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  • 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.
51

Alkaline earth and rare earth complexes for the ring opening polymerisation of cyclic esters

Clark, Lawrence January 2012 (has links)
This Thesis describes the use of alkaline earth and rare earth complexes bearing phenolate ligands as catalysts in the amine-initiated, immortal ring opening polymerisation (ROP) of cyclic esters. Mechanistic elucidation was performed and two propagation pathways are presented. Chapter One introduces cyclic esters and catalytic routes to polyesters by ROP. Common techniques for polymer characterisation are described and an overview of relevant phenolate-supported ROP catalysts is given. Reversible chain transfer in ROP is also discussed. Chapter Two describes the synthesis and characterisation of zwitterionic Group 3 complexes bearing bis(phenolate)-amino ligands and the development of the amine-initiated, immortal ROP methodology using this class of catalyst. Detailed studies into the ROP of rac-lactide using amines and a zwitterionic yttrium complex are presented and the mechanism of amine-initiated, immortal ROP was derived. Chapter Three documents further amine-initiated, immortal ROP studies using a zwitterionic yttrium complex as the catalyst. The preparation of multiarm polymers is described and further investigations using the cyclic esters, ε-caprolactone and rac-β-butyrolactone are presented. Chapter Four describes the use of Group 2 and lanthanide phenolate complexes in the amine-initiated ROP of rac-lactide. Bulk polymerisation studies revealed the generality of the amine-initiated, immortal ROP methodology and an alternative propagation pathway was derived from mechanistic studies. Chapter Five details the synthesis and characterisation of Group 3 amide complexes supported by phenolate-amino ligands. Each complex was screened for ROP capability and amine co-initiators were employed. Chapter Six contains experimental details and characterisation data for the new complexes and polymer products described in this Thesis. CD Appendix contains crystallography .cif files, supporting information for each Chapter and spreadsheets containing polymerisation data.
52

Hydroconversion de la tétraline sur catalyseurs à base d’iridium supporté sur silice-alumine / Tetralin hydroconversion over silica-alumina-supported iridium-based catalysts

Nassreddine, Salim 27 October 2010 (has links)
L’ouverture sélective de cycles aromatiques sur catalyseurs bifonctionnels peut en principe aboutir à une augmentation de l’indice de cétane des gazoles. Dans ce travail, nous nous sommes concentrés sur l’iridium supporté sur silice-alumine amorphe (ASA) comme catalyseur d’hydroconversion de la tétraline en présence de H2S à 250-350 °C dans un microréacteur continu sous pression (4 MPa). Une étude détaillée par analyse thermique et diffraction X in situ du processus de décomposition du précurseur acétylacétonate d’iridium a permis d’optimiser l’étape d’activation. Unesimple réduction sous H2 à 350 °C aboutit à des nanoparticules Ir finement dispersées (taille 1.4 ± 0.2nm). Le catalyseur Ir/ASA est stable et résiste à l’empoisonnement par le soufre, contrairement à Ir/SiO2 et Ir/Al2O3. Les principaux produits d’hydroconversion de la tétraline sont les produits d’hydrogénation (décalines) et les produits d’ouverture et de contraction de cycle (POCC). L’analyse par chromatographie en phase gazeuse bidimensionnelle (GC��GC-MS) montre que les POCC se répartissent en produits d’ouverture saturés et aromatiques, minoritaires, et en produits de contraction saturés et aromatiques, majoritaires. Les performances catalytiques de Ir/ASA ont pu être modifiéesvia des effets de support, d’alliage et de taille. Pour une composition Si:Al d’environ 0,5, l’acidité de Brönsted du support est maximale, ce qui conduit à une activité totale et une sélectivité en POCC maximales. D’autre part, l’activité augmente par ajout de palladium, et la sélectivité en POCC est maximale pour la composition Ir-Pd intermédiaire. Les analyses par TEM-EDX montrent que la teneur en Pd des nanoparticules augmente avec leur taille. Enfin, la sélectivité en POCC croîtconsidérablement avec la taille des particules, qui a été ajustée entre 2 et 8 nm par frittage thermiqueen atmosphère humide. Cela s’explique par une diminution du rapport entre les quantités de sitesmétalliques et de sites acides de Brönsted dans le cadre d’un mécanisme bifonctionnel. / Selective ring opening of aromatics over bifunctional catalysts is expected to increase gas oil cetane number. In this work, we have focused on iridium supported on amorphous silicaalumina (ASA) for catalytic hydroconversion of tetralin in the presence of H2S at 250-350 °C, using a continuous high-pressure (4 MPa) microreactor. A detailed study of the decomposition of the Ir acetylacetonate precursor by thermal analysis and in situ X-ray diffraction has allowed us to optimize the activation treatment. A simple reduction in H2 at 350 °C leads to well-dispersed nanoparticles (size 1.4 ± 0.2 nm). Unlike Ir/SiO2 and Ir/Al2O3 catalysts, Ir/ASA is stable and resists to poisoning by sulphur. The main tetralin hydroconversion products are hydrogenation products (decalins) and ringopening/contraction products (ROCP). Advanced analysis by tow-dimensional gas chromatography(GC��GC-MS) shows that ROCP are composed mostly of saturated and aromatic ring-contractionproducts, and to a lower extent of saturated and aromatic ring-opening products. The catalyticperformances of Ir/ASA could be modified through support, alloy and size effects. For a Si:Alcomposition of ca. 0.5, the Brönsted acidity of the support is maximal, which leads to the highest totalactivity and ROCP selectivity. Besides, the activity increases with palladium addition, and the ROCPselectivity is maximum at intermediate Ir-Pd composition. TEM-EDX analyses show that the Pdcontent of nanoparticles increases with their size. Finally, the ROCP selectivity increases dramaticallywith particle size, which was tuned in the 2-8 nm range by thermal sintering in a wet atmosphere. Thisis explained by a decrease of the amount of metallic sites with respect to Brönsted acid sites within abifunctional mechanism.
53

Estudos visando à síntese do tripanossomicida (±)-komaroviquinona / Studies toward the synthesis of trypanocidal (±)-komaroviquinone

Pereira, Rafael Fonseca 02 August 2011 (has links)
A doença de Chagas é uma doença endêmica causada pelo protozoário Trypanosoma cruzi que assola cerca de 15 milhões de pessoas na América Latina. Na busca de uma alternativa mais econômica e eficiente para o tratamento desta doença, Kiushi e colaboradores isolaram da planta Darcocephalum komarovi, a komaroviquinona. Após estudos \"in vitro\" de células humanas contaminadas com tripomastigotos do Trypanosoma cruzi, a komaroviquinona mostrou ser 15 a 300 vezes mais eficiente que os tratamentos atualmente disponíveis. Mesmo com este resultado animador, pouco se tem relatado sobre a síntese da komaroviquinona, existindo apenas 4 rotas sintéticas descritas na literatura, sendo duas delas enantiosseletivas. Baseado neste fato, o presente trabalho visa estudar uma forma de se obter a komaroviquinona de forma rápida e eficaz, utilizando, para tal fim, a estratégia de abertura de epóxidos por um aril-magnésio ou aril-lítio, como etapa chave. Pretende-se com esta estratégia sintetizar a komaroviquinona em 9 etapas, partindo de reagentes disponíveis comercialmente. Cabe ressaltar que esta estratégia possibilita a síntese de outros produtos naturais como o brussonol, que apresentou citotoxidade moderada em células de ovários do inseto Spodoptera frugiperda (Sf9) e células de ovário do mamífero hamster chinês (CHO), além de atividade citotoxicológica às células P388 leucêmicas de camundongo. Alguns resultados promissores foram obtidos como a preparação \"one pote\" da cetona 2-alil-3,3-dimetil-cicloexanona com rendimento na faixa entre 54-65 % e a preparação do respectivo epóxido com rendimento de 89 %. Além destes resultados, a reação de abertura de epóxido se mostrou eficiente quando utilizados organometálicos modelo (disponíveis comercialmente), sendo que os rendimentos foram de 53 % e 62%, dependendo do reagente de Grignard utilizado. Entretanto ainda se faz necessário otimizar as condições reacionais para aplicação dos organometálicos reais, precursores da komaroviquinona e do brussonol. / Chagas\'s disease is an endemic infection caused by the protozoan Trypanosoma cruzi, affecting near 15 milion of people in Latin America. In a search of an economical and efficient alternative for the treatment of this disease, Kiushi and colleagues isolated Komaroviquinone from the plant Darcocephalum komarovi. After in vitro studies of human cells (infected with trypomastigotes of Trypanosoma cruzi), komaroviquinone proved to be 15 to 300 times more efficient than the currently available prescriptions. Even with this encouraging result, little has been reported on the synthesis of komaroviquinone, and only four synthetic routes are described in the literature (two being enantioselective). Based on this fact, the present work deals with the study of a new strategy to synthesize komaroviquinone quickly and effectively, employing an epoxide ring-opening approach with aryl-magnesium and aril-lithium compounds as the key step. Using this strategy, komaroviquinone may be synthesized in 9 steps, starting from commercially starting materials. It should be noted that this strategy enables the synthesis of other natural products such as brussonol, which showed moderate cytotoxicity on insect-derived Spodoptera frugiperda pupal ovarian cells (Sf9), mammalian Chinese hamster ovary cell (CHO), and P388 murine leukemia cells. Some promising results were already obtained as the preparation one pote of ketone with yield in range of 54-65 % and the preptaration of the corresponding epoxide with 89 % yield. Besides this, the epoxide ring-opening approach could be applied with some aromatic model compounds (commercially available) with 53 % and 62 % yield, depending on the Grignard reagents employed. However, in order to prepare komaroviquinone, it is still necessary to optimize the reaction conditions so that the real aromatic derivatives (precursors of komaroviquinone and brussonol) may be used.
54

Desenvolvimento da metodologia de síntese e purificação dos dímeros L-lactídeo e glicolídeo para produção do poli (ácido lático-co-ácido glicólico) para utilização na produção de fontes radioativas / Development of a methodology for the synthesis and purification of the dimers L-lactide and glycolide for the production of poly(lactic acid-co-glycolic acid) for use in the manufacture of radioactive sources

Peleias Júnior, Fernando dos Santos 31 July 2017 (has links)
A Organização Mundial da Saúde (OMS) relata o câncer como uma das principais causas de morte no mundo. O câncer de próstata é o segundo tipo de câncer mais prevalente em homens, com cerca de 1,1 milhão de casos diagnosticados em 2012. Braquiterapia com iodo-125 é uma método de radioterapia que consiste na introdução de sementes com material radioativo no interior do órgão a ser tratado. As sementes de iodo-125 podem ser inseridas soltas ou em cordas poliméricas bioabsorvíveis, mais comumente o poli(ácido lático-co-ácido glicólico) (PLGA). A função do polímero é reduzir a possibilidade de migração das sementes, o que poderia ser prejudicial para órgãos e tecidos saudáveis. De modo a reduzir os custos do tratamento, a síntese dos dímeros L-lactídeo e glicolídeo, para posterior utilização para preparação do PLGA, por meio da polimerização por abertura de anel, é proposta neste trabalho. Adicionalmente, propõe-se a utilização do amino-alcóxido tris(fenolato) de zircônio (IV) como alternativa ao usual octanoato de estanho (SnOct2), uma vez que a toxicidade do estanho permanece como obstáculo na produção do PLGA para aplicações biomédicas. Embora o iniciador de zircônio seja mais lento do que o SnOct2, massas molares relativamente elevadas foram obtidas quando razões monômero/iniciador (M/I) de 1000/1 (24 h), e 5000/1 (48 h) foram utilizadas. Considerando que as unidades glicolila (GA) são mais reativas do que as unidades lactila (LA), tempos longos de reação são necessários para atingir uma razão LA/GA próxima do objetivo do trabalho (85/15). O grau de racemização também depende do iniciador utilizado. As reações de polimerização realizadas com o iniciador de zircônio mostraram um maior grau de racemização, quando comparadas com aquelas realizadas com o SnOct2. Também foi observado um ligeiro aumento na racemização com o tempo. Considerando os resultados obtidos na síntese e purificação dos dímeros, e na síntese do PLGA em condições semelhantes às industriais, foi possível preparar o polímero de alta massa molar com um custo dezenas de vezes inferior ao custo do PLGA no mercado internacional. Os efeitos da radiação gama no PLGA também foram estudados. Doses normalmente aplicadas para esterilizar materiais para aplicações biomédicas foram empregadas: 10, 18, 25 e 50 kGy. A massa molar de todas as amostras irradiadas diminuiu de uma forma proporcional à dose até 56% de perda para 10 kGy e 72% para 50 kGy porém, são menos pronunciadas para doses mais elevadas. Alterações nas propriedades térmicas, tais como temperatura de fusão, temperatura de transição vítrea e a entalpia de cristalização e fusão foram também observadas após a irradiação. / The World Health Organization (WHO), reports cancer a leading cause of death worldwide. Prostate cancer is the second most common cancer in men, with 1.1 million diagnoses in 2012. Brachytherapy is a method of radiotherapy where encapsulated radioactive sources (seeds) are placed inside or very close to the area requiring treatment. Iodine-125 seeds can be inserted loose or stranded in bioresorbable materials most commonly poly(lactic-co-glycolic) acid (PLGA). The main function of the polymer is to reduce the possibility of seeds migration, which could potentially harm healthy organs and tissues. In order to reduce the cost of the treatment, we propose in this work the synthesis of L-lactide and glycolide dimers, for the production of PLGA using the ring-opening polimerisation route. Additionally, we also propose the use of a Zr (IV) amine tris(phenolate) alkoxide initiator as an alternative to the usual SnOct2, which is still considered an unsolved problem for biomedical applications due to its toxicity. Although the zirconium alkoxide initiator is less active and slower than SnOct2, relatively high molecular weights were obtained at a temperature of 130°C, for a monomer to initiator ratio of 1000/1 (24 h), and 5000/1, in 48 h. Since glycolyl units are more reactive than lactyl counterpart, longer reaction times are needed to achieve a LA/GA ratio closer to the initial (85/15). The degree of racemisation of the polymer depended upon the initiator used. The reactions carried out with the zirconium initiator showed a higher degree of racemisation when compared to those carried out with SnOct2. A modest increase in the degree of racemisation with time was also observed. Considering the results obtained for the synthesis and purification of the dimers, and for the synthesis of PLGA under industrial-like conditions, we concluded that it was possible to produce a high molecular weight polymer that costs far less than the usual price of PLGA on the market. The effects of gamma radiation on PLGA were also studied. We used doses commonly applied to sterilise materials for biomedical applications: 10, 18, 25 and 50 kGy. All irradiated samples showed a reduction in the molecular weight in a dose dependent fashion - up to 56% loss for 10 kGy and 72% for 50 kGy - but these reductions were less pronounced for higher doses. Changes in thermal properties, such as melting point, glass transition temperature and enthalpy of crystallisation and fusion were also observed after irradiation.
55

Cyclic carbonates from sugars and carbon dioxide : synthesis, polymerisation and biomedical applications

Gregory, Georgina January 2017 (has links)
The biodegradability and when functionalised biocompatibility of aliphatic polycarbonates (APCs) makes them an attractive class of materials for biomedical applications such as tissue engineering scaffolds and drug-delivery carriers. One route to accessing a wide-range of well-defined and functional APCs is the controlled ring-opening polymerisation (ROP) of cyclic carbonates. In turn, these would ideally be prepared by the direct coupling of CO2 with diols to give water as the only by-product. In this way, the combination of CO2 and sugar-derived diols draws upon two natural renewable building blocks for the construction of polycarbonates that are anticipated to show good biocompatibility properties. Chapter 2 develops a simple and mild alternative to the traditional use of phosgene derivatives for the synthesis of six-membered cyclic carbonates from 1,3-diols and CO2. DFT calculations highlighted the need to lower both the CO2-insertion and ring-closing kinetic barriers to cyclic carbonate formation. Organic superbase, 1,8- diazabicyclo[5.4.0]undec-7-ene (DBU) enabled the formation of carbonate species at 1 atm CO2 pressure whereas, the introduction of a leaving group strategy lowered the cyclisation barrier. Mechanistic considerations suggested a kinetic preference for ring- closing via a nucleophilic addition-elimination pathway rather than a SN2-like intramolecular cyclisation. Chapter 3 applies the procedure with CO2 to the preparation of a novel monomer from natural sugar, ᴅ-mannose. ROP was carried out via an organocatalytic approach and a preference for head-tail linkages in the polycarbonate backbone indicated by NMR spectroscopy and supported by DFT calculations. Chapter 4 utilises CO2 to invert the natural stereochemistry of sugars and create a thymidine-based monomer. The thermodynamic parameters of the ROP with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) catalyst are determined and the properties of the polycarbonates investigated to include preliminary cell attachment studies. Finally, chapter 5 details the synthesis of cyclic carbonates from 2- deoxy-ᴅ-ribose and the investigation into the different ROP behaviour of the α- and β- anomers. The ability to tune the polymer properties through copolymerisation with trimethylene carbonate (TMC) is also discussed.
56

Alkaline earth hydroborate complexes for the ring-opening polymerisation of cyclic esters

Diteepeng, Nichabhat January 2018 (has links)
This Thesis describes the activity and mechanism of alkaline earth organohydroborate, tetrahydroborate and alkoxide catalysts for the ring-opening polymerisation (ROP) of cyclic esters including rac-, L-, D- and meso-lactide (LA), and rac-β-butyrolactone (rac-BBL). <b>Chapter One</b> introduces cyclic esters and general mechanisms for their ROP to give polyesters. Living and immortal ROP, an overview of stereocontrolled ROP, and determination of polylactide (PLA) stereosequences are given. Various techniques for polymer characterisations are also described. <b>Chapter Two</b> describes the activity and mechanism of heavy alkaline earth organohydroborate complexes for the ROP of LA. The synthesis and characterisation of alkaline earth alkoxide complexes serving as model species are also described, together with their activities for the ROP of LA. <b>Chapter Three</b> describes the activity and mechanism of a cyclic organohydroborate calcium complex for the ROP of LA. The role of borinic esters as chain transfer agents in the ROP of rac-LA is also discussed. <b>Chapter Four</b> describes the activity and mechanism of heavy alkaline earth tetrahydroborate complexes for the ROP of LA. The immortal ROP of rac-LA using heavy alkaline earth alkoxide complexes and borate esters as chain transfer agents is discussed. <b>Chapter Five</b> describes the activity and mechanism of alkaline earth organohydroborate, tetrahydroborate and alkoxide complexes for the ROP of rac-BBL. <b>Chapter Six</b> presents experimental procedures and characterising data for new complexes reported.
57

Desenvolvimento da metodologia de síntese e purificação dos dímeros L-lactídeo e glicolídeo para produção do poli (ácido lático-co-ácido glicólico) para utilização na produção de fontes radioativas / Development of a methodology for the synthesis and purification of the dimers L-lactide and glycolide for the production of poly(lactic acid-co-glycolic acid) for use in the manufacture of radioactive sources

Fernando dos Santos Peleias Júnior 31 July 2017 (has links)
A Organização Mundial da Saúde (OMS) relata o câncer como uma das principais causas de morte no mundo. O câncer de próstata é o segundo tipo de câncer mais prevalente em homens, com cerca de 1,1 milhão de casos diagnosticados em 2012. Braquiterapia com iodo-125 é uma método de radioterapia que consiste na introdução de sementes com material radioativo no interior do órgão a ser tratado. As sementes de iodo-125 podem ser inseridas soltas ou em cordas poliméricas bioabsorvíveis, mais comumente o poli(ácido lático-co-ácido glicólico) (PLGA). A função do polímero é reduzir a possibilidade de migração das sementes, o que poderia ser prejudicial para órgãos e tecidos saudáveis. De modo a reduzir os custos do tratamento, a síntese dos dímeros L-lactídeo e glicolídeo, para posterior utilização para preparação do PLGA, por meio da polimerização por abertura de anel, é proposta neste trabalho. Adicionalmente, propõe-se a utilização do amino-alcóxido tris(fenolato) de zircônio (IV) como alternativa ao usual octanoato de estanho (SnOct2), uma vez que a toxicidade do estanho permanece como obstáculo na produção do PLGA para aplicações biomédicas. Embora o iniciador de zircônio seja mais lento do que o SnOct2, massas molares relativamente elevadas foram obtidas quando razões monômero/iniciador (M/I) de 1000/1 (24 h), e 5000/1 (48 h) foram utilizadas. Considerando que as unidades glicolila (GA) são mais reativas do que as unidades lactila (LA), tempos longos de reação são necessários para atingir uma razão LA/GA próxima do objetivo do trabalho (85/15). O grau de racemização também depende do iniciador utilizado. As reações de polimerização realizadas com o iniciador de zircônio mostraram um maior grau de racemização, quando comparadas com aquelas realizadas com o SnOct2. Também foi observado um ligeiro aumento na racemização com o tempo. Considerando os resultados obtidos na síntese e purificação dos dímeros, e na síntese do PLGA em condições semelhantes às industriais, foi possível preparar o polímero de alta massa molar com um custo dezenas de vezes inferior ao custo do PLGA no mercado internacional. Os efeitos da radiação gama no PLGA também foram estudados. Doses normalmente aplicadas para esterilizar materiais para aplicações biomédicas foram empregadas: 10, 18, 25 e 50 kGy. A massa molar de todas as amostras irradiadas diminuiu de uma forma proporcional à dose até 56% de perda para 10 kGy e 72% para 50 kGy porém, são menos pronunciadas para doses mais elevadas. Alterações nas propriedades térmicas, tais como temperatura de fusão, temperatura de transição vítrea e a entalpia de cristalização e fusão foram também observadas após a irradiação. / The World Health Organization (WHO), reports cancer a leading cause of death worldwide. Prostate cancer is the second most common cancer in men, with 1.1 million diagnoses in 2012. Brachytherapy is a method of radiotherapy where encapsulated radioactive sources (seeds) are placed inside or very close to the area requiring treatment. Iodine-125 seeds can be inserted loose or stranded in bioresorbable materials most commonly poly(lactic-co-glycolic) acid (PLGA). The main function of the polymer is to reduce the possibility of seeds migration, which could potentially harm healthy organs and tissues. In order to reduce the cost of the treatment, we propose in this work the synthesis of L-lactide and glycolide dimers, for the production of PLGA using the ring-opening polimerisation route. Additionally, we also propose the use of a Zr (IV) amine tris(phenolate) alkoxide initiator as an alternative to the usual SnOct2, which is still considered an unsolved problem for biomedical applications due to its toxicity. Although the zirconium alkoxide initiator is less active and slower than SnOct2, relatively high molecular weights were obtained at a temperature of 130°C, for a monomer to initiator ratio of 1000/1 (24 h), and 5000/1, in 48 h. Since glycolyl units are more reactive than lactyl counterpart, longer reaction times are needed to achieve a LA/GA ratio closer to the initial (85/15). The degree of racemisation of the polymer depended upon the initiator used. The reactions carried out with the zirconium initiator showed a higher degree of racemisation when compared to those carried out with SnOct2. A modest increase in the degree of racemisation with time was also observed. Considering the results obtained for the synthesis and purification of the dimers, and for the synthesis of PLGA under industrial-like conditions, we concluded that it was possible to produce a high molecular weight polymer that costs far less than the usual price of PLGA on the market. The effects of gamma radiation on PLGA were also studied. We used doses commonly applied to sterilise materials for biomedical applications: 10, 18, 25 and 50 kGy. All irradiated samples showed a reduction in the molecular weight in a dose dependent fashion - up to 56% loss for 10 kGy and 72% for 50 kGy - but these reductions were less pronounced for higher doses. Changes in thermal properties, such as melting point, glass transition temperature and enthalpy of crystallisation and fusion were also observed after irradiation.
58

Designing star-like block-copolymers as compartmentalized nanostructures for drug delivery applications

Engstrand, Johanna January 2010 (has links)
<p>This thesis describes syntheses and characterization of star-like amphiphilic block copolymers consisting of poly(ethylene glycol) (PEG) as the hydrophilic block,polycarbonate as the hydrophobic block and an amine-containing dendrimer as the core molecule. The macromolecules were synthesized by either a convergent or adivergent approach that includes tandem click reactions and ring opening polymerizations (ROP) of methyl trimethyl carbonates (MTC) with differentfunctionalities. The ROP of MTC monomers was performed using organocatalysts that allow mild reaction condition and reasonable molecular weight distribution(PDI~1.3). These synthetic approaches provide the resultant polymers with three different conformations, which are; mikto-arm type, comb-block with short PEGbrushes, and linear block with long PEG chain. The star-like polymers that were synthesized were all water soluble and most of them formed nano aggregates inwater. Different morphologies were observed in AFM study depending on the polymer conformation. Interestingly, some of them had indications pointing towards alower critical solution temperature.</p>
59

Macromolecular Engineering of Cyclic Aliphatic Polyesters

Li, Haiying 25 January 2007 (has links)
Summary of the thesis This works aims at reporting a novel strategy that combines controlled ring-opening polymerization of lactones initiated by a cyclic tin(IV) dialkoxide and intramolecular cyclization by photo-cross-linking of pendant unsaturations next to the propagating sites. No linear species is ever involved in the polymerization, which allows higher molecular weight macrocycles to be prepared with high efficiency. Moreover, the synthetic route is very flexible to the point where macrocyclic polyesters with more complex although well-defined architectures, such as tadpole-shaped and sun-shaped copolyesters, can be tailored. Synthesis of well-defined star- and eight-shaped polyesters and twin tadpole-shaped amphiphilic copolymers has also been explored by using a spirocyclic tin(IV) alkoxide as initiator.
60

Bispyridylamides as ligands in asymmetric catalysis

Belda de Lama, Oscar January 2004 (has links)
This thesis deals with the preparation and use of chiralbispyridylamides as ligands in metal-catalyzed asymmetricreactions. The compounds were prepared by amide formation usingdifferent coupling reagents. Bispyridylamides havingsubstituents in the 4- or 6- positions of the pyridine ringswere prepared by functional group interconversion of the 4- or6- halopyridine derivatives. These synthetic approaches provedto be useful for various types of chiral backbones. Pseudo C2-symmetric bispyridylamides were also synthesizedby means of stepwise amide formation. The compounds were used as ligands in themicrowave-accelerated Mocatalyzed asymmetric allylic alkylationreaction. Ligands having ð-donating substituents in the4-positions of the pyridine rings gave rise to products withhigher branched to linear ratio. The catalytic reaction, whichproved to be rather general for allylic carbonates with anaromatic substituent, was used as the key step in thepreparation of (R)-baclofen. The Mo-bispyridylamide catalystprecursor was studied by NMR spectroscopy. Bispyridylamide complexes of metal alkoxides were alsoevaluated in the asymmetric addition of cyanide to aldehydesand the metal complexes involved were studied by NMRspectroscopy and X-ray crystallography. Chiral diamines wereused as additives to study the ring opening of cyclohexeneoxide with azide, catalyzed by Zr(IV)-bispyridylamidecomplexes. Various bispyridylamides were attached to solid supports oforganic or inorganic nature. The solid-supported ligands wereused in Mo-catalyzed asymmetric allylic alkylation reactionsand in the asymmetric addition of cyanide to benzaldehyde. Keywords:asymmetric catalysis, chiral ligand, pyridine,amide, allylic alkylation, enantioselective, cyanation,ring-opening, chiral Lewis acid.

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