Controlled free radical polymerization facilitates the production of polymers with highly defined microstructures like traditional ionic polymerization; but in contrast allows for previously unattainable monomer combinations such as acrylic acid in its non-protected form. Incorporation of acrylic acid into styrene was done by random copolymerization of acrylic acid (directly and in its protected form as tert-butyl acrylate) with styrene. Styrene/tert-butyl acrylate (S/t-BuA) as well as styrene/acrylic acid (S/AA) mixtures were copolymerized to form tapered or gradient copolymers. Using an alkoxyamine unimolecular initiator, 2-[N- tert-butyl-2,2-(dimethylpropyl)aminooxy] propionic acid (BlocBuilder RTM), along with additional free nitroxide (SG1), the effect of acid protection on polymerization kinetics and copolymer composition was determined. Adding 4.5 mol% SG1/BlocBuilderRTM greatly improved the control of S/t-BuA copolymerization with low polydispersities (1.14-1.22) whereas the S/AA required higher levels of SG1 to produce polymers with low polydispersities that were comparatively still broader compared to the S/t-BuA system (polydispersities ∼ 1.3-1.4 at 9 mol% SG1/BlocBuilderRTM). S/AA copolymerization required higher SG1 concentrations to compensate for degradation of SG1 by attack from the acrylic acid monomer.

Living anionic polymerization techniques were applied to the synthesis of arborescent (dendritic) well-defined graft polymers having core-shell morphologies, with a hydrophobic core and a hydrophilic shell. Cycles of polystyrene substrate acetylation and anionic grafting yielded successive generations of arborescent polystyrenes. The anionic polymerization of styrene with sec-butyllithium provided polystyryllithium serving as side chains. These were coupled with a linear acetylated polystyrene substrate to obtain a generation zero (G0) arborescent polymer. An analogous G0 hydroxyl-functionalized polystyrene substrate with hydroxyl end groups was also obtained by a variation of the same technique, using a bifunctional organolithium initiator containing a hydroxyl functionality protected by a silyl ether group to generate the polystyrene side chains. These were coupled with the linear acetylated polystyrene substrate and subjected to a deprotection reaction to give the G0 polymer functionalized with hydroxyl groups at the chain ends. A similar procedure was used to generate a hydroxyl-functionalized arborescent G1 polymer from the corresponding G0 acetylated polystyrene substrate. The growth of polyglycidol chain segments was attempted from the hydroxyl-functionalized cores, to form a hydrophilic shell around the hydrophobic cores, but led to extensive degradation. A click reaction was also developed to synthesize the amphiphilic copolymers and was much more successful. In this case alkyne-functionalized arborescent polystyrene substrates, obtained by a modification of the hydroxyl-functionalized arborescent polystyrenes, were coupled with azide-functionalized polyglycidol side chains.

This study was undertaken to prepare polystyrene (PS)/montmorillonite (MMT) nanocomposites by different methods, including melt intercalation, in-situ polymerization and masterbatch methods. The in-situ polymerization method consisted of dispersing the styrene monomer into the galleries of MMT followed by subsequent polymerization. The PS/MMT nanocomposites formed by melt intercalation method were prepared on a twin-screw extruder. The masterbatch method was in fact a two-step process. As the first step, a high clay content composite of polystyrene (masterbatch) was prepared by in-situ polymerization, and then the prepared masterbatch was diluted to desired compositions with commercial polystyrene in a twin-screw extruder.The structural, thermal and mechanical properties of the nanocomposites were examined. X-Ray diffraction (XRD) analysis showed that the d-spacing of the in-situ formed nanocomposites containing 0.73 and 1.6 wt. %organoclay increased from 32.9 &amp / #506 / to 36.3 and 36.8 &amp / #506 / respectively, indicating intercalation while the dspacing of the other prepared materials remained nearly unchanged compared to pure organoclay. At low clay content, (&lt / 1 wt.%), in-situ formed nanocomposites showed the best improvement in mechanical properties including tensile, flexural, impact strength and Young&rsquo / s modulus. In all the three methods, the addition of organoclay increased the Young&rsquo / s modulus compared to neat resin, but the maximum improvement was 88.5 %, obtained at 0.73 wt. % organoclay in the in-situ formed material. In-situ polymerization method did not prove to be efficient at high clay loadings in terms of mechanical properties. At high clay loadings, the effects of the three methods on promoting mechanical properties were not significantly different from each other. The glass transition temperature increased from 105.5 oC in the pure polystyrene to 108.4 oC in the in-situ formed nanocomposite at 0.73 wt % organoclay due to the restricted mobility of the polymer chains within the organoclay layers.

Thesis (M.E.)--University of Canterbury, 2007. / Typescript (photocopy). "May 2007." Includes bibliographical references (leaves 121-122). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 140-147).

Thesis (M.S.)--Mississippi State University. Department of Computational Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M.S.)--Michigan State University. Packaging, 2008. / Title from PDF t.p. (Proquest, viewed on Aug. 11, 2009) Includes bibliographical references.

A busca por materiais de origem natural, com menos impacto ambiental e com as mesmas propriedades de materis sintéticos está cada vez mais em foco nas pesquisas na área de engenharia. Um modo de fazer isto é o desenvolvimento de nancompósitos reforçados por materiais oriundos de fibras naturais visto que estas possuem em sua estrutura celulose e a celulose é o composto presente em maior quantidade no planeta. Dentro dos nanocompósitos existe a classe dos nanocompósitos expandidos que combinam boas propriedades mecânicas com densidade reduzida e capacidade superior de isolamento térmico e acústico, quando comparados aos nanocompósitos convencionais não expandidos. Nanocompósitos expandidos são materiais que possuem pelo menos três fases: uma contínua (matriz polimérica), a fase dispersa (elementos de reforço) e a presença de espaços vazios no interior da estrutura, denominadas células. O poliestireno (PS) é um polímero muito utilizado na produção de materiais expandidos. Nesse sentido, o presente estudo tem por objetivo, primeiramente a obtenção das nanofibras (NFC) e nanowhiskers (NWC) de celulose ambas extraídas de fibras de curauá (FC). As NFC foram obtidas pelo processo de desfibrilação e os NWC a partir do método de oxidação. Estas foram caracterizadas quanto sua morfologia por microscopia eletrônica de transmissão (MET), microscopia eletrônica de varredura com emissão de campo (MEV-FEG), grau de polimerização (GP), quanto sua estrutura cristalina (DRX), quanto suas propriedades térmicas (TG) e quanto a estrutura química (FTIR). Após, ocorreu o desenvolvimento de nanocompósitos de poliestireno (PS) reforçado com NFC e NWC, nas seguintes concentrações de reforço: 0,25%, 0,50% e 1,00% (m/m). Avaliou-se a influência da incorporação dos reforços na matriz por DMA onde observou-se um aumento no módulo de armazenamento e de perda para todos os nanocompósitos, em relação ao PS sem reforço. Após os nanocompósitos foram expandidos utilizando dióxido de carbono em estado supercrítico como agente expansor e os nanocompósitos expandidos foram avaliados por propriedades mecânicas (resistência à compressão), na morfologia final do nanocompósito expandido por MEV-FEG e por distribuição de tamanho de células. Nos nanocompósitos expandidos, a incorporação das NFC promoveu um aumento na resistência a compressão e uma diminuição no tamanho de células, quando comparado as amostras reforçadas com NWC e PS puro. De modo geral, a incorporação dos NWC nos nanocompósitos antes da expansão proporcionaram melhores resultados quando comprados ao reforçados com NFC. Por poutro lado a incorporação de NFC nos nanocompósitos expandidos proporcionaram melhores resultados quando comparados aos reforçados com NWC. / Submitted by cmquadros@ucs.br (cmquadros@ucs.br) on 2018-02-20T11:45:18Z No. of bitstreams: 1 Dissertacao Roberta Motta Neves.pdf: 2419021 bytes, checksum: 98834ba297d6c3752a7400aba41b8968 (MD5) / Made available in DSpace on 2018-02-20T11:45:18Z (GMT). No. of bitstreams: 1 Dissertacao Roberta Motta Neves.pdf: 2419021 bytes, checksum: 98834ba297d6c3752a7400aba41b8968 (MD5) Previous issue date: 2018-02-20 / The search for materials of natural origin, with less environmental impact and with the same properties of synthetic materials is increasingly focused on research in the field of engineering. One way to doing this is a development of nanocomposites reinforced with materials obtained from natural fibers, because that have on your biologic structure cellulose and the cellulose is present in greater quantity in the planet. Within the nanocomposites there is a class of expanded nanocomposites that combine good mechanical properties with reduced density and superior capacity of thermal and acoustic insulation when compared to conventional non-expanded nanocomposites. Expanded nanocomposites are materials that have at least three phases: a continuous (polymer matrix), the dispersed phase (reinforcing elements) and the presence of voids inside the structure, called cells. Polystyrene (PS) is a polymer widely used in the production of expanded materials. In this sense, the aim of the present study were firstly to obtain nanofibers (NFC) and nanowhiskers (NWC) of cellulose both extracted from curauá fibers (CF). The NFCs were obtained by the defibrillation process and the NWC from the oxidation method. These were characterized by their transmission electron microscopy (TEM), scanning electron microscopy with field emission (SEM), degree of polymerization (GP), their crystalline structure (XRD), and their thermal properties (TG) and the chemical structure by Fourier-transform infrared spectroscopy (FTIR). After that, the next step was the development of PS/NFC and PS/NWC nanocomposites in the following reinforcement concentrations: 0.25%, 0.50% and 1.00% (w/w). The influence of the incorporation of the reinforcements in the matrix by DMA was evaluated, where an increase in the storage and loss modulus was observed for all the nanocomposites, in relation to the PS without reinforcement. After the nanocomposites were expanded using carbon dioxide in the supercritical state as an expander and the expanded nanocomposites were evaluated by mechanical properties (compressive strength), in the final morphology of the expanded nanocomposite by SEM and by cell size distribution. In the expanded nanocomposites, the incorporation of the NFC promoted an increase in the compressive strength and a decrease in the cell size when compared to the samples reinforced with NWC and pure PS. In general, the incorporation of NWC in nanocomposites prior to expansion provided better results when purchased from NFC-reinforced ones. On the other hand, the incorporation of NFC in the expanded nanocomposites provided better results when compared to those reinforced with NWC.

Ionômeros são polímeros carregados que possuem uma variedade de propriedades elétricas e que recentemente vêm sendo aplicados como camadas de transporte em dispositivos poliméricos. Em particular, camadas ultrafinas de ionômeros são depositadas entre o eletrodo e o polímero eletrônico em OLEDs para aumentar a eficiência da injeção de cargas. Entretanto o sucesso desta aplicação envolve fenômenos de armazenamento e mecanismos de transportes de cargas dentro do ionômero que ainda não são claramente entendidos. Neste trabalho foi utilizada a técnica da corrente despolarização termoestimulada (TSDC) com o propósito de esclarecer alguns efeitos relacionados a esse fenômeno. Nós utilizamos o poliestireno sulfonado (X-SPS) com lítio (X = Li) ou potássio (X = K) como contraíon. Foram obtidos filmes ultrafinos com 50 nm de espessura por spincoating obtendo a estrutura metal-polímero-metal para estudo, tendo como metal o alumínio. A técnica de TSDC consiste no aquecimento de uma amostra previamente polarizada a um taxa de aquecimento constante e a corrente de despolarização é medida em função da temperatura da amostra. Os resultados experimentais mostraram que cada termograma apresenta dois picos, sendo que um dos deles mostrou-se fortemente dependente das condições de polarização, ou seja, dependendo da temperatura de polarização e da intensidade do campo de polarização. Os picos foram estudados através da cinética de primeira ordem para a dinâmica de armazenamento e transporte, e dos ajustes teórico-experimental foram obtidos importantes parâmetros, tal como, a energia de ativação e concentração de espécies ativas. / Ionomers are charged polymers that exhibit a great variety of electrical properties and more recently they have been applied as transport layers at polymer devices. In particular, thin films of ionomer have been deposited between the electrodes and the electronic polymers in OLEDs to improve the efficiency of the charge injection. Despite the success of such application, the involved phenomena related to the charge storage and transport mechanisms inside the ionomer thin layer are not clear yet. In this work we used thermal stimulated depolarization current technique (TSDC) with the purpose to elucidate such phenomena. We used for this a sulfonated polystyrene (X-SPS) having lithium (X = Li) or potassium (X = K) as cation counter-ions, and we make structure of metal-polymer-metal in which the polymer is a thin film of SPS, at about 50 nm thick and deposited by spincoating, having aluminum as metal. TSDC technique consists of warm up a previously polarized sample at a constant rate of heating and measure the depolarization current in function of the temperature. The experimental results showed that each thermogram presents two peaks, one of them very dependent on the polarization conditions, i. e., it depends on the polarization temperature and the intensity of the polarization bias. The peaks were studied by considering first order trapping-detrapping (or dipole relaxation) kinetics, from which important parameters, as the activation energy, were obtained.

Orientador: Fabio Augusto / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-17T12:13:43Z (GMT). No. of bitstreams: 1 Batista_AlexDomingues_M.pdf: 1225711 bytes, checksum: 108d27c49f0c885f3e6b3f3302d1efc7 (MD5) Previous issue date: 2010 / Resumo: No trabalho estudou-se o preparo de fibras para Microextração em Fase Sólida (SPME) com recobrimentos baseados em sílicas organicamente modificadas através de processo sol-gel. O modificador utilizado foi o viniltriemetoxisilano para a obtenção de um revestimento inicial que posteriormente foi recoberta com poliestireno através da polimerização de monômeros de estireno catalisada por luz ultravioleta. As fibras foram caracterizadas química e morfologicamente através de Microscopia Eletrônica de Varredura, Espectroscopia no Infravermelho e Análise Termogravimétrica. Os recobrimentos apresentaram uma estrutura compacta, sem a presença visível de poros com uma espessura de 97 mm. Eles se apresentaram estáveis termicamente até uma temperatura de aproximadamente 320°C. As fibras foram utilizadas com sucesso na quantificação de BTEX em água de torneira, as curvas analíticas obtidas apresentaram coeficientes de correlação linear acima de 0,99. Os limites de detecção calculados pela curva analítica foram para benzeno, tolueno, etilbenzeno e o-xileno foram respectivamente 0,023, 0,042, 0,027 e 0,061 mg.L. As novas fibras foram utilizadas também na quantificação de androstenona e escatol em toucinho suíno onde também observado um coeficiente de correlação linear para a curva analítica acima de 0,99. Os limites de detecção foram 0,003 mg.g para androstenona e 0,009 mg.g para escatol / Abstract: In this work we studied the preparation of fibers for Solid Phase Microextraction (SPME) with coatings based on organically modified silica via sol-gel process. Vinyltrimethoxysilane was used as modifier for obtaining an initial coat that was later covered with polystyrene by polymerizing styrene monomers catalyzed by ultraviolet light. The fibers were characterized chemically and morphologically by scanning electron microscopy, infrared spectroscopy and thermogravimetric analysis. The coatings had a compact structure without the visible presence of pores with a thickness of 97 micrometers. They showed thermal stability up to a temperature of about 320°C. The fibers were successfully used in the quantification of BTEX in tap water, the analytical curves showed correlation coefficients above 0.99. The detection limits were calculated by the analytical curve of benzene, toluene, ethylbenzene and o-xylene were respectively 0.023, 0.042, 0.027 and 0.061 mg.L. The new fibers were also used for quantification of skatole and androstenone in pig fat which also observed a linear correlation coefficient for the calibration curve above 0.99. The detection limits were 0.003 mg.g for androstenone and 0.009 mg.g for skatole / Mestrado / Quimica Analitica / Mestre em Química