<p>Dendrimers provide an ideal scaffold for molecular imaging and therapeutics due to their mono-disperse structure and easily modifiable core, interior, and periphery. The controlled-stepwise synthesis leads to perfect, defined architectures that can easily be modified to incorporate targeting and imaging moieties. Specifically poly (2,2-bis(hydroxymethyl)-propanoic acid) (PMPA) dendrimer structures exhibit excellent aqueous solubility, low toxicity, biocompatibility and biodegradability, which are necessary requirements for an ideal <em>in vivo</em> imaging scaffold.</p> <p>Fever of unknown origin (FUO) is a common condition involving elevated temperatures above 101°F, which goes undiagnosed after a week of investigation. The primary causes of FUO are infection and cancer, however methods of diagnosis are non-specific and quite slow. Developing a method to detect bacterial infections, and therefore rule out more severe conditions such as cancer, would be very useful in diagnosis of this condition. Approximately two thirds of infection cases in hospitals are determined to be caused by one of six pathogens known as the ESKAPE pathogens and developing a molecular imaging probe that would detect these specific pathogens would be a very useful FUO diagnostic tool.</p> <p>Siderophores are naturally occurring molecules that exhibit a high affinity for Fe³⁺, and are effective at entering bacterial cells after complexing iron. In particular, Desferal, a commercially available siderophore used for iron chelation therapy, has been successfully modified, radiolabeled, and studied as an imaging agent. Dendrimers were modified with Desferal and used to investigate the effect of multivalent display of siderophores on a single macromolecular structure.^1-3</p> <p>We herein discuss the preparation of a series of siderophore-terminated PMPA dendrimers that were radiolabeled and studied to compare bacterial uptake between a monomeric siderophore and a macromolecule displaying multiple siderophores on its periphery. To introduce Desferal to the periphery of a dendrimer, activated p-nitrophenyl carbonates were used. A series of Desferal-terminated dendrimers of generations 1-3 was synthesized in yields of 59-89 % and evaluated for suitability as an infection-imaging probe.</p> <p>The Desferal-terminated dendrimer series was evaluated for its affinity to iron(III) and gallium(III), as well as tested for steric hindrance effects at the periphery. The series was successfully radiolabeled with ⁶⁷Ga using mild conditions and <em>in vitro</em> bacterial uptake studies were performed with <em>Staphylococcus aureus</em>, one of the ESKAPE pathogens, to determine if multivalency increases bacterial uptake.</p> <p>Preliminary results indicate that the poor water solubility of the Desferal-terminated dendrimer series needs to be improved in order to increase bacterial uptake of the compounds, however viable candidates for metal chelation were successfully produced.</p> / Master of Science (MSc)

No / Flows of complex fluids need to be understood at both macroscopic and molecular scales, because it is the macroscopic response that controls the fluid behavior, but the molecular scale that ultimately gives rise to rheological and solid-state properties. Here the flow field of an entangled polymer melt through an extended contraction, typical of many polymer processes, is imaged optically and by small-angle neutron scattering. The dual-probe technique samples both the macroscopic stress field in the flow and the microscopic configuration of the polymer molecules at selected points. The results are compared with a recent "tube model" molecular theory of entangled melt flow that is able to calculate both the stress and the single-chain structure factor from first principles. The combined action of the three fundamental entangled processes of reptation, contour length fluctuation, and convective constraint release is essential to account quantitatively for the rich rheological behavior. The multiscale approach unearths a new feature: Orientation at the length scale of the entire chain decays considerably more slowly than at the smaller entanglement length.

No description available.

A series of polycarbonate-poly(butylene terephthalate) blends has been formed via melt blending in a torque rheometer. Initially polycarbonate and poly(butylene terephthalate) were blended alone to determine the extent to which the two homopolymers were able to cross-react (transesterify), and hence, how the morphology of the blends developed as a result of transesterification. Subsequently the degree of transesterification between the two homopolymers was controlled by the incorporation of an alkyl titanium catalyst, and the effect on morphological development determined. Resultant uncatalysed and catalysed materials were characterised by DSC, DMA, FTIR, microscopy, solubility studies and X-ray scattering. No evidence for direct inter-chain transesterification was seen for the uncatalysed blends. No new thermal transitions or absorptions were noted from DSC, DMA or FTIR, nor was there any evidence for phase refinement from microscopy, or variation in solubility behaviour. However, there was evidence for some degree of phase mixing from DMA damping behaviour, indicated by convolution of the PC and PBT transition peaks. Due to the lack of transesterification relatively coarse morphologies, indicative of an immiscible two phase blend, were apparent from microscopical analysis. Thermal behaviour of the uncatalysed blends showed evidence of thermal degradation above 270°C, promoting transesterification via acidolysis. As the degree of transesterification was increased (catalysed materials) the composition of the blends became increasingly complex, comprising mixtures of the homopolymers and various AB-type block copolymers of polycarbonate and poly(butylene terephthalate), with concomitant changes in their thermal behaviour. DSC and FTIR proved useful in analysing blends containing greater than 150 ppm of added catalyst, whilst DMA highlighted the subtle differences in the blends with less than 200 ppm additional titanium transesterification catalyst. Microscopical analysis provided visual evidence for the transformation in the materials morphology through progressive transesterification: the relatively coarse structure characteristic of two phase blends developing into a more refined sub-micron iv structure exhibited by blends containing a significant volume of interphase material. This morphological change was due to the formation of increasing concentrations of random block copolymers. At increasing degrees of transesterification this change in morphology was accompanied by variations in the solubility of the blends. With increasing amounts of additional catalyst up to 150 ppm, the blends became increasingly resistant to solvent (dichloromethane). Whereas above this level the blends became increasingly soluble, as copolymers of a more random nature (with increased solubility) were formed. X-ray scattering showed the pure PBT to exhibit highly reproducible crystallisation behaviour. In contrast a 50/50 blend showed a progressive reduction in the degree of crystallinity, melting and crystallisation temperatures with increasing transesterification.

No description available.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Hybrid A-B type block copolymers of polydimethylsiloxane (PDMS) and polystyrene (PS) were synthesised. Three different synthetic routes, which allowed control over polymer structure, were chosen to synthesise these block copolymers. The first technique, coupling of functional prepolymers, involved using anionic polymerisation to produce PDMS and PS functional prepolymers of controlled structure. These prepolymers were functionalised with either silane or allyl functionality and then coupled using a hydrosilylation reaction with Karstetds platinum catalyst. This technique was the least efficient in block synthesis due to the incompatibility of the disparate prepolymers. The second technique under study, sequential anionic polymerisation, gave excellent block copolymer formation with good control over the chain architecture. The final technique employed atom transfer radical polymerisation (ATRP) of styrene using a bromoisobutyrate functionalised PDMS macroinitiator. Silane functional PDMS molecules underwent a hydrosilylation reaction with allyl-2-bromo-2-methyl-propionate to produce the bromoisobutyrate functionalised polymer in excellent yields. Subsequent ATRP with styrene allowed the successful synthesis of block copolymers of controlled structure. Chromatographic systems that allowed liquid chromatography at the critical conditions (LC-CC) of PS and gradient elution chromatography (GEC) of the products were developed. GEC was used successfully in the monitoring of the presence and removal of PDMS homopolymer present in the block copolymer products. LCCC at the critical point of PS allowed successful chromatographic separation of PS homopolymer from the block material, as well as, the molecular weight distribution of the block material according to the segmental length of the PDMS component. LC-CC coupled to FT-IR using a LC-transform device allowed successful characterisation of the block copolymer chemical composition. Corona treatment was used to modify the surface structure of the block copolymer films. Optical microscopy and slow positron beam studies highlighted the formation of a thin silica like layer on the surface of the films after corona. The positron studies enabled determination of the silica like layer’s thickness. Contact angle studies provided the first evidence of hydrophobic loss and recovery for these PDMS containing hybrid polymer materials after corona treatment. A novel offline coupling technique was developed between LC-CC separation and transmission electron microscopy (TEM) analysis. This allowed easy sample preparation without the difficult bulk extraction procedures needed to remove homo-PS contaminants from the block copolymer. This technique also provided morphological information as a function of PDMS segmental length.

Dissertation (Ph.D.)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Self-emulsifiable and self-assembling nano-particle phosphated and siloxane-modified polyurethane dispersions, for use in metal coatings, were synthesised from a new phosphate monomer, a carboxylate monomer, a polysiloxane macroglycol and a . cycloaliphatic diisocyanate, and characterised. Crosslinked nano-particles of acrylic-modified, self-assembling, phosphated polyurethane dispersions with better water swell resistance were obtained using the phosphated nanoparticles as the 'seed' to polymerise monofunctional and multifunctional acrylic monomers in the dispersed phase. This was done by reacting 2-hydroxyethyl methacrylate end-capped polyurethane with monofunctional and multifunctional acrylate monomers in the dispersed phase. Phase inversion of the polyurethane resin from an organic solvent into dispersion was accompanied by three stages, as studied by viscosity and conductivity measurements. In an attempt to modify existing synthesis procedures of the traditional polyurethane acrylic dispersions for which organic solvents are used, polymerisable acrylic monomers were used as diluents during the urethane-forming reaction. This resulted in overcoming the limitations of the existing process. Particle-size analysis indicated that the above dispersions had smaller particle sizes, narrower distributions and better hydrophobicity than any reported to date. Aqueous vinylterminated phosphated polyurethane dispersions were studied for their viscosity behaviour under shear and showed Newtonian behaviour. The polyurethane dispersions were evaluated for their hydrolytic stability with respect to the location of the ionic groups on the segments. Greater hydrolytic stability was obtained when the ionic groups were on the urethane hard segment. The polyurethane dispersionsresponded well to UV curing, a curing technique that has not received much attention to date. The surface and interface analyses of the self-assembling coatings obtained from the phosphated and siloxane-modified polyurethane dispersions showed increased silicon enrichment at the coating/air interface and phosphorus enrichment at the metal/coating interface. Results of dynamic contact angle studies proved the poor wettability of the coatings, as shown by the increase in contact angle by probe liquids. Dynamic thermogravimetry studies of the phosphate-containing polyurethanes showed a decrease in activation energy with increasing phosphate content. This is a good indication that phosphate-containing polyurethanes could be used as fire retarding coatings that comply with fire limit regulations. / AFRIKAANSE OPSOMMING: Self-emulgeerbare en selfsamestellende, nanopartikel, fosfaat- en siloksaanbevattende poliuretaandispersies, vir gebruik as deklae vir metale, is gesintetiseer en gekarakteriseer. Die uitgangstowwe vir die ~ bereiding was 'n splinternuwe fosfaatmonomeer, 'n karboksilaatmonomeer, 'n polisiloksaanglikol en 'n siklo-alifatiese diisosianaat. Deur die polimerisasie van die monofunksionele en multifunksionele akriel-monomere in die dispergeerde fase in te ent met die fosfaat-bevattende nanopartikels, is kruisgebinde nanopartikels van akrielgemodifiseerde, selfsamestellende, fosfaatbevattende poliuretaandispersies met goeie waterswelweerstand berei. Dit is bewerkstellig deur poliuretaan, met reaktiewe hidroksietiel-endgroepe, te reageer met monofunksionele akrilaatmonomere in die gedispergeerde fase. Fase-omkering van die poli-uretaanhars uit die organiese oplosmiddel, tot in dispersie, het in drie stappe plaasgevind. Dit is bepaal deur viskositeit en konduktiwiteit. Bestaande metodes van sintese Vir tradisionele poli-uretaanakrieldispersies, waarvoor organiese oplosmiddels gebruik is, is gewysig om die beperkinge van die bestaande metodes te oorkom. Suskes is behaal met die gebruik van polimeriseerbare akrielmonomere as verdunningsmiddels in die uretaanvormingsreaksie. Partikelgrootte-analises het getoon dat die verkreë dispersies kleiner partikelgroottes, nouer verspreidings en beter hidrofobisiteit gehad het as enige wat tot dusver beskryf is. Die viskositeit van die wateroplosbare, vinielgetermineerde, fosfaatbevattende poliuretanandispersies is onder afskuiwing bepaal en het Newtoniese gedrag getoon. Die hidrolitiese stabiliteit van die poli-uretane, met betrekking tot die posisie van die ioniese groepe in die segmente, is bepaaL ..Die polimere met die ioniese groepe in die harde segment van die poli-uretaan het hoër hidrolitiese stabiliteit vertoon. Kruisbinding (verharding) deur middel van UV, wat tot dusver min aandag geniet het, was baie suksesvol. Analises van die oppervlakte en die tussenvlak van die selfsamestellende deklaag, wat van die fosfaat- en siloksaanbevattende dispersies berei is, het verhoogde siloksaanverryking by die deklaag/lug tussenvlak en verhoogde fosfaatverryking by die metaal/deklaag tussenvlak getoon. Resultate van dinamiese kontakhoekstudies het bewys dat die deklae swak benat is, dws daar was 'n toename in die kontakhoek deur peilvloeistowwe. Termogravimetriese studies het getoon dat daar 'n afname was in die aktiveringsenergie van die fosfaatbevattende poli-uretane met 'n toenemende fosfaatinhoud. Hierdie feit dui daarop dat hierdie poli-uretane moontlik as brandvertragende deklae gebruik kan word.

Chapter 1 describes work towards the synthesis of graphene nanoribbons with varying widths and edge structures. Interest in graphene comes from the high electron mobility at room temperature, exceptional thermal conductivity, and superior mechanical properties.¹ These properties enable graphene’s use in numerous applications such as transparent conducting electrodes, gas detection, transistors, energy storage devices, and polymer composites.¹ Density functional theory has predicted that the electronic properties of GNRs differ with changes in length, width, and differences in edge structure.⁵ First polyacetylene ladder polymers were developed as intermediates for nanoribbons with zig-zag edge structures. Experiments have shown evidence for polyacetylene structures within the material although conversion is too low to be used as a precursor for graphene nanoribbons. Next tetraethynylethene monomers were synthesized to study their use as monomers for Bergman polymerization in hopes of producing armchair edged nanoribbons. Polymers were made with both alkyl and carboxylic acid functionality. ortho-Acylphenols are useful reagents in the synthesis of many natural products, pharmaceuticals, agrichemicals, flavors, and fragrances²⁷,²⁸. For this reason, ketone directed hydroxylation of arenes catalyzed by Pd was developed by Dong and coworkers. During this work it was discovered that 1-acetylnaphthalene would polymerize under the reaction conditions. Chapter 2 describes the author’s efforts to understand the polymerization mechanism through the synthesis of a variety of substituted acetylnaphthalene derivatives and their polymerization. / text

<p>Atom transfer radical polymerization (ATRP) has proven to be a powerful technique to obtain polymers with narrow polydispersities and controlled molecular weight. It also offers control over chain-ends. The technique is the most studied and utilized of thecontrolled/”living” radical polymerization techniques since a large number of monomerscan be polymerized under simple conditions. ATRP can be used to obtain polymer graftsfrom multifunctional substrates. The substrates can be either soluble (i. e. based ondendritic molecules) or insoluble (such as gold or silicon surfaces). The large number ofgrowing chains from the multifunctional substrates increases the probability of inter-and intramolecular reactions. In order to control these kinds of polymerizing systems, andsuppress side-reactions such as termination, the concentration of propagating radicalsmust be kept low. To elaborate such a system a soluble multifunctional substrate, based on 3-ethyl-3-(hydroxymethyl)oxetane, was synthesized. It was used as a macroinitiatorfor the atom transfer radical polymerisation of methyl acrylate (MA) mediated byCu(I)Br and tris(2-(dimethylamino)ethyl)amine (Me6-TREN) in ethyl acetate at room temperature. This yielded a co-polymer with a dendritic-linear architecture. Since mostsolid substrates are sensitive to the temperatures at which most ATRP polymerisations are performed, lowering the polymerization temperatures are preferred. ATRP at ambienttemperature is always more desirable since it also suppresses the formation of thermally formed polymer. The macroinitiator contained approximately 25 initiating sites, which well mimicked the conditions on a solid substrate. The polymers had low polydispersity and conversions as high as 65% were reached without loss of control. The solid substrateof choice was cellulose fibers that prior to this study not had been grafted through ATRP.As cellulose fibers a filter paper, Whatman 1, was used due to its high cellulose content.The hydroxyl groups on the surface was first reacted with 2-bromoisobutyryl bromidefollowed by grafting of MA. Essentially the same reaction conditions were used that hadbeen elaborated from the soluble substrate. The grafting yielded fibers that were very hydrophobic (contact angles>100°). By altering the sacrificial initiator-to-monomer ratiothe amount of polymer that was attached to the surface could be tailor. PMA with degreesof polymerization (DP’s) of 100, 200 and 300 were aimed. In order to control that thepolymerizations from the surface was indeed “living” a second layer of a hydrophilicmonomer, 2-hydroxymethyl methacrylate (HEMA), was grafted onto the surface. Thisdramatically changed the hydrophobic behavior of the fibers.</p> / QC 20100524

No description available.