Search

Genom ringöppningssampolymerisation av utvalda epoxider och anhydrider möjliggjordes en enkel strategi för att syntetisera funktionella sampolymerer. Sampolymererna hade förmågan att bilda tvärbundna material, och var dessutom benägna för både hydrolytisk och enzymatisk nedbrytning. Användning av organokatalysatorn PPNCl gjorde det möjligt att bilda sampolymerer genom alternerande ringöppning av epoxider och anhydrider. Utbytet var högt, och polymererna nådde molekylvikter i intervallet 0,7–7,6 kg mol-1. De omättade bindningarna i sampolymerernas sidokedjor gav dem förmågan att bilda tvärbundna nätverk. Graden av tvärbindning dikterades av sampolymerernas molekylära struktur och molekylvikt. De termiska egenskaperna hos sampolymererna reglerades genom att variera anhydriden, där strukturella skillnader mellan de valda anhydriderna hade en inverkan Tg och T5%. Tvärbindningsreaktionen resulterade i en ökning av både Tg och T5% i förhållande till de ursprungliga linjära sampolymererna. De klyvbara estergrupperna i sampolymerkedjorna gjorde det möjligt för sampolymererna att genomgå både hydrolytisk och enzymatisk nedbrytning. De nedbrutna sampolymererna påvisade en förändring i molekylvikt och dispersitet, samt en ökad viktminskning. De nedbrutna tvärbundna materialen visade på större svällning och lägre gelinnehåll än de initiala värdena före nedbrytning. Dessa resultat ger en ökad förståelse kring hur strukturen hos epoxid/anhydrid-baserade sampolyestrar påverkar deras egenskaper, så som förmågan att bilda tvärbundna material samt deras nedbrytbarhet. Förhoppningen är att denna studie ska gynna utvecklingen av nya material inom denna klass av polyestrar, och vara till hjälp för att förutse deras potentiella tillämpningar. The ring-opening copolymerization of selected epoxides and anhydrides enabled a simple strategy to synthesize functional copolymers with the ability to form crosslinked materials and prone to hydrolytic and enzymatic degradation pathways. The synthesis utilized PPNCl as an organocatalyst and allowed the formation of copolymer chains by alternating ring-opening of epoxides and anhydrides in high yield and molar mass in the range of 0.7-7.6 kg mol-1. The pendant unsaturated bonds in the copolymer chains endowed the copolymers with the ability to form crosslinking networks. The degree of crosslinking was dictated by the molecular structure and molar mass of the copolymers. The thermal properties of the copolymers were regulated by varying the anhydrides, the difference in the structure of each anhydride influence the Tg and T5%. Crosslinking reaction indeed increased the Tg and T5% from the native copolymers. The presence of ester as cleavable groups in the copolymer chains allowed the copolymers to undergo hydrolytic and enzymatic degradation. The degraded copolymers showed a change in molar mass and dispersity and increased mass loss. The degraded crosslinked materials showed higher swelling ratio and lower gel content than the initial values before degradation. These results deliver a better understanding of the structure-property relationships, the ability to form crosslinked materials, and the degradation behavior of epoxides/anhydrides-based copolyesters. They should favor the design of new materials belonging to this class of polyesters and to envisage their potential applications.

Dissertation, RWTH Aachen University, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2023). = Dissertation, RWTH Aachen University, 2022, This thesis concerns itself with the synthesis of oxazolidinones and polyoxazolidinones from the corresponding epoxides and isocyanates. The oxazolidinone moiety is applied widely as constituent of antibiotics and auxiliaries in enantioselective organic synthesis. Because of the readily available raw materials, the oxazolidinone building block is likewise of interest for the synthesis of polyoxazolidinone-based high-performance thermoplastics. As will be shown in this thesis, the oxazolidinone moiety is obtained readily by conversion of epoxide and isocyanate, when a suitable catalyst is applied. For application in the polymerization reaction, the catalyst not only had to provide excellent activity, but also outstanding selectivity. The approach described in this thesis is divided into two parts. The first part (Chapter II) deals with the identification of a suitable catalyst. Catalysts were assessed in a model system comprising a monofunctional epoxide and isocyanate. The focus was placed on organic Lewis acid-base catalysts, as the catalyst needed to be metal-free. Literature-known tertiary ammonium salts were the starting point. Azaspiro and imidazolium salts proved to be selective catalysts, but their activity was not adequate for industrial application. Comparing tetrabutyl ammonium with tetrabutyl phosphonium bromide salts, we found that phosphonium catalysts not only were more active, but also provided similar or enhanced selectivity. The effect of the chemical groups attached to the phosphonium center were explored in detail. Substitution of alkyl by aryl groups led to drastic increase in activity, while the high selectivity was preserved. The activity was optimized further by amending the aryl group with adequate substituents. The catalysts developed this way were then applied to the polymerization reaction of difunctional epoxides with diisocyanates. As the polyoxazolidinone synthesis was subject to the formation of various side products, the selectivity of the catalyst was a central aspect. A suitable reactor system and appropriate reaction parameters had to be defined. Successfully, we synthesized polyoxazolidinones that performed as high-performance thermoplastics. The second part of this thesis (Chapter III) focuses on the chemical and thermophysical properties of the thermoplastics that were obtained. The polyoxazolidinones were thermally highly stable with glass transition temperatures of 170-180°C and decomposition temperatures up to 400°C. First tests showed that antioxidants have a beneficial effect on the thermal stability of polyoxazolidinones at elevated temperatures. Last but not least, the application aspects were explored by spinning polymer samples into fibers., Published by RWTH Aachen University, Aachen

Heutzutage werden Epoxidharzsysteme meist im schnell wachsenden Segment der Faserverbundwerkstoffe eingesetzt, für die eine große Vielfalt an unterschiedlichen Herstellungsverfahren existiert. Dennoch haben alle diese Verfahren die Gemeinsamkeit des Aushärteprozesses des Epoxidharzsystems, welcher einem charakteristischen Temperaturbereich unterliegt. Die Aushärtung selbst basiert auf einer exothermen chemischen Reaktion, die sich mit steigender Temperatur beschleunigt. Zudem haben Epoxidharzsysteme typischerweise eine geringe Wärmeleitfähigkeit. Dies kann insbesondere bei dickwandigen Bauteilen zu einer inhomogenen Temperaturverteilung mit Hot Spots und damit zu einer ungleichmäßigen Aushärtung führen. Auch eine lokale Degradation des Materials ist möglich. Darüber hinaus schrumpfen Epoxidharzsysteme während des Aushärteprozesses, wodurch Eigenspannungen und mögliche Schäden im fertigen Bauteil auch ohne zusätzliche Belastung herbeigeführt werden. Eine große Herausforderung bei der Herstellung von Faserverbundwerkstoffen besteht daher darin, die Temperatur innerhalb eines Bauteils zu kontrollieren, um Eigenspannungen und Materialschädigungen zu vermeiden. Numerische Simulationen sind in der Lage, einen tieferen Einblick in die Charakteristik des Aushärteprozesses von Epoxidharzsystemen zu geben. Zu diesem Zweck wird auf der Grundlage einer umfassenden experimentellen Untersuchung ein neues Konstitutivmodell der Thermoviskoplastizität mit Fokus auf das reine Epoxidharzsystem entwickelt, das sowohl die mechanischen als auch die thermischen Aspekte und deren Kopplung unter Berücksichtigung des Aushärtegrades umfasst. Die zugehörigen Materialparameter des Materialmodells werden in stark partitionierter und sequentieller Weise identifiziert, um den Konzepten der lokalen Identifizierbarkeit unter Berücksichtigung der Eindeutigkeit des resultierenden Parametersatzes zu genügen. Im Rahmen der Finite-Elemente-Methode wird das Materialmodell räumlich diskretisiert. Die Behandlung des resultierenden Systems von Algebro-Differentialgleichungen (DAE) erfolgt durch die Anwendung steif-genauer diagonal-impliziter Runge-Kutta (DIRK)-Verfahren. Darüber hinaus wird die Verwendung von eingebetteten DIRK-Verfahren erläutert, die eine elegante und effiziente Steuerung der Zeitschrittweite durch Abschätzung des lokalen Integrationsfehlers ermöglichen. Es wird gezeigt, dass die Evolutionsgleichung des Aushärtegrades inhärent instabile Eigenschaften aufweist. Dem kann nur durch ausreichend kleine Zeitschrittweiten und Verfahren höherer Ordnung begegnet werden, um den Rechenfehler zu minimieren. Eine kleine Zeitschrittweite während der gesamten Simulation führt jedoch zu langen Rechenzeiten. Daher ist eine zeitadaptive Steuerung der Schrittweite bei Aushärteprozessen unerlässlich. Das diskretisierte thermomechanisch gekoppelte Problem wird in dem hauseigenen Finite-Elemente-Programm TASAFEM implementiert. Es werden Simulationen eines reduzierten Wärmeleitungsproblems und des thermomechanisch gekoppelten Problems durchgeführt. Beide werden in innovativ konzipierten Experimenten unter Verwendung von thermografischen Messungen und Verformungsmessungen mittels digitaler Bildkorrelation (DIC) validiert. Abschließend werden weitere Simulationsbeispiele diskutiert., Nowadays, epoxy resin systems are usually applied in the rapidly growing fiber composite materials segment. A wide variation of diverse manufacturing processes exists. However, all these processes have one commonality, namely, the curing process of the epoxy resin system in a characteristic temperature range. Curing itself is based on an exothermic chemical reaction, which accelerates with rising temperature. Moreover, epoxy resin systems typically have a low heat conductivity. Particularly in thick-walled components, this might lead to an inhomogeneous temperature distribution with hot spots and, therefore, to uneven curing. Even local degradation of the material is possible. In addition, epoxy resin systems shrink during the curing process resulting in residual stresses and possible damage in the final component even without additional loading. Therefore, a major challenge in the manufacturing process of fiber composite materials is to control the temperature within a component in order to prevent residual stresses and degradation of the material. Numerical simulations have the ability to provide a deeper insight into the characteristics of the curing process of epoxy resin systems. For this purpose, a new constitutive model of thermo-viscoplasticity focused on the pure epoxy resin system is developed drawing on a comprehensive experimental investigation, which covers both the mechanical as well as the thermal aspects and their coupling under consideration of the degree of cure. The associated material parameters of the material model are identified in a strongly partitioned and sequential manner in order to follow the concepts of local identifiability considering the uniqueness of the resulting parameter set. Within the framework of the finite element method, the material model is spatially discretized. The treatment of the resulting system of differential-algebraic equations (DAE) is performed by applying stiffly accurate diagonally implicit Runge-Kutta (DIRK) methods. Moreover, the utilization of embedded DIRK methods is explained, which enables controlling the time step-size in an elegant and efficient manner by estimating the local integration error. It is shown that the evolution equation of the degree of cure exhibits inherently instable properties. This can only be countered by sufficiently small time step-sizes and methods of higher order to minimize the computational error. However, a small time step-size throughout the entire simulation leads to long calculation times. Consequently, time-adaptive step-size control is essential in curing processes. The discretized thermo-mechanically coupled problem is implemented in the in-house finite element code TASAFEM. Simulations of a reduced heat conduction problem and the thermo-mechanically coupled problem are performed. Both are validated in innovatively designed experiments using thermographic measurements as well as digital image correlation (DIC) measurements. Finally, further simulation examples are discussed.

People are naturally social, creative, and curious beings. All of these qualities manifest itself from an early age and therefore should start to be developed as soon as possible. From easier activities to more complicated ones. We assumed, that elementary school-aged children are creative enough, so we should attract them by learning new techniques, including the work with epoxy resin, which has a wide range of applications in arts, as well as in technology. With elementary school-aged children, we could begin with creating a epoxy resin rings. It is a moderately demanding process, and it is great to satisfy their sociability, creativity and curiousity, because there are no limits in work with epoxy resin, they will be curious to the result after polishing, and finally, the ring is the perfect fashion accessory or a gift for a friend, mother or grandmother... The main goals of this work were to create a production plan for manufactoring of epoxy resin rings with elementary school-aged children during workshops or in hobby groups in their leisure time, to make basic technological processes, the technical drawings, and the final product. Another goal was to try it with real children and to adapt the plant according to his abilities. The conclusions were largely in agreement with the assumptions, so based on that we suggest incorporating these activities into elementary school lessons or hobby groups. Človek je od prírody spoločenský, tvorivý a zvedavý tvor. Všetky tieto vlastnosti sa ozývajú, a mali by byť rozvíjané už od ranného veku. Od jednoduchších činností až po tie zložitejšie. Predpokladali sme, že kreativita detí na základných školách je už na toľko rozvinutá, že je potrebné ich zaujať a učiť novým technikám tvorenia. Medzi takéto patrí aj pomerne mladá technika práce s epoxidovou živicou. Tá má aj v umeleckom smere širokú paletu využitia. Jednou aktivitou, ktorou by sme mohli začať už práve s týmito deťmi, je výroba prsteňov. Táto stredne zložitá procedúra ich nielenže zaujme na niekoľko hodín, ale zároveň krásne naplní všetky hore zmienené aspekty. Ukojí ich tvorivosť- kreativite práce s epoxidovou živicou za medze nekladú, taktiež ich zvedavosť- čakanie, kým epoxid vytvrdne a následné esteticky príjemné prekvapenie po jeho vyleštení, no a samozrejme spoločenský aspekt- veď čím iným, než prsteňom by potešili svoje kamarátky, mamy, staré mamy... Cieľom tejto práce bolo vytvoriť plán tvorby prsteňov z epoxidovej živice s deťmi na druhom stupni ZŠ v rámci technických krúžkov či hodín techniky, spracovať základný technologický postup výroby, základnú výkresovú dokumentáciu a výrobok. Ďalším cieľom bolo si to s dieťaťom tohto veku reálne vyskúšať, a plán mu prispôsobiť. Zistenia sa vo veľkej miere zhodovali s predpokladmi, na základne čoho navrhujeme tieto aktivity začleniť do technických krúžkov či hodín techniky na základných školách.