes einen großen Einfluss auf diese Transferprozesse. Außerden hat auch hier die Ladungsträgerbalance Auswirkungen auf die Emission. Um den Ladungsträgereinfang in Fallenzuständen zu charakterisieren, wird eine Methode auf Grundlage der Messung des zeitaufgelösten Photostroms in organischen Mischfilmen weiterentwickelt. Die erzielten Ergebnisse zeigen, dass die Übertragung der für geordnete Systeme entwickelten Modelle des Ladungsträgertransportes nicht ohne weiteres auf Polymersysteme mit hoher Unordnung übertragen werden können. Abschließend werden zeitaufgelöste Messungen der Phosphoreszenz in entsprechenden Mischungen aus Polymeren und organometallischen Verbindungen vorgestellt. Auch diese Systeme enthalten üblicherweise weitere Komponenten, die den Ladungstransport verbessern. In diesen Filmen kann es zu einer Übertragung der Tripletts vom Emitter auf die weiteren Filmbestandteile kommen. Bei Kenntnis der in Frage kommenden Wechselwirkungen können die unerwünschten Prozesse vermieden werden. / Light-emitting diodes generate light from the recombination of injected charge carriers. This can be obtained in inorganic materials. Here, it is necessary to produce highly ordered crystalline structures that determine the properties of the device. Another possibility is the utilization of organic molecules and polymers. Based on the versatile organic chemistry, it is possible to tune the properties of the semiconducting polymers already during synthesis. In addition, semiconducting polymers are mechanically flexible. Thus, it is possible to construct flexible, large-area light sources and displays.<br> The first light-emitting diode using a polymer emitter was presented in 1990. Since then, this field of research has grown rapidly up to the point where first products are commercially available. It has become clear that the properties of polymer light-emitting diodes such as color and efficiency can be improved by incorporating multiple components inside the active layer. At the same time, this gives rise to new interactions between these components. While components are often added either to improve the charge transport or to change the emission, it has to made sure that other processes are not influenced in a negative manner. This work investigates some of these interactions and describes them with simple physical models.<br> First, blue light-emitting diodes based on polyfluorene are analyzed. This polymer is an efficient emitter, but it is susceptible to the formation of chemical defects that can not be suppressed completely. These defects form electron traps, but their effect can be compensated by the addition of hole traps. The underlying process, namely the changed charge carrier balance, is explained. In the following, blend systems with dendronized emitters that form electron traps are investigated. The different influence of the insulating shell on the charge and energy transfer between polymer host and the emissive core of the dendrimers is examined. In the blend, the nature of the excited states as well as the method of the charge transport through the layer are of great importance to the transfer. Again, the charge carrier balance influences the emission. To characterize the trapping of charges in trap states, a method based on the measurement of transient photocurrents is enhanced. The results show that models developed for ordered systems can not simply be transferred to polymer systems with a high degree of disorder. Finally, time-resolved measurements of the phosphorescence decay in blends of polymers with organo-metallic compounds are shown. Usually, these systems contain more components that facilitate charge transport. Thus, triplets may be transferred from the phosphorescent dye other components of the film. Knowing the underlying interactions, unwanted processes can be suppressed.

Eine Reihe 9,9-dialkylsubstituierter Polyfluorene mit linearen und verzweigtkettigen Alkylsubstituenten und einem Molekulargewicht von bis zu 200000 g/mol wurde synthetisiert und charakterisiert. Darüber hinaus wurden einige dieser Polymere mit einer geeigneten 'Lochtransport'-Funktionalität (Triphenylamin-Derivate) ausgestattet, um die Ladungstransporteigenschaften und das Molekulargewicht dieser Substanzen zu kontrollieren. Die thermische Orientierung dieser neuen Polymere auf geriebenen Polyimid-Schichten führte zu hoch anisotropen Filmen mit großen dichroischen Verhältnissen (Absorption parallel und senkrecht zur Reibungsrichtung gemessen). Ferner wurde eine Gruppe chiraler Polyfluorene synthetisiert und hinsichtlich ihrer chiroptischen Eigenschaften untersucht. Der mit diesen chiralen, konjugierten Polymeren erreichte Grad der Anisotropie in Absorption (CD), circular polarisierter Photolumineszenz (CPPL) und Elektrolumineszenz (CPEL) überstieg die bis dahin bekannten Werte um einen Faktor von 200. / A series of 9,9-dialkyl-poly(fluorene-2,7-diyl)s containing linear and branched alkyl substituents with a molecular weight of up to 200000 g/mol has been synthesized and characterized. Moreover, some of the polymers were end capped with a suitable hole transport functionality, such as a triphenylamine derivative, to improve their charge transport properties and to control the molecular weight. The thermal alignment of these novel polymers on a rubbed polyimide layer led to highly anisotropic film formation with large dichroic ratios (absorption parallel and perpendicular to the rubbing direction). Additionally a set of chiral polyfluorenes has been synthesized and investigated with respect to their chiroptical properties. The degrees of anisotropy in absorption (CD), circular polarized photoluminescence (CPPL) and electroluminescence (CPEL) found with these chiral conjugated polymers exceeded the yet known values by a factor of 200.

Polymeric and particulate organic carbon (POM) are fundamental compounds in the global cycling of carbon, and constitute significant amounts of BOD in municipal wastewater. The main objective of this work is to study molecular size effects on degradation dynamics in biofilm systems. Specifically, the effect of substrate molecular weight on degradation kinetics and transport dynamics, location of depolymerisation enzyme activity and depolymerisation intermediate formation dynamics are assessed. A mathematical model for biofilm degradation dynamics is presented, and used for data interpretation and simulations. Dextran, an -1,6 Glucan, was used as model substrate during batch degradation in a Rototorque biofilm reactor, in addition to batch tests on biofilm sub samples retrieved from the Rototorque, and during pure endo- and exo-Dextranase studies. Oxygen utilisation rate (OUR) estimates and bulk phase TOC mass balances were used to evaluate the effect of variable initial molecular weight on the observed half order removal coefficient (Harremoës, 1978; Rittmann and McCarty, 1980). Size exclusion-HPLC analysis for determination of bulk phase depolymerisation intermediates, and specific enzyme assays were used to evaluate transport dynamics of polymers and location of enzyme activity in the enhanced mixed population biofilm system. Dextran removal rate decrease with increasing Dextran molecular weight. The observed areal half order removal rate coefficient, k1/2,A, demonstrate an approximate 10-fold decrease in the 1-500 kDa range, showing negative logarithmic correlation to the initial MW of Dextran. A less distinct correlation is observed above this transition limit (1-10 MDa). Evaluation of the Thiele moduli, from one step depolymerisation modelling, suggests that the logarithmic reduction in observed removal rate is caused by combined reaction rate and transport limitations. Transport limitations dominates as the polymeric substrate size increase and hinders biofilm matrix diffusion, and the removal rate becomes a surface limited process. Removal of Dextran is biomass dependent in what appears to be a non-linear dependency on biofilm thickness. Expressed as biomass areal density (g/m2), no depolymerisation is observed for thin biofilms (0.7 g/m2), slow for medium (3.7 g/m2) and high for thicker biofilms (5.2 g/m2). Depolymerisation intermediates accumulated in the bulk phase over the entire Dextran size range during pure Dexranase studies, with even size distributions. Final products were oligo-isomaltoses (DP 2-6). Dextran was not depolymerised by -Glucosidase nor Oligo-1,6 Glucosidase. During biofilm reactor and slide sub-sample tests, low MW Dextran intermediates (1-10 kDa) accumulated in the bulk during depolymerisation of 160 kDa Dextran at 250 and 200 mg/l initial concentrations, but were not detected during experiments with 100 mg/l initial concentrations. Intermediate range Dextran (10-100 kDa) did not accumulate in either case. At the same conditions, some assimilable range Dextran (0.2-0.9 kDa) accumulated in the bulk liquid during initial 250 and 200 mg/l batches, but was not detected during 100 mg/l initial Dextran concentrations. The extent of bulk phase accumulation seems to depend on the biofilm growth rate, where more bulk phase accumulation is observed during experiments with starved compared to more actively growing biofilms. More intermediates accumulate during low MW initial standards, compared to higher. These observations indicate that the extent of bulk phase intermediate accumulation is balanced by the rate of depolymerisation, and the substrate uptake rate (growth). Accumulation of intermediate hydrolysis products in biofilm systems is therefore dependent on the slowly biodegradable organic (SBCOD) loading rate. Dextranase was detected in the cellular fraction of the biofilms. The enzyme activity was not detected in any other biofilm sub compartments, implying that the exogenous enzyme remains attached to the cells while working on polymers. These findings support the conceptual model of Confer and Logan (1998), implying that bulk phase intermediate accumulation observed in this study and by others, is not a result of enzymatic activity in the bulk phase, but transport of intermediates from the biofilm matrix.

Investigation of polymer-modified particles by means of solvatochromic probes concerning the polarity at the surface. Variation the concentration of the polymer-solution, molecular weight and degree of functionalization. Comparison of polarity parameters for sized glass fibers, obtained by inverse gas chromatography and solvatochromism. / Untersuchung polymermodifizierter Partikeloberflächen mittels solvatochromer Sonden bzgl. der Polarität an der Oberfläche. Variation der Konzentration der Polymerlösung, Molmasse der Polymere und Funktionalisierungsgrad. Vergleich der Polaritätswerte von geschlichteten Glasfasern, ermittelt aus IGC- und Solvatochromie-Messungen.

Die nucleophile aromatische Substitution von ausgewählten aktivierten Fluoraromaten mit Polyvinylaminen wurde in Wasser untersucht, um neue chromophore wasserlösliche Polyelektrolyte zu synthetisieren. Die Löslichkeit der nitrogruppentragenden Fluorverbindungen in Wasser wurde durch Komplexierung mittels 2,6-O-Dimethyl-beta-Cyclodextrin vermittelt. Die chromophoren Einheiten von funktionalisierten Polyvinylaminen weisen interessante optische Eigenschaften sowohl in Abhängigkeit vom pH-Wert als auch von der Natur des Lösungsmittels (Solvatochromie) auf. Ein direkter Zusammenhang zwischen der Struktur und der Reaktivität des jeweils eingesetzten Fluoraromaten bei der Substitutionsreaktion mit Polyvinylamin wurde durch die Bestimmung des Substitutionsgrades chromophorer Einheiten und durch kinetische Untersuchungen mit Hilfe der UV/vis-Spektroskopie nachweisbar. Weiterhin wurde die nucleophile aromatische Substitution von aktivierten Fluoraromaten mit Polyvinylaminen an der Grenzfläche Kieselgel/Wasser untersucht, um neue chromophore Hybridmaterialien zu erhalten.

Hyperbranched polymers (HBP) have drawn much attention and obtained intensive research activities from both industry and academia in the last three decades. They belong to a group of macromolecules called dendritic polymers, which have peculiar and often unique properties, which derive from their three-dimensional structure and the large number of functional groups. These structural characteristics provide high possibilities for controlling functional group interactions and modifications of other polymers in coatings and therefore, they are expected to result in novel materials with desired properties. They own a highly branched backbone, which gives access to many of reactive groups; their structure gives them excellent flow and processing properties, and they are characterized by lower viscosity than those of linear polymers of comparable molecular weight. Such properties make HBP extremely interesting for coatings and UV-curing applications and for this, they have attracted a great deal of attention for application, e.g. for powder coatings, high solid coatings, flame retardant coatings, barrier coatings for flexible packaging,and they have been recently suggested as a component of a dual-cure formulation based on an UV-curable epoxy resin and a functionalized alkoxysilane additive as an inorganic precursor to achieve advanced functional hybrid coatings. By pursuing this research line, we have synthesized an aliphatic–aromatic ethoxysilyl modified hyperbranched polyester system to be used in the preparation of UV-curable epoxy hybrid organic–inorganic coatings. The addition of ethoxysilyl-modified HBP could act as a coupling agent during the formation of the inorganic domains generated in-situ via sol-gel process starting from the alkoxysilane as inorganic precursors. The cured films were characterized in terms of their dynamic-mechanical properties and surface hardness: the obtained properties were discussed in relation to the achieved morphologies. In the present work, some aromatic hyperbranched polyesters (aHBP) and aliphatic-aromatic hyperbranched polyesters (aaHBP), OH terminated have been used as matrices for nanocomposites containing TiO2. The TiO2 nanoparticles were synthesized via sol-gel directly in a solution containing the HBP polyester as a stabilizer, and then the polymer/TiO2 hybrid mixtures were thermally cured by a curing agent to obtain a hard coating or a film. In order to determine the conditions in which it was possible to get the best dispersion and the properties for the final material, the starting HBP-OH was also partially modified with alkoxysilane groups by 3-isocyanatopropyltriethoxysilane (IPTES), yielding modified aliphatic-aromatic hyperbranched polyesters aaHBP(OH)-Si and modified aromatic hyperbranched polyesters aHBP(OH)-Si, enabling it to interact with the TiO2 network. Both materials obtained were then characterized, and their properties compared.

Zugl.: Stuttgart, Univ., Diss., 2006

Universiẗat, Diss., 2001--Duisburg.

Essen, Universiẗat, Diss., 2005--Duisburg.

Techn. University, Diss., 2007--Darmstadt.