Cyanate ester or triazine networks are attaining increasing importance as potential candidates for high temperature adhesives and composite matrices. Low toughness is a major drawback with most crosslinked thermosetting materials, including the cyanate ester networks. Considerable attention has been devoted to the aspect of toughening such brittle networks in our laboratories. Reactive functional thermoplastics not only enhance toughness but also impart highly desirable stability to solvent stress cracking without seriously affecting the moderately high modulus. Various aspects of this technology, have earlier been successfully applied to epoxy and bismaleimide systems. Careful control of the heterophase morphological structure is necessary to achieve significant toughening. This thesis has focused on modifications of a specific cyanate ester network system based on Bisphenol-A with thermoplastic modifiers, which were systematically varied with respect to back-bone molecular weight and chemistry. Hydroxyl or cyanato functional Bisphenol-A based amorphous poly(arylene ether)s have been successfully utilized to toughen the cyanate ester networks. Blends of reactive and non-reactive Bisphenol-A based amorphous poly(arylene ether sulfone)s were also demonstrated to be useful tougheners, apparently by allowing phase size control. The use of Bisphenol-A based amorphous polyarylene ether ketones (which are of lower polarity relative to the Bisphenol-A based polyarylene ether sulfones) resulted in larger, well defined morphologies which in turn resulted in tougher networks. It was demonstrated that either hydroxyl or cyanato reactive end-groups could be effectively utilized. Both were superior to non-reactive systems in terms of mechanical performance as well as solvent stability. One of the major drawbacks of this effort was that 3-4 fold improvements in toughness were attained but this was at the expense of the upper use temperature which dropped to a significant extent. Hydroxyl functional phenolphthalein based amorphous poly(arylene ether)s have also been successfully utilized to toughen the cyanate ester networks. This is significant in that toughened multi phase networks were generated without a sacrifice in either the Tg or the moderately high modulus of the unmodified cyanate ester networks. It has been demonstrated that the heterophase morphological structure which strongly influences mechanical performance is in turn influenced by the back-bone chemistry, molecular weight and end-functionality of the thermoplastic modifier. In addition, the kinetics of network formation also significantly influences the microphase separated morphologies. Generation and control of such microphase separated morphologies employing both thermal and microwave radiation has been investigated. An interdisciplinary investigation was undertaken to explore the feasibility of hydroxy functionalized phenolphthalein based poly(arylene ether sulfone) modified cyanate ester networks as potential candidates for high performance adhesive and composite matrix applications. Investigations into composite matrix applications, involved establishing models for the experimentally determined time and temperature dependent kinetics of cure as well as melt rheology. It is expected that these models will consequently complement efforts in establishing an optimized cure protocol for the fabrication of composite panels. Preliminary studies concerning aspects of fiber-matrix interfacial adhesion and the viability of thermoplastic modified cyanate ester networks as a structural adhesive have been conducted. / Ph. D.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Active materials are a subset of soft matter that is constantly being driven out of an equilibrium state due to the energy input from internal processes such as the hydrolysis of adenosine triphosphate (ATP) to adenosine diphosphate (ADP), as found in biological systems. Firstly, we construct and study a simple model of a flexible filament with an active crosslinker/molecular motor. We treat the system on a mesoscopic scale using a Langevin equation approach, which we analyse via a functional integral approach using the Martin-Siggia-Rose formalism. We characterise the steady state behaviour of the system up to first order in the motor force and also the autocorrelation of fluctuations of the position of the active crosslink on the filament. We find that this autocorrelation function does not depend on the motor force up to first order for the case where the crosslinker is located in the middle of the contour length of the filament. Properties that characterise the elastic response of the system are studied and found to scale with the autocorrelation of fluctuations of the active crosslink position. Secondly, we give a brief overview of the current state of dynamical polymer network theory and then propose two dynamical network models based on a Cayley-tree topology. Our first model takes a renormalisation approach and derive recurrence relations for the coupling constants of the system. The second model builds on the ideas of an Edwards type network theory where Wick’s theorem is employed to enforce the constraint conditions. Both models are examined using a functional integral approach. / AFRIKAANSE OPSOMMING: Aktiewe stelsels is ’n subveld van sagte materie fisika wat handel oor sisteme wat uit ekwilibruim gedryf word deur middel van interne prossesse, soos wat gevind word in biologiese stelsels. Eerstens konstruëer en bestudeer ons ’n model vir ’n buigbare filament met ’n aktiewe kruisskakelaar of molekulêre motor. Ons formuleer die stelsel op ’n mesoskopiese skaal deur gebruik te maak van ’n Langevin vergelyking formalisme en bestudeer die stelsel deur gebruik te maak van funksionaal integraal metodes deur middel van die Martin-Siggia-Rose formalisme. Dit laat ons in staat om die tydonafhankle gedrag van die stelsel te bestudeer tot op eerste orde in die motorkrag. Ons is ook in staat om die outokorrelasie fluktuasies van die posisie van die aktiewe kruisskakelaar te karakteriseer. Ons vind dat die outokorrelasie onafhanklink is van die motorkrag tot eerste orde in die geval waar die kruisskakelaar in die middel van die filament geleë is. Die elastiese eienksappe van die sisteem word ook ondersoek en gevind dat die skaleer soos die outokorrelasie van die fluktuasies van die aktiewe kruisskakelaar posisie. Tweedens gee ons ’n vlugtige oorsig van die huidige toestand van dinamiese polimeer netwerk teorie en stel dan ons eie twee modelle voor wat gebasseer is op ’n Caylee-boom topologie. Ons eerste model maak gebruik van ’n hernormering beginsel en dit laat ons toe om rekurrensierelasies vir die koppelingskonstates te verkry. Die tweede model bou op idees van ’n Edwards tipe netwerk teorie waar Wick se teorema ingespan word om die beperkingskondisies af te dwing. Beide modelle word met funksionaal integraal metodes bestudeer.

Thesis (MSc)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: We construct and study a simple model for an active gel of exible polymer filaments crosslinked by a molecular motor cluster that perform reversible work while translating along the filaments. The filament end points are crosslinked to an elastic background. In this sense we employ a simplified model for motor clusters that act as slipping links that exert force while moving along the strands. Using the framework of replica theory, quenched averages are taken over the disorder which originates from permanent random crosslinking of network end points to the background. We investigate how a small motor force contributes to the elastic properties of the network. We learn that in addition to the normal elastic response for the network there is an extra contribution to the network elasticity from the motor activity. This depends on the ratio of the entropic spring constant for the linked bio-polymerchain to the spring constant of the tether of the motor. / AFRIKAANSE OPSOMMING: Ons konstrueer en bestudeer 'n eenvoudige model vir 'n aktiewe netwerk van eksieble polimeerfilamente wat deur grosse van molekulere motors aan mekaar verbind word wat omkeerbare werk doen terwyl dit langs die filamente transleer. Die eindpunte van die filamente is aan 'n elastiese agtergrond verbind. In hierdie sin benut ons 'n eenvoudige model vir motorclusters wat as verskuifbare verbindings krag op die filamente tydens beweging kan uitoefen. Nie-termiese wanorde gemiddeldes word geneem oor die wanorde wat deur die lukrake permanente verbindings van netwerk eindpunte aan die agtergrond veroorsaak word. Ons ondersoek hoe 'n klein motorkrag tot die elastiese eienskappe van die netwerk bydra. Ons leer dat daar bo en behalwe die gewone elastiese respons vir die netwerk 'n elastiese bydrae as gevolg van die motors se aktiwiteit voorkom. Dit hang af van die verhouding van die entropiese veerkonstante van die biopolimerketting tot die veerkonstante van die anker van die motor.

This work presents the development of entropy-elastic gelatin based networks in the form of films or scaffolds. The materials have good prospects for biomedical applications, especially in the context of bone regeneration. Entropy-elastic gelatin based hydrogel films with varying crosslinking densities were prepared with tailored mechanical properties. Gelatin was covalently crosslinked above its sol gel transition, which suppressed the gelatin chain helicity. Hexamethylene diisocyanate (HDI) or ethyl ester lysine diisocyanate (LDI) were applied as chemical crosslinkers, and the reaction was conducted either in dimethyl sulfoxide (DMSO) or water. Amorphous films were prepared as measured by Wide Angle X-ray Scattering (WAXS), with tailorable degrees of swelling (Q: 300-800 vol. %) and wet state Young’s modulus (E: 70 740 kPa). Model reactions showed that the crosslinking reaction resulted in a combination of direct crosslinks (3-13 mol.-%), grafting (5-40 mol.-%), and blending of oligoureas (16-67 mol.-%). The knowledge gained with this bulk material was transferred to the integrated process of foaming and crosslinking to obtain porous 3-D gelatin-based scaffolds. For this purpose, a gelatin solution was foamed in the presence of a surfactant, Saponin, and the resulting foam was fixed by chemical crosslinking with a diisocyanate. The amorphous crosslinked scaffolds were synthesized with varied gelatin and HDI concentrations, and analyzed in the dry state by micro computed tomography (µCT, porosity: 65±11–73±14 vol.-%), and scanning electron microscopy (SEM, pore size: 117±28–166±32 µm). Subsequently, the work focused on the characterization of the gelatin scaffolds in conditions relevant to biomedical applications. Scaffolds showed high water uptake (H: 630-1680 wt.-%) with minimal changes in outer dimension. Since a decreased scaffold pore size (115±47–130±49 µm) was revealed using confocal laser scanning microscopy (CLSM) upon wetting, the form stability could be explained. Shape recoverability was observed after removal of stress when compressing wet scaffolds, while dry scaffolds maintained the compressed shape. This was explained by a reduction of the glass transition temperature upon equilibration with water (dynamic mechanical analysis at varied temperature (DMTA)). The composition dependent compression moduli (Ec: 10 50 kPa) were comparable to the bulk micromechanical Young’s moduli, which were measured by atomic force microscopy (AFM). The hydrolytic degradation profile could be adjusted, and a controlled decrease of mechanical properties was observed. Partially-degraded scaffolds displayed an increase of pore size. This was likely due to the pore wall disintegration during degradation, which caused the pores to merge. The scaffold cytotoxicity and immunologic responses were analyzed. The porous scaffolds enabled proliferation of human dermal fibroblasts within the implants (up to 90 µm depth). Furthermore, indirect eluate tests were carried out with L929 cells to quantify the material cytotoxic response. Here, the effect of the sterilization method (Ethylene oxide sterilization), crosslinker, and surfactant were analyzed. Fully cytocompatible scaffolds were obtained by using LDI as crosslinker and PEO40 PPO20-PEO40 as surfactant. These investigations were accompanied by a study of the endotoxin material contamination. The formation of medical-grade materials was successfully obtained (<0.5 EU/mL) by using low-endotoxin gelatin and performing all synthetic steps in a laminar flow hood. / Diese Arbeit beschreibt die Entwicklung Entropie-elastischer Gelatine-basierter Netzwerke als Filme und Scaffolds. Mögliche Anwendungen für die entwickelten Materialien liegen im biomedizinischen Bereich, insbesondere der Knochenregeneration. Im ersten Schritt der Arbeit wurden Entropie-elastische, Gelatine-basierte Hydrogel-Filme entwickelt, deren mechanische Eigenschaften durch die Veränderung der Quervernetzungsdichte eingestellt werden konnten. Dazu wurde Gelatine in Lösung oberhalb der Gel-Sol-Übergangstemperatur kovalent quervernetzt, wodurch die Ausbildung helikaler Konformationen unterdrückt wurde. Als Quervernetzer wurden Hexamethylendiisocyanat (HDI) oder Lysindiisocyanat ethylester (LDI) verwendet, und die Reaktionen wurden in Dimethylsulfoxid (DMSO) oder Wasser durchgeführt. Weitwinkel Röntgenstreuungs Spektroskopie (WAXS) zeigte, dass die Netzwerke amorph waren. Der Quellungsgrad (Q: 300-800 vol. %) und der Elastizitätsmodul (E: 70 740 kPa) konnten dabei durch die systematische Veränderung der Quervernetzungsdichte eingestellt werden. Die Analyse der Quervernetzungsreaktion durch Modellreaktionen zeigte, dass die Stabilisierung der Hydrogele sowohl auf kovalente Quervernetzungen (3-13 mol.-%) als auch auf Grafting von (5-40 mol.-%) und Verblendung mit Oligoharnstoffen (16-67 mol.-%) zurückgeführt werden kann. Die Erkenntnisse aus dem Umgang mit dem Bulk-Material wurden dann auf einen integrierten Prozess der Verschäumung und chemischen Quervernetzung transferiert, so dass poröse, dreidimensionale Scaffolds erhalten wurden. Dafür wurde eine wässrige Gelatinelösung in Gegenwart eines Tensids, Saponin, verschäumt, und durch chemische Quervernetzung mit einem Diisocyanat zu einem Scaffold fixiert. Die Scaffolds hergestellt mit unterschiedlichen Mengen HDI und Gelatine, wurden im trockenen Zustand mittels Mikro Computertomographie (µCT, Porosität: 65±11–73±14 vol.-%) und Rasterelektronenmikroskopie (SEM, Porengröße: 117±28–166±32) charakterisiert. Anschließend wurden die Scaffolds unter Bedingungen charakterisiert, die für biomedizinische Anwendungen relevant sind. Die Scaffolds nahmen große Mengen Wasser auf (H: 630 1680 wt.-%) bei nur minimalen Änderungen der äußeren Dimensionen. Konfokale Laser Scanning Mikroskopie zeigte, dass die Wasseraufnahme zu einer verminderten Porengröße führte (115±47–130±49 µm), wodurch die Formstabilität erklärbar ist. Eine Formrückstellung der Scaffolds wurde beobachtet, wenn Scaffolds im nassen Zustand komprimiert wurden und dann entlastet wurden, während trockene Proben in der komprimierten Formen blieben (kalte Deformation). Dieses Entropie-elastische Verhalten der nassen Scaffolds konnte durch die Verminderung der Glasübergangstemperatur des Netzwerks nach Wasseraufnahme erklärt werden (DMTA). Die zusammensetzungsabhängigen Kompressionsmoduli (Ec: 10 50 kPa) waren mit den mikromechanischen Young’s moduli vergleichbar, die mittels Rasterkraftmikroskopie (AFM) gemessen wurden. Das hydrolytische Degradationsprofil konnte variiert werden, und während des Abbaus kam es nur zu kontrolliert-graduellen Änderungen der mechanischen Eigenschaften. Während der Degradation konnte ein Anstieg der mittleren Porengröße beobachtet werden, was durch das Verschmelzen von Poren durch den Abbau der Wände erklärt werden kann. Die Endotoxinbelastung und die Zytotoxizität der Scaffolds wurden untersucht. Humane Haut-Fibroblasten wuchsen auf und innerhalb der Scaffolds (bis zu einer Tiefe von 90 µm). Indirekte Eluat-Tests mit L929 Mausfibroblasten wurden genutzt, um die Zytotoxizität der Materialien, insbesondere den Einfluss des Quervernetzertyps und des Tensids, zu bestimmen. Vollständig biokompatible Materialien wurden erzielt, wenn LDI als Quervernetzer und PEO40 PPO20-PEO40 als Tensid verwendet wurden. Durch den Einsatz von Gelatine mit geringem Endotoxin-Gehalt, und die Synthese in einer Sterilarbeitsblank konnten Materialien für medizinische Anwendungen (Endotoxin-Gehalt < 0.5 EU/mL) hergestellt werden.

Polymer networks are an important class of materials that are ubiquitously found in natural, biological, and man-made systems. The complex mesoscale structure of these soft materials has made it difficult for researchers to fully explore their properties. In this dissertation, we introduce a coarse-grained computational model for permanently cross-linked polymer networks than can properly capture common properties of these materials. We use this model to study several practical problems involving dry and solvated networks. Specifically, we analyze the permeability and diffusivity of polymer networks under mechanical deformations, we examine the release of encapsulated solutes from microgel capsules during volume transitions, and we explore the complex tribological behavior of elastomers. Our simulations reveal that the network transport properties are defined by the network porosity and by the degree of network anisotropy due to mechanical deformations. In particular, the permeability of mechanically deformed networks can be predicted based on the alignment of network filaments that is characterized by a second order orientation tensor. Moreover, our numerical calculations demonstrate that responsive microcapsules can be effectively utilized for steady and pulsatile release of encapsulated solutes. We show that swollen gel capsules allow steady, diffusive release of nanoparticles and polymer chains, whereas gel deswelling causes burst-like discharge of solutes driven by an outward flow of the solvent initially enclosed within a shrinking capsule. We further demonstrate that this hydrodynamic release can be regulated by introducing rigid microscopic rods in the capsule interior. We also probe the effects of velocity, temperature, and normal load on the sliding of elastomers on smooth and corrugated substrates. Our friction simulations predict a bell-shaped curve for the dependence of the friction coefficient on the sliding velocity. Our simulations also illustrate that at low sliding velocities, the friction decreases with an increase in the temperature. Overall, our findings improve the current understanding of the behavior of polymer networks in equilibrium and non-equilibrium conditions, which has important implications for synthesizing new drug delivery agents, designing tissue engineering systems, and developing novel methods for controlling the friction of elastomers.

"Multi-functionalized Side-chain Supramolecular Polymers:A Methodology Towards Tunable Functional Materials". Even as we see a significant growth in the field of side-chain supramolecular polymers in the last ten years, systems employing multiple non-covalent interactions have been scarcely studied. Non-covalent multi-functionalization provides unique advantages such as rapid optimization via reversible functionalization as well as for the tuning of materials properties by exploiting the differences in the nature of these reversible interactions. This thesis involves the design principles, synthesis & methodology of side-chain multi-functionalized polymers. The combination of the principles of a functionally tolerant & a controlled polymerization technique such as ROMP with multiple noncovalent interactions such as hydrogen bonding, metal coordination & Coulombic self-assembly has been used to synthesize multi-functionalized polymers. Furthermore, the orthogonality between hydrogen bonding, metal coordination & ionic self-assembly in random/block copolymers has been studied in detail. In order to validate the viability of this multi-functionalization methodology towards materials design non-covalent crosslinking of polymers was used as a potential application. Three classes of crosslinked networks have been studied: complementary multiple-hydrogen bonded networks, multiple-metal crosslinked networks, & multi-functionalized hydrogen bonded & metal coordinated networks. By using non-covalent multi-functionalization, important materials properties & its responsiveness towards chemical agents have been tuned & controlled to yield novel materials which would be difficult to be obtained via traditional covalent techniques or by using single non-covalent interactions.

Ces travaux de thèse ont permis d'élaborer un dispositif électroémissif (DEE) fin (140 µm) et flexible à base de réseaux interpénétrés de polymères (RIP). Pour ce faire, un polymère conducteur électronique, le poly (3,4-éthylènedioxythiophène) (PEDOT), est interpénétré dans une matrice hôte de manière à obtenir un système dont l'architecture monobloc est comparable à celle d'un dispositif tri-couches. Une fois le système gonflé par un liquide ionique, le 1-éthyl-3-méthylimidazolium bis-trifluorométhylsulfonylimide (EMImTFSI), les propriétés optiques du DEE sont modulables entre 24 et 51 % de réflexion dans le moyen infrarouge (bande III) en faisant varier la tension électrique appliquée aux bornes du dispositif de -1,5V à +1,5V. Les propriétés thermomécaniques du DEE proviennent essentiellement de la matrice hôte. Cette dernière est un RIP combinant la souplesse, la flexibilité et la résistance à la traction du caoutchouc nitrile (NBR) aux propriétés de conductivité ionique du poly(oxyde d'éthylène) (POE) en présence de l'EMImTFSI. / During this thesis a thin (140 µm) and flexible electroemissive device (EED), based on interpenetrating polymer networks (IPN), was elaborated. An electronic conducting polymer, poly (3,4-ethylenedioxythiophene) (PEDOT), is interpenetrated in a host matrix to obtain a system whose monoblock architecture is comparable to a three-layers device. Once the system is swollen by an ionic liquid, 1-ethyl-3-methylimidazolium bis-trifluoromethyl sulfonylimide (EMImTFSI), the EED optical properties are tunable between 24 and 51% reflection in the mid-infrared (Band III) by varying the electrical voltage applied across the device from -1.5 V to +1.5 V. The EED thermomechanical properties are mainly from the host matrix. This is an IPN combining flexibility and tensile strength of nitrile butadiene rubber (NBR) with the ionic conductivity properties of poly (ethylene oxide) (PEO) in the presence of EMImTFSI.

Title: Microstructure, swelling and deformation behavior of methacrylate hydrogels with interpenetrating network structure Author: Zhansaya Sadakbayeva Department: Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University in Prague Supervisor: Ing. Miroslava Dušková-Smrčková, Dr., Institute of Macromolecular Chemistry, Czech Academy of Sciences Consultant: Prof. Ing. Karel Dušek, DrSc., Institute of Macromolecular Chemistry, Czech Academy of Sciences Abstract: This work is devoted to interpenetrating polymer network (IPN) hydrogels prepared by sequential processes of redox-initiated radical polymerization of the first network prepared from 2-hydroxyethyl methacrylate (HEMA), and UV- initiated radical polymerization of the second network prepared from 2-hydroxyethyl methacrylate (HEMA) or glycerol methacrylate (GMA). Microstructure, swelling and deformation responses of the IPN hydrogels and their constituent network hydrogels were tested by various techniques. The microstructure of the first poly(HEMA) network was found sensitive to polymerization conditions. A novel route for one-step synthesis of double-porous poly(HEMA) cryogel was proposed. The formation of the second poly(GMA) network in the environment of non-porous and macroporous poly(HEMA) parent networks was...

A new tool (Infrasorb-12) for the screening of porosity is described, identifying high surface area materials in a very short time with high accuracy. Further, an example for the application of the tool in the discovery of new cobalt-based metal–organic frameworks is given. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Le sujet de cette thèse concerne le développement et la caractérisation de résines photosensibles pour le prototypage rapide. L'étude a tout d'abord consisté à optimiser des systèmes photoréticulables commerciaux : systèmes hybrides acrylates/époxydes. La réactivité des différentes formulations préparées ainsi que leurs propriétés thermomécaniques ont pu être évaluées grâce à la spectroscopie infrarouge à transformée de Fourier résolue dans le temps (RT-FTIR) et par analyse mécanique dynamique (DMA). En parallèle, une étude plus fondamentale visant à mieux comprendre et à contrôler la formation de réseaux polymères interpénétrés simultanés méthacrylate/époxyde a été menée. L'influence de paramètres physico-chimiques tels que l'intensité lumineuse, la concentration en photoamorceur sur les propriétés finales du matériau a notamment été abordée. Ensuite, des résines dont la chimie est moins conventionnelle ont été considérées. Comme très peu de ces monomères sont disponibles commercialement, certains d'entre eux ont dû être synthétisés. Certaines formulations ont démontré non seulement une bonne réactivité mais aussi d'intéressantes propriétés thermomécaniques et une limitation du retrait de polymérisation. Finalement, une méthode de mesure du retrait linéaire simple et facile à mettre en œuvre a été mise en place afin de comparer les différents systèmes chimiques proposés au cours de la thèse. L'utilisation de cet outil est très appréciable car il pourrait permettre de choisir le type de formulations induisant le moins de retrait possible lors de la réalisation d'un objet couche par couche. / The aim of this thesis is to develop and characterize UV curable resins for rapid prototyping application. The study started with the optimization of commercially available hybrid acrylate/epoxide systems (IPNs) commonly used in this industrial field. The reactivity of the different tested formulations in conjunction with their thermomechanical properties have been assessed by means of Real time Fourier transform infrared spectroscopy (RT FTIR) and Dynamic mechanical analysis (DMA). In the meantime, a more academic study has been performed on an epoxide/methacrylate mixture in order to get a better understanding and a control of the IPN formation. The influence of the light intensity and the photoinitiator concentration on the final properties has been examined. Then, UV curable resins whose chemistry is less conventional have been considered. Owing to the lack of commercial availability of some monomers, time has been spent to synthesize them. Some formulations display promising features especially in terms of reactivity, thermomechanical properties and linear shrinkage. Finally, a simple method to measure linear shrinkage has been set up to compare the different systems proposed during the thesis and thus evidences the less shrinkable UV curable system.