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Nagarajan, Pratapkumar. "Rapid production of polymer microstructures." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26539.
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Thesis (Ph.D)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2009.Committee Chair: Dr. Donggang Yao; Committee Member: Dr. John.Muzzy; Committee Member: Dr. Karl Jacob; Committee Member: Dr. Wallace W. Carr; Committee Member: Dr. Youjiang Wang. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Tonry, Catherine Elizabeth Henzell. "Computational electrohydrodynamics for fabricating polymer microstructures." Thesis, University of Greenwich, 2015. http://gala.gre.ac.uk/18149/.
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The aim of the work presented in this thesis is the development of two computational models of two processes that can be used to shape molten polymers on a micro-scale, namely Electrohydrodynamic Induced Patterning (EHDIP) and Electric Field Assisted Capillarity (EFAC). These related processes both use the dielectric forces at the interface between a polymer and another dielectric such as air. When the molten polymers are placed in a shaped electric field the imbalance in these dielectric forces causes the polymer to flow in a controlled way creating shapes in the polymer melt, this is the basis for the EHDIP process. The shaped electric field is controlled by the morphology of the top mask which acts as an electrode. This process is further extended by introducing a heavily wetted surface on the top mask which results in capillary forces that cause the polymer melt to coat the top mask creating a fully enclosed shape. This process can be used to create enclosed micro-channels or micro-capsules. Thus results and discussion presented herein highlight several possible application routes for industrial manufacturing. The process is discussed here for microstructures of 1 µm to 200 µm in size. The range at which the processes work is not fully understood, however the EHDIP process has been shown to work at a nanoscale producing structures around 100 nm in size. From a comprehensive literature review, the underlying theory and mechanisms of this process were identified and the governing equations derived. Computational models were developed based on the underlying physics. These models were initially developed in PHYSICA version 3g and later they were implemented into COMSOL Multiphysics as the latter proved to be more stable. The results from the computational models were compared to the limited experimental data available. The results from the computational models show that the mask shape was found to have the largest effect on the final structure of the shaped poly-mer. Due to capillary forces the shape of the microstructure at the top mask mimics the shape of the mask. In the lower section of the enclosed microstructure there is a force balance between surface tension, dielectric forces and internal pressure, giving a rounded morphology. Furthermore, by wetting the lower mask, flat bottomed structures can be produced. By both shaping and wetting the lower mask the shape of the microstructure can be even further modified. However, sharp cornered masks are unsuitable for this process. The effects of other key parameters such as air gap, contact angle, polymer permittivity and applied voltage were investigated through a sensitivity analysis. Changing the permittivity is shown to have an effect on the final microstructure. The change is small; however the permittivity does affect the speed of the process. The contact angle between the top mask and the polymer modifies the thickness of the polymer at the top of the structures. Increasing the contact angle causes a decrease in polymer thickness due to a reduction in the capillary force. The depth of the structures can be altered by changing the air gap; hence a larger air gap gives a deeper structure. The initial polymer thickness has no effect on the top of the structure but determines the thickness, shape and curvature of the lower part of the structure. The applied voltage controls the electrostatic forces and hence the speed of the process. For a low voltage the electrostatic forces are not strong enough to initiate the process and an enclosed microstructure does not form. If the voltage is too high, the structure forms quickly and bubbles can be entrapped at the top mask. With the correct mask shapes the processes can produce a wide variety of microstructures. These would have a wide range of applications either in the communications sector as fibre-optical wave-uides or in the biomedical sector as microstructures used in BioMEMS. Further development of the process is required to ensure that the process can be controlled. The models presented here are initial investigations of this but further experimental work is required along with the expansion of the model into three-dimensions.
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Dirckx, Matthew E. "Demolding of hot embossed polymer microstructures." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61520.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 219-229).
Polymer-based microfluidic "lab on a chip" technology promises to reduce cost and extend access to medical diagnostic tests that formerly required expensive and labor-intensive lab work. The predominant methods for manufacturing these devices are miniaturized molding processes including casting, injection molding, and hot embossing. These techniques have in common the use of a mold to define the shape of functional features (fluidic channels), the separation of the part from the mold as a process step (demolding), and the intended re-use of the mold to produce additional parts. The demolding step in particular poses significant challenges for mass production. Demolding affects several issues including production rate, part quality, and mold lifetime, and demolding-related defects are frequently observed. Despite its importance, there has been no comprehensive effort to analyze demolding theoretically or experimentally. This thesis aims to deepen the understanding of demolding of polymer microstructures in order to facilitate mass manufacturing of polymer-based devices with micro-scale functional features, such as microfluidic chips. A theory of demolding mechanics has been proposed that combines the effects of thermal stress, friction, and adhesion in a unified framework. A metric by which demolding can be characterized experimentally--the demolding work--has been proposed by analogy with interfacial fracture and has been related to underlying physical mechanisms. Finite element simulations based on this theory of demolding have been performed to investigate the effects of important parameters, including demolding temperature and feature geometry. A test method for characterizing demolding by directly measuring the demolding work for individual microstructures has been developed and applied to hot embossing to study the effects of process parameters such as demolding temperature, the effects of feature geometry and layout, and the impacts of mitigation strategies such as low-adhesion mold coatings. The results of these demolding experiments broadly agree with expected trends based on the theory of demolding mechanics proposed herein. A dimensionless parameter aggregating the effects of feature geometry and layout has been identified and related to the occurrence of demolding-related defects, the demolding process window, and the demolding temperature that minimizes the demolding work. These findings have been generalized to provide processing and design guidance for industrial application of polymer micro-molding.
by Matthew E. Dirckx.
Ph.D.
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Koucky, Michael Harten. "PIEZOELECTRIC POLYMER MICROSTRUCTURES FOR BIOMEDICAL APPLICATIONS." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1238080858.
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Rowland, Harry Dwight. "Thermomechanical Manufacturing of Polymer Microstructures and Nanostructures." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14642.
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Molding is a simple manufacturing process whereby fluid fills a master tool and then solidifies in the shape of the tool cavity. The precise nature of material flow during molding has long allowed fabrication of plastic components with sizes 1 mm 1 m. Polymer molding with precise critical dimension control could enable scalable, inexpensive production of micro- and nanostructures for functional or lithographic use.
This dissertation reports experiments and simulations on molding of polymer micro- and nanostructures at length scales 1 nm 1 mm. The research investigates two main areas: 1) mass transport during micromolding and 2) polymer mechanical properties during nanomolding at length scales 100 nm. Measurements and simulations of molding features of size 100 nm 1 mm show local mold geometry modulates location and rate of polymer shear and determines fill time. Dimensionless ratios of mold geometry, polymer thickness, and bulk material and process properties can predict flow by viscous or capillary forces, shape of polymer deformation, and mold fill time. Measurements and simulations of molding at length scales 100 nm show the importance of nanoscale physical processes distinct from bulk during mechanical processing. Continuum simulations of atomic force microscope nanoindentation accurately model sub-continuum polymer mechanical response but highlight the need for nanoscale material property measurements to accurately model deformation shape. The development of temperature-controlled nanoindentation enables characterization of nanoscale material properties. Nanoscale uniaxial compression and squeeze flow measurements of glassy and viscoelastic polymer show film thickness determines polymer entanglement with cooperative polymer motions distinct from those observed in bulk.
This research allows predictive design of molding processes and highlights the importance of nanoscale mechanical properties that could aid understanding of polymer physics.
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Yao, Hongyang. "Microstructures of poly(vinyl acetate) studied by nuclear magnetic resonance spectroscopy." W&M ScholarWorks, 1997. https://scholarworks.wm.edu/etd/1539623911.
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Carbon-13 NMR spectroscopy was used to investigate the microstructures of poly(vinyl acetate) prepared by solution polymerization in benzene. A series of aromatic compounds was synthesized in order to model the structures formed via chain transfer to solvent. The peaks near 126.5 and 128.5 ppm in the spectra of the polymer samples were assigned to a 1-phenyl-(2n + 1)-multi-acetoxyalkane (where n = 1, 2, 3, etc.) microstructure. The concentration of that structure obtained from NMR spectra was correlated with the concentration calculated from reported kinetic data.;Chain transfer to benzene was shown to occur by addition of the macroradical to benzene, followed by rearomatization involving loss of a hydrogen atom. No evidence was obtained for a transfer mechanism involving hydrogen abstraction from benzene, and the copolymerization of benzene with vinyl acetate also was shown to be absent. The transfer mechanism actually established accounts for the unexpectedly large transfer constant of benzene in vinyl acetate polymerization. General mechanisms are proposed for the solution polymerization of vinyl acetate in aromatic solvents.
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Laslau, Cosmin. "Novel fabrication and characterization methods for conducting polymer nanostructures and microstructures." Thesis, University of Auckland, 2012. http://hdl.handle.net/2292/19604.
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To develop devices based on conducting polymers for the benefit of humanity - such as, for example, artificial muscles and lab-on-a-chip diagnostics - we require the ability to reliably fabricate and understand these materials at the micro and nano scales. In this thesis I present research towards that goal, by developing novel experimental techniques for the fabrication and characterization of poly(3,4-ethylenedioxythiophene) (PEDOT) and polyaniline (PANI), two prominent conducting polymers. Many of the strategies presented herein are based on miniaturized pipettes driven by scanning ion conductance microscopy (SICM), with some complementary techniques also explored. I begin this thesis work by describing the construction of a low-cost SICM, and its further development to include novel modifications that enable its application to conducting polymers. One of these is the first SICM-based measurement of the ion flux that underpins PEDOT actuation, an important issue in artificial muscles and micropumps. Another is the first electrochemical fabrication of microscale PEDOT and PANI structures and arrays. This approach is then extended to map the activity of the resulting microstructures using modified SICM-based protocols. For example, it is demonstrated that pipette-defined cyclic voltammetry can yield highly localized characterization of microstructures, an important topic for biosensor applications. Indeed, this technique is demonstrated herein for the characterization of a PEDOT nanowire based DNA sensor. Finally, complementary studies on PANI nanostructures are also presented. The first synchrotron radiation studies of PANI nanotube self-assembly is undertaken, revealing crystallinity at critical early stages of the reaction. Furthermore, focused ion beam and electron microscopy techniques are used to perform studies on the electrical properties on individual PANI nanostructures. Both of these have relevance for potential integration with the aforementioned SICM-based techniques. Altogether, these methodological innovations and resulting findings represent significant advances in the burgeoning field of pipette-localized conducting polymer fabrication and characterization. I conclude the thesis with implications discussed for future fundamental research and device applications.
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JIANG, TAO. "ELECTRONIC PROPERTIES AND MICROSTRUCTURES OF AMORPHOUS SICN CERAMICS DERIVED FROM POLYMER PRECURSORS." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2988.
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Polymer-derived ceramics (PDCs) are a new class of high-temperature materials synthesized by thermal decomposition of polymeric precursors. These materials possess many unique features as compared with conventional ceramics synthesized by powder metallurgy based processing. For example, PDCs are neither amorphous nor crystalline. Instead, they possess nano-domain structures. Due to the direct chemical-to-ceramic processing, PDCs can be used for making components and devices with complex shapes. Thus, understanding the properties and structures of these materials are of both fundamental and practical interest. In this work, the structures and electronic behavior of polymer-derived amorphous silicon carbonitrides (SiCNs) were investigated. The materials were synthesized by pyrolysis of a commercially available liquid precursor. Ceramic materials with varied structures/properties were successfully synthesized by modifying the precursor and using different pyrolysis temperatures. The structures of the obtained materials were studied using XRD, solid state NMR, EPR, FTIR and Raman Spectroscope. The electronic behavior of the materials was investigated by measuring I-V curves, Hall effects, temperature dependent conductivity. The experiments were also performed to measure UV-Visible absorption and dielectric properties of the materials. This work leads to the following significant progresses: (i) developed quantitative technique for measuring free carbon concentration; (ii) achieved better understanding of the electronic conduction mechanisms and measured electronic structures of the materials for the first time; and (iii) demonstrated that these materials possess unusual dielectric behavior and provide qualitative explanations.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Materials Science & Engr PhD
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Prystaj, Laurissa Alia. "Effect of carbon filler characteristics on the electrical properties of conductive polymer composites possessing segregated network microstructures." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/31667.
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Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2009.Committee Chair: Rosario Gerhardt; Committee Member: Gleb Yushin; Committee Member: Hamid Garmestani. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Woelfle, Caroline. "Study of Nanoparticle/Polymer Composites: I) Microstructures and Nonlinear Optical Solutions Based on Single-Walled Carbon Nanotubes and Polymers and II) Optical Properties of Quantum Dot/Polymer Composites." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/26657.
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The overall research theme of this dissertation was the study of nanoparticle/polymer composites. Two types of nanoparticles were utilized: Single-Walled Carbon Nanotubes and quantum dots. Chapter 1 of this thesis comprises an extensive literature review on Carbon Nanotubes, which presents theoretical aspects relevant to the structure and properties of CNTs, methods of purifying and solubilizing CNTs in aqueous and organic solvents and selected applications. This literature review is followed by the study and comparison of the optical limiting performances of different Single-Walled Carbon Nanotubes/conjugated polymer dispersions (Chapter 2). The results obtained are discussed in terms of dispersion of the SWNTs in the polymer solutions and resulting SWNT bundle diameters. Chapter 3 presents the spontaneous assembly of dendrimer patterns induced by SWNTs. Finally, chapter 4 presents a new method for fabricating quantum dot/polymer composites, which uses the extraction of positively charged quantum dot into a hydrophobic liquid. The resulting solution is used as a compatible polymerization medium for poly(methylmethacrylate ) networks enabling the formation of transparent and fluorescent composites.Ph. D.
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Cano, Camilo I. "Polyimide Microstructures From Powdered Precursors: Phenomenological and Parametric Studies on Particle Inflation." Akron, OH : University of Akron, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1123710711.
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Dissertation (Ph.D.)--University of Akron, Dept. of Polymer Engineering, 2005."August, 2005." Title from electronic dissertation title page (viewed 09/24/2005) Includes bibliographical references.
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Bello, Carlos A. "Microsphere-aided characterization of stimuli-responsive polymer networks." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002788.
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Svedberg, Malin. "Microstructures for Chemical Analysis : Design, Fabrication and Characterisation." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4792.
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Maier, Thomas Robert. "The effects of polymer microstructure and macrostructure on SBR/polybutadiene blend miscibility, phase morphology, and cured rubber properties." Case Western Reserve University School of Graduate Studies / OhioLINK, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1061908392.
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Dupin, Stephane. "Etude fondamentale de la transformation du polyamide 12 par frittage laser : mécanismes physico-chimiques et relations microstructures/propriétés." Thesis, Lyon, INSA, 2012. http://www.theses.fr/2012ISAL0062/document.
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Les procédés de fabrication additive permettent, à partir d’un fichier de CAO, la fabrication de pièces complexes sans outillage, dans des délais de développement très courts et avec une grande flexibilité. Parmi les procédés de fabrication additive employés avec les polymères, le frittage laser de poudre est le plus utilisé. Ces travaux de thèse sont consacrés à l’étude et la compréhension des mécanismes fondamentaux impliqués lors du procédé de frittage laser de poudres de polyamide 12. Au cours du procédé de frittage laser de nombreux paramètres interviennent. Ainsi l’énergie fournie à la poudre par l’intermédiaire du rayon laser dépend de la puissance de celui-ci, de la vitesse de balayage et de l’espacement entre deux balayages successifs. De plus, le matériau subit un cycle thermique sévère : avant d’être frittée, la poudre est préchauffée. Puis, dans le bac de fabrication, la poudre non frittée ainsi que les pièces séjournent pendant toute la durée de la fabrication à des températures élevées. Cette histoire thermique entraîne un vieillissement et donc une modification des propriétés de la poudre ce qui complique sa réutilisation. L’influence de ces différents paramètres sur la microstructure et les propriétés mécaniques des pièces finales a été mise en évidence. De plus l’utilisation de différentes poudres de polyamide 12 a permis l’identification des paramètres-clés de la matière.Le frittage laser des polymères semi-cristallins est régi par plusieurs mécanismes fondamentaux : la fusion des particules de poudre, l’interdiffusion des chaînes macromoléculaires aux interfaces, la coalescence des particules fondues, la densification et enfin la cristallisation. L’étude et la modélisation de la cristallisation ont été effectuées pour l’un des polyamides 12 employés au cours de cette thèse. De ce traitement théorique ont pu être déduits les temps de maintien du polymère à l’état fondu au cours du procédé. Dans une seconde phase, des analyses rhéologiques menées dans le cadre de la viscoélasticité linéaires des polymères à l’état fondu ont permis de déduire les temps d’interdiffusion des chaînes macromoléculaires. Par ailleurs, le processus de coalescence des particules de poudres à l’état fondu a été suivi expérimentalement et modélisé pour différentes températures. Ces temps ont été confrontés à la durée de maintien du polymère à l’état fondu, confirmant ainsi la bonne consolidation obtenue lors du frittage du polyamide 12. En conclusion, ce travail contribue à la compréhension des différents mécanismes physico-chimiques intervenant au cours du frittage laser : il permet d’expliciter de façon assez approfondie les relations entre les propriétés des poudres, les paramètres du procédé et les propriétés finales des pièces. De nombreuses préconisations relatives à l’optimisation des propriétés des poudres pourront être déduites de ce travail et aideront au développement de nouveaux matériaux adaptés à ce procédéAdditive processing technologies are aimed at manufacturing parts directly from a computer-aided design (CAD) file, without the need for tooling. Therefore flexibility of production increases and manufacturing of small to mid-size series of very complex or even customized parts becomes possible within reduced development time and expenses. Because of the good mechanical properties obtained in the parts, the most commonly used among additive technologies for polymers is laser sintering (LS). The objective of this work is to contribute to a better understanding of the different physical mechanisms involved during laser sintering of polyamide 12 powders. Many operating variables impact the laser sintering process. Especially, the energy supplied to the powder with the laser beam depends on its power, its displacement velocity and the scan spacing. Moreover, the polymer material undergoes a quite severe thermal treatment : before its sintering, the powder is preheated, then in the build tank the sintered parts and the un-sintered surrounding powder remain until the end of the job at elevated temperatures. This thermal history induces ageing, which modifies some powder features and hinders its future reuse. The influence of the parameters mentioned above on the part microstructure and mechanical properties was investigated. Moreover the use of different polyamide 12 powders enabled to identify the key material characteristics towards the physical processes involved in LS and towards the final properties of parts. The laser sintering of semi-crystalline polymers is governed by several fundamental mechanisms: melting of particles, interdiffusion of macromolecular chains at interfaces, coalescence of molten particles, then densification and finally crystallisation. The study and modelling of crystallisation were carried out with one of the PA12 powders used in the first part of this work. From this modelling, the time during which the polymer remains in the molten state during the process was estimated. Next, a rheological analysis made within the framework of linear viscoelasticity of polymer melts allowed to compute the interdiffusion time of the macromolecular chains. Moreover, the coalescence process of molten particles was observed at different temperatures and modeled. The characteristic times thus estimated for these physical processes were opposed to the time during which the polymer remains in the molten state and confirmed the good consolidation obtained by laser sintering of polyamide 12. In conclusion this work contributes to understand the different physico-chemical mechanisms involved during polymer laser sintering by specifying the relations between powder parameters, process variables and final properties of parts. Many recommendations for the optimisation of powder properties can be derived from this work for the purpose of developing new polymeric materials adapted to this process
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Maiko, Khumo Gwendoline. "Multidimensional separation of complex polymers according to microstructure." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86227.
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Thesis (PhD)--Stellenbosch University, 2014.ENGLISH ABSTRACT: Complex polymer systems have multiple distributions with regard to molecular parameters such as molar mass, functionality, chemical composition, molecular architecture and microstructure. These distributions affect the properties of the polymers making it necessary to develop separation methods to be able to correlate structure to property. A single onedimensional chromatographic method is usually not sufficient to separate these complex polymers with respect to all the distributions. Hence, multidimensional liquid chromatography is necessary for the complete analysis of complex polymers using two or more chromatographic techniques before detection. In this work, two novel liquid chromatographic methods were developed to separate complex polymers according to microstructure. Comprehensive two-dimensional liquid chromatography (LC x LC) was carried out to observe the correlation between microstructure and molar mass. The separation according to microstructure was coupled to NMR (LC-NMR) to observe, identify and quantify the different microstructural components during chromatographic elution. The first chromatographic method separated hydrogenated and deuterated polystyrene homopolymers with respect to the isotope effect. For the LC x LC experiments, liquid chromatography at critical conditions (LCCC) was employed as the first dimension separating according to the isotope effect and size exclusion chromatography (SEC) as the second dimension separating according to molar mass. The LC x LC results of the blends showed that there was an improvement in isotopic separation with an increase in molar mass. The LCNMR coupling using both 1H and 2H NMR detection allowed for the identification of low molar mass blend components which were not sufficiently separated by liquid chromatography. The second chromatographic method separated stereoregular poly(methyl methacrylate)s (PMMAs) with respect to tacticity. The LC x LC experiments of stereoregular PMMAs utilised solvent gradient liquid chromatography as the first dimension to separate according to tacticity and size exclusion chromatography (SEC) as the second dimension to separate according to molar mass. The LC x LC results showed a change in the triad composition with elution of the stereoregular PMMAs with a slight influence of molar mass. The LC-NMR coupling allowed the observation of the triad composition during chromatographic elution.
AFRIKAANSE OPSOMMING: Komplekse polimeriese sisteme het meervoudige verspreidings ten opsigte van molekulêre parameters, soos byvoorbeeld, molêre massa, funksionaliteit, chemiese samestelling, molekulêre argitektuur en mikrostruktuur. Hierdie verspreidings beïnvloed die eienskappe van die polimere en dus is dit nodig om skeidingsmetodes te ontwikkel ten einde polimeerstruktuur met polimeereienskappe te kan korreleer. ‘n Enkele een-dimensionele chromatografiese metode is gewoonlik nie voldoende om hierdie komplekse polimere te skei met betrekking tot al die verspreidings nie. Multidimensionele vloeistofchromatografie, met die insluiting van twee of meer chromatografiese tegnieke, is dus nodig om polimere te skei voor waarneming kan plaasvind. Twee nuwe chromatografiese metodes is ontwikkel om komplekse polimere volgens mikrostruktuur te skei. Twee-dimensionele vloeistofchromatografie (LC x LC) is uitgevoer ten einde die korrelasie tussen mikrostruktuur en molêre massa te ondersoek. Daarna is die skeiding wat op mikrostruktuur gebasseer is, gekoppel aan KMR (LC-KMR) om die verskillende mikrostrukturele komponente gedurende chromatografiese eluering waar te neem, te identifiseer en te kwantifiseer. Die eerste chromatografiese metode het die gehidrogeneerde en gedeutereerde polistireen geskei met betrekking tot die isotoopeffek. Hier het die LC x LC skeiding bestaan uit vloeistofchromatografie onder kritiese kondisies (LCCC) as die eerste dimensie, wat skeiding bewerkstellig het gebasseer op die isotoopeffek, en grootte-uitsluitingschromatografie (SEC) as die tweede dimensie, wat skeiding bewerkstellig het gebasseer op die molêre massa. Die LC x LC resultate van die vermengings het ‘n verbetering in isotopiese skeiding met ‘n toename in molêre massa getoon. Deur gebruik te maak van die LC-KMR koppeling, waar beide 1H en 2H KMR waarneming gebruik is, was dit moontlik om die lae-molêre-massakomponente van vermengings wat nie volledig d.m.v. LC geskei kon word nie, te identifiseer. Die tweede chromatografiese metode het stereoreëlmatige polimetielmetakrilate (PMMAs) m.b.t. taktisiteit geskei. Die LC x LC skeiding van stereoreëlmatige PMMAs het bestaan uit oplosmiddel -gradiënt-LC as eerste dimensie om volgens taktisiteit te skei, en SEC as tweede dimensie om volgens molêre massa te skei. Die LC x LC resultate het ‘n molêre massa afhanklikheid van stereoreëlmatige PMMAs op taktisiteit getoon. Die LC-KMR koppeling het dit moontlik gemaak om die triade-samestelling gedurende chromatografiese eluering waar te neem.
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Gerislioglu, Selim. "Microstructure Characterization of Polymers and Polymer-Protein Bioconjugates by Hyphenated Mass Spectrometry." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1534269781343128.
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Adams, Friederike [Verfasser], Bernhard [Akademischer Betreuer] Rieger, Richard [Gutachter] Fischer, Wolfgang [Gutachter] Eisenreich, Ning [Gutachter] Zhang, and Bernhard [Gutachter] Rieger. "From Michael-type systems to biobased lactones: Designing novel polymer microstructures with modified bis(phenolate)lanthanides / Friederike Adams ; Gutachter: Richard Fischer, Wolfgang Eisenreich, Ning Zhang, Bernhard Rieger ; Betreuer: Bernhard Rieger." München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1189316633/34.
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Hoffmann, Frank. "Photochemische Fixierung von Strukturen in Grenzflächen mit polymeren Bürsten." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1202481743602-80877.
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Binäre Polymerbürsten bestehen aus zwei verschiedenen Polymertypen, die nebeneinander auf dem gleichen Trägermaterial verankert sind. Wenn diese Polymere unterschiedliche Benetzungseigenschaften haben, können damit schaltbare Oberflächen produziert werden. Abhängig vom Lösungsmittel, dem man die binäre Polymerbürste aussetzt, streckt sich entweder das hydrophile oder das hydrophobe Polymer zum Lösungsmittel hin, während die zweite Komponente nahe der Oberfläche verbleibt. Durch diese vertikale Phasenseparation kann temporär eine bestimmte Oberflächeneigenschaft erzeugt werden. Allerdings verschwindet diese sofort wieder, wenn ein anderes Lösungsmittel die binäre Bürste benetzt, sei es durch direkten Kontakt oder über die Gasphase. In der vorliegenden Arbeit wurde untersucht, ob es möglich ist, neuartige schaltbare binäre Polymerbürsten bestehend aus einem hydrophilen und einem hydrophoben Polymer angebunden auf Siliziumwafern herzustellen, deren Schaltfähigkeit durch photochemische Vernetzung unterbunden werden kann. Geprüft worden ist unter anderem, inwiefern sich hydrophober und hydrophiler Zustand der Schicht fixieren lassen und ob daraus resultierend, eine entsprechende Strukturierung der Oberfläche nach Bestrahlung durch eine geeignete Fotomaske oder durch fokussiertes Licht nachweisbar ist. Als hydrophobe Komponente wurden photovernetzbare Styren/2-(4’-Styryl)-inden-Copolymere verwendet, als hydrophile Komponente kam Polyvinylpyridin zum Einsatz. Mit einem speziellen Oberflächeninitiator konnten durch „Grafting from“ binäre Polymerbürsten mit bis zu 300 nm Schichtdicke erzeugt werden. Es ist gelungen, diese schaltbaren Schichten durch selektive photochemische Vernetzung einer der Bürstenkomponenten im hydrophilen oder im hydrophoben Zustand zu fixieren, was durch Kontaktwinkelmessung nachgewiesen werden konnte. Wie beabsichtigt, verlieren dabei die vernetzten Bereiche ihre Schaltfähigkeit. Es ließen sich feine Oberflächenstrukturen mittels Bestrahlung durch eine Fotomaske erzeugen, die sichtbar werden, wenn man sie mit Wasser benetzt bzw. Wasserdampf aussetzt.
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Strand, Seth R. "Effects of Friction Stir Welding on Polymer Microstructure." Diss., CLICK HERE for online access, 2004. http://contentdm.lib.byu.edu/ETD/image/etd338.pdf.
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Hoffmann, Frank. "Photochemische Fixierung von Strukturen in Grenzflächen mit polymeren Bürsten." Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A24051.
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Binäre Polymerbürsten bestehen aus zwei verschiedenen Polymertypen, die nebeneinander auf dem gleichen Trägermaterial verankert sind. Wenn diese Polymere unterschiedliche Benetzungseigenschaften haben, können damit schaltbare Oberflächen produziert werden. Abhängig vom Lösungsmittel, dem man die binäre Polymerbürste aussetzt, streckt sich entweder das hydrophile oder das hydrophobe Polymer zum Lösungsmittel hin, während die zweite Komponente nahe der Oberfläche verbleibt. Durch diese vertikale Phasenseparation kann temporär eine bestimmte Oberflächeneigenschaft erzeugt werden. Allerdings verschwindet diese sofort wieder, wenn ein anderes Lösungsmittel die binäre Bürste benetzt, sei es durch direkten Kontakt oder über die Gasphase. In der vorliegenden Arbeit wurde untersucht, ob es möglich ist, neuartige schaltbare binäre Polymerbürsten bestehend aus einem hydrophilen und einem hydrophoben Polymer angebunden auf Siliziumwafern herzustellen, deren Schaltfähigkeit durch photochemische Vernetzung unterbunden werden kann. Geprüft worden ist unter anderem, inwiefern sich hydrophober und hydrophiler Zustand der Schicht fixieren lassen und ob daraus resultierend, eine entsprechende Strukturierung der Oberfläche nach Bestrahlung durch eine geeignete Fotomaske oder durch fokussiertes Licht nachweisbar ist. Als hydrophobe Komponente wurden photovernetzbare Styren/2-(4’-Styryl)-inden-Copolymere verwendet, als hydrophile Komponente kam Polyvinylpyridin zum Einsatz. Mit einem speziellen Oberflächeninitiator konnten durch „Grafting from“ binäre Polymerbürsten mit bis zu 300 nm Schichtdicke erzeugt werden. Es ist gelungen, diese schaltbaren Schichten durch selektive photochemische Vernetzung einer der Bürstenkomponenten im hydrophilen oder im hydrophoben Zustand zu fixieren, was durch Kontaktwinkelmessung nachgewiesen werden konnte. Wie beabsichtigt, verlieren dabei die vernetzten Bereiche ihre Schaltfähigkeit. Es ließen sich feine Oberflächenstrukturen mittels Bestrahlung durch eine Fotomaske erzeugen, die sichtbar werden, wenn man sie mit Wasser benetzt bzw. Wasserdampf aussetzt.
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Reuter, Danny. "Entwicklung einer Dünnschichtverkappungstechnologie für oberflächennahe Mikrostrukturen." Doctoral thesis, Universitätsbibliothek Chemnitz, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200800721.
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In der vorliegenden Arbeit wird ein neues Verfahren zur Dünnschichtverkappung von oberflächennahen Mikrostrukturen vorgestellt. Ausgehend von den speziellen Anforderungen an die Verkappung oberflächennaher Mikrostrukturen, insbesondere von Strukturen mit hohem Aspektverhältnis, wurden die Verwendung eines Fluor-Kohlenstoff-Polymers als Opferschichtmaterial und die Eignung unterschiedlicher Schichtstapel zur Realisierung der Dünnschichtkappe untersucht. Die resultierende Technologie ermöglicht eine durchgehend trockenchemische Prozessierung. Für die Abschätzung der notwendigen Schichtdicken und den geometrischen Entwurf der Kappenstrukturen, wurden auf Basis der Plattentheorie analytische und numerische Modelle erstellt. Verschiedene Materialkombinationen bestehend aus Siliziumoxid, Siliziumnitrid und Aluminium wurden hinsichtlich ihrer mechanischen und thermomechanischen Eigenschaften untersucht und bewertet. Ein weiterer Schwerpunkt lag auf der Entwicklung und Optimierung der Opferschichtprozesse, sowie deren Integration in die Gesamttechnologie. Die Eignung der plasmagestützten Prozesse zur Abscheidung und Strukturierung des Opferpolymers wurde durch die Fertigung von verkapselten Beschleunigungssensoren nachgewiesen. Ein ausreichender hermetischer Verschluss der Dünnschichtkappe konnte durch die Messung der viskosen Dämpfung an Feder-Masse-Schwingern bestätigt werden.
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Kumar, Charchit. "Quantitative and qualitative investigation of adhesion and friction on textured surfaces : inspiration from insect-plant interactions." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE008.
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L’adhérence et le frottement existent dans de nombreux systèmes techniques ainsi que dans les systèmes naturels. Ces deux phénomènes ont une influence importante sur la durabilité et l’efficacité des dispositifs techniques. Une approche reconnue pour ajuster précisément ces caractéristiques - outre le fait de modifier les propriétés physico-chimiques - est la texturation des surfaces en contact. Les surfaces de feuilles de plantes sont souvent décorées avec des morphologies de surface diverses, et présentent ainsi des fonctionnalités de surface remarquables. Cette thèse visait à réaliser une étude systématique de la mécanique de l’adhérence et du frottement sur des surfaces micro-structurées, répliquées à partir de surfaces de feuilles végétales, en contact avec une sonde qui s’inspire de l’organe adhérent d’un insecte. Les morphologies de surface de trois feuilles végétales différentes ont été directement transférées sur un polymère viscoélastique. Pour ce faire, trois approches différentes de reproduction ont fait l’objet d’une étude approfondie. La microscopie électronique à balayage et la microscopie confocale à balayage laser ont été utilisées pour l'évaluation qualitative et quantitative de la qualité de reproduction. Concernant l’étude de la mécanique du contact, un nano-indenteur a été modifié, permettant d’enregistrer les images in situ des contacts réels. Des tests de pull-off ont été menés afin d’évaluer quantitativement l’effet de la pré-charge sur la force d’adhésion et pour comprendre les modes distincts de collage/décollement. Des essais de frottement ont été effectués afin d’examiner l’effet de la charge normale et de la vitesse de glissement sur la force de frottement. Les résultats ont été discutés en fonction de la topographie de chaque surfaceAdhesion and friction exist in many technical systems as well as in natural ones. Both phenomena have a profound influence on the durability and efficiency of technical systems. A well-recognised way to tune these characteristics - besides altering the physicochemical properties - is the texturing of the interacting surfaces. Inspiringly, plant leaf surfaces are often decorated with diverse surface morphologies, and so show remarkable functionalities. This thesis aimed to perform a systematic investigation of adhesion and friction mechanics on micro-structured surfaces replicated from plant leaves, in contact with a probe, which was inspired from an insect’s adhesive pad. Surface morphologies of three different plant leaves were directly transferred onto a viscoelastic polymer. For this, three different replication approaches were comprehensively explored. Scanning electron microscopy and confocal laser scanning microscopy were used for the qualitative and quantitative evaluation of replication ability. For the contact mechanics investigation, a high-resolution nanoindenter was modified, with incorporating a unique feature to record the in-situ real-contact images. Pull-off tests were carried out to quantitatively evaluate the effect of pre-load on adhesion force characteristics and to understand distinct attachment-detachment modes. Friction investigations were performed to examine the effect of normal load and sliding speed on the friction force. Results were discussed with regard to each surface’s topography
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Ye, Changhuai. "Microstructure Alignment and Mechanical Properties of Block Copolymer and Crystalline Polymer Thin Films." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1475553221643627.
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Zaikov, Vadim Guennadievich. "A study of poly(vinyl chloride) microstructure." W&M ScholarWorks, 1997. https://scholarworks.wm.edu/etd/1539623916.
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High-field {dollar}\sp{lcub}13{rcub}{dollar}C and {dollar}\sp1{dollar}H NMR spectroscopies were used to investigate some unusual features of the molecular microstructure of poly(vinyl chloride) (PVC).;Several model monochloroalkenes were synthesized in order to determine {dollar}\sp{lcub}13{rcub}{dollar}C shift increments for the replacement of H by Cl at positions that are near an isolated internal double bond. These increments then were used to predict the {dollar}\sp{lcub}13{rcub}{dollar}C shifts of the internal allylic chloride structure in PVC. The predictions were not satisfactory, because, as expected, the increments were not additive.;It was shown that during conventional VC polymerization, the chloroallylic chain end (-CH{dollar}\sb2{dollar}CH=CHCH{dollar}\sb2{dollar}Cl) does not copolymerize with the monomer and is not destroyed by a mechanism involving allylic rearrangement, macroradical addition, and chlorine-atom {dollar}\beta{dollar}-scission to produce a -CHClCH{dollar}\sb2{dollar}CH=CHCH{dollar}\sb2{dollar}CHCl- structure. Nevertheless, that mechanism was found to operate during the preparation of a special type of PVC (made at 0{dollar}\sp\circ{dollar}C with (t-Bu){dollar}\sb2{dollar}Mg initiation) which contained the rearranged chain end, -CH{dollar}\sb2{dollar}-CHClCH=CH{dollar}\sb2,{dollar} at an abnormally high concentration.;During the preparation of PVC under subsaturation VC pressures, small amounts of a 1,3-di(2-chloroethyl) branch structure were found to be formed by a "double backbiting" mechanism involving two intramolecular H abstractions in succession. The presence of this structural defect was established by the 125.77-MHz {dollar}\sp{lcub}13{rcub}{dollar}C NMR spectra of reductively dechlorinated PVC specimens. at 55-80{dollar}\sp\circ{dollar}C, the two backbites leading to the defect differ substantially in relative rate, in that the backbiting:addition rate ratio is larger for the second backbite by a factor of 15-16, irrespective of temperature. No evidence was obtained for the presence of the 2-ethyl-n-hexyl branch structure that would have resulted from double backbiting by an alternative route. These findings were confirmed by spectral comparisons with the {dollar}\sp{lcub}13{rcub}{dollar}C shifts of two separately synthesized models, 9,11-diethylnonadecane and 9-(2-ethyl-n-hexyl)heptadecane.;Polymerizations of VC were performed in the presence of two potential transfer agents, trans-1-chloro-2-hexene and trans-1,5-dichloro-2-pentene. Preliminary examination of the resulting polymers by high-field NMR provided evidence for the destruction of the -CH{dollar}\sb2{dollar}CH=CHCH{dollar}\sb2{dollar}Cl chain end, during polymerization, by a mechanism involving H abstraction to form the -CH{dollar}\sb2{dollar}CH=CHC{dollar}\sp{lcub}\cdot{rcub}{dollar}HCl radical, followed by the addition of that species to VC in order to give the -CH{dollar}\sb2{dollar}CH=CHCHClCH{dollar}\sb2{dollar}- structure.
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Cheguettine, Yasmina. "Propriétés de transport électronique et structure des composites polyaniline (PPA)-acétate de cellulose." Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10028.
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Cette etude porte pour une majeure partie sur les mecanismes du transport electrique dans les composites polyaniline dopee a l'acide phenyl phosphonique (pani(ppa))/acetate de cellulose. Dans ces materiaux, le seuil de percolation pour la conduction electrique peut etre abaisse a de tres faibles fractions volumiques de polyaniline (moins de 0. 1%). Afin d'ameliorer la comprehension des proprietes de transport on a mene aussi une etude structurale de ces composites. Les proprietes de conduction sont etudiees aux echelles macroscopique et mesoscopique par differentes methodes de mesure. La caracterisation electrique de tels echantillons montre que la conduction electrique de ces materiaux est decrite par des lois typiques des systemes desordonnes. Dans une deuxieme partie, nous avons cherche a visualiser la structure de ces composites, par tem, afm et diffraction x. Ce travail permet de correler certaines observations microstructurales aux mecanismes de conduction et de plus d'acceder aux grandeurs caracteristiques evoquees dans les modeles. On a ainsi la mise en evidence d'elements constitutifs de la phase conductrice de taille caracteristique d'environ 10 nm et de leur agencement en agregats plus ou moins lineaires. On etablit aussi la structure semicristalline de pani(ppa).
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Assender, Hazel Elaine. "Magnetically induced microstructures in liquid crystalline polymers." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321035.
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Khatri, Bilal [Verfasser], and Thomas [Akademischer Betreuer] Hanemann. "Rapid prototyping of functional microstructured polymer-based composites." Freiburg : Universität, 2018. http://d-nb.info/1187133248/34.
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Nicholson, Lee Matthew. "Modelling of microstructural development in polymer films." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627418.
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Lippmann, Milena. "The microstructure of confined and thin polymer films." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=979725062.
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Kota, Arun Kumar. "Processing-structure-microstructure-property relationships in polymer nanocomposites." College Park, Md.: University of Maryland, 2007. http://hdl.handle.net/1903/7857.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Zeng, Shunjie. "Polymer modified cement: hydration microstructure and diffusion properties." Thesis, Aston University, 1996. http://publications.aston.ac.uk/14155/.
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Investigations concentrated on the styrene butadiene rubber (SBR) latex and formulations included standard carboxylated and special carboxylated latexes. The aqueous component, containing the stabilisers and antifoaming agent but not the polymer solids, was also used. For comparison, limited investigations were carried out using other polymer types e.g. acrylic, ethylene-vinyl acetate (EVA), and redispersible powders rather than emulsions. The major findings were: 1) All latex systems investigated acted as retarders for cement hydration. The extent of retardation depends on the type of polymer. The mechanism for cement hydration may be changed, and excessive retardation influences properties. 2) Polymer modified cements exhibited either similar or coarser pore structures compared with unmodified cements. Results suggest that polymer mainly exists in a mixture of cement hydrates and polymer phase. Very little evidence was found for the formation of a distinct polymer film phase. 3) During the first few days of curing the polymer solids are removed from the pore solution and concentrations of OH-, Na+ and K+ are reduced. These observations are probably a result of polymer-cement surface interactions since there was no evidence of any chemical reactions or degradation of the polymer. 4) Improved diffusional resistance of modified cements depends on the ability to achieve adequate workability at low w/c ratio, rather than modification of matrix structure.
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Tran, Hoang Vi. "The Influence of Microstructure on the Thermal Degradation Behavior of Poly(vinyl Chloride)." W&M ScholarWorks, 1997. https://scholarworks.wm.edu/etd/1539626102.
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Velazquez, Alberto. "Microstructure and thermal stability of PVC and chemically modified PVC." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74243.
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This thesis describes a study of the effect of microstructure on the thermal stability of poly(vinyl chloride), PVC, vinyl chloride-ethylene, VC-E, and vinyl chloride-propylene, VC-P, copolymers obtained by chemical modification of PVC. The VC-E copolymers, with an ethylene content between 1.1 and 21 mole %, are random copolymers with approximately the same degree of polymerization as the original PVC. A decrease in the number of defect sites is observed with extent of reaction. Concomitantly, the syndiotacticity increases. The VC-P copolymers, with propylene content of ca. 0.1%, also have less labile chlorines than the homopolymer since these react preferentially.The thermal stability of solid state samples was studied, at temperatures between 150 and 190$ sp circ$C under a nitrogen atmosphere, using a conductimetric method to measure evolved HCl. The thermal stability of the modified samples is improved relative to that of the initial homopolymers. For the VC-E copolymers, a linear relationship is observed between the rates of degradation and the number of labile chlorines, total double bonds and the degree of syndiotacticity. The role of syndiotacticity on the thermal degradation behavior is confirmed in results obtained with two unmodified PVC samples, with a similar number of defect sites but different syndiotacticity. The more syndiotactic resin shows a higher thermal stability. The average polyene sequence length is independent of the ethylene concentration. Thus, the ethylene units do not interfere in the development of polyene sequences.
The VC-P copolymers also show improved thermal stability as compared to that of PVC. However, the improvement is less than that of the VC-E copolymers, due to a lower extent of substitution of labile sites.
PVC previously saturated with HCl shows a markedly increased rate of degradation reflecting the autocatalytic role of HCl. For the PVC coated samples, a decrease in the degradation rates with decreasing PVC film thickness is observed due to more efficient removal of HCl. The PVC mixtures with Chromosorb W or silica gel exhibit a decrease in the dehydrochlorination rate constants with decreasing PVC content. The inert substrate acts as a diluent and avoids agglomeration of the samples and thus facilitates the removal of HCl.
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Qie, Lili. "Performance Improvement of Latex-based PSAs Using Polymer Microstructure Control." Thesis, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/19727.
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This thesis aims to improve the performance of latex-based pressure-sensitive adhesives (PSAs). PSA performance is usually evaluated by tack, peel strength and shear strength. Tack and peel strength characterize a PSA’s bonding strength to a substrate while shear strength reflects a PSA’s capability to resist shear deformation. In general, increasing shear strength leads to a decrease in tack and peel strength. While there are several commercial PSA synthesis methods, the two most important methods consist of either solvent-based or latex-based techniques. While latex-based PSAs are more environmentally compliant than solvent-based PSAs, they tend to have much lower shear strength, at similar tack and peel strength levels. Therefore, the goal in this thesis was to greatly improve the shear strength of latex-based PSAs at little to no sacrifice to tack and peel strength.
In this study, controlling the polymer microstructure of latexes or their corresponding PSA films was used as the main method for improving the PSA performance. The research was sub-divided into four parts. First, the influence of chain transfer agent (CTA) and cross-linker on latex polymer microstructure was studied via seeded semi-batch emulsion polymerization of butyl acrylate (BA) and methyl methacrylate (MMA). Three techniques were used to produce the latexes: (1) adding CTA only, (2) adding cross-linker only, and (3) adding both CTA and cross-linker. It was found that using CTA and cross-linker simultaneously allows one to expand the range of latex microstructural possibilities. For example, latexes with similar gel contents but different Mc (molecular weight between cross-links) and Mw (molecular weight of sol polymers) could be produced if CTA and cross-linker concentration are both increased. However, for the corresponding PSAs with similar gel contents, the relationship between their polymer microstructure and performance was difficult to establish as almost all of the medium and high gel content PSAs showed very low tack and peel strength as well as extremely large shear strength readings.
In the second part of this thesis, in order to improve the tack and peel strength of medium and high gel content PSAs, the monomer composition and emulsifier concentration were varied. It was found that changing the monomer mixture from BA/MMA to BA/acrylic acid (AA)/2-hydroxyethyl methacrylate (HEMA) while simultaneously decreasing emulsifier concentration dramatically improved the corresponding PSAs’ shear strength as well as tack and peel strength. The addition of polar groups to the PSA increased its cohesive strength due to the presence of strong hydrogen bonding; meanwhile, PSA films’ surface tension increased.
In the third part, two series of BA/AA/HEMA latexes were generated by varying the amounts of CTA either in the absence or presence of cross-linker. The latexes produced in the absence of cross-linker exhibited significantly larger Mc and Mw compared to their counterparts with similar gel contents prepared with cross-linker. The PSAs with the larger Mc and Mw showed much larger shear strengths due to improved entanglements between the polymer chains.
In the final part of the thesis, the performance of the BA/AA/HEMA PSAs was further improved by post-heating. Compared with original latex-based PSAs with similar gel contents, heat-treated PSAs showed not only significantly improved shear strengths, but also much larger tack and peel strengths. The different shear strengths were related to the PSAs’ gel structures, which were discrete in the original PSAs but continuous in the heat-treated PSAs. The improved tack and peel strengths were related to the PSA films’ surface smoothness. During the post-heating process, the PSA polymer flowed, resulting in much smoother surfaces than the original PSA films. In addition, the effect of post-heating was related to the polymer microstructure of the untreated PSAs. Decreasing the amount of very small or very big polymers or simultaneously increasing Mc and Mw could lead to post-treated PSAs with significantly better performance. Moreover, it was found that by optimizing the polymer microstructure of the original latex-based PSAs, it was possible to obtain a treated PSA with similar or even better performance than a solvent-based PSA with similar polymer microstructure.
Our original objective was surpassed: in two cases, not only was shear strength greatly improved, but so were tack and peel strength due to the simultaneous modification of PSA bulk and surface properties.
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Andrews, G. W. "Piezoelectric properties and microstructure of poly(vinylidene fluoride)." Thesis, University of Brighton, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233373.
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Huang, Yuan. "Microstructure-property relationships in toughened epoxy polymers." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46829.
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Trzaskowski, Justyna [Verfasser]. "Precise Microstructure Polymer Nanocrystals via Olefin Metathesis / Justyna Trzaskowski." Konstanz : Bibliothek der Universität Konstanz, 2016. http://d-nb.info/1114894540/34.
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MING, YAN LIU. "Comportement viscoplastique des polymères techniques a grande déformation et à grande vitesse de déformation (loi de comportement-critère de la rupture-essais dynamiques-identification, optimisation)." Paris, CNAM, 1986. http://www.theses.fr/1986CNAM0075.
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Étude de polymère semicristallins. Modèle microstructural: influence de la vitesse de déformation et de la température. Proposition d'un modèle cisaillement de la rupture ductile. Essais de torsion à grande vitesse avec le système a de Hopkinson et la machine d'inertie
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Li, Linlin. "Microstructure characterization of polymers by modern NMR techniques." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1353000762.
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Delzenne, Pascale. "Piézoélectricité et microstructure dans des polymères ferroélectriques : PVF2 et P(VF2-F3E)." Grenoble 1, 1986. http://www.theses.fr/1986GRE10033.
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Etude de la microstructure polyfluorure de vinylidene (pvf::(2)) en phase beta orientee par diffusion rx centrale. L'organisation, la forme et les dimensions des cristallites sont caracterisees. Analyse de la transition ferro-para electrique du copolymere p(vf::(2)-f::(3)e). Mise en evidence du desordre dynamique de la phase paraelectrique qui induit une reorganisation de la microstructure du polymere oriente par laminage
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Vautrin-Ul, Christine. "Polymérisation cationique du penta-1,3-diène et copolymérisation avec l'isobutène : contribution à la synthèse de nouveaux copolymères triblocs." Vandoeuvre-les-Nancy, INPL, 1996. http://www.theses.fr/1996INPL082N.
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Cette étude est consacrée à la polymérisation cationique du penta-1,3-diène ou pipérylène (PD) et à sa copolymérisation avec l'isobutène (IB), l'objectif principal étant la préparation de copolymères triblocs constitués d'une séquence centrale élastomère polyisobutène et de deux segments rigides de type poly(penta-1,3-diène) partiellement cyclisé. La première partie de ce travail traite de la polymérisation cationique de chacun des isomères cis et trans du penta-1,3-diène et d'un pipérylène technique (mélange cis/trans: 45/55) contenant 10% d'impuretés (hydrocarbures en C5). Une analyse complète de la microstructure complexe de ces matériaux est effectuée ainsi que l'étude de l'influence de différents paramètres expérimentaux. Il est montré que la nature du monomère utilisé (isomère pur ou mélange technique) n'a pas d'influence notable sur sa polymérisation par voie électrophile. La seconde partie décrit la copolymérisation du pipérylène technique avec l'isobutène. D’une part, la préparation de copolymères statistiques montre que l'incorporation des deux monomères PD et IB dans la chaine correspond à un schéma cinétique à effet terminal. Les valeurs des rapports de réactivité rib=1,1 et rpd=1,3 révèlent un comportement quasi aléatoire avec une faible propension à la formation de séquences homogènes. D’autre part, trois échantillons de copolymères triblocs sont synthétisés par addition séquentielle des monomères. Ils sont composés d'un bloc central polyisobutène dont la masse molaire moyenne en nombre (Mn) a été ajustée entre 5 000 et 25 000 g. Mol-1 et de deux segments polydiéniques caractérisés par une masse molaire globale (Mn) proche de 7 000 g. Mol-1 et un taux de cyclisation compris entre 35 et 50%
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Nadal, i. Soy Josep. "Noves aproximacions a la síntesi i caracterització de poliglicols al·lílics, polihidrosiloxans i surfactants copolimèrics. Avaluació d'aquests surfactants en formulacions de poliuretà." Doctoral thesis, Universitat de Girona, 2002. http://hdl.handle.net/10803/8030.
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Els polímers són una sèrie de compostos que troben un ampli ventall d'aplicacions en la indústria actual. Un exemple són les espumes de poliuretà, estructures de tipus cel·lular obtingudes mitjançant la reacció química entre compostos de tipus isocianat i compostos de tipus poliol (polièters amb diferent nombre de grups hidroxil). És imprescindible l'ús d'additius d'estructura tensioactiva (surfactants de silicona) per estabilitzar el procés d'espumació i per proporcionar una estructura cel·lular ordenada i homogènia en mida i distribució. La síntesis i caracterització de les molècules precursores (polihidrosiloxans i polièters al·lílics), l'estudi de la reacció d'hidrosililació com a via d'obtenció dels diferents surfactants per reacció d'addició entre els polihidrosiloxans i els polièters al·lílics i la caracterització i avaluació en formulacions comercials de poliuretà dels surfactants sintetitzats han constituït els objectius del present treball.MEMÒRIA
La Tesi Doctoral ha estat presentada seguint el següent esquema:
CAPÍTOL I. INTRODUCCIÓ A LA QUÍMICA DEL POLIURETÀ.
Es presenten els principis de la química del poliuretà, fent esment dels recents avenços en la síntesis i caracterització d'aquests compostos polimèrics, així com un apartat concret centrat en els surfactants de silicona. Es presenten les estructures habituals d'aquests compostos comercials i es detallen les reaccions de síntesi i les característiques físiques que aquests compostos proporcionen a les espumes de poliuretà.
CAPÍTOL II. OBJECTIUS.
1.- Síntesis y caracterització d'una àmplia gamma de poliglicols al·lílics i de polihidrosiloxans amb grups hidrur reactius, ambdós precursors d'estructures polimèriques de tipus surfactant.
2.- Estudi de la reacció d'hidrosililació com a via de formació d'enllaços Si-C no hidrolitzables, mitjançant la reacció d'addició entre els substrats al·lílics insaturats i els polisiloxans amb grups hidrur reactius.
3.- Caracterització de les estructures polimèriques de tipus surfactant sintetitzades i avaluació d'aquestes en formulacions de poliuretà, a fi de relacionar l'estructura química d'aquests oligómers amb els efectes físics que originen en l'espuma de poliuretà.
CAPÍTOL III. SÍNTESI I CARACTERITZACIÓ DE SUBSTRATS AL·LÍLICS INSATURATS DE TIPUS POLIGLICOL.
S'han caracteritzat per HPLC-UV una sèrie de polietilenglicols comercials. S'ha estudiat la reacció de derivatització al·lílica sobre els grups hidroxil dels polièters comercials (PEG, PPG i copolímers PEG-PPG) i s'han caracteritzat exhaustivament els productes sintetitzats (1H,13C-RMN, GC, GC-MS, FTIR, ESI-MS, HPLC-UV). S'ha iniciat un estudi de polimerització aniònica sobre nous epòxids amb un punt de diversitat molecular, sintetitzant-se i caracteritzant-se els corresponents nous polièters obtinguts.
CAPÍTOL IV. SÍNTESI I CARACTERITZACIÓ DE POLIHIDROSILOXANS REACTIUS.
S'estudia la síntesis de polihidrosiloxans amb grups hidrur reactius, mitjançant la reacció de polimerització aniònica d'obertura d'anell ("AROP, anionic ring opening polimerization") i mitjançant la reacció de polimerització per equilibració catiònica. Es presenta una caracterització exhaustiva dels productes sintetitzats i es descriu la naturalesa de la microestructura polimèrica a partir de la distribució bivariant dels copolímers PDMS-co-PHMS (poli(dimetilsiloxà)-co-poli(hidrometilsiloxà)).
CAPÍTOL V. ESTUDI SISTEMÀTIC DE LA REACCIÓ D'HIDROSILILACIÓ.
S'ha estudiat la reacció d'hidrosililació amb la finalitat de sintetitzar estructures copolimèriques poliglicol-polisiloxà a partir de la reacció de polisiloxans hidrur reactius i polièters al·lílics. S'han provat diferents catalitzadors (Pt/C 5%, cat. de Speier i cat. de Karstedt), s'han sintetitzat diferents estructures tensoactives (lineals i ramificades) i s'ha modelitzat les diferents reaccions secundàries observades, per presentar un estudi mecanístic de la reacció d'hidrosililació aplicada a la síntesis de molècules d'elevat PM a partir de la reacció entre substrats al·lílics insaturats i polihidrosiloxans.
CAPÍTOL VI. AVALUACIÓ DELS SURFACTANTS EN FORMULACIONS DE POLIURETÀ.
S'ha estudiat la idoneïtat dels surfactants de silicona sintetitzats en diferents formulacions de poliuretà comercials. S'ha relacionat el comportament físic d'aquests surfactants en les espumes de poliuretà amb la seva estructura química a partir de l'anàlisi per microscòpia electrònica de rastreig.
CAPÍTOL VII. CONCLUSIONS.
S'han esposat les conclusions extretes de cada capítol.
The present review has been structured in three parts, firstly a general introduction to polyurethane chemistry and the specific role that silicone surfactants develop, secondly a memory that contents a concise description of the PhD Thesis structure and finally the presentation of the results obtained and their discussion.
1.- INTRODUCTION
Polyurethane is one of the most important polymers used in the industry worldwide. The reaction, discovered in 1937 by Otto Bayer, consists in a polyaddition reaction between hydroxyl compounds and isocyanate groups. This reaction forms the new urethane group (strictly a carbamat group) that provide the chemical structure of the polymer. In the presence of different amounts of water, another reaction is involved, between isocyanate groups and water, in order to obtain urea groups. This reaction is very important because, besides generates new polyurea structures it generates carbon dioxide (CO2), the blowing aggent mostly used in the formulations of polyurethane.
Actually, a lot of applications of polyurethane products take advantage on the specific cellular structure that presents, specially flexible foams in mattresses, sofas, seats, rigid foams as insulation panels and semi-rigid foams in the automotive industry. The cellular structure is obtained in the foaming process of the reaction, which involves the generation of a gas (usually CO2 although other compounds like pentane, HCFC's and external CO2 had been used) and the growing of the cell because of the exothermic process. The foaming process is usually an unstable state that needs the participation of a surfactant, a silicone structure that provides the necessary stabilizing capacity in the foaming process. Moreover, another important feature of silicone surfactants is to improve the order and distribution of the cells in the foam.
Generally, the chemical structure of silicone surfactants is co polymeric, consisting in an hydrophobic part composed by the polysiloxane group and an hydrophilic part, usually being made up of different types of polyether structures. This different physical behaviour in the same molecule provides the specific characteristics of silicone surfactants. In order to obtain commercially available surfactants, it has been necessary to study the synthesis and the characterization of the components in the surfactant molecule (the polyether and the polysiloxane groups) and to perform a study of the hydrosilylation, the chemical reaction that generates the co polymeric structure by the reaction between the polyether and the polysiloxane constituents.
2.- PhD THESIS STRUCTURE
The thesis has been organized in seven chapters, being the first of them the introduction to polyurethane chemistry. In the second chapter are exposed the aims of the work. The third chapter is the synthesis and characterization of polyether type unsaturated substrates, the fourth is the synthesis and characterization of reactive polyhydrosiloxanes and the fifth is the systematic study on the hydrosilylation reaction. The evaluation of surfactants in different polyurethane formulations is described in the sixth chapter whereas the concluding remarks have been reported in the seventh chapter.
3.- RESULTS AND DISCUSSION
The first part of this study details the synthesis and characterization of unsaturated polyethers, substrates of the hydrosilylation reaction. Thus, the allylic modification of commercial monohidroxy polyethers has allowed the synthesis of this unsaturated substrates that can react through hydrosilylation reaction with Si-H bonds. In order to obtain new polyether structures, an investigation about the anionic polymerisation of new epoxies has been developed. These new polyether structures have been extensively characterized to estimate the polymerization degree and their molecular weight.
The synthesis and characterization of reactive polysiloxane compounds (containing Si-H bonds in their structure) has been the second aim of this work. In order to obtain these polysiloxane structures, both anionic polymerization of cyclic trisiloxane compounds and cationic polymerization have been studied. Its interesting to emphasize that the results have shown that the microstructure of the copolymeric poly(dimethylsiloxane)-co-poly(hidromethylsiloxane) is statistical in the monomeric distribution (based on MALDI-TOF-MS and 29Si-RMN results), thus the chemical composition along the polymer chain become constant.
Little information has been reported in the literature about the hydrosilylation as source of polymer structures. In order to clarify the synthetic behaviour of the reaction between polysiloxanes with Si-H bonds and allylic polyethers, an exhaustive study of the hydrosilylation as been developed. Different catalysts (Speier's, Karstedt's and an heterogeneous Pt/C 5% have been studied), concluding that the Karstedt catalyst has given the better behaviour.
Finally, the evaluation of the surfactant structures synthesized in different commercially available polyurethane formulations as allowed obtaining a relation between the chemical structure of the silicone surfactant and the physical behavior in the foaming process. SEM has been the technique of choice to better characterize the otained foams.
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Singamaneni, Srikanth. "Microstructures and multifunctional microsystems based on highly crosslinked polymers." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29746.
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Thesis (Ph.D)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2010.Committee Chair: Tsukruk, Vladimir; Committee Member: Gall, Ken; Committee Member: Griffin, Anselm; Committee Member: Jang, Seung Soon; Committee Member: Thio, Yonathan. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Stephens, Julian Andrew. "Control of the morphology and microstructure of conjugated polymer systems." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627064.
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Ji, Guang. "Study on Microstructure and Adhesion Property of Electrospun Polymer Blends." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1435789657.
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Li, Qianqian. "Synthesis, mechanical properties and microstructure of carbon nanotube polymer composites." Thesis, University of Edinburgh, 2006. http://hdl.handle.net/1842/12416.
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A commercial block copolymer (BC) was first introduced as a dispersing agent to disperse CNTs homogenously in an elastomeric epoxy resin. Single wall CNTs (SWNTs) and multiwall CNTs (MWNTs) were both used to reinforce this epoxy resin. By adding the BC, mechanical properties of CNT/epoxy resin composites were increased dramatically compared to CNT composites without BC. Optical microscopy and scanning electron microscopy were conducted to study the microstructure of CNT/copolymer/epoxy resin composites. It has been confirmed that by using BC, CNTs were dispersed more homogenously in the epoxy resin matrix. Furthermore, improved mechanical properties of composites were achieved by using small amount of BC. The effects of different preparation procedures and different concentrations of materials were also studied. The optimum ultrasonic time and power were decided after trying different options. Ethanol was chosen as a solvent in order to help improving the dispersion. Thus, the optimum proportions of CNT/BC and CNT/epoxy resin were determined for further systematic studies. Finally, SWNT composites and MWNT composites were produced by adding the same mass weight CNTs and by adding the same surface area CNTs. In both cases, SWNT composites presented the best mechanical properties compared to MWNT composites. By adding the same mass weight, the MWNT composites with smaller diameter were stronger because of overall higher surface area; while by adding amounts with the same total surface area, the results were opposite.
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Gupta, Vinay Kumar Kornfield Julia A. Kornfield Julia A. "Controlling molecular and microstructural alignment in anisotropic polymer systems /." Diss., Pasadena, Calif. : California Institute of Technology, 1996. http://resolver.caltech.edu/CaltechETD:etd-12132007-085351.
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Jeromenok, Jekaterina. "Polymers from the natural product betulin : a microstructural investigation." Phd thesis, Universität Potsdam, 2012. http://opus.kobv.de/ubp/volltexte/2012/6138/.
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Porous materials (e.g. zeolites, activated carbon, etc.) have found various applications in industry, such as the use as sorbents, catalyst supports and membranes for separation processes. Recently, much attention has been focused on synthesizing porous polymer materials. A vast amount of tailor-made polymeric systems with tunable properties has been investigated. Very often, however, the starting substances for these polymers are of petrochemical origin, and the processes are all in all not sustainable. Moreover, the new polymers have challenged existing characterizing methodologies. These have to be further developed to address the upcoming demands of the novel materials. Some standard techniques for the analysis of porous substances like nitrogen sorption at 77 K do not seem to be sufficient to answer all arising questions about the microstructure of such materials. In this thesis, microporous polymers from an abundant natural resource, betulin, will be presented. Betulin is a large-scale byproduct of the wood industry, and its content in birch bark can reach 30 wt.%. Based on its rigid structure, polymer networks with intrinsic microporosity could be synthesized and characterized. Apart from standard nitrogen and carbon dioxide sorption at 77 K and 273 K, respectively, gas sorption has been examined not only with various gases (hydrogen and argon) but also at various temperatures. Additional techniques such as X-ray scattering and xenon NMR have been utilized to enable insight into the microporous structure of the material. Starting from insoluble polymer networks with promising gas selectivities, soluble polyesters have been synthesized and processed to a cast film. Such materials are feasible for membrane applications in gas separation. Betulin as a starting compound for polyester synthesis has aided to prepare, and for the first time to thoroughly analyse a microporous polyester with respect to its pores and microstructure. It was established that nitrogen adsorption at 87 K can be a better method to solve the microstructure of the material. In addition to that, other betulin-based polymers such as polyurethanes and polyethylene glycol bioconjugates are presented. Altogether, it has been shown that as an abundant natural resource betulin is a suitable and cheap starting compound for some polymers with various potential applications.Das Bestreben, ölbasierte Produkte durch nachwachsende Rohstoffe zu ersetzen, hat dazu geführt, dass in immer größerer Zahl günstige, reichlich vorhandene Naturstoffe als Ausgangsstoffe für chemische Synthesen untersucht werden. In dieser Arbeit werden Polymere auf Basis von Betulin, einem aus Birkenrinde extrahierten Naturstoff, vorgestellt. Betulin ist zu 30 Gewichtsprozent in Birkenrinde enthalten. Da Betulin ein Nebenprodukt der Holzindustrie ist, ist es kostengünstig und sein Einsatz als Ausgangsstoff äußerst lukrativ. Die ersten Berichte über Betulin-basierte Polymere sind in den 1980er Jahren in Russland und Finnland erschienen, in den Ländern mit großen natürlichen Vorkommen an Birken. Betulin wurde in dieser Arbeit verwendet, um sogenannte mikroporöse Polymere herzustellen. Dies sind Stoffe mit Poren von molekularer Dimension. Mikroporöse Materialien sind wegen ihrer potentiellen Anwendung als Katalysatorträger und Gasseparationsmembranen hochinteressant. Die Klasse mikroporöser Polymere wurde durch die Synthese von unlöslichen Betulin-basierten Polyesternetzwerken erweitert. Außerdem gelang es, lösliche Polyester in Form dünner Filme herzustellen. Diese zeigten vielversprechende Ergebnisse in der Trennung von Stickstoff und Kohlendioxid und weisen somit Potential für die Nutzung als Membran auf. Dies könnte z. B. für Kohlendioxid-Reduzierung in Postcombustion-Verfahren interessant sein. Überdies wurde gezeigt, dass Stickstoffadsorption bei 77 K nicht ohne weiteres als Standardmethode für die Analyse von mikroporösen Materialien geeignet ist und dass die mikroporösen Materialien ferner durch Stickstoffadsorption bei 87 K und andere Gassorptionsmethoden bei verschiedenen Temperaturen zu charakterisieren sind. Diese Arbeit trägt zum besseren Verständnis mikroporöser Polymere bei.
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Lämmel, Marc, Evelin Jaschinski, Rudolf Merkel, and Klaus Kroy. "Microstructure of sheared entangled solutions of semiflexible polymers." Forschungszentrum Jülich, 2016. https://ul.qucosa.de/id/qucosa%3A15029.
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We study the influence of finite shear deformations on the microstructure and rheology of solutions of entangled semiflexible polymers theoretically and by numerical simulations and experiments with filamentous actin. Based on the tube model of semiflexible polymers, we predict that large finite shear deformations strongly affect the average tube width and curvature, thereby exciting considerable restoring stresses. In contrast, the associated shear alignment is moderate, with little impact on the average tube parameters, and thus expected to be long-lived and detectable after cessation of shear. Similarly, topologically preserved hairpin configurations are predicted
to leave a long-lived fingerprint in the shape of the distributions of tube widths and curvatures. Our numerical and experimental data support the theory.