Tesi sul tema "Polystyrene"

Styrene was recovered from polystyrene (molecular weight of 138 000) by thermolysis in a nitrogen atmosphere at temperatures between 368$ sp circ$C and 407$ sp circ$C. The results were independent of the initial weight of polystyrene which was varied between 30 and 480 grams. Up to 70% of the polystyrene was converted to styrene. The styrene yield increased with temperature. At higher temperatures, the residue left in the reactor consisted mainly of styrene monomer, dimer and trimer (MW of 190). The maximum rate constant of volatile production was found to fit a first order model. The activation energy obtained was 166.5 kJ/mol, which is in accordance with literature values.

2010 - 2011
La sintesi di materiali polimerici da metodo di modificazione, per ottenere le proprietà desiderate in polimeri, è un argomento importante in chimica dei polimeri e tecnologia. Molto spesso, proprietà desiderate non sono raggiungibili dalle proprietà di un omopolimero singolo. Una strategia comunemente utilizzato per raggiungere questo scopo è l'ancoraggio di gruppi funzionali specifici lungo le catene polimeriche In questo contesto che l'interesse nella funzionalizzazione di polistirene sindiotattico (s-PS) sorge, uno semi-cristallina polimero termoplastico che dispone di basso costo e eccellenti proprietà meccaniche e dielettriche, eccellente resistenza al calore e resistenza ai solventi. Inoltre, il sPS ha un polimorfismo complessa e la peculiarità che due delle sue forme note cristalline sono nanoporoso che sono caratterizzate della presenza di spazi vuoti (cavità nel δ-form e canali in forma ε) all'interno del reticolo cristallino, in grado per accogliere piccole molecole. Questa tesi presenta nuova strategia selettiva funzionalizzazione per solo fase amorfa di s-PS che al tempo stesso non cambia la fase cristallina e pertanto tutte le caratteristiche del s-PS. La solfonazione permette di introdurre un gruppo polare acido sulle catene polimeriche della fase amorfa di s-PS, che rende il polimero idrofilo, con una capacità di scambio protonico, da qui l'idea di usare pellicole solfonati di sPS come membrane polyelectrolytic in carburante cellule. [a cura dell'autore]
X n.s.

Plusieurs copolymeres triblocs polystyrene bloc polyisoprene bloc polystyrene, sis, ont ete soumis a l'examen des relations structures chimiques et microscopiques proprietes physiques et mecaniques. La viscosite des solutions des sis dissous dans du toluene suit une loi fonction de ne#c#c#e, nombre de nuds equivalents developpes par la chaine totale, dans le milieu. Cette loi est en ne#c#c#e#3#,#4, tant que le milieu reste concentre et enchevetre. Pour les analyses en mecanique dynamique mesurees entre 100c et +200c, nous avons montre l'importance du role joue par la longueur de chacun des blocs. On doit considerer a la fois les effets d'enchevetrements du bloc polystyrene et les nature et qualite de la morphologie. Dans le cas des elastomeres, le module tangent a la courbe de traction, etg, suit une loi derivee du modele de nielsen. Les diagrammes de mooney rivlin revelent quant a eux l'importance du role tenu par les nodules de polystyrene. Selon la longueur du segment polystyrene, celui-ci, en plus de sa fonction d'agent de reticulation chimique, peut ou non etre assimile a une charge renforcante. Le traitement des courbes d'hysterese constitue un double moyen de distinction des morphologies et de mise en evidence de phenomenes anormaux de dissipation d'energie

Les comportements photochimiques du polystyrène, du polyacrylonitrile et du poly(styrene-co-acrylonitrile), sous irradiations a courte longueur d'onde (egale a 254 nm) et a grandes longueurs d'onde (superieures ou egales a 300 nm), ont été étudiés. Différentes techniques d'identification des photoproduits formes lors de l'irradiation des polymères sous forme de films solides ont été utilisées: spectroscopies irtf et uv-visible, chromatographie hplc. D'autres méthodes, permettant de transformer spécifiquement les photoproduits, ont été associées a ces techniques analytiques: traitements chimiques (sf#4,nh#3,hcl,ch#3oh,h#2o) et traitements physiques (photolyse, thermolyse et thermooxydation). L'identification des photoproduits et la caractérisation de leur stabilité thermique et photochimique ont permis d'établir le mécanisme de photooxydation de chacun des trois polymères étudiés

This thesis is concerned to the development of novel engineered surface materials using nitrogen-doped carbon nanotubes (CNx) that were grafted with polystyrene (PS) chains using in situ radical polymerization controlled by nitroxides. The in situ polymerization method involved two main steps, the radical attachment of a system initiator-controller that could follow a Nitroxide Mediated Radical Polymerization (NMRP) in solution. The chemically modified carbon nanotubes were used in the preparation of polymer-nanotube composites with the aim of improving the dispersion of nanotubes within the matrix, but also the interfacial adhesion between them. The produces polymer-grafted Cnxnanotubes were used as nanofillers using several kind of matrices (amorphous PS, semicrystalline polyethylene oxide (PEO) and immiscible blends PS-PEO. An extensive characterization was performed on the obtained modified CNx nantubes and polymer-nanotube composites in order to evaluate their physical and chemical properties
Cette thèse concerne le développement de nouveaux matériaux à base de nanotubes de carbone dopés à l’azote (CNx) sur lesquels des chaînes de polystyrène (PS) ont été greffés in situ par polymérisation radicalaire contrôlée par des nitroxides. La méthode de polymérisation in situ se décompose en deux étapes principales : l’attachement radicalaire d’un système initiateur – contrôleur, suivi d’une polymérisation radicalaire type NMRP (Nitroxide Mediated Polymerization) en solution. Les nanotubes de carbone modifiés chimiquement sont ensuite utilisés pour l’élaboration de composites polymères – nanotubes. Le greffage de polymère est censé améliorer la dispersion des nanotubes dans la matrice ainsi que l’adhésion interfaciale nanotubes-matrice. Plusieurs types de matrices sont étudiées (PS amorphe, PEO semi-cristallin et mélanges PS-PEO). Une caractérisation approfondie a été menée sur les composites à renfort de nanotubes greffés, pour évaluer l’impact du greffage sur les propriétés mécaniques et électriques des composites

The topic of my thesis are menhirs. Specifically, the largest Czech menhir known as the Stone Shepherd (3200 cm). The aim of this work was to transfer the exact shape and size of this megalith and materialize it here in Brno. This goal required the use of many procedures. At the beginning there was a photo shoot, then a 3D program, 3D program editing, and slicing into contour lines. Then I projected the menhir on a wall in real size and traced it to polystyrene boards. The next step was to cut out all 104 plates on a band saw and I could go to gluing and folding the whole object. The final step was to paint the object in white. The result is a simple and clean polystyrene object. I did not cover the contour lines - I present the object in the most direct form possible. The styrofoam megalith, despite its size, is a sculpture in the interior. Ideally, I would create an installation that would create a separate, isolated space for the object.

The diploma thesis deals with radical bulk polymerization of styrene. Recent knowledges about mono- and multifunctional initiators of radical polymerization and coordination polymerization of styrene with metalocene initiators are summarized in theoretical part. Experimental part of diploma thesis is focused on relationship between polymerization conditions and conversion, molecular mass and distribution of molecular mass. Experiments carried out with monofunctional initiators (dibenzoylperoxide, dilauroylperoxide, tert-butylperbenzoate) and with bifunctional initiators (Luperox 101 and Luperox 256). Polymerizations took place at temperatures from 80 to 134 °C, reaction time was from 1 to 24 hours, and pressure was 100 and 500 kPa. Conversion of monomer was determined by gravimetry and infrared spectroscopy. Molecular mass and indexes of polydisperzity were measured by gel permeation chromatography in solutions of polystyrene with tetrahydrofurane at temperature 23 °C.

Polystyrene, PS, is a preferable polymer in industry, but, its brittle characteristic restricts its utilization. The aim of this study is to improve the impact strength of PS by the help of elastomeric materials SEBS-g-MA and E-BA-GMA. In order to prevent the reduction in the tensile strength of the materials, three different types of organic montmorillonites, MMT, (Cloisite®
30B, 25A and 15A) were used as fillers. Nanocomposite preparation was performed in a co-rotating twin screw extruder. Initially elastomer and organoclay contents were kept at 5wt% and 1-2wt% respectively. Well dispersed silicate layers were obtained for the nanocomposite containing SEBS-g-MA and Cloisite®
25A owing to the high viscosity of SEBS-g-MA and the solubility of polystyrene end block of SEBS with PS matrix. Owing to higher hydrophobicity of Cloisite®
15A a better dispersion was expected compared to Cloisite®
25A, but, it was concluded that two long aliphatic tails of Cloisite®
15A limited the access of polymer chains to the clay surface. The desired impact strength values could not be achieved by using 5wt% elastomeric materials
therefore, it was decided to increase the SEBS-g-MA content up to 15, 20, 30 and 40wt%. With increasing elastomer content, increasing average elastomer domain size was obtained. Also, it was observed that with the addition of organoclay, the elastomeric domain size increases since the clay particles reside in the elastomer phase and at the interphase between elastomer and PS. The mechanical test results showed that the nanocomposites containing 15 and 20wt% SEBS-g-MA have the optimum average domain size that results in better impact strength values without deteriorating tensile properties.

This thesis examines the processing behaviour of molten polystyrenes with different molecular weights and architectures, using experimental results obtained from a micro-scale processing apparatus and numerical simulations applying both empirical and molecular-based constitutive models. Processing experiments were performed using a multi-pass rheometer, a two piston capillary-type machine which principally employed a contraction then expansion slit geometry. This was able to provide flow-induced birefringence and pressure difference data at a range of flow rates from ten gram sample quantities. The parameters required to rheologically characterise the linear and non-linear viscoelastic behaviour of the polystyrenes were obtained from experiments performed using parallel plate strain-controlled rheometers. A commercial grade polydisperse polystyrene was used as a reference material and to validate the techniques used. Five monodisperse polystyrenes with molecular masses ranging from 66,000 to 485,000 kg/kmol were studied, together with two differently weighted blends of two of these. As well as these linear molecules of varying molecular weight distribution, observations were made of two polystyrenes with branched structures, one an asymmetric H, and the other a comb structure. Experimental data from the range of materials tested has shown that it is possible to distinguish differences between the types using flow birefringence in a processing flow. Monodisperse polystyrenes are notable for a high degree of symmetry between entry and exit patterns for lower molecular weights and flow rates. Blends of a small proportion of low molecular weight monodisperse with high molecular weight showed significantly improved processability, and similar birefringence to the broadly polydisperse type. Branched molecules were seen to exhibit transient stress fangs in start-up flow. A further significant experimental observation was the onset of instabilities and breakdown of continuum flow in high molecular weight monodisperse polystyrenes. The experimental data was compared with the predictions made by advanced numerical simulations, and it was found that empirical models gave generally good steady state predictions in most cases, while a molecular approach was able to predict the different transient behaviour characteristic of long chain branching, and make predictions for more extreme experimental conditions.

Polymers have ideal bulk properties for many applications. However, adhesion to many polymers is poor without surface pretreatment. This can result, for example, in peeling paint and printing, adhesive joint failure and bio-incompatibility. In applications such as painting, printing, adhesive bonding and biocompatibility, various cleaning or surface chemical modifications may be employed. A commodity polymer where pretreatment IS sometimes needed is polystyrene. This project investigated, in detail, the effects of a novel method of modification namely mediated electrochemical oxidation (MEO), as a mode of surface modification on polystyrene and a comparison was made with other polymers. The resulting modification was investigated using a range of surface analysis techniques to obtain complementary information. These included; X-ray photoelectron spectroscopy, contact angles, static secondary ion mass spectrometry, atomic force microscopy, chemical derivatisation, scanning electron microscopy, attenuated total reflection Fourier Transform infrared spectroscopy and composite lap shear joint testing. It has been shown that MEO modifies the surface of polystyrene introduced oxygen mainly as hydroxyl groups, and a small number of carbonyl groups, that are positioned only on the backbone hydrocarbon chain. This modification improved adhesion, was stable and samples could be stored in aqueous media. The resulting hydroxylation was further derivatised using an - amino acid to provide a specialised surface. This was very different from the multiple oxygen functionalities introduced in the comparison studies by UV/ozone and plasma treatments.

Lors de ce travail, de fins films de polystyrène ont été déposés dans la post-décharge d’une torche plasma atmosphérique commerciale, mais aussi dans la décharge d’une DBD (Décharge à Barrière Diélectrique), conçue et développée par nos soins au laboratoire. Une DBD est un procédé permettant d’obtenir des plasmas froids à pression atmosphérique.

Nos résultats ont montré que la DBD permettait d’obtenir des films de polystyrène de meilleure qualité (degré d’oxydation moindre…) qu’avec la torche commerciale en raison de l’atmosphère contrôlée de l’enceinte DBD. Les films sont déposés en présence d’un gaz porteur (Ar ou He dans la DBD). Nous avons pu mettre en évidence l’influence de la nature de ce gaz porteur sur la structure des films (degré de branchement, et de réticulation des films et de préservation des cycles aromatiques de la molécule de départ).

Les dépôts de polystyrène sulfoné ont été synthétisés dans la DBD en une seule étape, par « copolymérisation » de deux précurseurs (styrène et acide trifluorométhane sulfonique) injectés simultanément dans la décharge. Ces membranes pourraient servir d’électrolyte dans les piles à combustibles miniaturisées de type PEMFC (« Polymer Electrolyte Membrane Fuel Cell »), utilisant de l’hydrogène ou du méthanol et ce pour des applications portables.

L’acide trifluorométhane sulfonique permet le greffage de groupements sulfoniques échangeurs d’ions (nécessaires pour la conductivité de la membrane) sur le squelette de polystyrène.

La complémentarité des différentes techniques spectroscopiques utilisées -Spectroscopie des Photoélectrons X (XPS), Infra-Rouge à Transformée de Fourier (FTIR), Spectroscopie des Ions Secondaires (SIMS) statique et dynamique- ont montré que les groupements acides sulfoniques (bien préservés dans la décharge à pression sub-atmosphérique) étaient bien greffés dans la matrice de polystyrène, et ce sur toute l’épaisseur de la membrane. L’influence des paramètres (température de l’acide, tension appliquée entre les électrodes, nature du gaz porteur…) sur la quantité de groupements ionisables greffés, sur la vitesse de dépôt et aussi sur la morphologie des films a été étudiée respectivement par XPS et par microscopie.

En plus des dépôts sur substrats usuels (Si, acier…) utilisés pour les caractérisations chimiques, nous avons synthétisé les films directement sur des électrodes de carbone enrichies en platine.

Nous avons déposé le catalyseur à partir d’une solution colloïdale de platine nébulisée dans la post-décharge d’une torche plasma atmosphérique sur des couches de carbones poreuse et sur du carbone vitreux (utilisé comme modèle pour le profilage par SIMS dynamique) dans différentes configurations et ce pour différents paramètres afin de constituer des électrodes servant de substrat pour l’adhésion de la membrane-plasma pour des perspectives d’assemblage membrane-électrodes pour PAC. /

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Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Due to brittleness of polystyrene, PS, its usage area is restricted. To solve this problem and expand the usage area of PS, it can be blended and impact modified with an elastomeric material. In this study, the decrease in the modulus and tensile strength imparted by impact modification was overcome by reinforcing this mixture by incorporating organoclays and producing nanocomposites. This study consists of two parts. In the first part of this study three different types of aliphatic elastomeric materials and three different types of organoclays were used and their effects on the morphology, mechanical, thermal, and rheological properties of PS were investigated. Lotader AX8900, Lotader AX8840 and Lotader 2210 were chosen as the aliphatic elastomeric compatibilizers
and Cloisite

In this work the nonlinear behavior of concentrated polystyrene solution was examined using sliding plate rheometer developed at McGill University. In this rheometer a novel transducer is used to measure the shear stress and an optical system is used to measure birefringence during flows involving high shear rates.
The steady shear stress was found to be independent of shear rate at high shear rates. The Cox-Merz rule was found to be valid for concentrations less than 0.199 g.cm$ sp{-3}$, but a deviation from the rule was observed for higher concentrations. Sigmoidal damping functions, based on both the shear stress measurements and the birefringence measurements, were determined. The exponential stress coefficient and the third normal stress difference were calculated from experimental data for different values of exponential rate constant and different strain scale factor. The exponential rate constant was shown to have a strong influence on both the exponential stress coefficient and the third normal stress difference.

The delta-phase of the syndiotactic polystyrene/ethylbenzene system, as formed by crystallisation from dilute solution, is shown to result in a lamellar morphology, with a monoclinic crystal lattice similar to that already reported for the complex with toluene. The temperature/concentration phase diagram for sPS/ethylbenzene gels was obtained using DSC. This shows the presence of three polymer/solvent compounds, one of which contains 0.25 solvent molecules per monomer unit. For this latter compound, the stoichiometry corresponds to that proposed by Chatani et al. for the delta-phase of sPS in toluene. Combined SAXS, FTIR, DSC and TGA measurements show that an increase in the X-ray long period between 80 and 120°C is related to solvent loss and decomplexation. There is also some temporary loss in helical order. SANS measurements on the delta-phase reveal negligible isotopic fractionation. The small increase in the in-plane radius of gyration with increasing molecular weight is interpreted as evidence of a sheetlike molecular conformation, with superfolding at higher molecular weights leading to a multiple sheet structure. On transformation to the solvent-free gamma-phase, an increase in radius of gyration results from a displacement of crystal stems out of the delta-phase sheets. Further support to these conclusions is brought by intermediate and wide angle neutron scattering. Data for delta-phase are shown to be consistent with sheetlike arrangements of crystal stems along the a direction. Adjacent stems therefore show an alternation in helicity. Simulations based on a statistical model have been used to calculate statistical parameters, such as the probability of adjacency (P[A]), for which optimum agreement is found for a value of 0.8. Radii of gyration obtained from simulations are in good agreement with experimental values. The molecular weight range studied appears to cover the change from a single sheet structure to a superfolded double sheet. The same stem statistics (with P[A] = 0.8) apply, irrespective of molecular weight. Scattering data from the gamma-phase of sPS are well reproduced by a model involving some movement of stems out of the planes of sheets. SANS measurements have been made using tilted samples in order to separate in-plane and out-of-plane radii of gyration. Comparison between the out-of-plane radius and the long spacing determined from small angle X-ray measurements shows close agreement for the lower molecular weight in both delta- and gamma-phases, while R[Z] is a factor of 2 larger for the higher molecular weight. This indicates that each molecule occupies a single lamella at the lower molecular weight and, on average, two lamellae at the higher one, in both delta- and gamma-phases. The implication is that the delta- to gamma-phase transition only involves a reorganisation of chain segments within those lamellae which originally contained the molecule.

It is shown by methods of electronic microscopy that polystyrene film forms during evaporation of sol-vent from a solution of polystyrene in o-xylene. This film consists of polystyrene molecules integrated in aggregates. According to IR-spectroscopy data it was suggested that noncovalent interaction of phenyl ring with fullerene molecule occurs in the composite material. The studied films possess antimicrobial proper-ties. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35444

Structural and Dynamical Properties of Atactic Polystyrene in the Interface and Interphase Region Surrounding Grafted and Ungrafted Silica Nanoparticles The composite industry has long achieved enhanced material properties by mixing micro sized inorganic filler particles with a polymer matrix1,2. This is because the combination of two or more different materials can have a synergistic effect on the overall composite material properties imparting advantages that are absent in the individual constituents. A well-known example is that of adding carbon black as reinforcing material to increase tire strength, toughness, and resistance to tear and abrasion3,4. To achieve improved materials performance, the design of conventional composites has typically focused on reducing the dimensions of the filler particles. This is done in order to increase the filler surface area to enable greater interaction with the polymer matrix. Consequently, these efforts have received a significant boost with the dawn of the ‘nano era’. Wherein experimental methods and tools are now used to synthesize, characterize, and investigate matter at the nano-scale level [10-9 m] which is close to molecular and atomic dimensions. The advent of such methods is exciting as it suddenly offers new possibilities of creating novel materials that can be tailored at very small dimensions. This expectation has been derived from the notion that the behavior of materials at their nanoscale level directly influences their microscopic properties and consequently their bulk macroscopic characteristics. As is typical in any emerging field, the challenge is to understand the fundamental aspects that control the final observable properties of these composite materials. In contrast to the behavior of materials in conventional composites, recent experimental observations of polymer nanocomposites have demonstrated multifunctional changes in their properties. Examples include - but are not limited to - the decrease in the polymer viscosity5, shifts in the polymer glass transition temperature6,7, and changes in the composite material’s thermo-mechanical8,9 properties. However, what is still lacking and remains unclear are the fundamental explanations for the differences in the behavior between conventional composites and nanocomposites. In order to address questions pertaining to these differences, this PhD work was part of a large European Union consortium of universities and industrial partners, NanoModel. The aim of the group was to develop a unified scientific understanding from both experimentalists and theoreticians on the behavior of polymers in the presence of a surface. Such understanding of the important controlling parameters would ultimately support the design of industrial polymer nanocomposite materials. Therefore, both the structural and dynamical investigations always sought to address some of several important open questions that necessitated this work. These questions include among other things: (1) Does a nanoparticle influence the behavior of the surrounding polymer? (2) Since the dispersion state of the nanoparticles is known to control the resulting nanocomposite properties, which controlling parameters are important in obtaining a well-mixed polymer nanocomposite? (3) What role does the size/dimension of the nanoparticle play? (4) Is it necessary to graft or attach polymers to the filler particles, in other words, functionalizing the nanoparticles to facilitate their dispersion in the polymer melt? (5) How long should the grafted polymer chains be relative to the bulk polymer and which grafting density is optimal to achieve a good dispersion state? (6) To what extent are the polymer properties in the interface (next to the surface) and interphase (where grafted and bulk free polymer chains mix) region changed if they are at all? (7) Which parameters influence the width or extent of both the interface and interphase region? (8) Can we observe the same phenomena or changes by employing both experimental and theoretical approaches? Therefore, the contribution of this PhD thesis within the NanoModel framework was to investigate the structural and dynamical properties of atactic polystyrene in the vicinity of a silica nanoparticle as a model system for polymer nanocomposites at the atomistic level (see Figure 1.1 for a simulation snapshot). This model system was chosen because of its importance to the NanoModel partners since bulk polystyrene is an important, largely used, and well characterized polymer while silica is a typical traditional filler particle. Naturally, consortium partners like BASF would find it invaluable to produce new tailored plastics with superior properties to the traditional ones. At the same time, partners like BOSCH and CRP-FIAT would benefit from knowing the nanoparticle effect on the mechanical properties and the processing of the nanocomposite which directly impacts their injection molding processes for example. On the experimental front, Fribourg University, Juelich, and Epidoris were involved in nanocomposite sample preparation and characterization. These experimental results validated those obtained from computational studies from TU Darmstadt, National University of Athens, Trieste University, and BASF. Therefore, the influence of the nanoparticles of various diameters (3.0, 4.0, and 5.0 nm) and grafting states (0.0, 0.5, and 1.0 chains/nm2) on atactic polystyrene was studied. To perform this work, a computer molecular dynamics (MD) simulation tool, YASP10, was employed. This tool numerically solves Newton’s equations of motion for a system of interacting atoms to generate a trajectory of their movements. Following this, the resulting trajectories can be analyzed for different properties that characterize the structure, dynamics, and thermodynamics of the system. The use of atomistic MD simulations has the advantage of being able to investigate both static and dynamic properties of a system in fine detail. The ensuing results have the benefit of being related to experimental observations such as those probed by nuclear magnetic resonance11 (NMR) and dielectric spectroscopy12 (DS) studies. Additionally, other experimental techniques like neutron, x-ray, and light scattering now allow the determination of the atomistic structure of a material. Thus, computer modeling techniques interface with and complement experimental methods in understanding the link between structural and dynamical properties of polymers. While many experimental5,6,9,13-20 investigations have been performed to study the behavior of polymers at surfaces, very few atomistic21-25 computer modeling studies have been done. This necessitates the development a unified theoretical and experimental understanding of the polymer static and dynamic modifications in the presence of a surface. This is important because such changes determine in part the overall material properties. Examples of these material properties include their mechanical strength, appearance, how well they can be processed, and the duration of the polymer aging process. Additionally, this work sets a foundation for coarse-grained simulations, which investigate longer polymer chains and bigger systems. Static and dynamic properties of polymers determine whether nanoparticles form clusters or are well dispersed in a polymer melt. This is a pivotal challenge in experimental techniques because it is difficult to control the dispersion of nanoparticles, which finally determines the resulting material properties. Parameters that influence the static, dynamic, and nanoparticle dispersion state include - but are not limited to - the nanoparticle size, grafting density, the ratio of the length of grafted to free chains, and surface-polymer interactions. Therefore, developing an understanding of how these parameters interplay with each other will aid in the control and tailoring of the final nanoparticle dispersion state. The first half of this cumulative PhD thesis, chapter 2, presents results of the atactic polystyrene structure around the nanoparticle. The quantities of interest were the polymer density, radius of gyration, and its orientation relative to the nanoparticle surface. The analysis of the computer simulation output trajectory files resolved these polymer properties as a function of distance from the nanoparticle surface to quantify the surface effect. Varying both the polymer grafting density and the nanoparticle surface curvature enabled the understanding of how these two parameters interplay and influence the polymer’s structural properties. For instance, the extents of the polymer density modifications under the influence of the nanoparticle surface indicate the wettability of the surface by the polymer. This is important in mitigating adhesive failure and mechanical stress distribution in the nanocomposite material. At the same time, the density changes directly influence the polymer dynamical properties like the glass transition temperature and polymer aging processes. Therefore, understanding and being able to control these changes is vital since polymer properties like the elastic modulus and conductivity amongst many other physical properties change significantly around the polymer glass transition. These observations underscore not only the importance of the polymer in the interface region but also the width of the interphase region. The latter is influenced by the nanoparticle grafting state and the nanoparticle curvature as investigated in this work but also on the length ratio between the grafted and free polymer chains. While changes in the polymer radius of gyration give a measure of how stretched a polymer coil is, this has the effect of directly influencing the packing of polymer chains and their orientation. Additionally, the induced orientation of the polymer and its segments is important in processes that depend on transport properties such as electrical and thermal conductivity. Therefore, the different polymer structural properties are interlinked and understanding their cause-and-effect gives tuning parameters in the design of polymer nanocomposites. Complementary to structural properties discussed in chapter 2, chapter 3 forms the second half of this thesis and discusses the dynamical properties of the polymer. These included the mean-squared displacement (MSD) of the polymer chain center-of-mass and reorientational dynamics of intramolecular segment vectors. These quantities were also calculated under different nanoparticle grafting states and surface curvature. Changes in the polymer chain MSD and the reorientation of its end-to-end vector have given a measure of the global polymer mobility. To understand the local dynamics at the monomer level, the reorientation of a three-monomer and the C-Cpara segment vector as well as the backbone C-H bond vector was investigated (see Figure 1.2). The advantage of obtaining such a local resolution is that it allows for comparison with experimental NMR and DS studies which probe the C-H bond vector and the C-Cpara segment vectors, respectively. To develop a unified understanding, explanations of the dynamical property changes were linked to the previously observed structural properties either in the interface or interphase region, see chapter 2. The objectives to this thesis were to use the molecular dynamics simulation tool (YASP), setup the model system under investigation, perform the simulations, and write analysis programs to determine the different polymer properties. Therefore, I interpreted, understood, and explained my results in light of their interconnectedness as well as results from other simulations and experimental work on polymer nanocomposite systems. Finally, this work ends with chapter four which encompasses the conclusions and an outlook for further investigations.

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

The thermolysis of mixtures of polyethylene and polystyrene was investigated. Overall liquid production for the mixture was above the values predicted from individual polymer reactions. No detrimental effects on the styrene production were evident, as over 50% of the initial polystyrene charge was converted to styrene for polystyrene and for mixtures. There were, however, some differences in the secondary products. No incorporation of one polymer onto another was observed, either in the liquid or the residue.
Different reaction conditions were examined. It was determined that using a single reaction temperature (445$ sp circ$C) was as effective at separating the aromatic and aliphatic products as using two different reaction temperatures.
Polystyrene was found to catalyze the thermolysis of polyethylene. Conventional catalysts (Mordenite and FCC zeolite) affected the overall production and product distributions for mixtures and polyethylene, while only changing the product distribution for polystyrene. Hydrogen in the purge gas only slightly decreased the ratio of 1-alkenes to n-alkanes.
Recycled plastics yielded results similar to virgin polymers, although overall liquid production was decreased (probably due to the additives present in the plastics).

The micellization of polystyrene based block copolymers was investigated in aqueous and in organic media. Micelles formed from polystyrene-b-poly(sodium acrylate) (PS-b-PANa) in sodium chloride solutions were investigated by static light scattering (SLS). The aggregation numbers (N$ rm sb{agg})$ were influenced by low salt concentrations ($<$0.10 M) and they were essentially independent of the soluble block lengths. The core radii ($ rm sb{e}$ agreed well with previous solid state results on similar samples studied by small-angle X-ray scattering (SAXS). It was thus concluded that no supermicellar aggregates were present and that the cores were solvent free.
A method to evaluate the critical micelle concentrations (cmc's) of block copolymer micelles by SLS was developed to account for the effects of polydispersity on the cmc. It was found that for block copolymers which have a significant dependence of the cmc on the insoluble block length and which are polydisperse only the present approach was able to evaluate the cmc.
The micellization of PS-b-PANa and PS-b-poly(acrylic acid) (PS-b-PAA) block copolymers were investigated in organic solvents. The cmc's were found to range from $1 times10 sp{-7} { rm to} 5 times10 sp{-9}$ M for insoluble block lengths ranging from 2.6 to 18 units. The N$ rm sb{agg}$ and R$ rm sb{e}$ values for four PS-b-PANa series in tetrahydrofuran, were found to be a function of the length of both blocks. The effect of the degree of neutralization of the PAA block on micellization was probed by SLS and SAXS; micelle formation was found to commence at 5% neutralization. The distribution of water between toluene and the polar cores of block ionomer and sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles was investigated by proton chemical shift measurements as a function of temperature. The amount of water solubilized and the thermodynamic parameters of transfer were found to be a function of the core nature.

Thermolysis of mixtures of linear low density polyethylene, LLDPE, and polystyrene, PS, was investigated. Mixtures having various polyethylene/polystyrene ratios were reacted in a stirred, batch reactor under a nitrogen atmosphere at moderate temperatures, ranging between 350 and 420$ sp circ$C. The major products collected included a volatile product, which was liquid at room temperature, and a wax-like residue. The liquid products were consistently found to contain over 90 percent styrene and toluene with the yield of styrene decreasing as the percentage of polyethylene in the mixture increased. Two fractions were identified in the residue: a high molecular weight polyethylene fraction and a lower molecular weight polystyrene fraction. A significant increase in the solubility of the residue in organic solvents at room temperature was observed as the polystyrene content was raised. The residue became completely soluble in chloroform at a 60/40 ratio of polyethylene/polystyrene. The effect of temperature on the degradation of a selected mixture was also investigated. At temperatures below 390$ sp circ$C, the volatile/residue ratio was independent of the reaction temperature. Above 390$ sp circ$C, the styrene and total liquid product yields increased with increasing temperature, while the yield of residue decreased.

Polystyrene (PS) carrying a terminal nitroxide group was synthesised by anionic polymerisation. The ESR spectra of the PS in bulk and in blends with polyisoprene (PIP) recorded over a range of temperatures indicate that the motional freedom of a proportion of the labelled PS chain ends is enhanced by the presence of PIP especially at elevated temperatures (above ca. 400K). The possibility that this effect is due to a trend towards macroscopic miscibility between the two homopolymers at temperatures in the region of 400K is ruled out by a range of experiments including differential scanning calorimetry and interfacial tension measurements. It is concluded that in PS/PIP blends there is a greater than average concentration of PS chain ends in the PIP-enriched environment of the phase boundaries. This work provides the first experimental verification of the prediction, based on thermodynamic considerations, that in immiscible blends of polymers chain ends are located in preference to internal segments at the interfacial region (interphase).

Chapter 1 introduces the motivation behind and the methods for the use of insoluble polymers for the heterogenisation of well-defined homogenous catalysts. The use of diol ligands and polymer-supported catalysts in the Diels-Alder reaction and dialkylzinc addition to aldehydes is also reviewed. Finally, the aims of this work are outlined. Chapter 2 evaluates various routes for the synthesis of diol-functionalised resins. The grafting of triol compounds to preformed chloromethylated resins was undertaken through formation of an ether linkage, leaving a pendant diol. Emphasis was placed on incorporating an alkyl spacer between the diol moiety and the resin in order to distance the supported Lewis acid from the polymer matrix in subsequent catalysis applications. A relationship between the size of alcohol substrates and ease of reaction with chloromethylated resins is reported; due to mass transport effects, the grafting of larger residues is considerably more difficult. Chapter 3 discusses the synthesis of polystyrene resins possessing a chiral diol-functionality introduced via asymmetric dihydroxylation of alkenes. The asymmetric dihydroxylation process is reviewed. Two contrasting strategies for diol-functionalised resin preparation are described: (a) solution-phase alkene dihydroxylation followed by grafting and (b) dihydroxylation of an alkene moiety already bound to the solid-phase. Chapter 4 investigates supported-diol-titanium species as Lewis acids and probes the effect of alkyl spacer length on their activity in the Diels-Alder reaction of methyl acrylate and cyclopentadiene. The incorporation of a nine-carbon methylene spacer led to an improvement in catalyst activity. The application of polymer-bound Ti-based Lewis acids in the asymmetric Diels-Alder reaction of methacrolein and cyclopentadiene and diethylzinc addition to benzaldehyde is also reported. In both cases low ee's were observed.

The paper describes the frequency dependences of the electrophysical parameters (capacitance, dielectric constant, dielectric loss tangent, and resistivity) of polystyrene films filled with small additions of fullerenes (up to 1 wt % of C60). The composite materials obtained were concluded to be nonpolar. The dielectric constant as a function of the film composition passes through a minimum at 0.035 wt of C60. The polymer maintains good insulating properties when filled with fullerenes. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35431

Polystyrene (PS) is a non-polar polymer that has limited surface properties since it lacks polar functional groups. In this project, different polar functional groups were incorporated onto PS by various methods such as surface treatments (flame treated and chromic acid treated), non-reactive and reactive compounding (at different loadings of copolymers) and grafting of copolymer chains induced by UV irradiation. These functional groups, namely carboxylic acid, hydroxyl, styrene maleic anhydride (compounded and grafted) and poly(vinyl methyl ether) (PVME), introduced during treatment and modification of PS, may diffuse away from the surface into the bulk and vice versa. The treated and modified surfaces were investigated and compared using a range of surface analysis techniques, which include X-ray photoelectron spectroscopy (XPS), attenuated total reflection infrared spectroscopy (ATR-IR), atomic force microscopy (AFM) and contact angle measurement in conjunction with chemical derivatisation.

Thesis (M.S.)--University of Akron, Dept. of Polymer Science, 2008.
"December, 2008." Title from electronic thesis title page (viewed 01/13/2010) Advisor, Judit E. Puskas; Faculty Reader, Gary R. Hamed; Department Chair, Ali Dhinojwala; Dean of the College, Stephen Z. D. Cheng; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Thesis (M.Sc.)--City University of Hong Kong, 2001.
"A dissertation submitted in part-fulfilment of the requirements for the degree of Master of Science of City University of Hong Kong." Title from title screen (viewed on Sept. 4, 2006) Includes bibliographical references.

The structure and association behaviour of poly(styrene-alt-maleic anhydride) (SMA) and poly(styrene-alt-N,N-dimethylpropylamide) (SMI) polymers were studied using molecular modeling. The conformational studies were carried out at a semi-empirical PM3 level. SMA and SMI polymers were found to associate into nanotubes. These nanotubes have primary, secondary and tertiary structures. The primary structure is the conformation the polymer takes depending on the degree of protonation and its chirality. The secondary structure is the association of many polymers to form a nanotube structure. The tertiary structure is a higher order aggregation between the nanotubes.