From large polycyclic aromatic hydrocarbons to extended aromate-rich networks

The common ground of this study is the development of novel synthetic strategies to extended one-, two- and three-dimensional aromate-rich systems for which a number of applications are envisaged. rnThe point of departure is the synthesis and characterization of highly symmetric macrocyclic PAHs (polycyclic aromatic hydrocarbons) for which various aspects of supramolecular chemistry will be investigated. The versatility of the Yamamoto macrocyclization will be demonstrated on the basis of a set of cyclic trimers that exhibit a rich supramolecular chemistry. 1,10-phenanthroline, triphenylene and ortho-terphenyl building blocks have been successfully assembled to the corresponding macrocycles following the newly developed synthetic route. Scanning-tunneling microscopy (STM) and two-dimensional wide-angle X-ray scattering (2D-WAXS) were used to study the two- and three-dimensional self-assembly, respectively.rnSecondly, the development of chemical approaches to highly shape-anisotropic graphene nanoribbons (GNRs) and related nanographene molecules shall be discussed. Aryl-aryl coupling was used for the bottom-up fabrication of dendronized monomers, polymers and model compounds. Subsequently, these structures were converted into the final graphene material using oxidative (Scholl-type) cyclodehydrogenation. The GNRs thus obtained are characterized by an unprecedented length and lateral extension. The relevance of structural tailoring in the field of well-defined graphene materials is discussed in detail as only the chemical approach provides full geometry control. rnLastly, novel pathways towards the synthesis of extended three-dimensional networks that are dominated by nitrogen-rich motifs will be presented. If porous, these materials hold a great potential in the fields of gas and energy storage as well as for applications in catalysis. Hence, poly(aminal) networks based on melamine as crosslinking unit were synthesized and characterized with respect to the applications mentioned above. As set of conjugated poly(azomethine) networks was investigated regarding their use as a novel class of organic semiconductors for photocatalytic water splitting. The network structures described in this chapter can also be subjected to a controlled pyrolysis yielding mesoporous, nitrogen-rich carbon materials that were evaluated as active component for supercapacitors.rn

Functionalization of hyperbranched polycarbosilanes - block copolymers and electrochemistry

Polycarbosilanes are a class of polymers at the interface between organic and inorganic chemistry. They are characterized by a high thermal and chemical inertness and high flexibility, especially pronounced for branched structures. Linear polycarbosilanes are well known as precursors for the preparation of SiCx ceramics. Additionally, more sophisticated architectures like dendrimers, hyperbranched polymers or block copolymers have been the subject of research for more than a decade. The scope of this work was to expand the properties and fields of application for polycarbosilane-containing structures. Thus, the work is divided in two major parts. The first part covers the synthesis and characterization of hyperbranched polycarbosilanes containing organometallic moieties. Hyperbranched poly-carbosilanes were synthesized using hydrosilylation of diallylmethylsilane and methyldiundecenylsilane. The degree of branching for polydiallymethylsilane was determined using standard 1H-NMR spectroscopy. The functional building blocks ferrocenyldimethylsilane and diferrocenylmethylsilane were synthesized which contain an isolated ferrocene unit or two ferrocenes bridged by silicon, respectively. Hyperbranched polycarbosilanes functionalized with ferrocenyl moieties were synthesized by modification of preformed polymers or by copolymerization of AB2 carbosilane monomers with AX-type ferrocenylsilanes. Polymers with Mn = 2500-9000g/mol and ferrocene contents of up to 67wt% were obtained. Electrochemical characterization by cyclic voltammetry revealed that polymers functionalized with isolated ferrocene units showed a single reversible oxidation wave, while voltammograms for polymers functionalized with diferrocenyl silane exhibited two well-separated reversible oxidation-reduction waves. This shows that the polymer bound ferrocenes bridged by silicon are electronically communicating and thus oxidation of the first ferrocene shifts the oxidation potential for the adjacent one. The polymers were utilized successfully for the preparation of modified electrodes with persistent and reproducible electrochemical response in organic solvents as well as in aqueous solution. The presented work has proven that ferrocenyl-functionalized hyperbranched polymers exhibit similar electrochemical properties as the analogous dendrimers. In a further approach it was shown that hyperbranched polymers containing organometallic moieties can be synthesized by polymerization of a new ferrocene-containing AB2 monomer - diallylferrocenylsilane. The second part of this work is dedicated to the preparation of core-functional hyperbranched polycarbosilanes. Low molecular weight ambifunctional molecules were synthesized that contain double bonds for the attachment of a polycarbosilane polymer as well as a second functionality available for further reaction and modification. Reactive vinyl groups in the core molecule allow an efficient attachment of hyperbranched polycarbosilane which was proven by MALDI-ToF and GPC. In combination with slow monomer addition techniques molecular weight and polydispersity of the polymers were controlled successfully. Core-functional polymers were characterized by NMR-spectroscopy, MALDI-ToF and GPC. Polymers with polydispersities <2 and molecular weights up to 5300g/mol were obtained. Transformation of the double bonds of the carbosilane was demonstrated with various silanes using hydrosilylation reaction or hydrogenation. Additionally, the core-functionality was varied resulting in polymers with bromo-, phthalimide-, amine- or azide moieties. Thus, a versatile synthetic strategy was developed that allows the synthesis of tailor-made polymers.A promising approach is the application of the polymer building blocks in copolymer synthesis. Bisglycidolization of amine-functional polycarbosilanes produces macro-initiators that are suitable for the multibranching-ring opening polymerization of glycidol. This experiments lead to the first example of hyperbranched-hyperbranched amphiphilic block copolymers, hb-PG-b-hb-PCS. Furthermore, the implementation of copper-catalyzed cycloaddition between azide-functional polycarbosilane and alkyne-functional poly(ethoxyethyl glycidylether) resulted in linear-hyperbranched block copolymers. The facile removal of acetal protecting groups provided convenient access to lin-PG-b-hb-PCS.

Laser heating of polymers

Zur Untersuchung von Effekten beim Laserheizen von Polymeren wurde ein Temperaturmessaufbau entwickelt. Das Messprinzip basiert auf der Auswertung der thermischen Emission. Der Messaufbau besteht aus einer hochauflösenden Kamera, ausgestattet mit Bildverstärker, sowie Interferenzfiltern um eine spektrale Auflösung zu gewährleisten und einem gepulster NIR-Heizlaser. Die Pulsdauer des Lasers liegt in der Größenordnung von 10 µs, der Strahldurchmesser durch entsprechende Fokussierung in der Größenordnung von 10 µm. Mittels Fit des Planck‘schen Strahlungsgesetzes an die aufgenommene thermische Emission konnten 2D Temperaturgraphen erhalten werden. Eine Ortsauflösung von 1 µm und eine Zeitauflösung von 1 µs konnten realisiert werden. In Kombination mit Finite-Elemente-Simulationen wurde mit diesem Aufbau die Laserablation verschiedener Polymere untersucht. Dabei hat sich gezeigt, dass bei Polymeren mit einem Glasübergang im Temperaturbereich zwischen Raum- und Zerfallstemperatur, photomechanische Ablation stattfand. Die Ablationsschwelle lag für diese Polymere mehrere 10 K über dem Glasübergang, weit unter der Zerfallstemperatur aus thermogravimetrischen Experimenten mit typischen Heizraten von 10 K/min. Bei hohen Laserenergien und damit verbundenen hohen Temperaturen konnte dagegen thermischer Zerfall beobachtet werden. Ein Übergang des Mechanismus von photomechanischer Ablation zu Ablation durch thermischen Zerfall ergab sich bei Temperaturen deutlich über der Zerfallstemperatur des Polymers aus der Thermogravimetrie. Dies wurde bedingt durch die kurzen Reaktionszeiten des Laserexperiments in der Größenordnung der Pulsdauer und steht im Einklang mit dem Gesetz von Arrhenius. Polymere ohne Glasübergang im Heizbereich zeigten dagegen keine photomechanische Ablation, sondern ausschließlich thermischen Zerfall. Die Ablationsschwelle lag auch hier bei höheren Temperaturen, entsprechend dem Gesetz von Arrhenius. Hohe Temperaturen, mehrere 100 K über der Zerfallstemperatur, ergaben sich darüber hinaus bei hohen Laserenergien. Ein drastisches Überhitzen des Polymers, wie in der Literatur beschrieben, konnte nicht beobachtet werden. Experimentelle Befunde deuten vielmehr darauf hin, dass es sich bei dem heißen Material um thermische Zerfallsprodukte, Polymerfragmente, Monomer und Zerfallsprodukte des Monomers handelte bzw. das Temperaturprofil der Zerfallsreaktion selbst visualisiert wurde.

Functional silicones and silicone-containing block copolymers

Polysiloxanes can be synthesized and subsequently modified (i) by the attachment of small molecules that change the properties of the silicone in such a way that it becomes more hydrophilic, but under the premise that this does not go together with a loss of the silicone-specific features. This can be done by adding hydrophilic sidechains to a polysiloxane. Polyethers like poly(ethylene glycol) or hyperbranched polyether-polyols are suitable in this regard. In order to assure that the silicone properties retain, these side groups can be attached to only one part of the polysiloxane backbone, which results in a block copolymer that consists of a common polysiloxane and a second block of the modified structure. (ii) Polysiloxanes can be equipped with functional groups that are capable of initializing polymerization of a different monomer (macroinitiator approach). For example, hydroxyl groups are used to initiate the ring opening polymerization of cyclic esters, or ATRP macroinitiators can be synthesized to add a second block via controlled radical polymerization. Stimuli responsive polymers like poly(oligoethylene glycol methacrylate) (POEGMA) can be added via this route to create “smart” siloxane-containing block copolymers that respond to certain stimuli. rnAn important premise for all synthetic routes is to achieve the targeted structure in a process as simple as possible, because facile availability of the material is crucial with regard to industrial applicability of the invented products. rnConcerning characterization of the synthesized macromolecules, emphasize is put on their (temperature dependent) aggregation behavior, which can be investigated by several microscopic and scattering methods, their behavior at the interface between silicone oils and water and their thermal properties.rnrn

Template-assisted patterning of functional polymers

In this thesis, anodic aluminum oxide (AAO) membranes, which provide well-aligned uniform mesoscopic pores with adjustable pore parameters, were fabricated and successfully utilized as templates for the fabrication of functional organic nanowires, nanorods and the respective well-ordered arrays. The template-assisted patterning technique was successfully applied for the realization of different objectives:rnHigh-density and well-ordered arrays of hole-conducting nanorods composed of cross-linked triphenylamine (TPA) and tetraphenylbenzidine (TPD) derivatives on conductive substrates like ITO/glass have been successfully fabricated. By applying a freeze-drying technique to remove the aqueous medium after the wet-chemical etching of the template, aggregation and collapsing of the rods was prevented and macroscopic areas of perfectly freestanding nanorods were feasible. Based on the hole-conducting nanorod arrays and their subsequent embedding into an electron-conducting polymer matrix via spin-coating, a novel routine concept for the fabrication of well-ordered all-organic bulk heterojunction for organic photovoltaic applications was successfully demonstrated. The increased donor/acceptor interface of the fabricated devices resulted in a remarkable increase of the photoluminescence quenching compared to a planar bilayer morphology. Further, the fundamental working principle of the templating approach for the solution-based all-organic photovoltaic device was demonstrated for the first time.rnFurthermore, in order to broaden the applicability of patterned surfaces, which are feasible via the template-based patterning of functional materials, AAO with hierarchically branched pores were fabricated and utilized as templates. By pursuing the common templating process hierarchically polymeric replicas, which show remarkable similarities with interesting biostructures, like the surface of the lotus leaf and the feet of a gecko, were successfully prepared.rnIn contrast to the direct infiltration of organic functional materials, a novel route for the fabrication of functional nanowires via post-modification of reactive nanowires was established. Therefore, reactive nanowires based on cross-linked pentafluorophenylesters were fabricated by utilizing AAO templates. The post-modification with fluorescent dyes was demonstrated. Furthermore, reactive wires were converted into well-dispersed poly(N-isopropylacrylamide) (PNIPAM) hydrogels, which exhibit a thermal-responsive reversible phase transition. The reversible thermal-responsible swelling of the PNIPAM nanowires exhibited a more than 50 % extended length than in the collapsed PNIPAM state. rnLast but not least, the shape-anisotropic pores of AAO were utilized to uniformly align the mesogens of a nematic liquid crystalline elastomer. Liquid crystalline nanowires with a narrow size distribution and uniform orientation of the liquid crystalline material were fabricated. It was shown that during the transition from the nematic to the isotropic phase the rod’s length shortened by roughly 40 percent. As such these liquid crystalline elastomeric nanowires may find application, as wire-shaped nanoactuators in various fields of research, like lab-on-chip systems, micro fluidics and biomimetics.rn

Synthetic routes toward functional block copolymers and bioconjugates via RAFT polymerization

Synthetic Routes toward Functional Block Copolymers and Bioconjugates via RAFT PolymerizationrnSynthesewege für funktionelle Blockcopolymere und Biohybride über RAFT PolymerisationrnDissertation von Dipl.-Chem. Kerstin T. WissrnIm Rahmen dieser Arbeit wurden effiziente Methoden für die Funktionalisierung beider Polymerkettenenden für Polymer- und Bioanbindung von Polymeren entwickelt, die mittels „Reversible Addition-Fragmentation Chain Transfer“ (RAFT) Polymerisation hergestellt wurden. Zu diesem Zweck wurde ein Dithioester-basiertes Kettentransferagens (CTA) mit einer Aktivestereinheit in der R-Gruppe (Pentafluorphenyl-4-phenylthiocarbonylthio-4-cyanovaleriansäureester, kurz PFP-CTA) synthetisiert und seine Anwendung als universelles Werkzeug für die Funktionalisierung der -Endgruppe demonstriert. Zum Einen wurde gezeigt, wie dieser PFP-CTA als Vorläufer für die Synthese anderer funktioneller CTAs durch einfache Aminolyse des Aktivesters genutzt werden kann und somit den synthetischen Aufwand, der üblicherweise mit der Entwicklung neuer CTAs verbunden ist, reduzieren kann. Zum Anderen konnte der PFP-CTA für die Synthese verschiedener Poly(methacrylate) mit enger Molekulargewichtsverteilung und wohl definierter reaktiver -Endgruppe verwendet werden. Dieses Kettenende konnte dann erfolgreich mit verschiedenen primären Aminen wie Propargylamin, 1-Azido-3-aminopropan und Ethylendiamin oder direkt mit den Amin-Endgruppen verschiedener Peptide umgesetzt werden.rnAus der Reaktion des PFP-CTAs mit Propargylamin wurde ein Alkin-CTA erhalten, der sich als effizientes Werkzeug für die RAFT Polymerisation verschiedener Methacrylate erwiesen hat. Der Einbau der Alkin-Funktion am -Kettenende wurde mittels 1H und 13C NMR Spektroskopie sowie MALDI TOF Massenspektroskopie bestätigt. Als Modelreaktion wurde die Kopplung eines solchen alkin-terminierten Poly(di(ethylenglykol)methylethermethacrylates) (PDEGMEMA) mit azid-terminiertem Poly(tert-butylmethacrylat), das mittels Umsetzung einer Aktivester-Endgruppe erhalten wurde, als kupferkatalysierte Azid-Alkin-Cycloaddition (CuAAC) durchgeführt. Die Aufarbeitung des resultierenden Diblockcopolymers durch Fällen ermöglichte die vollständige Abtrennung des Polymerblocks 1, der im Überschuss eingesetzt wurde. Darüber hinaus blieb nur ein sehr kleiner Anteil (< 2 Gew.-%) nicht umgesetzten Polymerblocks 2, was eine erfolgreiche Polymeranbindung und die Effizienz der Endgruppen-Funktionalisierung ausgehend von der Aktivester--Endgruppe belegt.rnDie direkte Reaktion von stimuli-responsiven Polymeren mit Pentafluorphenyl(PFP)ester-Endgruppen, namentlich PDEGMEMA und Poly(oligo(ethylenglykol)methylethermethacrylat), mit kollagen-ähnlichen Peptiden ergab wohl definierte Polymer-Peptid-Diblockcopolymere und Polymer-Peptid-Polymer-Triblockcopolymer unter nahezu quantitativer Umsetzung der Endgruppen. Alle Produkte konnten vollständig von nicht umgesetztem Überschuss des Homopolymers befreit werden. In Analogie zu natürlichem Kollagen und dem nicht funktionalisierten kollagen-ähnlichen Peptid bilden die PDEGMEMA-basierten, entschützten Hybridcopolymere Trimere mit kollagen-ähnlichen Triple-Helices in kalter wässriger Lösung, was mittels Zirkular-Dichroismus-Spektroskopie (CD) nachgewiesen werden konnte. Temperaturabhängige CD-Spektroskopie, Trübungsmessungen und dynamische Lichtstreuung deuteten darauf hin, dass sie bei höheren Temperaturen doppelt stimuli-responsive Überstrukturen bilden, die mindestens zwei konformative Übergänge beim Aufheizen durchlaufen. Einer dieser Übergänge wird durch den hydrophoben Kollaps des Polymerblocks induziert, der andere durch Entfalten der kollagen-ähnlichen Triple-Helices.rnAls Ausweitung dieser synthetischen Strategie wurde homotelecheles PDEGMEMA mit zwei PFP-Esterendgruppen dargestellt, wozu der PFP-CTA für die Funktionalisierung der -Endgruppe und die radikalische Substitution des Dithioesters durch Behandlung mit einem Überschuss eines funktionellen AIBN-Derivates für die Funktionalisierung der -Endgruppe ausgenutzt wurde. Die Umsetzung der beiden reaktiven Kettenenden mit dem N-Terminus eines Peptidblocks ergab ein Peptid-Polymer-Peptid Triblockcopolymer.rnSchließlich konnten die anorganisch-organischen Hybridmaterialien PMSSQ-Poly(2,2-diethoxyethylacrylat) (PMSSQ-PDEEA) und PMSSQ-Poly(1,3-dioxolan-2-ylmethylacrylat) (PMSSQ-PDMA) für die Herstellung robuster, peptid-reaktiver Oberflächen durch Spin Coaten und thermisch induziertes Vernetzen angewendet werden. Nach saurem Entschützen der Acetalgruppen in diesen Filmen konnten die resultierenden Aldehydgruppen durch einfaches Eintauchen in eine Lösung mit einer Auswahl von Aminen und Hydroxylaminen umgesetzt werden, wodurch die Oberflächenhydrophilie modifiziert werden konnte. Darüber hinaus konnten auf Basis der unterschiedlichen Stabilität der zwei hier verglichenen Acetalgruppen Entschützungsprotokolle für die exklusive Entschützung der Diethylacetale in PMSSQ-PDEEA und deren Umsetzung ohne Entschützung der zyklischen Ethylenacetale in PMSSQ-PDMA entwickelt werden, die die Herstellung multifunktioneller Oberflächenbeschichtungen z.B. für die Proteinimmobilisierung ermöglichen.

Phenothiazine based polymers for energy and data storage application

Die vorliegende Arbeit befasst sich mit der Synthese und Charakterisierung von Polymeren mit redox-funktionalen Phenothiazin-Seitenketten. Phenothiazin und seine Derivate sind kleine Redoxeinheiten, deren reversibles Redoxverhalten mit electrochromen Eigenschaften verbunden ist. Das besondere an Phenothiazine ist die Bildung von stabilen Radikalkationen im oxidierten Zustand. Daher können Phenothiazine als bistabile Moleküle agieren und zwischen zwei stabilen Redoxzuständen wechseln. Dieser Schaltprozess geht gleichzeitig mit einer Farbveränderung an her.rnrnIm Rahmen dieser Arbeit wird die Synthese neuartiger Phenothiazin-Polymere mittels radikalischer Polymerisation beschrieben. Phenothiazin-Derivate wurden kovalent an aliphatischen und aromatischen Polymerketten gebunden. Dies erfolgte über zwei unterschiedlichen synthetischen Routen. Die erste Route beinhaltet den Einsatz von Vinyl-Monomeren mit Phenothiazin Funktionalität zur direkten Polymerisation. Die zweite Route verwendet Amin modifizierte Phenothiazin-Derivate zur Funktionalisierung von Polymeren mit Aktivester-Seitenketten in einer polymeranalogen Reaktion. rnrnPolymere mit redox-funktionalen Phenothiazin-Seitenketten sind aufgrund ihrer Elektron-Donor-Eigenschaften geeignete Kandidaten für die Verwendung als Kathodenmaterialien. Zur Überprüfung ihrer Eignung wurden Phenothiazin-Polymere als Elektrodenmaterialien in Lithium-Batteriezellen eingesetzt. Die verwendeten Polymere wiesen gute Kapazitätswerte von circa 50-90 Ah/kg sowie schnelle Aufladezeiten in der Batteriezelle auf. Besonders die Aufladezeiten sind 5-10 mal höher als konventionelle Lithium-Batterien. Im Hinblick auf Anzahl der Lade- und Entladezyklen, erzielten die Polymere gute Werte in den Langzeit-Stabilitätstests. Insgesamt überstehen die Polymere 500 Ladezyklen mit geringen Veränderungen der Anfangswerte bezüglich Ladezeiten und -kapazitäten. Die Langzeit-Stabilität hängt unmittelbar mit der Radikalstabilität zusammen. Eine Stabilisierung der Radikalkationen gelang durch die Verlängerung der Seitenkette am Stickstoffatom des Phenothiazins und der Polymerhauptkette. Eine derartige Alkyl-Substitution erhöht die Radikalstabilität durch verstärkte Wechselwirkung mit dem aromatischen Ring und verbessert somit die Batterieleistung hinsichtlich der Stabilität gegenüber Lade- und Entladezyklen. rnrnDes Weiteren wurde die praktische Anwendung von bistabilen Phenothiazin-Polymeren als Speichermedium für hohe Datendichten untersucht. Dazu wurden dünne Filme des Polymers auf leitfähigen Substraten elektrochemisch oxidiert. Die elektrochemische Oxidation erfolgte mittels Rasterkraftmikroskopie in Kombination mit leitfähigen Mikroskopspitzen. Mittels dieser Technik gelang es, die Oberfläche des Polymers im nanoskaligen Bereich zu oxidieren und somit die lokale Leitfähigkeit zu verändern. Damit konnten unterschiedlich große Muster lithographisch beschrieben und aufgrund der Veränderung ihrer Leitfähigkeit detektiert werden. Der Schreibprozess führte nur zu einer Veränderung der lokalen Leitfähigkeit ohne die topographische Beschaffenheit des Polymerfilms zu beeinflussen. Außerdem erwiesen sich die Muster als besonders stabil sowohl mechanisch als auch über die Zeit.rnrnZum Schluss wurden neue Synthesestrategien entwickelt um mechanisch stabile als auch redox-funktionale Oberflächen zu produzieren. Mit Hilfe der oberflächen-initiierten Atomtransfer-Radikalpolymerisation wurden gepfropfte Polymerbürsten mit redox-funktionalen Phenothiazin-Seitenketten hergestellt und mittels Röntgenmethoden und Rasterkraftmikroskopie analysiert. Eine der Synthesestrategien geht von gepfropften Aktivesterbürsten aus, die anschließend in einem nachfolgenden Schritt mit redox-funktionalen Gruppen modifiziert werden können. Diese Vorgehensweise ist besonders vielversprechend und erlaubt es unterschiedliche funktionelle Gruppen an den Aktivesterbürsten zu verankern. Damit können durch Verwendung von vernetzenden Gruppen neben den Redoxeigenschaften, die mechanische Stabilität solcher Polymerfilme optimiert werden. rn rn

Solubility, diffusivity and permeability of gases in glassy polymers

Gas separation membranes of high CO2 permeability and selectivity have great potential in both natural gas sweetening and carbon dioxide capture. Many modified PIM membranes results permselectivity above Robinson upper bound. The big problem that should be solved for these polymers to be commercialized is their aging through time. In high glassy polymeric membrane such as PIM-1 and its modifications, solubility selectivity has more contribution towards permselectivity than diffusivity selectivity. So in this thesis work pure and mixed gas sorption behavior of carbon dioxide and methane in three PIM-based membranes (PIM-1, TZPIM-1 and AO-PIM-1) and Polynonene membrane is rigorously studied. Sorption experiment is performed at different temperatures and molar fraction. Sorption isotherms found from the experiment shows that there is a decrease of solubility as the temperature of the experiment increases for both gases in all polymers. There is also a decrease of solubility due to the presence of the other gas in the system in the mixed gas experiments due to competitive sorption effect. Variation of solubility is more visible in methane sorption than carbon dioxide, which will make the mixed gas solubility selectivity higher than that of pure gas solubility selectivity. Modeling of the system using NELF and Dual mode sorption model estimates the experimental results correctly Sorption of gases in heat treated and untreated membranes show that the sorption isotherms don’t vary due to the application of heat treatment for both carbon dioxide and methane. But there is decrease in the diffusivity coefficient and permeability of pure gases due to heat treatment. Both diffusivity coefficient and permeability decreases with increasing of heat treatment temperature. Diffusivity coefficient calculated from transient sorption experiment and steady state permeability experiment is also compared in this thesis work. The results reveal that transient diffusivity coefficient is higher than steady state diffusivity selectivity.

Sulfur-containing polymers for surface attachment

Different concepts for the synthesis of sulfur-containing polymers as well as their adsorption onto gold surfaces were studied. The present work is divided into three parts. The main part focuses on the synthesis of poly(1,2-alkylene sulfides) (“polysulfides”) with complex architectures on the basis of polyether-based macroinitiators by the anionic ring-opening polymerization of ethylene sulfide and propylene sulfide. This synthetic tool kit allowed the synthesis of star-shaped, brush-like, comb-like and pom-pom-like polysulfides, the latter two with an additional poly(ethylene glycol) chain. Additionally, the number of polysulfide arms as well as the monomer composition could be varied over a wide range to obtain copolymers with multiple thioether functionalities.rnThe second section deals with the synthesis of a novel lipoic acid-based initiator for ring-opening polymerizations for lactones and epoxides. A straightforward approach was selected to accomplish the ability to obtain tailored polymers with a common used disulfide-anchoring group, without the drawbacks of post-polymerization functionalization. rnIn the third part, a new class of block-copolymers consisting of polysulfides and polyesters were investigated. For the first time this approach enabled the use of hydroxyl-terminated poly(propylene sulfide) as macroinitiator for the synthesis of a second block.rnThe adsorption efficiency of those different polymer classes onto gold nanoparticles as well as gold rnsupports was studied via different methods.rn

Novel materials for direct X-ray detectors based on semiconducting organic polymers

Conventional inorganic materials for x-ray radiation sensors suffer from several drawbacks, including their inability to cover large curved areas, me- chanical sti ffness, lack of tissue-equivalence and toxicity. Semiconducting organic polymers represent an alternative and have been employed as di- rect photoconversion material in organic diodes. In contrast to inorganic detector materials, polymers allow low-cost and large area fabrication by sol- vent based methods. In addition their processing is compliant with fexible low-temperature substrates. Flexible and large-area detectors are needed for dosimetry in medical radiotherapy and security applications. The objective of my thesis is to achieve optimized organic polymer diodes for fexible, di- rect x-ray detectors. To this end polymer diodes based on two different semi- conducting polymers, polyvinylcarbazole (PVK) and poly(9,9-dioctyluorene) (PFO) have been fabricated. The diodes show state-of-the-art rectifying be- haviour and hole transport mobilities comparable to reference materials. In order to improve the X-ray stopping power, high-Z nanoparticle Bi2O3 or WO3 where added to realize a polymer-nanoparticle composite with opti- mized properities. X-ray detector characterization resulted in sensitivties of up to 14 uC/Gy/cm2 for PVK when diodes were operated in reverse. Addition of nanoparticles could further improve the performance and a maximum sensitivy of 19 uC/Gy/cm2 was obtained for the PFO diodes. Compared to the pure PFO diode this corresponds to a five-fold increase and thus highlights the potentiality of nanoparticles for polymer detector design. In- terestingly the pure polymer diodes showed an order of magnitude increase in sensitivity when operated in forward regime. The increase was attributed to a different detection mechanism based on the modulation of the diodes conductivity.

Biomimetic coating of organic polymers with a protein-functionalized layer of calcium phosphate: the surface properties of the carrier influence neither the coating characteristics nor the incorporation mechanism or release kinetics of the protein

Polymers that are used in clinical practice as bone-defect-filling materials possess many essential qualities, such as moldability, mechanical strength and biodegradability, but they are neither osteoconductive nor osteoinductive. Osteoconductivity can be conferred by coating the material with a layer of calcium phosphate, which can be rendered osteoinductive by functionalizing it with an osteogenic agent. We wished to ascertain whether the morphological and physicochemical characteristics of unfunctionalized and bovine-serum-albumin (BSA)-functionalized calcium-phosphate coatings were influenced by the surface properties of polymeric carriers. The release kinetics of the protein were also investigated. Two sponge-like materials (Helistat® and Polyactive®) and two fibrous ones (Ethisorb and poly[lactic-co-glycolic acid]) were tested. The coating characteristics were evaluated using state-of-the-art methodologies. The release kinetics of BSA were monitored spectrophotometrically. The characteristics of the amorphous and the crystalline phases of the coatings were not influenced by either the surface chemistry or the surface geometry of the underlying polymer. The mechanism whereby BSA was incorporated into the crystalline layer and the rate of release of the truly incorporated depot were likewise unaffected by the nature of the polymeric carrier. Our biomimetic coating technique could be applied to either spongy or fibrous bone-defect-filling organic polymers, with a view to rendering them osteoconductive and osteoinductive.

Pericellular fibronectin is required for RhoA-dependent responses to cyclic strain in fibroblasts

To test the hypothesis that the pericellular fibronectin matrix is involved in mechanotransduction, we compared the response of normal and fibronectin-deficient mouse fibroblasts to cyclic substrate strain. Normal fibroblasts seeded on vitronectin in fibronectin-depleted medium deposited their own fibronectin matrix. In cultures exposed to cyclic strain, RhoA was activated, actin-stress fibers became more prominent, MAL/MKL1 shuttled to the nucleus, and mRNA encoding tenascin-C was induced. By contrast, these RhoA-dependent responses to cyclic strain were suppressed in fibronectin knockdown or knockout fibroblasts grown under identical conditions. On vitronectin substrate, fibronectin-deficient cells lacked fibrillar adhesions containing alpha5 integrin. However, when fibronectin-deficient fibroblasts were plated on exogenous fibronectin, their defects in adhesions and mechanotransduction were restored. Studies with fragments indicated that both the RGD-synergy site and the adjacent heparin-binding region of fibronectin were required for full activity in mechanotransduction, but not its ability to self-assemble. In contrast to RhoA-mediated responses, activation of Erk1/2 and PKB/Akt by cyclic strain was not affected in fibronectin-deficient cells. Our results indicate that pericellular fibronectin secreted by normal fibroblasts is a necessary component of the strain-sensing machinery. Supporting this hypothesis, induction of cellular tenascin-C by cyclic strain was suppressed by addition of exogenous tenascin-C, which interferes with fibronectin-mediated cell spreading.

Observation of ventilation-induced Spo(2) oscillations in pigs: first step to noninvasive detection of cyclic recruitment of atelectasis?

High arterial partial oxygen pressure (Pao(2)) oscillations within the respiratory cycle were described recently in experimental acute lung injury. This phenomenon has been related to cyclic recruitment of atelectasis and varying pulmonary shunt fractions. Noninvasive detection of Spo(2) (oxygen saturation measured by pulse oximetry) as an indicator of cyclic collapse of atelectasis, instead of recording Pao(2) oscillations, could be of clinical interest in critical care. Spo(2) oscillations were recorded continuously in three different cases of lung damage to demonstrate the technical feasibility of this approach. To deduce Pao(2) from Spo(2), a mathematical model of the hemoglobin dissociation curve including left and right shifts was derived from the literature and adapted to the dynamic changes of oxygenation. Calculated Pao(2) amplitudes (derived from Spo(2) measurements) were compared to simultaneously measured fast changes of Pao(2), using a current standard method (fluorescence quenching of ruthenium). Peripheral hemoglobin saturation was capable to capture changes of Spo(2) within each respiratory cycle. For the first time, Spo(2) oscillations due to cyclic recruitment of atelectasis within a respiratory cycle were determined by photoplethysmography, a technology that can be readily applied noninvasively in clinical routine. A mathematic model to calculate the respective Pao(2) changes was developed and its applicability tested.