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<p>A novel strategy for synthesising segmented poly(urethane urea) (PUU) without using a chain extender but nevertheless with the opportunity to vary the hard segment content has been developed. The strategy is based on amine formation from isocyanate upon reaction with water. By adding a dissolved soft segment to an excess of diisocyanate followed by the addition of water in the gas phase, amines are formed <i>in situ</i>. Urea linkages are then formed when these amines react with the excess of isocyanate groups. The gas phase addition facilitates addition in a slow and continuous manner. The hard segment content can easily altered by varying the diisocyanate/soft segment ratio. Even though the strategy is shown to be applicable to different diisocyanates, the focus has been on the potentially biodegradable methyl-2,6-diisocyanatehexanoate (LDI) and 1.4-butanediisocyanate (BDI) and various well known biodegradable polyesters and polycarbonates. </p><p>All the synthesised materials exhibited pronounced phase separation and hydrogen bonding within the hard domains. However, a major increase in hydrogen bonding strength was seen when a symmetric diisocyanate was used instead of an asymmetric. Based on FTIR measurements, PUUs with BDI and a polydisperse hard segment can exhibit the same degree of phase separation and hydrogen bonding as the monodisperse product.</p><p>The elastic properties of this new group of PUUs were exceptional with an elongation at break from 1600% to almost 5000% and the elastic modulus could be varied from a few MPa up to a couple of hundreds. </p><p>Hydrolytic degradation was greater in the polyester-based than in the polycarbonate-based PUUs due to the more reactive ester bonds. Low mass loss but a considerable loss in molecular weight was seen in the polyester PUUs. The tensile strength decreased dramatically due to the loss of strain hardening.</p><p>An MTT seeding assay using human fibroblasts and an in vivo biocompatibility study were performed and no signs of cytotoxicity were seen and the inflammatory response was comparable to other inert polymers.</p><p>A biodegradable PUU with properties that can be tailored through an easy synthesis is here presented. </p>

A novel strategy for synthesising segmented poly(urethane urea) (PUU) without using a chain extender but nevertheless with the opportunity to vary the hard segment content has been developed. The strategy is based on amine formation from isocyanate upon reaction with water. By adding a dissolved soft segment to an excess of diisocyanate followed by the addition of water in the gas phase, amines are formed in situ. Urea linkages are then formed when these amines react with the excess of isocyanate groups. The gas phase addition facilitates addition in a slow and continuous manner. The hard segment content can easily altered by varying the diisocyanate/soft segment ratio. Even though the strategy is shown to be applicable to different diisocyanates, the focus has been on the potentially biodegradable methyl-2,6-diisocyanatehexanoate (LDI) and 1.4-butanediisocyanate (BDI) and various well known biodegradable polyesters and polycarbonates. All the synthesised materials exhibited pronounced phase separation and hydrogen bonding within the hard domains. However, a major increase in hydrogen bonding strength was seen when a symmetric diisocyanate was used instead of an asymmetric. Based on FTIR measurements, PUUs with BDI and a polydisperse hard segment can exhibit the same degree of phase separation and hydrogen bonding as the monodisperse product. The elastic properties of this new group of PUUs were exceptional with an elongation at break from 1600% to almost 5000% and the elastic modulus could be varied from a few MPa up to a couple of hundreds. Hydrolytic degradation was greater in the polyester-based than in the polycarbonate-based PUUs due to the more reactive ester bonds. Low mass loss but a considerable loss in molecular weight was seen in the polyester PUUs. The tensile strength decreased dramatically due to the loss of strain hardening. An MTT seeding assay using human fibroblasts and an in vivo biocompatibility study were performed and no signs of cytotoxicity were seen and the inflammatory response was comparable to other inert polymers. A biodegradable PUU with properties that can be tailored through an easy synthesis is here presented.

Imagemaking is a universal impulse experienced by all human cultures. In the continual pursuit to create compelling and engaging forms, efforts to permit images to interact in dynamic ways in extended space have been the subject of considerable exploration. The often sought-after goal is to break the surface of the paper without sacrificing the essence of the image. My current research is the investigation of Smooth-On 300 series Semi-Rigid Urethane Casting Resin and its interaction with various laser jet inks on diverse paper or paper analogous mediums. Purely on accident, it was discovered that one could easily transfer printed images onto the casting resin if it was poured directly on the print. This has allowed for a method of image manipulation in a manner that has yet to be thoroughly explored. Several experimental pours and projects have been completed to test the limits and potentiality of this new media. The results seem promising and warrant farther exploration of this exciting new development.

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Our ability to recall information and events is astounding and dependent on the medial temporal lobe (MTL) memory system. The synaptic interconnections between the neocortex (nCTX), entorhinal cortex (EC), and hippocampus (HPC) are the anatomical basis of this memory system. The electrophysiological basis of memory formation in this system is largely unknown, but the activity patterns that occur during slow wave sleep (SWS) are thought to play an important role. One prominent activity pattern that occurs during SWS is the slow oscillation (SO). It is a large-amplitude rhythm of ~1Hz that was first described in the nCTX and only occurs during SWS and deep anaesthesia. Using the urethane-anaesthetised rat, I provide the first description of the SO in the HPC in Chapter 2. I found that the SO in the HPC was dynamically coordinated with that in the nCTX. Because the EC is the anatomical interface between the nCTX and HPC, I hypothesised that it could be responsible for this coordination. Chapter 3 characterises the SO in the EC and its coordination with both the nCTX and HPC. My results suggested that the synaptic interconnections between the nCTX and HPC via the EC were not solely responsible for SO coordination across these structures. Another possibility is that SO coordination across the nCTX, EC, and HPC occurs via the nucleus reuniens thalami (NReu). In Chapter 4, I delivered trains of electrical stimulation to the frontal cortex (fCTX) to enhance the SO in the nCTX and assess any effect in the HPC. In addition, I delivered the same stimulation trains directly to the medial prefrontal cortex (mpfCTX) and NReu. I found that repeated stimulation in each structure entrained the hippocampal SO. I also found that repeated stimulation of the fCTX and mpfCTX enhanced SO coordination across the nCTX and HPC, but repeated stimulation of the NReu did not. My results suggested that SO coordination across the nCTX and HPC occurs via both the EC and NReu. Understanding the coordination of SO activity across these structures will provide insight to the electrophysiological basis of the MTL memory system and the role of SWS in its function.

Made available in DSpace on 2014-10-09T12:33:38Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:04Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:33:38Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:04Z (GMT). No. of bitstreams: 0 / Neste trabalho foram avaliadas as propriedades de um adesivo estrutural uretânico que visavam colagens de peças automotivas compostas por combinações de compósitos, termoplásticos e metais, que requerem do adesivo um elevado desempenho e compatibilidade com esses materiais. Para tanto, foram avaliadas as resistências ao cisalhamento de juntas formadas com estes substratos e o adesivo uretânico em diversas condições de exposição, que visam simular os efeitos deletérios que estas juntas estarão expostas durante sua utilização. Estes métodos permitiram caracterizar o adesivo como estrutural para tais aplicações, pois em todos os ensaios a fratura se deu fora da área de colagem, levando a conclusão de que a junta formada é mais resistente do que o substrato isoladamente. Foram desenvolvidos dois inovadores tratamentos de superfície alternativos ao lixamento, que foram o desengraxe com solventes e tratamento com plasma. Estes tratamentos tem contribuído significativamente om a comunidade e a partir deste estudo tem sido utilizados na indústria. A avaliação do comportamento térmico do adesivo e dos substratos permitiu o desenvolvimento de métodos de análise da composição das frações de massa de matriz polimérica, cargas minerais e fibra de vidro de modo prático, rápido e preciso, por uso da termogravimetria. A calorimetria diferencial exploratória possibilitou avaliar as transições vítreas dos substratos e do adesivo, bem como a energia liberada na reação do adesivo uretânico. Os fenômenos de interação química entre o adesivo e os substratos foram investigados pelo uso da técnica de espectroscopia infravermelho por reflectância atenuada, onde pode-se de forma inédita comprovar a existência de reações covalentes e de hidrogênio entre o adesivo e os substratos, que explicam a elevada aderência deste adesivo.Os resultados de todos os ensaios e análises levam à conclusão final que o adesivo uretânico, embora muitas vezes não considerado como estrutural, é um candidato plenamente capacitado ao trabalho de adesão estrutural, especialmente para uso automotivo nas condições descritas neste trabalho. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1980 / Includes bibliographical references. / by Marcos German Ortiz Molina. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Mechanical Engineering

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