Techn. Hochsch., Diss., 2002--Aachen.

Multifunctional monomers on the basis of acryl- and methacryl derivatives were synthesized and different protective groups were used. After polymerization the protective groups were removed by different methods. Various initiators for the NMP of the monomers were synthesized and the reaction conditions were optimized. The results showed that NMP was not a suitable method for multifunctional acryl- and methacryl derivatives to achieve well-defined homopolymers, although it was successful for control of polymerization of styrene and block copolymerization of multifunctional acryl- and methacryl derivatives with alkoxyamine terminated polystyrene. The ATRP of multifunctional acrylates and methacrylates has been successfully performed, as well as the block copolymerization of multifunctional acrylates and methacrylates. Relatively low polydispersities of the corresponding polymers (PD=1.18-1.36) and reasonably high rates of polymerization could be achieved when Me6TREN and PMDETA were used as ligands. However, the ATRP of multifunctional acrylamides and methacrylamides failed. The RAFT-polymerization of styrene, acrylamide and acrylate using BDTB as a CTA and AIBN as an initiator afforded polymers with narrow molecular weight distribution (PD=1.13-1.26). A kinetic investigation and the further synthesis of block copolymers using dithioester-terminated homopolymers as macroCTAs showed that the RAFT polymerization of acrylamide M9b proceeded in a living manner. However, BDTB does not control the reaction of methacrylic monomers, such as methacrylates and methacrylamides. The bulk phase behavior of the block copolymers were examined by means of DSC and the surface behaviors of block copolymers as thin layers were examined with AFM. Two-phase transitions in the block copolymers were observed clearly by DSC, indicative of the appearance of phase separations, which were seen in an AFM image. In conclusion, multifunctional acryl- and methacryl derivatives failed to achieve well-defined homopolymers by NMP. However, this method was successful for block copolymerization of multifunctional acryl- and methacryl derivatives with alkoxyamine terminated polystyrene. Multifunctional acrylates and methacrylates were successfully homopolymerized and block copolymerized by ATRP. Multifunctional acrylates and acrylamides were suitable for homopolymerization and block copolymerization by the RAFT process. Thus far, it is difficult to homopolymerize multifunctional methacrylamides in controlled way.

The synthesis and polymerization of macromonomers containing a polymerizable styrene head group and a tail of ethylene oxide derivatives of different character were investigated. The synthesis of macromonomers was based on living anionic polymerization of oxiranes. Two monomers were used: 1-ethoxyethyl glycidyl ether (glycidol acetal), which after hydrolysis forms hydrophilic glycidol blocks and glycidyl phenyl ether forming hydrophobic blocks. Polymerizable double bonds were introduced by terminating the living chain with p-(chloromethyl)styrene. However, MALDI-TOF-MS end group analysis showed that all synthesized macromonomers were a mixture of the macromonomer and the non-functionalized oligomer. The degree of functionalization varied from 55 to 75 %. The obtained macromonomers showed amphiphilic properties and formed micelles in water. The determined critical micellization (CMC) concentration for poly(glycidol) macromonomer (DP = 50) was ca. 10 g/L, while the poly(glycidol) block macromonomers with hydrophobic spacer showed CMC on the level 0,7 g/L. The conventional free radical and controlled free radical polymerisation (ATRP) were used for preparation of polymacromonomers with different properties. The radical polymerization of the macromonomers was carried out in water using AVA as initiator and in the mixture of water/benzene (10/1 v/v) using AIBN. Core-shell polymers of different character and molar masses with polydispersity indices from 1,4 -3,0 were obtained. The ATRP carried out in water using PEO macroinitiator led to polymacromonomers with polydispersity indices from 1,1 to 1,3 and desiried molecular weight. In all cases the conversion of macromonomer (able to polymerization) was close to 100%. The polymerization product could easily be separated from the unable to reaction residue.

The synthesis and polymerization of macromonomers containing a polymerizable styrene head group and a tail of ethylene oxide derivatives of different character were investigated. The synthesis of macromonomers was based on living anionic polymerization of oxiranes. Two monomers were used: 1-ethoxyethyl glycidyl ether (glycidol acetal), which after hydrolysis forms hydrophilic glycidol blocks and glycidyl phenyl ether forming hydrophobic blocks. Polymerizable double bonds were introduced by terminating the living chain with p-(chloromethyl)styrene. However, MALDI-TOF-MS end group analysis showed that all synthesized macromonomers were a mixture of the macromonomer and the non-functionalized oligomer. The degree of functionalization varied from 55 to 75 %. The obtained macromonomers showed amphiphilic properties and formed micelles in water. The determined critical micellization (CMC) concentration for poly(glycidol) macromonomer (DP = 50) was ca. 10 g/L, while the poly(glycidol) block macromonomers with hydrophobic spacer showed CMC on the level 0,7 g/L. The conventional free radical and controlled free radical polymerisation (ATRP) were used for preparation of polymacromonomers with different properties. The radical polymerization of the macromonomers was carried out in water using AVA as initiator and in the mixture of water/benzene (10/1 v/v) using AIBN. Core-shell polymers of different character and molar masses with polydispersity indices from 1,4 -3,0 were obtained. The ATRP carried out in water using PEO macroinitiator led to polymacromonomers with polydispersity indices from 1,1 to 1,3 and desiried molecular weight. In all cases the conversion of macromonomer (able to polymerization) was close to 100%. The polymerization product could easily be separated from the unable to reaction residue.

This thesis describes the covalent modification of carbon electrodes with a monolayer of polymerisation initiators and the growth of polymer brushes by surface initiated atom transfer radical polymerisation (SI-ATRP). Monolayer modification was sought to preserve the underlying electrode properties and topography and to produce a well-organised layer from which the polymer brushes can be grown. This work investigated two approaches for immobilising a monolayer of polymerisation initiators. Firstly, the electrochemical grafting of protected aryl diazonium salts produced a covalently anchored monolayer of tether groups that can participate in subsequent amide coupling and click reactions, to covalently anchor the polymerisation initiator. Secondly, specific reactions between the electrode surface and appropriate polymerisation initiator derivatives have been used to covalently anchor the initiators. For most systems, electro-active ferrocene (Fc) groups were reacted with modified surfaces as model reactants to enable the electrochemical estimation of the surface concentration of the polymer initiator groups. Film thickness measurements of the ethynylaryl (Ar-Eth) monolayer were carried out using atomic force microscopy confirming a monolayer. XPS analysis confirmed the presence of bromine on most of the polymerisation initiator modified samples. Modification of surfaces with polymer brushes can introduce new surface properties, such as switchable wettability, while maintaining the underlying bulk substrate properties. This work focused on examining SI-ATRP at each of the polymerisation initiator monolayers, with the aim to identify the most promising system(s) for further investigation. Polymer brushes of poly(3-(methacryloylamino)propyl)-N,N’-dimethyl(3-sulfopropyl)-ammonium hydroxide) (PMPDSAH) were grown from initiators tethered through the aryl diazonium salts modification procedure. Redox probe voltammetry and XPS analysis indicated that the grafting from polymerisation by the copper catalysed SI-ATRP was successful. Polymer brushes of poly(methyl methacrylate) PMMA were grown from the Ar-Eth modified monolayer by three SI-ATRP procedures: a standard procedure, an electrochemically mediated SI-ATRP method and a one-pot copper catalysed azide-alkyne click (CuAAC) reaction and SI-ATRP reaction from the Ar-Eth monolayer. Redox probe voltammetry and AFM images provided evidence for the growth of polymer brushes by these three methods. The successful one-pot CuAAC/SI-ATRP reaction for simultaneous coupling of the polymerisation initiator to the surface and polymerisation is a new approach for the production of polymer brushes and it minimises the number of surface modification steps needed. This method appears most promising for further development.

No description available.

Molecularly imprinted polymers (MIPs) are a novel, promising family of porous materials with potential applications ranging from separations, chemical sensing and catalysis to drug delivery and artificial immunoassays. The unique feature of these materials is their biomimetic molecular recognition functionality. Molecular recognition is the biological phenomenon of specific, selective and strong association between a substrate and a ligand. In man made MIPs this functionality is implemented via templated synthesis protocol. MIPs are synthesized in the presence of additional template molecules which form complexes with functional monomers in the pre‐polymerization mixture. After polymerization, the template is removed, leaving cavities in the structure which are complementary in shape and interaction patterns to the template molecules. These cavities act as mimics of biological receptors and are able to recognize and rebind template molecules. Although the imprinting concept is simple in principle, synthesis of MIPs with precisely controlled characteristics and performance remains a challenging task. Composition, polymerization conditions, template removal process and application conditions all affect the properties of MIPs. The material is affected at different scales, but crucially at the microscopic level, the number, fidelity and accessibility of binding sites are dependent on all the factors mentioned. The full potential of these materials can only be achieved if researchers can control and optimize the properties of MIPs through detailed understanding of adsorption and molecular recognition processes in these materials. The objective of this work is to, using computer simulations and statistical mechanics; develop a fundamental description of MIP formation and function, and to link morphological features of the model materials to their molecular recognition capabilities. In general, molecular simulations employed in this study should allow easier and more efficient exploration of a vast number of factors influencing the behaviour of MIPs. At the heart of the approach developed in this thesis is a computational strategy that imitates all the stages of MIP formation and function. First, the model simulates the pre‐polymerization mixture, allowing the formation of template‐functional monomer complexes. (This stage is implemented via canonical Monte Carlo simulation). Complexes can have different structures, depending on the chemical nature of template and functional monomer; therefore complexes can have a range of association constants. The distribution of template‐functional monomer complexes also translates into a distribution of binding sites of different specificity after template removal. In the second stage of the process, adsorption simulations (grand canonical Monte Carlo) are performed for a variety of model MIPs prepared to assess the role of various processing conditions such as composition, density and binding sites degeneration. This strategy was first applied to a simplified description of MIP species in order to identify the minimal model capable of molecular recognition and thus shed the light on the very nature of this phenomenon. In the developed model, the molecular species are constructed from hard spheres, featuring small interaction sites on their surfaces. The bond between two interaction sites has the strength and topological features of a typical hydrogen bond. The model exhibits molecular recognition, being able to preferentially adsorb template molecules. The associations between template and functional monomers were analyzed and classified to describe the distribution of binding sites and their heterogeneity. Using this model, several experimental trends typically observed in MIP studies could be explained, such as maximum in the selectivity as a function of monomer concentration. Using this model, we were also able to explore hypothetical, alternative protocols for MIP synthesis in order to improve their performance. These include the use of alternative templates and the post‐synthetic surface modifications of MIPs. The general strategy to modelling MIP, employed in this thesis, was then applied to a more detailed description of MIPs with realistic force field potentials for all the species involved. This more elaborate model is simulated with a combination of molecular dynamics (MD) and Monte Carlo techniques. This detailed model provided a wealth of information on various types of complexes observed in the pre‐polymerization mixture. Specifically, it revealed the relative weight of different interactions in the complex and their role in the binding energy of adsorbates. These simulations also provided the comparison of the relative contribution of different types of interactions (van der Waals, Coulombic) involved in a molecular recognition process. We believe the insights gained in this work will contribute to the development of rational MIP design strategies. In the discussion of the results of the thesis we speculate on how these models can be further developed in order to generate quantitative predictions and what type of systems it would be interesting and important to investigate in the future.

The aim of this project has been to develop the field of group 4 indenyl metallocene complexes based upon highly methylated ligands. Previous studies have shown that these compounds can be extremely active ethylene polymerisation catalysts, and, as such, are of both significant academic and commercial interest <strong>Chapter One</strong> introduces metallocene chemistry, discussing developments within the field and the effects of permethylation on indenyl rings. A synopsis of the rise of the ansa-bridge is provided, in addition to highlights from recent zirconocene chemistry. A feature on olefin polymerisation is included, spanning heterogeneous catalysts, homogeneous metallocenes and post metallocenes, as well immobilised complexes and their supports. <strong>Chapter Two</strong> charts updates to syntheses of bridged and unbridged permethylindenyl ligands. The developments have allowed for their use as viable industrial procedures. <strong>Chapter Three</strong> is an account of the group 4 organometallic chemistry of the indenyl ligands from Chapter Two. Four bridged metallocenes, including rac-SBI*ZrCl₂ and meso-EBI*Zr(CH₂Ph)₂, are reported. In addition, six unbridged analogues comprising rac/meso-Ind^#<sub style='position: relative; left: -.8em;'>2</sub>MCl₂ (M = Zr, Hf) and rac/meso-Ind^#<sub style='position: relative; left: -.8em;'>2</sub>(CH₂Ph)₂ are described as well as a half-metallocene. The complexes are characterised by single crystal X-ray diffraction and variable temperature NMR spectroscopy. DFT calculations have been performed, with representations of their optimised geometries and frontier MOs given. <strong>Chapter Four</strong> describes a reliable, reproducible procedure for immobilising group 4 complexes on the surface of solid supports; in total 19 catalysts are prepared. In addition to SSMAO, two new inorganic supports (LDHMAO and Solid MAO) are utilised. The latter has never previously been described in the academic literature. These catalysts have been characterised by IR, UV/visible and solid-state NMR spectroscopy in addition to SEM imaging. Zr K-edge EXAFS experiments were conducted and exceptionally clear data are reported. <strong>Chapter Five</strong> investigates the aforementioned complexes as both solution- and slurry-phase ethylene polymerisation catalysts. Numerous parameters are tested including temperature and time dependence and all of the catalysts produce high molecular weight polymer in the range 150-300,000 daltons. The activity of rac SBI*ZrCl₂ in solution exceeds 22,500 kg_PE/mol_Zr/h/bar, and 7,500 kg_PE/molZr/h/bar immobilised on Solid MAO. meso-EBI*Zr(CH₂Ph)₂ displays double the activity of its dichloride analogue. 1-hexene co polymerisation is carried out as part of a high throughput screening study and activities in excess of 30,000 kg_PE/molZr/h/bar are reported. Scale-up polymerisation runs are also disclosed. The resultant polymer has been characterised by GPC, as well as X-ray diffraction, SEM, ¹³C NMR and IR spectroscopy. <strong>Chapter Six</strong> provides the experimental details and characterising data for the previous chapters. An Appendix consists of crystal structure data while the Electronic Appendix contains the CIFs, DFT output files and the raw polymerisation data.

This Thesis describes the synthesis and characterisation of new Group 2 tetrahydroborate, alkoxide and organohydroborate complexes and their uses as catalysts for the living ROP and immortal ring-opening polymerisation (iROP) of &epsilon;- caprolactone and rac-lactide. <strong>Chapter One</strong> introduces cyclic esters and possible mechanistic pathways leading to polyesters by ROP. Living and immortal ROP, including their kinetic characteristics are discussed. An overview of ROP from an industrial perspective is also given. <strong>Chapter Two</strong> describes the synthesis and characterisation of a new series of Group 2 tetrahydroborate complexes supported by a 3-methyl, 5-tert-butyl tris(pyrazolyl)hydroborate ligand. Their activities towards the ROP of &epsilon;-caprolactone are presented. Detailed mechanistic studies using spectroscopic techniques are discussed and a new mechanism is proposed. <strong>Chapter Three</strong> describes the ROP of rac-lactide using the Group 2 tetrahydroborate complexes introduced in Chapter Two, including their mechanistic studies. <strong>Chapter Four</strong> introduces the new immortal ROP using trialkyl borate and organoborane derivatives as chain-transfer agents (CTAs). The immortal ROP of &epsilon;- caprolactone and rac-lactide using Group 2 initiators with trialkyl borates/organoboranes as CTAs from either in situ generation or external addition is discussed. Possible immortal ROP pathways using this new class of CTAs are illustrated. <strong>Chapter Five</strong> details the synthesis and characterisation of a new series of Group 2 organohydroborate complexes. The &epsilon;-caprolactone and rac-lactide ROP activity shown by the complexes presented is discussed and compared with those obtained from the corresponding tetrahydroborate analogues. <strong>Chapter Six</strong> contains experimental details and characterising data for the new complexes reported in this Thesis. <strong>CD Appendix</strong> contains .CIF files for all the new crystallographically-characterised complexes.

Die Kompositschrumpfung während der Polymerisation führt zum Aufbau von Spannungen und somit auch zur Höckerdeformation. In extrahierten menschlichen Molaren wurden 48 MOD-Kavitäten präpariert. Die standardisierten Präparationen waren approximal 5,5 mm breit und tief, okklusal 3,5 mm breit und in den Versuchsgruppen mit flachen Kavitäten 3 mm tief, in den Versuchsgruppen mit tiefen Kavitäten, 4,5 mm tief. Untersucht wurden die Höckerdeformationen unter Verwendung der Hybridkomposite Tetric Ceram® (Vivadent) und Grandio® (Voco). Bedingt durch den unterschiedlichen Füllstoffgehalt unterschieden sich die beiden Komposite in Kontraktion und E-Modul. Neben der unterschiedlichen Kavitätentiefe wurde auch der Einfluss von zwei verschiedenen Schichttechniken auf die Deformation überprüft. Bei der herkömmlichen Dreischichttechnik wurden die approximalen Kästen mit drei horizontalen Schichten gefüllt, wobei sich die ersten beiden Schichten auf die gesamte Kavität erstreckten. Mit der dritten Schicht wurden jeweils die Randleisten modelliert. Der verbliebene okklusale Kasten wurde mit zwei diagonalen Schichten beschickt, zunächst der Bereich der Scherhöcker, abschließend der Bereich der Stützhöcker. Im Gegensatz dazu wurden bei der Schalentechnik die approximalen Wände als ganzes modelliert. Hierzu wurde eine vertikale Kompositschicht an die Matrize adaptiert. Mit zwei horizontalen Schichten wurde die Kavität bis auf einen flachen okklusalen Kasten gefüllt. Dieser wurde genau wie bei der herkömmlichen Dreischichttechnik mit zwei diagonalen Schichten beschickt. Während der Polymerisation der einzelnen Schichten wurde die bukko-linguale Höckerdeformation mit Hilfe induktiver Wegaufnehmer aufgezeichnet. Die Ergebnisse zeigen eine größere Höckerdeformation bei den Restaurationen der tiefen Kavitäten, was auf stärkere Schwächung der Zahnhartsubstanz, ungünstigeren Konfigurationsfaktor und eine größere Masse schrumpfenden Komposits zurückzuführen ist. Weiterhin löste Grandio® trotz hohem Füllstoffgehalt und der daraus resultierenden geringen Schrumpfung eine stärkere Höckerauslenkung aus als das Feinpartikelhybridkomposit Tetric Ceram® (P<0.001). Erklären lässt sich das durch das hohe E-Modul des „Nanohybridkomposits“, weshalb Schrumpfungsspannungen während der Polymerisation schlechter ausgeglichen werden und so, bei stabilem Komposit-Dentin-Verbund, voll auf die Zahnhartsubstanz übertragen werden. Schalen- und Schichttechnik sind hinsichtlich der Summe der Höckerdeformationen äquivalent. Zwar werden die Maxima der Höckerkontraktionen in unterschiedlichen Schichten während der Restauration hervorgerufen, was auf die variierenden Konfigurationsfaktoren und Kompositmassen zurückzuführen ist, auf die Gesamtkontraktion hat die Art der Schichtung jedoch keinen signifikanten Einfluss. Trotz geringerer Schrumpfung erzeugt das Komposit mit dem höheren E-Modul die stärkere Höckerdeformation, da Schrumpfungsspannungen schlechter ausgeglichen werden als bei Komposit mit niedrigerem Elastizitätsmodul. Bei der Auswahl eines geeigneten Komposits sollte also nicht alleine Wert auf die in vitro ermittelte Polymerisationskontraktion gelegt werden, sondern ebensoviel auf den C-Faktor und das E-Modul. Zusammenfassend lässt sich feststellen, dass die Spannungsentwicklung während der Polymerisation nicht nur von der Polymerisationskontraktion des Komposits, sondern auch vom Elastizitätsmodul des Komposit sowie vom C-Faktor der eingebrachten Kompositschicht beeinflusst wird. / Examination of the cusp deflection during filling 48 human molars (MOD cavities) in 8 groups. Following subjects have been tested: - two different composite Material: 1 hybridcomposite Tetric Ceram® (Vivadent) 2 nano-hybridcomposit Grandio® (Voco) - two different types of cavities: 3mm and 4,5mm deep - two different filling techniques with different configuration factors