Functional polymer based nanoparticles : development of defined complex structures as basis for in-vitro and in-vivo applications

In Rahmen der vorliegenden Arbeit wurde ein neuartiger Zugang zu einer Vielzahl von Polymerstrukturen auf Basis des klinisch zugelassenen Polymers Poly(N-(2-Hydroxypropyl)-methacrylamide) (PHPMA) entwickelt. Der synthetische Zugang beruht zum einen auf der Verwendung von Reaktivesterpolymeren und zum anderen auf der Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerisationsmethode. Diese Form einer kontrollierten radikalischen Polymerisation ermöglichte es, neben der Synthese von besser definierten Homopolymeren auch statistische und Blockcopolymere herzustellen. Die Reaktivesterpolymere können durch einfache Aminolyse in HPMA-basierte Systeme überführt werden. Somit können sie als eine vielversprechende Basis zur Synthese von umfangreichen Polymerbibliotheken angesehen werden. Die hergestellten Polymere kombinieren verschiedene Funktionalitäten bei konstantem Polymerisationsgrad. Dies ermöglicht eine Optimierung auf eine gezielte Anwendung hin ohne den Parameter der Kettenlänge zu verändern.rnIm weiteren war es durch Verwendung der RAFT Polymerisation möglich partiell bioabbaubare Blockcopolymere auf Basis von Polylactiden und HPMA herzustellen, in dem ein Kettentransferreagenz (CTA) an ein wohl definiertes Polylactid Homopolymer gekoppelt wurde. Diese Strukturen wurden in ihrer Zusammensetzung variiert und mit Erkennungsstrukturen (Folaten) und markierenden Elementen (Fluoreszenzfarbstoffe und +-emittierenden Radionukleide) versehen und im weiteren in vitro und in vivo evaluiert.rnAuf Grund dieser Errungenschaften war es möglich den Einfluss der Polymermikrostruktur auf das Aggregationsverhalten hin mittel Lichtstreuung und Fluoreszenzkorrelationsspektroskopie zu untersuchen. Es konnte gezeigt werden, dass erst diese Informationen über die Überstrukturbildung die Kinetik der Zellaufnahme erklären können. Somit wurde die wichtige Rolle von Strukturwirkungsbeziehungen nachgewiesen.rnSomit konnte neben der Synthese, Charakterisierung und ersten biologischen Evaluierungen ein Beitrag zum besseres Verständnis zur Interaktion von polymeren Partikeln mit biologischen Systemen geleistet werden.

Anisotrope Kolloide aus flüssigkristallinen Polymeren

In dieser Arbeit wurden Kolloide aus flüssigkristallinen Polymeren dargestellt und untersucht.rnrnDie Methode der Dispersionspolymerisation zur Darstellung von Kolloiden aus flüssigkristallinen Polyacrylaten wurde in unpolare Lösungsmittel adaptiert, umrneine Manipulierbarkeit anisotroper Kolloide durch elektrische Felder zu erreichen.rnDazu wurden ein Gemisch aus THF und Siliconöl als Reaktionsmischung gewähltrnund polysiloxanbasierte Polymere und Copolymere als Stabilisatoren eingesetzt.rnDabei auftretende unerwartete Auswirkungen auf die Mesogenkonfiguration führtenrnzu einer Untersuchung der Abhängigkeit der Mesogenkonfigurationen von der Oberflächenverankerung der Mesogene. Schließlich wurde eine Kontrolle derrnOberfl¨achenverankerung der Mesogene und somit eine Kontrolle der Mesogenkonfigurationen unter Ausnutzung der Eigenschaften flüssigkristallin/nicht flüssigkristalliner Blockcopolymere erreicht. Zu diesem Zweck wurde auch ein neuer Makroinitiator entwickelt. Kleine Kolloide konnten mittels eines elektrischen Feldes gedreht bzw. zu Linien angeordnet werden.rnrnEinige neue Polysiloxane wurden zum Einbau in flüssigkristalline Kolloide viarnMiniemulsion synthetisiert. Sie wurden charakterisiert und in Kolloide überführt. Aufgrund zu hoher Übergangstemperaturen konnten bei den meisten jedoch keine Strukturen aus phasenseparierten Polysiloxane gefunden werden. Die Ausbildung der Strukturen in solchen Kolloiden konnte aber trotzdem verstanden werden.rnrnAus vernetzten Hauptkettenpolymeren sollten aktuierende Kolloide hergestelltrnwerden. Dazu wurde das entsprechende Hauptkettenpolymer hergestellt, charakterisiert und per Miniemulsion in Kolloide überführt. Die dargestellten Kolloide wurden unter dem TEM geheizt und zeigten Formänderungen, die jedoch nicht kontrolliert und noch irreversibel waren.

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.

Hyperbranched polyglycerols as building blocks for complex amphiphilic structures: synthesis, characterization and applications

Among hyperbranched polymers, polyglycerol is one of the most promising and commonly used macromolecules due to its biocompatibility and versatility. However, the synthesis of high molecular weight polyglycerols still involves many intricacies and has only been understood to a limited extent. Furthermore, only few complex structures like star or block copolymers incorporating polyglycerol have been realized so far. Particularly biocompatible block copolymers are considered promising candidates for biomedical applications.rnThe scope of this thesis was the enhancement of the synthetic process leading to polyglycerol derivatives which implies improved molecular weight control for a broad molecular weight range as well as the assembly of more complex structures like amphiphilic block copolymers. Further insight into the relation between reaction solvent, degree of deprotonation during the ring-opening multibranching polymerization of glycidol and the characteristics of the obtained polymers were achieved within the scope of this work. Based on these results, a novel concept for the preparation of hyperbranched polyglycerols with molecular weights up to 20,000 g/mol was developed, applying a two step synthesis pathway. Starting from a partially deprotonated TMP core, low molecular weight hb-PGs were prepared using the known synthetic protocol that has been established since the late 1990ies. In a subsequent reaction sequence, these well defined polymers were used as hyperbranched macroinitiator cores in order to obtain high molecular weight hb-PGs with remarkably low polydispersity (Mw/Mn < 1.8). Molecular weight control was shown to be excellent and undesired low molecular weight side products were absent. Furthermore, the technique of continuous spin fractionation has been discovered as an efficient method for polyglycerol work-up to remove quantitatively residual monomer- and oligomer traces from hb-PG compositions to result in samples with significantly reduced polydispersities. Based on these results the synthesis of amphiphilic block copolymers containing hydrophilic hyperbranched polyglycerol blocks and linear, apolar poly(propylene oxide) blocks has been significantly improved and augmented to hb-PG-b-l-PPO-b-hb-PG ABA block copolymers. The influence of different polyglycerol-based amphiphiles on the fibril formation was studied by Thioflavin T Fluorescence showing remarkable increasing lag times which is promising in order to enhance the stability of this protein. In addition the first synthesis of poly(glyceryl glycerols) (PGG), introducing a new solketyl glycidyl ether monomer (IGG) was shown. It was furthermore demonstrated that core-functional carbosilane wedges allow application in block copolymer synthesis. Bisglycidolized amine functional polymers were successfully employed as macroinitiators for glycidol polymerization. This resulted in the first example of amphiphilic hyperbranched-hyperbranched polymer structures. Finally, it has been shown that the previously reported synthetic pathway to carboxylated hyperbranched polyglycerol polyelectrolytes can also be applied for the amphiphilic linear-hyperbranched block copolymers. These novel biocompatible and highly amphiphilic polyelectrolytes offer great potential for further investigations. rnrn

Hundertneunundzwanzig Xe NMR for investigations of complex and dynamic systems

In this work, the remarkable versatility and usefulness of applications of Xe-129 NMR experiments is further extended. The application of Xe-129 NMR spectroscopy to very different system is studied, including dynamic and static, solid and liquid, porous and non-porous systems. Using the large non-equilibrium polarization created by hyperpolarization of Xe-129, time-resolved NMR measurements can be used for the online-monitoring of dynamic systems. In the first part of this work, several improvements for medical applications of hyperpolarized Xe-129 are achieved and their feasibility shown experimentally. A large gain in speed and reproducibility of the accumulation process of Xe-129 as ice and an enhancement of the usable polarization in any experiment requiring prior accumulation are achieved. An enhancement of the longitudinal relaxation time of Xe-129 is realized by admixture of a buffer gas during the storage of hyperpolarized Xe-129. Pursuing the efforts of simplifying the accumulation process and enhancing the storage time of hyperpolarized Xe-129 will allow for a wider use of the hyperpolarized gas in (medical) MRI experiments. Concerning the use of hyperpolarized Xe-129 in MRI, the influence of the diffusion coefficient of the gas on parameters of the image contrast is experimentally demonstrated here by admixture of a buffer gas and thus changing the diffusion coefficient. In the second part of this work, a polymer system with unique features is probed by Xe-129 NMR spectroscopy, proving the method to be a valuable tool for the characterization of the anisotropic properties of semicrystalline, syndiotactic polystyrene films. The polymer films contain hollow cavities or channels with sizes in the sub-nanometer range, allowing for adsorption of Xe-129 and subsequent NMR measurements. Despite the use of a ’real-world’ system, the transfer of the anisotropic properties from the material to adsorbed Xe-129 atoms is shown, which was previously only known for fully crystalline materials. The anisotropic behavior towards atomar guests inside the polymer films is proven here for the first time for one of the phases. For the polymer phase containing nanochannels, the dominance of interactions between Xe-129 atoms in the channels compared to interactions between Xe atoms and the channel walls are proven by measurements of a powder sample of the polymer material and experiments including the rotation of the films in the external magnetic field as well as temperature-dependent measurements. The characterization of ’real-world’ systems showing very high degrees of anisotropy by Xe-129 are deemed to be very valuable in future applications. In the last part of this work, a new method for the online monitoring of chemical reactions has been proposed and its feasibility and validity are experimentally proven. The chemical shift dependence of dissolved Xe-129 on the composition of a reaction mixture is used for the online monitoring of free-radical miniemulsion polymerization reactions. Xe-129 NMR spectroscopy provides an excellent method for the online monitoring of polymerization reactions, due to the simplicity of the Xe-129 NMR spectra and the simple relationship between the Xe-129 chemical shift and the reaction conversion. The results of the time-resolved Xe-129 NMR measurements are compared to those from calorimetric measurements, showing a good qualitative agreement. The applicability of the new method to reactions other than polymerization reactions is investigated by the online monitoring of an enzymatic reaction in a miniemulsion. The successful combination of the large sensitivity of Xe-129, the NMR signal enhancements due to hyperpolarization, and the solubility of Xe-129 gives access to the large new field of investigations of chemical reaction kinetics in dynamic and complex systems like miniemulsions.

Complex colloids by the emulsion solvent evaporation process

In this thesis, different complex colloids were prepared by the process of solvent evaporation from emulsion droplets (SEED). The term “complex” is used to include both an addressable functionality as well as the heterogeneous nature of the colloids.Firstly, as the SEED process was used throughout the thesis, its mechanism especially in regard to coalescence was investigated,. A wide variety of different techniques was employed to study the coalescence of nanodroplets during the evaporation of the solvent. Techniques such as DLS or FCS turned out not to be suitable methods to determine droplet coalescence because of their dependence on dilution. Thus, other methods were developed. TEM measurements were conducted on mixed polymeric emulsions with the results pointing to an absence of coalescence. However, these results were not quantifiable. FRET measurements on mixed polymeric emulsions also indicated an absence of coalescence. Again the results were not quantifiable. The amount of coalescence taking place was then quantified by the application of DC-FCCS. This method also allowed for measuring coalescence in other processes such as the miniemulsion polymerization or the polycondensation reaction on the interface of the droplets. By simulations it was shown that coalescence is not responsible for the usually observed broad size distribution of the produced particles. Therefore, the process itself, especially the emulsification step, needs to be improved to generate monodisperse colloids.rnThe Janus morphology is probably the best known among the different complex morphologies of nanoparticles. With the help of functional polymers, it was possible to marry click-chemistry to Janus particles. A large library of functional polymers was prepared by copolymerization and subsequent post-functionalization or by ATRP. The polymers were then used to generate Janus particles by the SEED process. Both dually functionalized Janus particles and particles with one functionalized face could be obtained. The latter were used for the quantification of functional groups on the surface of the Janus particles. For this, clickable fluorescent dyes were synthesized. The degree of functionality of the polymers was found to be closely mirrored in the degree of functionality of the surface. Thus, the marriage of click-chemistry to Janus particles was successful.Another complex morphology besides Janus particles are nanocapsules. Stimulus-responsive nanocapsules that show triggered release are a highly demanding and interesting system, as nanocapsules have promising applications in drug delivery and in self-healing materials. To achieve heterogeneity in the polymer shell, the stimulus-responsive block copolymer PVFc-b-PMMA was employed for the preparation of the capsules. The phase separation of the two blocks in the shell of the capsules led to a patchy morphology. These patches could then be oxidized resulting in morphology changes. In addition, swelling occurred because of the hydrophobic to hydrophilic transition of the patches induced by the oxidation. Due to the swelling, an encapsulated payload could diffuse out of the capsules, hence release was achieved.The concept of using block copolymers responsive to one stimulus for the preparation of stimulus-responsive capsules was extended to block copolymers responsive to more than one stimulus. Here, a block copolymer responsive to oxidation and a pH change as well as a block copolymer responsive to a pH change and temperature were studied in detail. The release from the nanocapsules could be regulated by tuning the different stimuli. In addition, by encapsulating stimuli-responsive payloads it was possible to selectively release a payload upon one stimulus but not upon the other one.In conclusion, the approaches taken in the course of this thesis demonstrate the broad applicability and usefulness of the SEED process to generate complex colloids. In addition, the experimental techniques established such as DC-FCCS will provide further insight into other research areas as well.

Self assembled monolayers for engineering of structured inorganic materials in the micrometer and submicrometer range

Deutsch:In der vorliegenden Arbeit konnten neue Methoden zur Synthese anorganischer Materialien mit neuartiger Architektur im Mikrometer und Nanometer Maßstab beschrieben werden. Die zentrale Rolle der Formgebung basiert dabei auf der templatinduzierten Abscheidung der anorganischen Materialien auf selbstorganisierten Monoschichten. Als Substrate eignen sich goldbedampfte Glasträger und Goldkolloide, die eine Mittelstellung in der Welt der Atome bzw. Moleküle und der makroskopischen Welt der ausgedehnten Festkörper einnehmen. Auf diesen Substraten lassen sich Thiole zu einer monomolekularen Schicht adsorbieren und damit die Oberflächeneigenschaften des Substrates ändern. Ein besonderer Schwerpunkt bei dieser Arbeit stellt die Synthese speziell auf die Bedürfnisse der jeweiligen Anwendung ausgerichteten Thiole dar.Im ersten Teil der Arbeit wurden goldbedampfte Glasoberflächen als Template verwendet. Die Abscheidung von Calciumcarbonat wurde in Abhängigkeit der Schichtdicke der adsorbierten Monolage untersucht. Aragonit, eine der drei Hauptphasen des Calciumcarbonat Systems, wurde auf polyaromatischen Amid - Oberflächen mit Schichtdicken von 5 - 400 nm Dicke unter milden Bedingung abgeschieden. Die einstellbaren Parameter waren dabei die Kettenlänge des Polymers, der w-Substituent, die Bindung an die Goldoberfläche über Verwendung verschiedener Aminothiole und die Kristallisationstemperatur. Die Schichtdickeneinstellung der Polymerfilme erfolgte hierbei über einen automatisierten Synthesezyklus.Titanoxid Filme konnten auf Oberflächen strukturiert werden. Dabei kam ein speziell synthetisiertes Thiol zum Einsatz, das die Funktionalität einer Styroleinheit an der Oberflächen Grenze als auch eine Möglichkeit zur späteren Entfernung von der Oberfläche in sich vereinte. Die PDMS Stempeltechnik erzeugte dabei Mikrostrukturen auf der Goldoberfläche im Bereich von 5 bis 10 µm, die ihrerseits über die Polymerisation und Abscheidung des Polymers in den Titanoxid Film überführt werden konnten. Drei dimensionale Strukturen wurden über Goldkolloid Template erhalten. Tetraethylenglykol konnte mit einer Thiolgruppe im Austausch zu einer Hydroxylgruppe monofunktionalisiert werden. Das erhaltene Molekül wurde auf kolloidalem Gold selbstorganisiert; es entstand dabei ein wasserlösliches Goldkolloid. Die Darstellung erfolgte dabei in einer Einphasenreaktion. Die so erhaltenen Goldkolloide wurden als Krstallisationstemplate für die drei dimensionale Abscheidung von Calciumcarbonat verwendet. Es zeigte sich, dass Glykol die Kristallisation bzw. den Habitus des krsitalls bei niedrigem pH Wert modifiziert. Bei erhöhtem pH Wert (pH = 12) jedoch agieren die Glykol belegten Goldkolloide als Template und führen zu sphärisch Aggregaten. Werden Goldkolloide langkettigen Dithiolen ausgesetzt, so führt dies zu einer Aggregation und Ausfällung der Kolloide aufgrund der Vernetzung mehrer Goldkolloide mit den Thiolgruppen der Alkyldithiole. Zur Vermeidung konnte in dieser Arbeit ein halbseitig geschütztes Dithiol synthetisiert werden, mit dessen Hilfe die Aggregation unterbunden werden konnte. Das nachfolgende Entschützten der Thiolfunktion führte zu Goldkolloiden, deren Oberfläche Thiol funktionalisiert werden konnte. Die thiolaktiven Goldkolloide fungierten als template für die Abscheidung von Bleisulfid aus organisch/wässriger Lösung. Die Funktionsweise der Schutzgruppe und die Entschützung konnte mittels Plasmonenresonanz Spektroskopie verdeutlicht werden. Titanoxid / Gold / Polystyrol Komposite in Röhrenform konnten synthetisiert werden. Dazu wurde ein menschliches Haar als biologisches Templat für die Formgebung gewählt.. Durch Bedampfung des Haares mit Gold, Assemblierung eines Stryrolmonomers, welches zusätzlich eine Thiolfunktionalität trug, Polymerisation auf der Oberfläche, Abscheidung des Titanoxid Films und anschließendem Auflösen des biologischen Templates konnte eine Röhrenstruktur im Mikrometer Bereich dargestellt werden. Goldkolloide fungierten in dieser Arbeit nicht nur als Kristallisationstemplate und Formgeber, auch sie selbst wurden dahingehend modifiziert, dass sie drahtförmige Agglormerate im Nanometerbereich ausbilden. Dazu wurden Template aus Siliziumdioxid benutzt. Zum einen konnten Nanoröhren aus amorphen SiO2 in einer Sol Gel Methode dargestellt werden, zum anderen bediente sich diese Arbeit biologischer Siliziumoxid Hohlnadeln aus marinen Schwämmen isoliert. Goldkolloide wurden in die Hohlstrukturen eingebettet und die Struktur durch Ausbildung von Kolloid - Thiol Netzwerken mittels Dithiol Zugabe gefestigt. Die Gold-Nanodrähte im Bereich von 100 bis 500 nm wurden durch Auflösen des SiO2 - Templates freigelegt.

5-substituted triazolinyls as novel counter radicals in controlled radical polymerization

The work is devoted to synthesis of new triazolinyl stable radical derivatives with different substituents at the 5-position of the triazolinyl ring. Obtained results showed great influence of these substituents on the stability of the radical. Electron-rich aromatic substituents at this position stabilize the radical while electron-poor aromatics decrease the stability of the triazolinyl. The triazolinyl radicals synthesized were used as additives for kinetic investigations of controlled radical polymerization of styrene and methylmethacrylate (MMA). The studies performed showed that the more stable radicals provide better control for the polymerization of styrene. In the same time certain instability of the radical is required for realization of controlled polymerization of methylmethacrylate. Based on the kinetic investigations controlled radical polymerization of a variety of monomers including 4-vinylpyridine (4-VP), ethylmethacrylate (EMA), 2,2,2-trifluoroethylmethacrylate (FEMA) and n-butylmethacrylate (BMA)was successfully carried out. Polystyrene and polymethylmethacrylate macroinitiators prepared by triazolinyl mediated controlled radical polymerization were efficiently reinitiated in the presence of a variety of monomers leading to the formation of block copolymers. Using this method PS-b-P-4-VP, PMMA-b-PS, PMMA-b-PBMA, PMMA-b-PFEMA, and PMMA-b-Poly-tert-butylacrylate were successfully synthesized. The results obtained during this work showed the efficiency and flexibility of the method allowing preparation of a range of advanced macromolecular structures.

Nanosized polymer carriers for metallocene catalysts in heterogeneous olefin polymerization

Das Ziel der vorgelegten Arbeit war die Synthese von definierten, sphärischen Polystyrolpartikeln im Größenbreichen von Nanometern, die als Träger für die Immobilisierung von Metallocenkatalysatoren verwendet werden sollten. Ein wichtiger Anspruch an das System war dabei die Möglichkeit einer homogene Verteilung des Metallocenes auf dem Träger and eine homogene Fragmentierung des geträgerten Katalysators während der Polymerisation im Polymerprodukt. Für diese Zielsetzung wurden unterschiedliche Polystyrolnanopartikel hergestellt. Die Polystyrolnanopartikel waren mit unterschiedlichen funktionellen Gruppen wie Polyethylenoxid- und Polypropylenoxidketten oder Hydroxygruppen auf der Oberfläche versehen, um den Metallocenkatalysator und den Cokatalysator MAO immobilisieren zu können. In verschiedenen Experimenten wurde der Einfluss dieser Polystyrolnanopartikel als Träger auf die Katalysatoreigenschaften wie Aktivität oder Produktivität und die Eigenschaften des produzierten Polyolefins wie z.B. Molekulargewicht und Morphologie untersucht. Im Vergleich zu den PS- Nanopartikeln wurden außerdem PS-Mikropartikel, Silica und Dendrimere als Träger in der heterogenen Olefinpolymerisation eingesetzt. Von all diesen Trägersystemen wurde das Fragmentierungsverhalten durch konfocale Fluoreszenzmikroskopie untersucht. Aus den erhaltenen Ergebnissen kann geschlossen werden, dass die hergestellten Polystyrolnanopartikel neuartige und leistungsfähige Träger für heterogene Polymerisationsprozesse darstellen. Die hergestellten Polystyrolnanopartikel besaßen eine wohldefinierte sphärische Struktur, die eine homogene Verteilung des immobilisierten Metallocenkatalysators und somit auch eine vollständige Fragmentierung des geträgerten Katalysators im hergestellten Polyolefin ermöglichte. Die Katalysatorsysteme, die aus den PS- Nanopartikeln und dem Metallocenkatalysator zusammengesetzt waren, wurden in verschiedenen Polymerisationen wie der Ethylen- oder Propylenhomopolymersation und der Copolymerisation von Ethen mit α- Olefinen getestet. Die Oberflächen- funktionalisierten PS Nanopartikel immobilisierten den Metallocenkatalysator ausreichend gut, so dass kein „Leachen“ (Ablösen) des Katalysators von der Trägeroberfläche festgestellt werden konnte und deshalb Polymer von sehr guter Morphologie erhalten wurde. Um die Fragmentierung des Katalysators und den inneren Aufbau des Polymers näher untersuchen zu können, wurde die konfocale Fluoreszenzmikroskopie für das PS- Nanopartikelträgersystem angewendet. Durch farbstoffmarkierte Trägerpartikel konnte die Verteilung des fragmentierten Katalysators innerhalb des Polymers sichtbar gemacht und analysiert werden. Dabei wurde festgestellt, dass sich PS- Nanopartikel und auch Dendrimere als Träger ähnlich verhalten wie Ziegler- Natta- Katalysatoren, die auf MgCl2 immobilisiert für die heterogene Olefinpolymerisation verwendet werden. Das Fragmentierungsverhalten der Silica oder PS- Mirkopartikel geträgerten Systeme entsprach dagegen dem schichtweisen Fragmentierungsverhalten wie es bereits von Fink und Mitarbeitern beschrieben wurde.

From polymer precursors to metal oxides

We report on a strategy to prepare metal oxides including binary oxide and mixed metal oxide (MMO) in form of nanometer-sized particles using polymer as precursor. Zinc oxide nanoparticles are prepared as an example. The obtained zinc polyacrylate precursor is amorphous as confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The conversion from polymer precursor to ZnO nanocrystals by thermal pyrolysis was investigated by means of XRD, thermogravimetric analysis (TGA) and electron microscopy. The as-synthesized ZnO consists of many individual particles with a diameter around 40 nm as shown by scanning electron microscopy (SEM). The photoluminescence (PL) and electron paramagnetic (EPR) properties of the material are investigated, too. Employing this method, ZnO nanocrystalline films are fabricated via pyrolysis of a zinc polyacrylate precursor film on solid substrate like silicon and quartz glass. The results of XRD, absorption spectra as well as TEM prove that both the ZnO nanopowder and film undergo same evolution process. Comparing the PL properties of films fabricated in different gas atmosphere, it is assigned that the blue emission of the ZnO films is due to crystal defect of zinc vacancy and green emission from oxygen vacancy. Two kinds of ZnO-based mixed metal oxide (Zn1-xMgxO and Zn1-xCoxO) particles with very precise stoichiometry are prepared by controlled pyrolysis of the corresponding polymer precursor at 550 oC. The MMO crystal particles are typically 20-50 nm in diameter. Doping of Mg in ZnO lattice causes shrinkage of lattice parameter c, while it remains unchanged with Co incorporation. Effects of bandgap engineering are seen in the Mg:ZnO system. The photoluminescence in the visible is enhanced by incorporation of magnesium on zinc lattice sites, while the emission is suppressed in the Co:ZnO system. Magnetic property of cobalt doped-ZnO is checked too and ferromagnetic ordering was not found in our samples. An alternative way to prepare zinc oxide nanoparticles is presented upon calcination of zinc-loaded polymer precursors, which is synthesized via inverse miniemulsion polymerization of the mixture of the acrylic acid and zinc nitrate. The as-prepared ZnO product is compared with that obtained from polymer-salt complex method. The obtained ZnO nanoparticles undergo surface modification via a phosphate modifier applying ultrasonication. The morphology of the modified particles is checked by SEM. And stability of the ZnO nanoparticles in aqueous dispersion is enhanced as indicated by the zeta-potential results.

High quality colloidal crystals with different architectures and their optical properties

In this present work high quality PMMA opals with different sphere sizes, silica opals from large size spheres, multilayer opals, and inverse opals were fabricated. Highly monodisperse PMMA spheres were synthesized by surfactant-free emulsion polymerization (polydispersity ~2%). Large-area and well-ordered PMMA crystalline films with a homogenous thickness were produced by the vertical deposition method using a drawing device. Optical experiments have confirmed the high quality of these PMMA photonic crystals, e.g., well resolved high-energy bands of the transmission and reflectance spectra of the opaline films were observed. For fabrication of high quality opaline photonic crystals from large silica spheres (diameter of 890 nm), self-assembled in patterned Si-substrates a novel technique has been developed, in which the crystallization was performed by using a drawing apparatus in combination with stirring. The achievements comprise a spatial selectivity of opal crystallization without special treatment of the wafer surface, the opal lattice was found to match the pattern precisely in width as well as depth, particularly an absence of cracks within the size of the trenches, and finally a good three-dimensional order of the opal lattice even in trenches with a complex confined geometry. Multilayer opals from opaline films with different sphere sizes or different materials were produced by sequential crystallization procedure. Studies of the transmission in triple-layer hetero-opal revealed that its optical properties cannot only be considered as the linear superposition of two independent photonic bandgaps. The remarkable interface effect is the narrowing of the transmission minima. Large-area, high-quality, and robust photonic opal replicas from silicate-based inorganic-organic hybrid polymers (ORMOCER® s) were prepared by using the template-directed method, in which a high quality PMMA opal template was infiltrated with a neat inorganic-organic ORMOCER® oligomer, which can be photopolymerized within the opaline voids leading to a fully-developed replica structure with a filling factor of nearly 100%. This opal replica is structurally homogeneous, thermally and mechanically stable and the large scale (cm2 size) replica films can be handled easily as free films with a pair of tweezers.

Latexpartikel als Trägermaterialien in der durch Postmetallocene katalysierten Ethenpolymerisation

Die vorliegende Arbeit beschäftigte sich mit der Immobilisierung von Postmetallocenen auf einem organischen Trägermaterial für die heterogene Ethenpolymerisation. Dabei konnte gezeigt werden, dass sich mit nukleophilen Gruppen funktionalisierte Latexpartikel als Trägermaterial für empfindliche Bis(phenoxyimin)titankatalysatoren eignen. Durch geschickte Kombination aus Trägermaterial, Katalysator und Cokatalysator wurde ein Katalysatorsysteme erhalten, das ultrahochmolekulares Polyethylen mit einem Molekulargewicht Mw von bis zu 7.000.000 g/mol (GPC, PS-Standard) bei einer enger Molekulargewichtsverteilung von weniger als 3 erzeugt. Die erhaltenen Produktivitäten erreichten dabei die Anforderungen an industriellen Katalysatorsystemen. Erstaunlich war, dass nukleophile Gruppen auf den Latexpartikeln, die dafür bekannt sind, dass sie den Katalysator deaktivieren können, ein wichtige Schutzfunktion für den Titankatalysator bilden. So konnte gezeigt werden, dass Pyridingruppen auf der Oberfläche der Latexpartikel als Scavenger gegen Trimethylaluminium wirken, welches ansonsten den aktiven Titankomplex zersetzen würde. An ausgewählten Systemen auf der Basis unterschiedlicher Postmetallocene und einem Metallocen für die Ethenpolymerisation wurde durch Anwendung verschiedener Methoden das Polymerisationsverhalten der Latex-geträgerten Katalysatorsysteme untersucht. Eine Methode war die so genannte Videomikroskopie, bei der in Gasphase Ethen polymerisiert wird und so das Wachstumsverhalten der Katalysatorpartikel analysiert werden kann. In Kombination mit einer kinetischen Kontrolle des Monomerumsatzes in Suspensionspolymerisation, konnte gezeigt werden, dass die auf Latexpartikel geträgerten Katalysatorsysteme ein anderes Polymerisationsverhalten besitzen wie in der Literatur beschriebene Silica-geträgerte Katalysatoren. Dies kann auf die unterschiedliche Beschaffenheit des Trägermaterials zurückgeführt werden. Während das harte Silica-Material Monomer nur in den Poren aufnimmt und so rasch nach Beginn der Polymerisation in eine diffusionskontrollierte Polymerisation übergeht, quillt das organische Trägermaterial mit dem Monomeren an und kann den aktiven Katalysator damit bedienen bis weiteres Monomer von außen in das Katalysatorpartikel nach diffundiert ist. Durch die weiche Beschaffenheit der organischen Latexpartikel kann das entstehende Polymer das Katalysatorpartikel außerdem leicht auseinandertreiben werden. Die Polymerisation kann so im ganzen Katalysatorpartikel beginnen, während das Silica-Trägermaterial nur langsam von außen nach innen fragmentieren kann.

Functional thin films fabricated by plasma polymerization and their biological applications

Plasma polymerization technique is widely accepted as an effective and simple method for the preparation of functional thin films. By careful choice of precursors and deposition parameters, plasma polymers bearing various functional groups could be easily obtained. In this work, I explored the deposition of four kinds of plasma polymerised functional thin films, including the protein-resistant coatings, the thermosensitive coatings, as well as, the coatings bearing amine or epoxide groups. The deposited plasma polymers were characterized by various techniques, such as X-ray photoelectron spectroscopy, atom force microscopy, Fourier transform infrared spectroscopy, surface plasmon resonance spectroscopy, optical waveguide spectroscopy, and so on. As expected, high retention of various functional groups could be achieved either at low plasma input power or at low duty cycle (duty cycle = Ton/(Ton+Toff)). The deposited functional thin films were found to contain some soluble materials, which could be removed simply by extraction treatment. Besides the thermosentive plasma polymer (see Chapter 9), other plasma polymers were used for developing DNA sensors. DNA sensing in this study was achieved using surface plasmon enhanced fluorescence spectroscopy. The nonfouling thin films (i.e., ppEO2, plasma polymerization of di(ethylene glycol) monovinyl ether) were used to make a multilayer protein-resistant DNA sensor (see Chapter 5). The resulted DNA sensors show good anti-fouling properties towards either BSA or fibrinogen. This sensor was successfully employed to discriminate different DNA sequences from protein-containing sample solutions. In Chapter 6, I investigated the immobilization of DNA probes onto the plasma polymerized epoxide surfaces (i.e., ppGMA, plasma polymerization of glycidyl methacrylate). The ppGMA prepared at a low duty cycle showed good reactivity with amine-modified DNA probes in a mild basic environment. A DNA sensor based on the ppGMA was successfully used to distinguish different DNA sequences. While most DNA detection systems rely on the immobilization of DNA probes onto sensor surfaces, a new homogeneous DNA detection method was demonstrated in Chapter 8. The labeled PNA serves not only as the DNA catcher recognizing a particular target DNA, but also as a fluorescent indicator. Plasma polymerized allylamine (ppAA) films were used here to provide a positively charged surface.

Modeling of complex chemical reactions and macromolecular orientation phenomena in confined geometries

The cooperative motion algorithm was applied on the molecular simulation of complex chemical reactions and macromolecular orientation phenomena in confined geometries. First, we investigated the case of equilibrium step-growth polymerization in lamellae, pores and droplets. In such systems, confinement was quantified as the area/volume ratio. Results showed that, as confinement increases, polymerization becomes slower and the average molecular weight (MW) at equilibrium decreases. This is caused by the sterical hindrance imposed by the walls since chain growth reactions in their close vicinity have less realization possibilities. For reactions inside droplets at surfaces, contact angles usually increased after polymerization to compensate conformation restrictions imposed by confinement upon growing chains. In a second investigation, we considered monodisperse and chemically inert chains and focused on the effect of confinement on chain orientation. Simulations of thin polymer films showed that chains are preferably oriented parallel to the surface. Orientation increases as MW increases or as film thickness d decreases, in qualitative agreement with experiments with low MW polystyrene. It is demonstrated that the orientation of simulated chains results from a size effect, being a function of the ratio between chain end-to-end distance and d. This study was complemented by experiments with thin films of pi-conjugated polymers like MEH-PPV. Anisotropic refractive index measurements were used to analyze chain orientation. With increasing MW, orientation is enhanced. However, for MEH-PPV, orientation does not depend on d even at thicknesses much larger than the chain contour length. This contradiction with simulations was discussed by considering additional causes for orientation, for instance the appearance of nematic-like ordering in polymer films. In another investigation, we simulated droplet evaporation at soluble surfaces and reproduced the formation of wells surrounded by ringlike deposits at the surface, as observed experimentally. In our simulations, swollen substrate particles migrate to the border of the droplet to minimize the contact between solvent and vacuum, which costs the most energy. Deposit formation in the beginning of evaporation results in pinning of the droplet. When polymer chains at the substrate surface have strong uniaxial orientation, the resulting pattern is no longer similar to a ring but to a pair of half-moons. In a final stage, as an extension for the model developed for polymerization in nanoreactors, we studied the effect of geometrical confinement on a hypothetical oscillating reaction following the mechanism of the so called periodically forced Brusselator. It was shown that a reaction which is chaotic in the bulk may be driven to periodicity by confinement and vice-versa, opening new perspectives for chaos control.

Thermal fluctuations and boundary conditions in the lattice Boltzmann method

The lattice Boltzmann method is a popular approach for simulating hydrodynamic interactions in soft matter and complex fluids. The solvent is represented on a discrete lattice whose nodes are populated by particle distributions that propagate on the discrete links between the nodes and undergo local collisions. On large length and time scales, the microdynamics leads to a hydrodynamic flow field that satisfies the Navier-Stokes equation. In this thesis, several extensions to the lattice Boltzmann method are developed. In complex fluids, for example suspensions, Brownian motion of the solutes is of paramount importance. However, it can not be simulated with the original lattice Boltzmann method because the dynamics is completely deterministic. It is possible, though, to introduce thermal fluctuations in order to reproduce the equations of fluctuating hydrodynamics. In this work, a generalized lattice gas model is used to systematically derive the fluctuating lattice Boltzmann equation from statistical mechanics principles. The stochastic part of the dynamics is interpreted as a Monte Carlo process, which is then required to satisfy the condition of detailed balance. This leads to an expression for the thermal fluctuations which implies that it is essential to thermalize all degrees of freedom of the system, including the kinetic modes. The new formalism guarantees that the fluctuating lattice Boltzmann equation is simultaneously consistent with both fluctuating hydrodynamics and statistical mechanics. This establishes a foundation for future extensions, such as the treatment of multi-phase and thermal flows. An important range of applications for the lattice Boltzmann method is formed by microfluidics. Fostered by the "lab-on-a-chip" paradigm, there is an increasing need for computer simulations which are able to complement the achievements of theory and experiment. Microfluidic systems are characterized by a large surface-to-volume ratio and, therefore, boundary conditions are of special relevance. On the microscale, the standard no-slip boundary condition used in hydrodynamics has to be replaced by a slip boundary condition. In this work, a boundary condition for lattice Boltzmann is constructed that allows the slip length to be tuned by a single model parameter. Furthermore, a conceptually new approach for constructing boundary conditions is explored, where the reduced symmetry at the boundary is explicitly incorporated into the lattice model. The lattice Boltzmann method is systematically extended to the reduced symmetry model. In the case of a Poiseuille flow in a plane channel, it is shown that a special choice of the collision operator is required to reproduce the correct flow profile. This systematic approach sheds light on the consequences of the reduced symmetry at the boundary and leads to a deeper understanding of boundary conditions in the lattice Boltzmann method. This can help to develop improved boundary conditions that lead to more accurate simulation results.