Oligodeoxynucleotide-polypeptide block copolymers

Synthesis and characterization of monodisperse oligonucleotide-polypeptide di- and triblock copolymers are described. These block copolymers are promising building blocks for the formation of defined structures by sequential DNA self-assembly. The oligonucleotide sequences (ODN, 46 bases) obtained from standard solid phase synthesis were designed to form four-arm DNA junctions. The hybridization of the four single stranded oligonucleotides at room temperature to a stable four-arm junction is selective and quantitative. The junctions exhibit good thermal stability as proven by polyacrylamide gel electrophoresis (PAGE) and UV analysis. The second block consists of monodisperse elastin-like polypeptides (ELPs) with a pentapeptide repeat unit of (Val-Pro-Gly-Val-Gly) synthesized by genetic engineering. ODN-ELP diblock copolymers were obtained either by thiol coupling or by activated ester chemistry. Taking advantage of the endgroup control of both components (ODN, ELP), combination of the two different synthetic approaches leads to the synthesis of ODN-ELP-ODN triblock copolymers. Dynamic light scattering measurements of the single components and the synthesized diblock copolymers reveal their monodispersity. Hybridization of four ODN-ELP diblock copolymers carrying the four junction sequences shows quantitative self-assembly. In conclusion, this work provides the first example of the synthesis of perfectly defined ODN-ELP block copolymers and their potential use in DNA self-assembly.

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.

Strukturbildung durch Selbstorganisation von Oligonukleotiden

Die DNA-Doppelhelix ist eine relativ dicke (Ø ≈ 2 nm), kompakte und dadurch auf kurzen Längenskalen relativ steife Verbindung (lp[dsDNA] ≈ 50-60 nm), mit einer klar definierten Struktur, die durch biologische Methoden sehr präzise manipuliert werden kann. Die Auswirkungen der primären Sequenz auf die dreidimensionale Strukturbildung ist gut verstanden und exakt vorhersagbar. Des Weiteren kann DNA an verschiedenen Stellen mit anderen Molekülen verknüpft werden, ohne dass ihre Selbsterkennung gestört wird. Durch die helikale Struktur besteht außerdem ein Zusammenhang zwischen der Lage und der räumlichen Orientierung von eingeführten Modifikationen. Durch moderne Syntheseverfahren lassen sich beliebige Oligonukleotidsequenzen im Bereich bis etwa 150-200 Basen relativ preiswert im Milligrammmaßstab herstellen. Diese Eigenschaften machen die DNA zu einem idealen Kandidaten zur Erzeugung komplexer Strukturen, die durch Selbsterkennung der entsprechenden Sequenzen gebildet werden. In der hier vorgelegten Arbeit wurden einzelsträngige DNA-Abschnitte (ssDNA) als adressierbare Verknüpfungsstellen eingesetzt, um verschiedene molekulare Bausteine zu diskreten nicht periodischen Strukturen zu verbinden. Als Bausteine dienten flexible synthetische Polymerblöcke und semiflexible Doppelstrang-DNA-Abschnitte (dsDNA), die an beiden Enden mit unterschiedlichen Oligonukleotidsequenzen „funktionalisiert“ sind. Die zur Verknüpfung genutzten Oligonukleotidabschnitte wurden so gewählt (n > 20 Basen), dass ihre Hybridisierung zu einer bei Raumtemperatur stabilen Doppelstrangbildung führt. Durch Kombination der Phosphoramiditsynthese von DNA mit einer festkörpergestützten Blockkopplungsreaktion konnte am Beispiel von Polyethylenoxiden ein sehr effektiver Syntheseweg zur Herstellung von ssDNA1-PEO-ssDNA2-Triblockcopolymeren entwickelt werden, der sich problemlos auf andere Polymere übertragen lassen sollte. Die Längen und Basenabfolgen der beiden Oligonukleotidsequenzen können dabei unabhängig voneinander frei gewählt werden. Somit wurden die Voraussetzungen geschaffen, um die Selbsterkennung von Oligonukleotiden durch Kombination verschiedener Triblockcopolymere zur Erzeugung von Multiblockcopolymeren zu nutzen, die mit klassischen Synthesetechniken nicht zugänglich sind. Semiflexible Strukturelemente lassen sich durch die Synthese von Doppelstrangfragmenten mit langen überstehenden Enden (sticky-ends) realisieren. Die klassischen Ansätze der molekularen Genetik zur Erzeugung von sticky-ends sind in diesem Fall nicht praktikabel, da sie zu Einschränkungen im Bezug auf Länge und Sequenz der überhängenden Enden führen. Als Methode der Wahl haben sich zwei verschiedene Varianten der Polymerase Kettenreaktion (PCR) erwiesen, die auf der Verwendung von teilkomplementären Primern beruhen. Die eigentlichen Primersequenzen wurden am 5´-Ende entweder über ein 2´-Desoxyuridin oder über einen kurzen Polyethylenoxid-Spacer (n = 6) mit einer frei wählbaren „sticky-end-Sequenz“ verknüpft. Mit diesen Methoden sind sowohl 3´- als auch 5´-Überhänge zugänglich und die Länge der Doppelstrangabschnitte kann über einen breiten Molmassenbereich sehr exakt eingestellt werden. Durch Kombination derartiger Doppelstrangfragmente mit den biosynthetischen Triblockcopolymeren lassen sich Strukturen erzeugen, die als Modellsysteme zur Untersuchung verschiedener Biomoleküle genutzt werden können, die in Form eines mehrfach gebrochenen Stäbchens vorliegen. Im letzten Abschnitt wurde gezeigt, dass durch geeignete Wahl der überstehenden Enden bzw. durch Hybridisierung der Doppelstrangfragmente mit passenden Oligonukleotiden verzweigte DNA-Strukturen mit Armlängen von einigen hundert Nanometern zugänglich sind. Im Vergleich zu den bisher veröffentlichten Methoden bietet diese Herangehensweise zwei entscheidende Vorteile: Zum einen konnte der Syntheseaufwand auf ein Minimum reduziert werden, zum anderen ist es auf diesem Weg möglich die Längen der einzelnen Arme, unabhängig voneinander, über einen breiten Molmassenbereich zu variieren.

DNA-Polymer-Hybride als molekulare Bausteine

Die DNA hat sich durch die herausstechende Eigenschaft zur Selbstorganisation in den Naturwissenschaften zu einem beliebten Werkzeug entwickelt. In dieser Arbeit wurde die Oligonukleotidselbsterkennung zum Aufbau komplexer Multiblockcopolymere genutzt. Dabei dienten komplementäre einzelsträngige Oligonukleotidsequenzen (ssDNA) als adressierbare Verbindungsstücke zwischen synthetischen Blöcken. Als Bausteine wurden asymmetrische Dreiblockcopolymere der Form DNA1-Polymer-DNA2 aus einer flexiblen Polymereinheit (PEO bzw. PPO) die an beiden Enden mit unterschiedlichen Oligonukleotidsequenzen „funktionalisiert“ ist, verwendet. Diese Bausteine konnten durch die Kombination von Festphasensynthese der Oligonukleotide und Blockkopplung dargestellt werden. Die Oligonukleotidsequenzen wurden so gewählt, dass deren Hybridisierung zu einer bei Raumtemperatur stabilen Verbindung führt. Durch die Verwendung dieser Bausteine erhält man ein modulares System, dass sich durch seine hohe Flexibilität auszeichnet. Aus den dargestellten Dreiblockcopolymeren konnten verschiedene alternierende Multiblockcopolymere aufgebaut werden, wobei die Anzahl der Blöcke (von 11 bis 15) und das PEO / PPO- Verhältnis variiert wurden. Derartige Strukturen sind auf der Grundlage chemischer Synthesen unerreichbar. Die Flexibilität dieses modularen Systems konnte gezeigt werden, indem einzelne Blockbausteine zur Strukturaufklärung einfach ausgetauscht oder weggelassen werden konnten. Durch geeignete Wahl der DNA-Sequenzen konnte zusätzlich das Polymerisationsverhalten dieser Bauelemente untersucht werden. Die Integration längerer kettensteifer DNA-Abschnitte in die Multiblockstrukturen erfolgte durch die Verwendung teilkomplementärer Oligonukleotide. Diese bieten den Vorteil, dass bis zu einer Größe von etwa 150 bp sowohl die Länge als auch die Sequenz der Doppelstrangabschnitte und sticky-ends frei variiert werden können. Die biosynthetischen Dreiblockcopolymere dienten hier als Linkermoleküle zwischen den einzelnen dsDNA-Blöcken. Nach diesem Konzept wurde ein Nonamer als Modellsystem eines mehrfach gebrochenen Stäbchens synthetisiert. Außerdem wurden mit Hilfe der Polymerase Kettenreaktion (PCR) semiflexible DNA Abschnitte erzeugt. Durch die Wahl des Synthesewegs konnte sowohl die Länge der semiflexiblen Einheit als auch die Länge und die Sequenz des sticky-ends variiert werden. Anhand dieser Modellverbindungen wurde dann das Hybridisierungsverhalten in Abhängigkeit der Linker- und Segmentlängen untersucht.

Structure property relations in complex copolymer systems

A thorough investigation was made of the structure-property relation of well-defined statistical, gradient and block copolymers of various compositions. Among the copolymers studied were those which were synthesized using isobornyl acrylate (IBA) and n-butyl acrylate (nBA) monomer units. The copolymers exhibited several unique properties that make them suitable materials for a range of applications. The thermomechanical properties of these new materials were compared to acrylate homopolymers. By the proper choice of the IBA/nBA monomer ratio, it was possible to tune the glass transition temperature of the statistical P(IBA-co-nBA) copolymers. The measured Tg’s of the copolymers with different IBA/nBA monomer ratios followed a trend that fitted well with the Fox equation prediction. While statistical copolymers showed a single glass transition (Tg between -50 and 90 ºC depending on composition), DSC block copolymers showed two Tg’s and the gradient copolymer showed a single, but very broad, glass transition. PMBL-PBA-PMBL triblock copolymers of different composition ratios were also studied and revealed a microphase separated morphology of mostly cylindrical PMBL domains hexagonally arranged in the PBA matrix. DMA studies confirmed the phase separated morphology of the copolymers. Tensile studies showed the linear PMBL-PBA-PMBL triblock copolymers having a relatively low elongation at break that was increased by replacing the PMBL hard blocks with the less brittle random PMBL-r-PMMA blocks. The 10- and 20-arm PBA-PMBL copolymers which were studied revealed even more unique properties. SAXS results showed a mixture of cylindrical PMBL domains hexagonally arranged in the PBA matrix, as well as lamellar. Despite PMBL’s brittleness, the triblock and multi-arm PBA-PMBL copolymers could become suitable materials for high temperature applications due to PMBL’s high glass transition temperature and high thermal stability. The structure-property relation of multi-arm star PBA-PMMA block copolymers was also investigated. Small-angle X-ray scattering revealed a phase separated morphology of cylindrical PMMA domains hexagonally arranged in the PBA matrix. DMA studies found that these materials possess typical elastomeric behavior in a broad range of service temperatures up to at least 250°C. The ultimate tensile strength and the elastic modulus of the 10- and 20-arm star PBA-PMMA block copolymers are significantly higher than those of their 3-arm or linear ABA type counterparts with similar composition, indicating a strong effect of the number of arms on the tensile properties. Siloxane-based copolymers were also studied and one of the main objectives here was to examine the possibility to synthesize trifluoropropyl-containing siloxane copolymers of gradient distribution of trifluoropropyl groups along the chain. DMA results of the PDMS-PMTFPS siloxane copolymers synthesized via simultaneous copolymerization showed that due to the large difference in reactivity rates of 2,4,6-tris(3,3,3-trifluoropropyl)-2,4,6-trimethylcyclotrisiloxane (F) and hexamethylcyclotrisiloxane (D), a copolymer of almost block structure containing only a narrow intermediate fragment with gradient distribution of the component units was obtained. A more dispersed distribution of the trifluoropropyl groups was obtained by the semi-batch copolymerization process, as the DMA results revealed more ‘‘pure gradient type’’ features for the siloxane copolymers which were synthesized by adding F at a controlled rate to the polymerization of the less reactive D. As with trifluoropropyl-containing siloxane copolymers, vinyl-containing polysiloxanes may be converted to a variety of useful polysiloxane materials by chemical modification. But much like the trifluoropropyl-containing siloxane copolymers, as a result of so much difference in the reactivities between the component units 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane (V) and hexamethylcyclotrisiloxane (D), thermal and mechanical properties of the PDMS-PMVS copolymers obtained by simultaneous copolymerization was similar to those of block copolymers. Only the copolymers obtained by semi-batch method showed properties typical for gradient copolymers.

Coil-ring-coil block copolymers as building blocks of supramolecular hollow cylindrical brushes

This work describes the synthesis of a new class of rod-coil block copolymers, oligosubstituted shape persistent macrocycles, (coil-ring-coil block copolymers), and their behavior in solution and in the solid state.The coil-ring-coil block copolymers are formed by nanometer sized shape persistent macrocycles based on the phenyl-ethynyl backbone as rigid block and oligomers of polystyrene or polydimethylsiloxane as flexible blocks. The strategy that has been followed is to synthesize the macrocycles with an alcoholic functionality and the polymer carboxylic acids independently, and then bind them together by esterification. The ester bond is stable and relatively easy to form.The synthesis of the shape persistent macrocycles is based on two separate steps. In the first step the building blocks of the macrocycles are connected by Hagiara-Sogonaschira coupling to form an 'half-ring' as precursor, that contains two free acetylenes. In the second step the half-ring is cyclized by forming two sp-sp bonds via a copper-catalyzed Glaser coupling under pseudo-high-dilution conditions. The polystyrene carboxylic acid was prepared directly by siphoning the living anionic polymer chain into a THF solution, saturated with CO2, while the polydimethylsiloxane carboxylic acid was obtained by hydrosilylating an unsaturated benzylester with an Si-H terminated polydimethylsiloxane, and cleavage of the ester. The carbodiimide coupling was found to be the best way to connect macrocycles and polymers in high yield and high purity.The polystyrene-ring-polystyrene block copolymers are, depending on the molecular weight of the polystyrene, lyotropic liquid crystals in cyclohexane. The aggregation behavior of the copolymers in solution was investigated in more detail using several technique. As a result it can be concluded that the polystyrene-ring-polystyrene block copolymers can aggregate into hollow cylinder-like objects with an average length of 700 nm by a combination of shape complementary and demixing of rigid and flexible polymer parts. The resulting structure can be described as supramolecular hollow cylindrical brush.If the lyotropic solution of the polystyrene-ring-polystyrene block copolymers are dried, they remain birefringent indicating that the solid state has an ordered structure. The polydimethylsiloxane-ring-polydimethylsiloxane block copolymers are more or less fluid at room temperature, and are all birefringent (termotropic liquid crystals) as well. This is a prove that the copolymers are ordered in the fluid state. By a careful investigation using electron diffraction and wide-angle X-ray scattering, it has been possible to derive a model for the 3D-order of the copolymers. The data indicate a lamella structure for both type of copolymers. The macrocycles are arranged in a layer of columns. These crystalline layers are separated by amorphous layers which contain the polymers substituents.

Silicon-containing block copolymers with well-defined, branched architectures

In the past decade, block copolymers (BCPs) have attracted increasing scientific and technological interest because of their inherent capability to spontaneously self-assemble into ordered arrays of nanostructures. The importance of nanostructures in a number of applications has fostered the need for well-defined, complex macromolecular architectures. In this thesis, the influence of macromolecular architecture on the bulk morphologies of novel linear-hyperbranched and linear brush-like diblock copolymer structure is investigated. An innovative, generally applicable strategy for the preparation of these defined diblock copolymers, consisting of linear polystyrene and branched polycarbosilane blocks, is demonstrated. Furthermore, complete characterization and solid-state morphological studies are provided. Finally, the concept is extended to linear-hyperbrached and linear brush-like polyalkoxysilanes. A shift of the classical phase boundaries to higher PS weight fractions as well as the appearance of new morphologies confirms the dramatic effect that polymer topology has on the morphology of BCPs.

DNA block copolymers - synthesis, morphologies and applications

The last decades have witnessed significant and rapid progress in polymer chemistry and molecular biology. The invention of PCR and advances in automated solid phase synthesis of DNA have made this biological entity broadly available to all researchers across biological and chemical sciences. Thanks to the development of a variety of polymerization techniques, macromolecules can be synthesized with predetermined molecular weights and excellent structural control. In recent years these two exciting areas of research converged to generate a new type of nucleic acid hybrid material, consisting of oligodeoxynucleotides and organic polymers. By conjugating these two classes of materials, DNA block copolymers are generated exhibiting engineered material properties that cannot be realized with polymers or nucleic acids alone. Different synthetic strategies based on grafting onto routes in solution or on solid support were developed which afforded DNA block copolymers with hydrophilic, hydrophobic and thermoresponsive organic polymers in good yields. Beside the preparation of DNA block copolymers with a relative short DNA-segment, it was also demonstrated how these bioorganic polymers can be synthesized exhibiting large DNA blocks (>1000 bases) applying the polymerase chain reaction. Amphiphilic DNA block copolymers, which were synthesized fully automated in a DNA synthesizer, self-assemble into well-defined nanoparticles. Hybridization of spherical micelles with long DNA templates that encode several times the sequence of the micelle corona induced a transformation into rod-like micelles. The Watson-Crick motif aligned the hydrophobic polymer segments along the DNA double helix, which resulted in selective dimer formation. Even the length of the resulting nanostructures could be precisely adjusted by the number of nucleotides of the templates. In addition to changing the structural properties of DNA-b-PPO micelles, these materials were applied as 3D nanoscopic scaffolds for organic reactions. The DNA strands of the corona were organized by hydrophobic interactions of the organic polymer segments in such a fashion that several DNA-templated organic reactions proceeded in a sequence specific manner; either at the surface of the micelles or at the interface between the biological and the organic polymer blocks. The yields of reactions employing the micellar template were equivalent or better than existing template architectures. Aside from its physical properties and the morphologies achieved, an important requirement for a new biomaterial is its biocompatibility and interaction with living systems, i.e. human cells. The toxicity of the nanoparticles was analyzed by a cell proliferation assay. Motivated by the non-toxic nature of the amphiphilic DNA block copolymers, these nanoobjects were employed as drug delivery vehicles to target the anticancer drug to a tumor tissue. The micelles obtained from DNA block copolymers were easily functionalized with targeting units by hybridization. This facile route allowed studying the effect of the amount of targeting units on the targeting efficacy. By varying the site of functionalization, i.e. 5’ or 3’, the outcome of having the targeting unit at the periphery of the micelle or in the core of the micelle was studied. Additionally, these micelles were loaded with an anticancer drug, doxorubicin, and then applied to tumor cells. The viability of the cells was calculated in the presence and absence of targeting unit. It was demonstrated that the tumor cells bearing folate receptors showed a high mortality when the targeting unit was attached to the nanocarrier.

An alternative blocking layer for titanium dioxide (TiO 2) solar cell applications

In hybrid organic solar cells a blocking layer between transparent electrode and nanocrystalline titania particles is essential to prevent short-circuiting and current loss through recombination at the electrode interface. Here the preparation of a uniform hybrid blocking layer which is composed of conducting titania nanoparticles embedded in an insulating polymer derived ceramic is presented. This blocking layer is prepared by sol-gel chemistry where an amphiphilic block copolymer is used as a templating agent. A novel poly(dimethylsiloxane) containing amphiphilic block copolymer poly(ethyleneglycol)methylethermethacrylate-block-poly(dimethylsiloxane)-block-poly(ethyleneglycol)methylethermethacrylate has been synthesized to act as the templating agent. Plasma treatment uncovered titania surface from any polymer. Annealing at 450°C under nitrogen resulted in anatase titania with polymer derived silicon oxycarbide ceramic. Electrical characterization by conductive scanning probe microscopy experiments revealed a percolating titania network separated by an insulating ceramic matrix. Scanning Kelvin probe force microscopy showed predominant presence of titania particles on the surface creating a large surface area for dye absorption. The uniformity of the percolating structures was proven by microbeam grazing incidence small angle x-ray scattering. First applications in hybrid organic solar cells in comparison with conventional titanium dioxide blocking layer containing devices revealed 15 fold increases in corresponding efficiencies. Poly(dimethylsiloxane)-block-poly(ethyleneglycol)methylethermethacrylate and poly(ethyleneoxide)-poly(dimethylsiloxane)methylmethacrylate diblock copolymers were also synthesized. Their titania nanocomposite films were compared with the integrated blocking layer. Liner poly(ethyleneoxide) containing diblock copolymer resulted in highly ordered foam like structures. The effect of heating temperature rise to 600°C and 1000°C on titania morphology was investigated by scanning electron and force microscopy and x-ray scattering. Sol-gel contents, hydrochloric acid, titania precursor and amphiphilic triblock copolymer were altered to see their effect on titania morphology. Increase in block copolymer content resulted in titania particles of diameter 15-20 nm.

DNA block copolymers – from micelles to machines

DNA block copolymer, a new class of hybrid material composed of a synthetic polymer and an oligodeoxynucleotide segment, owns unique properties which can not be achieved by only one of the two polymers. Among amphiphilic DNA block copolymers, DNA-b-polypropylene oxide (PPO) was chosen as a model system, because PPO is biocompatible and has a Tg < 0 °C. Both properties might be essential for future applications in living systems. During my PhD study, I focused on the properties and the structures of DNA-b-PPO molecules. First, DNA-b-PPO micelles were studied by scanning force microscopy (SFM) and fluorescence correlation spectroscopy (FCS). In order to control the size of micelles without re-synthesis, micelles were incubated with template-independent DNA polymerase TdT and deoxynucleotide triphosphates in reaction buffer solution. By carrying out ex-situ experiments, the growth of micelles was visualized by imaging in liquid with AFM. Complementary measurements with FCS and polyacrylamide gel electrophoresis (PAGE) confirmed the increase in size. Furthermore, the growing process was studied with AFM in-situ at 37 °C. Hereby the growth of individual micelles could be observed. In contrast to ex-situ reactions, the growth of micelles adsorbed on mica surface for in-situ experiments terminated about one hour after the reaction was initiated. Two reasons were identified for the termination: (i) block of catalytic sites by interaction with the substrate and (ii) reduced exchange of molecules between micelles and the liquid environment. In addition, a geometrical model for AFM imaging was developed which allowed deriving the average number of mononucleotides added to DNA-b-PPO molecules in dependence on the enzymatic reaction time (chapter 3). Second, a prototype of a macroscopic DNA machine made of DNA-b-PPO was investigated. As DNA-b-PPO molecules were amphiphilic, they could form a monolayer at the air-water interface. Using a Langmuir film balance, the energy released owing to DNA hybridization was converted into macroscopic movements of the barriers in the Langmuir trough. A specially adapted Langmuir trough was build to exchange the subphase without changing the water level significantly. Upon exchanging the subphase with complementary DNA containing buffer solution, an increase of lateral pressure was observed which could be attributed to hybridization of single stranded DNA-b-PPO. The pressure versus area/molecule isotherms were recorded before and after hybridization. I also carried out a series of control experiments, in order to identify the best conditions of realizing a DNA machine with DNA-b-PPO. To relate the lateral pressure with molecular structures, Langmuir Blodgett (LB) films were transferred to highly ordered pyrolytic graphite (HOPG) and mica substrates at different pressures. These films were then investigated with AFM (chapter 4). At last, this thesis includes studies of DNA and DNA block copolymer assemblies with AFM, which were performed in cooperation with different group of the Sonderforschungsbereich 625 “From Single Molecules to Nanoscopically Structured Materials”. AFM was proven to be an important method to confirm the formation of multiblock copolymers and DNA networks (chapter 5).

Proton-conducting copolymers, blends and composites with phosphonic acid as protogenic group

ABSTRACT: In this work, proton conducting copolymers, polymer blends and composites containing phosphonic acid groups have been prepared. Proton conduction mechanisms in these materials are discussed respectively in both, the anhydrous and humidified state. Atom transfer radical copolymerization (ATRCP) of diisopropyl-p-vinylbenzyl phosphonate (DIPVBP) and 4-vinyl pyridine (4VP) is studied for the first time in this work. The kinetic parameters are obtained by using the 1H-NMR online technique. Proton conduction in poly(vinylbenzyl phosphonic acid) (PVBPA) homopolymer and its statistical copolymers with 4-vinyl pyridine (poly(VBPA-stat-4VP)s) are comprehensively studied in both, the “dry” and “wet” state. Effects of temperature, water content and polymer composition on proton conductivities are studied and proton transport mechanisms under various conditions are discussed. The proton conductivity of the polymers is in the range of 10-6-10-8 S/cm in nominally dry state at 150 oC. However, proton conductivity of the polymers increases rapidly with water content in the polymers which can reach 10-2 S/cm at the water uptake of 25% in the polymers. The highest proton conductivity obtained from the polymers can even reach 0.3 S/cm which was measured at 85oC with 80% relative humidity in the measuring atmosphere. Poly(4-vinyl pyridine) was grafted from the surface of SiO2 nanoparticles using ATRP in this work for the first time. Following this approach, silica nanoparticles with a shell of polymeric layer are used as basic particles in a polymeric acidic matrix. The proton conductivities of the composites are studied under both, humidified and dry conditions. In dry state, the conductivity of the composites is in the range of 10-10~10-4 S/cm at 150 oC. While in humid state, the composites show much higher proton conductivity. The highest proton conductivity obtained with the composites is 0.5 S/cm measured at 85oC with 80% relative humidity in the measuring atmosphere. The miscibility of poly (vinyl phosphonic acid) and PEO is studied for the first time in this work and a phase diagram is plotted based on a DSC study and optical microscopy. With this knowledge, homogeneous PVPA/PEO mixtures are prepared as proton-conducting polymer blends. The mobility of phosphonic acid groups and PEO in the blends is determined by 1H-MAS-NMR in temperature dependent measurements. The effect of composition and the role of PEO on proton conduction are discussed.

Hyperverzweigte Lacton-Copolymere: enzymatische Synthese, Charakterisierung und Darstellung strukturierter Polymernetzwerke = (Hyperbranched lactone copolymers by enzyme catalysis: synthesis, characterization and preparation of structured polymer networks)

Hyperverzweigte Polymere erfuhren in den letzten Jahren immer mehr Beachtung, da sie im Vergleich zu ihren linearen Analoga besondere Eigenschaften besitzen. Im Jahre 2002 wurde die erste enzymkatalysierte Darstellung hyperverzweigter Poly(epsilon-caprolacton)e (hb-PCL) beschrieben. Hier ermöglichte das Konzept der konkurrierenden ringöffnenden Polymerisation und Polykondensation die Kontrolle der Eigenschaften des dargestellten Polymers. Detaillierte Untersuchungen in Hinblick auf Grenzen und Möglichkeiten, aber auch die Synthese im Technikumsmaßstab sind wesentliche Aspekte dieser Arbeit. Außerdem wird ein neues Konzept eingeführt, das Reknitting genannt wurde. Ziel desselben ist das Recycling kommerziellen, linearen PCLs mittels Umesterung zu hb-PCL durch Enzymkatalyse. Diese hb-PCLs zeigen vergleichbare Eigenschaften zu den aus den Comonomeren dargestellten. Ausgehend von hb-PCL sollte eine geeignete Route zu methacrylierten Vernetzerverbindungen entwickelt werden. Aus Mischungen derselben mit 2-Hydroxyethylmethacrylat wurden komplexe Netzwerkarchitekturen durch Copolymerisation erhalten. Diese Netzwerke wurden in Hinblick auf ihre mechanisch physikalischen Eigenschaften untersucht. Zuletzt wurden Screeningexperimente an anderen zyklischen Estern durchgeführt, da ein Transfer des oben vorgestellten Konzepts angestrebt wurde. Zwei neue hyperverzweigte Polymerklassen, hb-Poly(delta-valerolacton) und hb-Polytrimethylencarbonat wurden detaillierter untersucht und in Ihren Eigenschaften mit hb-PCL verglichen.

From amphiphilic block copolymers to ferrocenyl-functionalized polymers for biosensoric applications

The present thesis can be divided in three main parts. In all parts new polymer architecturesrnwere synthesized and characterized concerning their special features.rnThe first part will emphasize the advantage of a polystyrene-block-(hyperbranchedrnpolyglycerol) copolymer in comparison to an analogue polystyrene-block-(linear polyglycerol)rncopolymer. Therefore a synthethic route to prepare linear block copolymersrnhas been developed. Two strategies were examined. One strategy was based on thernclassic, sequential anionic polymerization; the second strategy was based on arn“Click-Chemistry” coupling reaction. In a following step glycidol was hypergraftedrnfrom these block copolymers by applying a hypergrafting reaction with glycidol. Thernbehavior of the amphiphilic block copolymers synthesized was studied in differentrnsolvents. Furthermore the polarity of the solvent was changed to form the correspondingrninverse micelles. DLS, SLS, SEC-MALLS-VISCO, AFM and Cyro TEMrnmeasurements were performed to obtain a visual image from the appearance of thernaggregates. It was found that a linear-hyperbranched architecture is necessary, ifrnwell defined, monodisperse aggregates are required, e.g. for the preparation of orderedrnnanoarrays. Linear-linear block copolymers formed only polydisperse aggregates.rnAdditionally it was found that size distribution could be improved dramaticallyrnby passing the aggregates through a SEC column with large pores. The SEC columnsrnacted like a template in which the aggregates adopt a more stable conformation.rnIn the second part anionic polymerization was employed to synthesize silaneendfunctionalizedrnmacromonomers with different molecular weights based on polybutadienernand polyisoprene. These were polymerized by a hydrosilylation reaction inrnbulk to obtain branched polymers, using Karstedt’s catalyst. Surprisingly the additionrnof monofunctional silanes during the polymerization had only a minimal effect concerningrnthe degree of polymerization. It was possible to introduce silanes without increasingrnthe overall number of reaction steps by a very convenient “pseudo-copolymerization”rnmethod. All branched polymers were analyzed by SEC, SEC-MALLS,rnSEC-viscometry, 1H-NMR-spectroscopy and DSC concerning their branching ratio.rnThe branching parameters for the branched polymers exhibited similar characteristicsrnas hyperbranched polymers based on AB2 monomers. Detailed kinetic study showedrnthat the polymerization occurred very rapidly in comparison to the hydrosilylation polymerizationrnof classical AB2 type carbosilanes monomers.rnThe last part will deal with ferrocenyl-functionalized polymers. On the one hand,rnferrocenyl-functionalized polyglycerols (PG) were studied. Esterification of PGs withrndifferent molecular weight using ferrocenemonocarboxylic acid gave the ferrocenylrnfuntionalized polymers in high yields. On the other hand three different block copolymersrnwere prepared with different ratios of styrene to butadiene units (10:1, 4:1, 2:1).rnThe double bonds of the 1,2-PB block were hydrosilylated using silanes bearing onern(HSiMe2Fc) or two (HSiMeFc2) ferrocene units. High degrees of functionalizationrnwere obtained (up to 83 %). In this manner, six different ferrocenyl-rich block copolymersrnwith different fractions of ferrocene were prepared and analyzed, employingrnNMR-spectroscopy, SEC, SEC/MALLS/viscometry, DLS and cyclic voltammetry. Thernredox properties of the studied polymers varied primarily with the nature of the silanernunit attached. Additionally, the redox properties in solution of the studied polymersrnwere influenced by the block length ratio of the block copolymers. Unexpectedly, withrnincreasing block length of the ferrocenyl block the fraction of active ferrocenes decreased.rnNevertheless, in case of thin monolayer films this behaviour was not observed.rnAll polymers (PG and PS-b-PB based) exhibited good electrochemical propertiesrnin a wide range of solvents, which rendered them very interesting for biosensoricrnapplications.

Synthesis and characterization of temperature- and light-responsive polymers and block copolymers

In summary, thermoresponsive polyacrylamides with various amounts of different photoswitchable side groups, i. e. azobenzene, salicylideneaniline and fulgimide were successfully prepared. As such, in a first step three different chromophores with an amine functionality were synthesized. The synthesis of the stimuli-responsive materials was based on the RAFT polymerization of activated ester acrylates followed by a polymer analogous reaction with different amines. The procedure has been designed to allow the synthesis of well-defined materials with functional groups. All copolymers prepared in this way showed a LCST in aqueous solution. The LCST was in general decreased by increasing the amount of hydrophobic dye incorporated into the thermoresponsive polymer. However, in the case of the fulgimide, the LCST was hardly affected by the chromophore. For azobenzene containing PNIPAM polymers and analogues, higher LCST values were measured after irradiation of the polymer sample solutions with UV-light (Delta LCSTmax = 7.3°C). A reversible light-induced solubility change within a certain temperature range was possible. In contrast to this, irradiated samples of salicylideneaniline containing thermoresponsive copolymers showed an irreversible increase in the LCST (Delta LCSTmax = 13.0°C). Fulgimide chromophores did not influence the LCST of PNIPAM based copolymers after UV-light exposure.rnSimilar to the thermoresponsive polyacrylamides with azobenzene side groups, poly(oligo(ethylene glycol) methyl ether methacrylate) [P(OEGMA)] polymers with azobenzene end groups showed a LCST shift upon UV-irradiation. These polymers were synthesized by RAFT polymerization using a functional chain transfer agent (CTA). For this, PFP-CTA was used as a RAFT-agent for end group functionalization of (thermoresponsive) polymers. In contrast to the statistically arranged copolymers with azobenzene side groups, P(OEGMA) polymers with terminal azobenzene showed a linear increase of the LCST shifts with increasing amount of chromophore (Delta LCSTmax = 4.3°C). Noteworthy, the chemical nature of the end group exhibited a strong influence on the LCST in the case of short thermoresponsive P(OEGMA) polymers.rnThe investigation on temperature- and lightresponsive polymers was transferred onto block copolymers capable to self-assemble into polymeric micelles. Therefore, PEO-b-PNIPAM block copolymers with azobenzene moieties were synthesized successfully. These polymers showed a “smart” behavior in aqueous solution, as the reversible formation and disruption of the micelles could either be controlled by temperature or using light as a stimulus. The usefulness of these materials was demonstrated by encapsulation of a hydrophobic dye in the core of the micelle. Such materials might have a great potential as a model system for several technical or biological applications.rnFinally, double thermoresponsive block copolymers forming micellar structures in a certain temperature range with functional end groups could successfully be synthesized. These “smart materials” based on POEGMA-b-PNIPMAM have been demonstrated to be very promising for a temperature selective immobilization on a protein surface. This might be a suitable concept for further biological applications.rnConcluding, different thermoresponsive copolymers and block copolymers with lightresponsive moieties arranged along the backbone or located at the chain ends were successfully prepared and investigated. By controlling the nature of functional groups and their respective incorporation ratios, the LCST could be dialed in precisely. Further, the LCST of the polymers could be triggered by light. A light-controlled disruption of micellar structures could be shown for functional block copolymers. The importance of end groups of thermoresponsive polymers was demonstrated by a temperature-controlled protein-polymer binding of a terminal biotin-functionalized double thermoresponsive polymer. The synthetic approaches and the material properties presented here should be promising for further research and applications beyond this dissertation.rn