• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 148
  • 108
  • 38
  • 23
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 415
  • 120
  • 111
  • 105
  • 61
  • 61
  • 61
  • 53
  • 52
  • 51
  • 45
  • 45
  • 39
  • 38
  • 33
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
151

Glycosaminoglycan (GAG) functionalised electrospun poly(lactic-co-glycolic acid) (PLGA) scafffolds for the propagation and differentiation of mouse and human embryonic stem cells

Meade, Kate January 2010 (has links)
Embryonic stem (ES) cells have the capacity to form any cell type. However, their propagation and differentiation is limited by current two dimensional (2D) culture techniques which offer little flexibility in terms of surface structure and functionalisation with bioactive molecules. The aim of the current work was to produce a novel scaffold that could manipulate ES cell behaviour using both architectural and biological cues. Electrospinning is a flexible technique that creates nonwoven meshes that mimic the fibrous architecture of the ECM. Initial work focused on investigating the suitability of electrospun poly(lactic-co-glycolic acid) (PLGA) meshes for 2D and three dimensional (3D) culture of mouse ES cells, with the hypothesis that the fibrous architecture would assist in maintaining pluripotency. The study also sought to functionalise the scaffolds with biologically active molecules. Heparan sulphate proteoglycans (HSPGs) reside at the cell surface and within the ECM where they mediate growth factor binding, assist cell attachment and stabilise the ECM. Furthermore, ES cells modulate their own microenvironment by controlling the composition of heparan sulphate (HS), regulating the binding of growth factors such as fibroblast growth factor (FGF) family members. Therefore, we aimed to immobilise HS and heparin (a highly sulphated structural analogue of HS) on the fibre surface in a form that was freely accessible for protein/cell interactions and that retained its biological activity. Electrospinning parameters were optimised to produce microfibre electrospun meshes with an average fibre diameter of 570nm. Cell morphology, proliferation and pluripotency were monitored using an Oct4-GFP reporter cell line and results compared with flat spin coated films. To investigate the potential for 3D culture, spinning parameters were altered to increase fibre diameter to >3micro metre with infiltration assessed using pro-migratory E-cadherin-/- ES cells. Scaffolds were coated with plasma polymerised allylamine (ppAm) to enable non-covalent immobilisation of HS/heparin. Ligand binding assays with the link module of TSG-6 and anti-heparin/HS antibodies were used to probe HS/heparin presentation on the fibre surface. The biological activity of the immobilised HS/heparin was analysed by testing the ability of coated scaffolds to rescue the neural differentiation capacity HS deficient EXT1-/- ES cells. Finally, human ES cells were cultured on the surface of ppAm scaffolds +/- HS in both unconditioned and mouse embryonic fibroblast (MEF) conditioned media for 5 days. Both microfibre meshes and flat spin coated films supported the attachment, growth and pluripotency of mouse ES cells. Cells adopted distinct morphologies, with mouse ES cells aggregating in rounded colonies on microfibre scaffolds and demonstrating increased spreading on spin coated films. Fibres >3micro metre created a thicker mesh with potential for 3D culture supporting the infiltration of E-cadherin-/- ES cells. ppAm enabled non-covalent immobilisation of HS/heparin in a form that was free to participate in protein interactions and which presented essential sulphation motifs within the HS/heparin chains. Bound HS was biologically active and functioned in synchrony with FGF4 to enhance neural differentiation of EXT1-/- ES cells. The constructs also supported the attachment and growth of human ES cells, with HS functionalised scaffolds demonstrating a slight increase in compatibility during culture in unconditioned media. The successful functionalisation of electrospun meshes with HS/heparin creates a highly versatile scaffold for ES cell culture and differentiation. The architecture of the meshes can be manipulated to either serve as a fibrous substrate for maintenance of pluripotency or support the formation of complex cell interactions present in vivo. The immobilisation of HS provides an extra dimension of versatility, as the scaffold can be tailored with specific HS species, potentially enabling the differential regulation of growth factor binding.
152

New main group and rare earth ring-opening polymerisation catalysts

Core, Bryony A. January 2015 (has links)
This Thesis describes the synthesis and characterisation of new Group 2, Group 3 and lanthanide amide, alkyl, halide, borohydride and alkoxide complexes, and their uses as catalysts for the living ROP and immortal ring-opening polymerisation (iROP) of rac-, L, D- and meso-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 and a literature review are also given. <strong>Chapter Two</strong> describes the synthesis and characterisation of a new series of magnesium and zinc amide, alkyl, halide, borohydride and alkoxide complexes supported by a carbazole-bis(dimethyloxazoline) ligand. Their activities towards the ROP of rac-, L- and meso-lactide are presented. Detailed mechanistic studies using spectroscopic techniques are discussed and a new mechanism is proposed. <strong>Chapter Three</strong> describes the synthesis and characterisation of a new series of calcium, strontium, yttrium, lanthanum and samarium amide, alkyl, halide, borohydride and alkoxide complexes supported by a carbazole-bis(dimethyloxazoline) ligand. Their activities towards the ROP of rac-, L- and meso-lactide are presented. Detailed mechanistic studies using spectroscopic techniques are discussed. <strong>Chapter Four</strong> describes the synthesis and characterisation of a new series of magnesium, calcium, strontium, yttrium, lanthanum and samarium amide, halide and borohydride complexes supported by a chiral carbazole-bis(isopropyloxazoline) ligand. Their activities towards the ROP of rac-, L-, D- and meso-lactide are presented. <strong>Chapter Five</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.
153

Synthese anorganisch-organischer Polyfurfurylalkohol-Nanokomposite durch die Zwillingspolymerisation: Synthese anorganisch-organischer Polyfurfurylalkohol-Nanokompositedurch die Zwillingspolymerisation

Grund, Silke 06 August 2010 (has links)
In der vorliegenden Arbeit wird die kationische Polymerisation neuer Furanmonomere beschrieben, die zu anorganisch-organischen Nanokompositen führt. Die kationische Polymerisation des Tetrafurfuryloxysilans steht dabei im Vordergrund. Ausgehend von den synthetisierten Kompositen wird die Herstellung von anorganischen Oxiden durch thermische Oxidation und von Kohlenstoffmaterialien durch thermische Behandlung in Schutzgasatmosphäre beschrieben. Die Charakterisierung der Komposite, Oxide und Kohlenstoffmaterialien erfolgt mittels Festkörper-NMR-Spektroskopie, Röntgenbeugung und Elektronenmikroskopie. Das Prinzip der neu entdeckten Zwillingspolymerisation wird vorgestellt und anhand verschiedener Beispiele auf seine weitere Anwendbarkeit zur Synthese anorganisch-organischer Kompositmaterialien überprüft.
154

Synthesis and characterization of stimuli-responsive microgels based on poly(glycidol)block copolymers

Mendrek, Sebastian 05 April 2006 (has links)
New water soluble, attainable to ATRP polymerization Cl-terminated poly(glycidol) macroinitiators were prepared by modification of (Omega)-hydroxyl group of poly(glycidol acetal) using 2-chloropropionyl chloride fallowed by selective acidic deprotection of acetal groups. The obtained macroinitiators of different molar masses were successfully employed in ATRP of NIPAM and 4VP to give well-defined stimuli sensitive block copolymers of targeted molar ratio of blocks. The results obtained from light scattering methods showed formation of stable aggregates upon stimuli (pH or temperature) by all the obtained polymers. Additionally, photocrosslinkable block copolymers of glycidol and NIPAM having incorporated moieties of chromophore (2-(dimethyl maleinimido)-N-ethyl-acryl amide) were prepared using macroinitiator technique and used to synthesis of temperature sensitive microgels. Conjunction points have been successfully formed by UV irradiation of polymer water solution above cloud point. The influence of such parameters like block ratio, block length, amount of chromophore, concentration, irradiation time, temperature and heating rate on the properties of obtained microgels was investigated. The obtained core-shell structures were stable under critical conditions and showed continuous volume phase separation process upon increase of temperature, fully reversible and reproducible (no hysteresis effect). Thus, the proposed method not only gave the opportunity to control size or swelling degree of microgels, but also diminished gradient in crosslinking density (random chromophore distribution in polymer backbone), improved colloid stability (poly(glycidol) shell) and completely eliminated additives (surfactants, initiators, stabilizers).
155

Development of an Expancel Product through Optimisation of Polymer Composition and the Suspension Stabilising System / Utveckling av en Expancel-produkt genom optimering av polymersammansättning och stabilisering av suspensionen

Berggren, Frida January 2014 (has links)
Thermally expandable microspheres are spherical particles around 5-­‐40 µm in size, consisting of a polymeric shell in which a blowing agent has been encapsulated. The microspheres are expanded upon heating, resulting in a particularly low density. Microspheres are therefore suitable to use as light weight filler or as foaming agent. AkzoNobel is world leading in the production of expandable microspheres, which are commercialised under the name Expancel. Sustainability is a great focus at AkzoNobel and two issues that AkzoNobel works with today is to develop products free from chlorine and Me1. The aim with this thesis has been to investigate whether it is possible to produce microspheres free from these chemicals and to see if they can be a more sustainable alternative to one of the existing Expancel grades. In this study, the microspheres have been produced through free radical suspension polymerisation and analysed by measuring mainly the particle size and expansion properties. The polymeric shell was composed of the monomers acrylonitrile, methacrylonitrile, and methyl acrylate. The main focus has been to evaluate the silica-­‐based stabilisation system, which stabilise the monomer droplets during the suspension polymerisation. The stabilisation is possible due to the formation of silica flocs that is adsorbed on the surface of the droplets. It has been investigating how different parameters, e.g. amount of stabiliser or mixing procedure, affects the formation of silica flocs and the stabilisation of monomer droplets. For the silica-­‐based system, it was found that the mixing order, stirring rate, and amount of stabilisers affect the formation of flocs. It was also seen that the amount of stabiliser affect the stabilisation of droplets, and that some stabilisers is more significant than others. Microspheres without chlorine and Me1 have successfully been produced in laboratory scale (50 mL and 1 L). The expansion and size of the microspheres produced in this study was relatively similar to one of the existing Expancel grades. However, the reproducibility of polymerisations in 1 litre reactors has been poor. / Termiskt expanderbara mikrosfärer är sfäriska partiklar, ca 5-­‐40 µm i diameter, som består av ett polymerskal som innesluter en drivgas. Mikrosfärerna expanderar när de utsätts för värme och erhåller då en mycket låg densitet. De är därför lämpliga att använda som fyllmedel då låg vikt är önskvärt eller som skummedel. AkzoNobel är världsledande inom produktion av expanderbara mikrosfärer, som marknadsförs under namnet Expancel. Hållbar utveckling är en viktig fråga för AkzoNobel och två problem som de står inför idag är att utveckla produkter fria från klor och Me1. Målet med detta examensarbete har varit att undersöka om det är möjligt att framställa mikrosfärer fria från dessa kemikalier och om de framtagna mikrosfärerna skulle kunna vare ett hållbarare alternativ till en av de befintliga Expancel-­‐ produkterna. I den här studien har mikrosfärerna framställts genom suspensionspolymerisation som initierats av fria radikaler och de har analyserats främst genom att mäta partikelstorlek och expansionsegenskaper. Polymerskalet bestod av monomererna akrylnitril, metakrylnitril och metylakrylat. I det här arbetet har det viktigaste varit att utvärdera det silikabaserade stabiliseringssystemet som stabiliserar monomerdropparna vid polymerisationen. Stabiliseringen är möjlig eftersom silika bildar flockar som adsorberar på ytan av monomerdropparna. Olika parametrar, exempelvis mängd stabiliseringsmedel och satsningsförfarande, har därför varierats för att undersöka vilken effekt det får på flockningen av silika och stabiliseringen av monomerdroppar. Satsningsordning och omrörningshastiget för stabiliseringssystemet samt mängd stabiliseringsmedel är några av de faktorer som påverkar bildningen av flockar. Det konstaterades även att mängd stabiliseringsmedel påverkar stabiliseringen utav monomerdropparna. Fulländade mikrosfärer utan klor och Me1 har framställts i laboratorieskala (50 mL och 1 L) och partikelstorleken samt expansionsegenskaper är jämförbara med en av Expancels nuvarande produkter. Dock har reproducerbarheten i 1 litersskala varit otillfredsställande.
156

Untersuchungen zu photovernetzbaren und biokompatiblen (Hybrid-)Polymeren / Investigations of photo-curable and biocompatible (hybrid) polymers

Beyer, Matthias January 2013 (has links) (PDF)
Die Arbeit beschäftigte sich mit Untersuchungen zu photovernetzbaren und –strukturierbaren (Hybrid-)Polymeren, um Grundlagen für die Herstellung von Trägergerüststrukturen (Scaffolds) auf Basis photovernetzbarer (Hybrid-)Polymere zu legen und damit in der Zukunft patientenindividuelle medizinische Werkstücke, die beliebig durch Zwei-Photonen-Absorptionsprozesse in drei Dimensionen strukturierbar sind, für die Regenerative Medizin zu ermöglichen. Dafür wurden zunächst die zum Teil in der Literatur unbekannten unterschiedlichen Monomere Acr-1, MAcr-2, Acr-3, MAcr-4 und DiMAcr-5 synthetisiert. Dabei handelt es sich um einfache und gut vergleichbare organische (Meth-)Acrylat-Monomere, die mono- bzw. difunktional in ihren photochemisch reaktiven Gruppen sind. Die synthetisierten organischen Monomere Acr-3, MAcr-4 und DiMAcr-5 wurden in verschiedenen Verhältnissen mit dem anorganisch-organischen Methacrylat-basierten Hybridpolymers ORMOCER® I kombiniert. Die (Co-)Polymerisation der unterschiedlichen Formulierungen wurde in situ mittels UV-DSC-Untersuchung verfolgt. Dabei wurden bei diesen Untersuchungen zum Teil deutliche Unterschiede im Reaktionsverlauf der einzelnen Materialformulierungen festgestellt. So konnten zum Beispiel bei Monomermischungen ein schnellerer Polymerisationsverlauf sowie eine höhere maximale Polymerisationsrate als bei den jeweiligen Einzelkomponenten beobachtet werden (Synergieeffekt). Diese Beobachtungen wurden anhand der Monomerstruktur (unterschiedliche Diffusionsfähigkeiten im vergelten, aber noch nicht erstarrten System durch Mono- bzw. Difunktionalität) und der Art der funktionellen Gruppe (Acrylat- bzw. Methacrylatgruppe) erklärt. Weiterhin wurden der Einfluss des verwendeten Photoinitiators und dessen eingesetzte Konzentration auf die photochemisch-induzierte Copolymerisation eines ausgewählten Systems beleuchtet. Dazu wurden verschiedene Einflussfaktoren der Initiation betrachtet. Neben der eingesetzten Initiatorkonzentration spielen auch die Absorptionseigenschaften, die umgebende Matrix und die Initiatoreffizienz eine große Rolle für den Reaktionsverlauf der photochemischen Vernetzung. Weiterhin wurden die Photoinitiatoren in unterschiedlichen Konzentrationen eingesetzt, um die dadurch induzierte Veränderung des Reaktionsverlaufs zu betrachten. Aus den Einflüssen auf die Reaktionsverläufe konnte geschlossen werden, dass diese sowie auch die maximale Polymerisationsrate RP,max und damit die Reaktionskinetik nicht in jedem Fall linear mit der Initiatorkonzentration zunehmen muss. Erste generelle 2PP-Strukturierungen wurden zudem an ausgewählten Material-formulierungen durchgeführt. Dabei zeigte sich, dass alle Formulierungen bei bestimmten Parameterkombinationen aus Laserleistung und Schreibgeschwindigkeit mittels 2PP strukturiert werden konnten. Außerdem wurden bei den verschiedenen Formulierungen bei gleicher Parameterkombination unterschiedliche Strukturbreiten und damit erstmalig unterschiedliche Strukturvolumina beobachtet. Diese unterschiedlichen Volumina konnten erstmalig mit den unterschiedlichen Reaktionsverläufen der Materialformulierungen korreliert werden. Dabei zeigte sich, dass das chemische Wechselwirkungsvolumen von der Funktionalität der eingesetzten Materialkomponenten abhängig ist, da davon der Grad an Quervernetzung abhängt, der bestimmt, ob ausreichend vernetzte Voxel und Strukturen entstehen, die durch einen Entwicklungsschritt nicht mehr entfernt werden. Im zweiten Teil der Arbeit wurde ein biokompatibles und photostrukturierbares Hybridpolymer (RENACER® MB-I) entwickelt, welches mittels 2PP strukturiert werden konnte, was anhand kleiner wie auch großer Scaffolds mit dem Material demonstriert wurde. Dazu wurde das kommerziell erhältliche Alkoxysilan-Molekül O-(Methacryloxyethyl)-N-(triethoxysilylpropyl)urethan als Precursor verwendet. Durch eine bewusst unvollständige Hydrolyse- und Kondensationsreaktion konnte aus dem Precursorsilan ein Hybridpolymerharz hergestellt werden, welches anorganisch vorverknüpft war. Weiterhin wies es sowohl als Volumenpolymer, als auch in Form von Scaffold-Strukturen eine sehr gute Biokompatibilität auf. Um zu untersuchen, ob die im Hybridpolymer enthaltenen prinzipiell degradierbaren Gruppen unter physiologischen Bedingungen tatsächlich degradieren und Teile aus dem Polymerverband herausgelöst werden können, wurde ein selbstentwickeltes Verfahren für stationäre Degradations-untersuchungen in phosphat-gepufferter Saline (PBS, pH = 7,4) verwendet. Die durch die photochemische Polymerisation neu entstandenen Ketten besaßen ihrer Natur gemäß keine hydrolysierbaren Einheiten, weshalb das Hybridpolymer nicht vollständig degradieren kann. Es konnte jedoch ein prinzipieller Zugang zu Gerüstträgerstrukturen auf Basis photovernetzbarer Polymere für die Regenerative Medizin geschaffen werden. / The objective was the investigation of photo-curable and patternable (hybrid) polymers for applications in regenerative medicine, in order to explore basic principles for scaffold fabrication by two-photon polymerization. This would enable patient-individual medical implants. As model systems for subsequent investigations, the monomers Acr-1, MAcr-2, Acr-3, MAcr-4, and DiMAcr-5 were synthesized. These compounds are well comparable organic (meth)acrylate monomers with a functionality of one and two, respectively. The monomers Acr-3, MAcr-4, and DiMAcr-5 were combined with a well-known methacrylate-based inorganic-organic hybrid polymer ORMOCER® I in different molar ratios. After preparation of the monomers and their formulations with ORMOCER® I introducing defined amounts of photoinitiator Irgacure® 369 into the material systems, the materials’ reaction was monitored in situ by photo-DSC investigations. In particular, the effect of the different monomer ratios on the copolymerization behavior was studied in more detail. A higher maximum polymerization rate and, therewith, a higher reaction speed was found for all formulations of monomer mixtures in contrast to the corresponding individual monomers (synergy effect). Moreover, by comparing the various organic monomers, considerable differences could be identified in between acrylates and methacrylates as well as for the mono- and difunctional species. These effects were explained by means of the type of their photochemically organically cross-linkable functional groups and thus their resulting reactivity as well as by the monomer structure and functionality itself, resulting in different diffusion abilities of mono-, oligo- and polymeric species within gelled systems. Furthermore, the influence of several photoinitiators and the initiator concentration on the photochemically induced copolymerization was investigated. Besides the initiator concentration, also the initiators’ absorption properties, the resin matrix and the initiators’ efficiency play an important role for the reaction profile of the photochemical cross-linking. All different photoinitiators were introduced into the model system in three different concentrations to explore the induced alterations on the reaction profile. For some of the investigated initiators, the maximum polymerization rate RP,max and, therewith, the overall reaction kinetics increased with increasing photoinitiator concentration, but for other initiators, the maximum polymerization rate RP,max was lowered at increased initiator concentrations. Thus, a general relationship between the photoinitiator concentration and the maximum polymerization rate RP,max could not be identified. First structures were generated out of selected mixtures by two-photon polymerization in order to demonstrate the novel materials’ ability of being patterned in three dimensions. Three dimensional structures were generated with specific parameter combinations of laser power and writing speed, whereas each parameter set corresponds to an individual exposure dose deposited in the materials’ volume. In particular, different structure widths were observed for different material formulations fabricated with the same parameter sets. Thus, it was possible for the first time to experimentally observe different chemical interaction volumes. These interaction volumes were correlated to the different reaction profiles of the material formulations, which were received via 1PP photo-DSC measurements. It was shown that the structure volume depends on the functionality of the employed monomers, because their degree of cross-linking depends on their functionality. The degree of cross-linking which results upon polymerization determines, whether a structure maintains stable during the subsequent development process. In the second part of this work, a biocompatible and photo-patternable hybrid material was developed. Commercially available O-(methacryloxyethyl)-N-(triethoxysilylpropyl)-urethane was chosen for an intentional incomplete hydrolysis and condensation reaction in order to receive a RENACER® resin, which includes functional groups for subsequent organic cross-linking. This material showed a very good patterning performance, which was demonstrated by a series of structures and scaffolds. The material yields a good biocompatibility. In order to investigate, whether the hydrolysable functional groups within the hybrid polymer actually degrade under physiological conditions, a procedure routine for stationary degradation studies in phosphate-buffered saline (PBS) was developed. The carbon chain generated through photochemical cross-linking, has no hydrolyzable groups and naturally cannot be degraded, resulting in a hybrid polymer which is not completely degradable. However, a principal access to scaffolds for regenerative medicine on the basis of photo-curable polymers was accomplished which was the purpose of this work.
157

Synthese, Untersuchung und Polymerisation neuartiger Sandwichkomplexe / Synthesis, Investigation and Polymerization of new Sandwich Compounds

Dück, Klaus January 2015 (has links) (PDF)
In dieser Dissertation werden die Ergebnisse zur Synthese und Polymerisation gespannter Manganoarenophane vorgestellt. Weiterhin wird die Reaktivität von Bis(benzol)titan und die Synthese von ansa-Verbindungen dieses Komplexes, sowie Untersuchungen zu deren Eigenschaften beschrieben. Zum Vergeleich wird auch der Komplex Bis(mesityl)titan untersucht. Die Polymerisation von zinnverbrückten, gespannten Vanadium-Sandwichkomplexen und die Untersuchungen der paramagnetischen Eigenschaften ist ebenso in dieser Dissertationsschrift beschrieben. Zusätzlich wird die Synthese heteroleptischer Sandwichkomplexe des Scandiums und Yttriums dargestellt, sowie deren Ringsubstitution. Die Vorarbeiten zur Synthese heteroleptischer Sandwichkomplexe der Lanthanoide bildet ebenso einen Bestandteil dieser Schrift, wie die Synthese von ansa-Komplexen des Thorocens und Uranocens via flytrap-Methode. / This Dissertation presents the results of the synthesis and polymerization of strained Manganoarenophanes. Furthermore the reactivity of bis(benzene)titanium and the synthesis of its ansa-compounds, as well as property investigations are shown. Comparative studies of the complex bis(mesityl)titanium are also described. The polymerization of tin-bridged, strained Vanadium sandwich compounds and the investigations of their paramagnetic properties are also described within this dissertation. Additionally the synthesis of heteroleptic sandwich complexes of Scandium and Yttrium and their ring substitution are presented. First results concerning the synthesis of heteroleptic sandwich complexes of the Lanthanides are a part of this work as well as the synthesis of ansa-compounds of Thorocene and Uranocene via flytrap-method.
158

ATRP Grafting from Gel Coated Microspheres

Robinson, Erica 08 1900 (has links)
<p> Swellable microspheres prepared by the precipitation polymerisation of divinylbenzene-80 (DVB-80) and 2-hydroxyethyl methacrylate (HEMA), in a solvent mixture of methyl ethyl ketone (MEK) and heptane, were functionalised with 2bromopropionyl bromide, and 2-bromoisobutyryl bromide to prepare Atom Transfer Radical Polymerisation (ATRP) initiators. </p> <p> Methyl acrylate (MA) and methyl methacrylate (MMA) were grafted from the microspheres using CuBr and either 4,4'-dinonyl-2,2'-dipyridyl (dNbipy), or N,N,N',N",N"-pentamethyldiethylenetriamine (PMDET A) ligands. The morphology of the grafted microspheres was studied using electron microscopy (ESEM and TEM) and x-ray microspectroscopy. Adding equimolar sacrificial initiator resulted in improved control over the grafting and gave grafted and soluble polymer, with narrow polydispersity (PDI) and number average molecular weight (Mn) close to expected values. </p> <p> Base catalysed transesterification was used to cleave the grafted polymer. It was found that adding free initiator permits grafting from within lightly cross-linked gels to be carried out with good control over Mn and PDI. </p> / Thesis / Master of Science (MSc)
159

Controlled delivery of cytokine growth factors mediated by core-shell particles with poly(acrylamidomethylpropane sulphonate) shells

Platt, L., Kelly, L., Rimmer, Stephen 28 November 2013 (has links)
No / Core-shell particles have been prepared by surfactant-free emulsion polymerisations of butyl methacrylate in the presence of either linear or highly branched poly(acrylamidomethylpropane sulphonate)s (L-PAMPS or HB-PAMPS) with dithioate end groups: using a "shell-first" approach. In this method the water soluble PAMPS shells were anchored to the cores by polymerisation of BMA from the chain ends. The linear PAMPS produced non-crosslinked poly(AMPS-BMA) particles but the multiple chain ends of the highly branched PAMPS led to crosslinked particles. The particles were loaded with vascular endothelial growth factor or platelet derived growth factor, both of which are cytokines that are known to be important in the production of new blood vessels. The release of the growth factors was shown to be controlled by the architecture of the shell and we propose a mechanism that involves both ionic interaction of the PAMPS with the heparin-binding domains of the growth factors and size exclusion mediated diffusion.
160

Exploiting nucleobase-containing materials : from monomers to complex morphologies using RAFT dispersion polymerization

Kang, Y., Pitto-Barry, Anaïs, Willcock, H., Quan, W-D., Kirby, N., Sanchez, A.M., O'Reilly, R.K. 09 November 2014 (has links)
Yes / The synthesis of nucleobase-containing polymers was successfully performed by RAFT dispersion polymerization in both chloroform and 1,4-dioxane and self-assembly was induced by the polymerizations. A combination of scattering and microscopy techniques were used to characterize the morphologies. It is found that the morphologies of self-assembled nucleobase-containing polymers are solvent dependent. By varying the DP of the core-forming block, only spherical micelles with internal structures were obtained in chloroform when using only adenine-containing methacrylate or a mixture of adenine-containing methacrylate and thymine-containing methacrylate as monomers. However, higher order structures and morphology transitions were observed in 1,4-dioxane. A sphere-rod-lamella-twisted bilayer transition was observed in this study. Moreover, the kinetics of the dispersion polymerizations were studied in both solvents, suggesting a different formation mechanism in these systems. / University of Warwick, Swiss National Science Foundation, EPSRC, Birmingham Science City, Advanatfe West Midlands (AWM), European Regional Development Fund (ERDF), Science City Research Alliance, Higher Education Funding Council for England (HEFCE)

Page generated in 0.1068 seconds