This thesis focuses on how the properties of polymer thin films depend on the film thickness and molecular weight (Mw). Previous studies of polystyrene (PS) films coated on silica with Mw of 2.4 and 212 kg/mol found that the viscosity of the films decreases with decreasing film thickness. A two-layer model assuming a 3 nm thick mobile layer situated at the top surface of the film and hydrodynamically coupled to a bulklike inner layer is able to describe the viscosity of the films. To better understand the dynamics exhibited by the surface mobile layer, this work extends the measurement to various other Mw up to 2316 kg/mol. The result shows that the viscosity of the films also decreases with decreasing film thickness and can be described by the same two-layer model. But there are exceptional findings as well. Specifically, the viscosity of the high-Mw films (> 60 kg/mol) exhibit a Mw^0 dependence, distinctly different from the Mw^3.4 dependence exhibited by the viscosity of the bulk polymer. Moreover, the surface chains in the high-Mw films, as inferred from the two-layer model, are in an unphysically stretched state. These observations led to the conjecture that the viscosity reduction in the high-Mw films is due to a different mechanism from that in the lower Mw films which is directly tied to the surface mobile layer as in the two-layer model. To scrutinize this conjecture, viscosity measurement is extended to PS films doped with Dioctyl phthalate (DOP). A previous experiment showed that the influence of the surface on the overall dynamics in this system is likely to be much smaller than in the undoped films. The measurement results are examined to determine, among other things, whether the viscosity reduction relative to that in the undoped films is weaker in the low-Mw than in the high-Mw regime.

This master thesis focuses on the effect of cultivation parameters on hyaluronic acid synthesis during its biotechnological production. The cultivation parameters were temperature of the cultivation, aeration, agitation, carbon source and addition of phosphatidylcholine. Changes in molecular weight and yield of hyaluronic acid, growth of biomass and medium viscosity were observed. From the obtained data we learned, that the specific growth rate greatly impacts final characteristics of hyaluronic acid. Under suboptimal temperatures a high molecular weight polymer was synthesised along with comparable yields from the control cultivation. High temperatures (40 °C) caused a dip in molecular weight. The next cultivation parameters were aeration and agitation. The highest molecular weights were obtained in cultivations with high agitation rates and intensive aeration, specifically 1 vvm/800 rpm and 2 vvm/800 rpm. Agitation had a bigger influence on molecular weight than aeration. When the carbon source was changed from sucrose to glucose, the lowest molecular weight and yield were obtained. Addition of phosphatidylcholine with concentration 160 mg/l had a positive effect on the cultivation, where the molecular weight grew and biomass growth was higher.

The cell wall of Candida albicans is central to the yeasts ability to withstand osmotic challenge, to adhere to host cells, to interact with the innate immune system and ultimately to the virulence of the organism. Little is known about the effect of culture conditions on the cell wall structure and composition of C. albicans. We examined the effect of different media and culture temperatures on the molecular weight (Mw), polymer distribution and composition of cell wall mannan and mannoprotein complex. Strain SC5314 was inoculated from frozen stock onto yeast peptone dextrose (YPD), blood or 5 serum agar media at 30 or 37°C prior to mannan/mannoprotein extraction. Cultivation of the yeast in blood or serum at physiologic temperature resulted in an additive effect on Mw, however, cultivation media had the greatest impact on Mw. Mannan from a yeast grown on blood or serum at 30°C showed a 38.9 and 28.6 increase in Mw, when compared with mannan from YPD-grown yeast at 30°C. Mannan from the yeast pregrown on blood or serum at 37°C showed increased Mw (8.8 and 26.3) when compared with YPD mannan at 37°C. The changes in Mw over the entire polymer distribution were due to an increase in the amount of mannoprotein (23.8-100) and a decrease in cell wall mannan (5.7-17.3). We conclude that C. albicans alters the composition of its cell wall, and thus its phenotype, in response to cultivation in blood, serum and/or physiologic temperature by increasing the amount of the mannoprotein and decreasing the amount of the mannan in the cell wall.

Thermomechanical recycling of polyethylene terephthalate (PET) typically includes a decrease in the polymer´s intrinsic viscosity and therefore a reduction of the molecular weight. Consequently, thermomechanical recycling is usually a downcycling of the product. However current methods to increase the molecular weight such as solid-state polymerization or the usage of chain extenders are time consuming or introduce foreign molecules into the PET´s molecular chain. Thus, the aim of this work was to try to increase the molecular weight in the molten state in an extruder, to decrease the processing times. The processing times are reduced compared to the solid-state polymerization because in the molten state the movability of the polymer chain is increased. Moreover, no supplementary substances are added for the processing so that no foreign structures are introduced during reprocessing. Virgin PET pellets were extruded at 285°C, 290°C and 295°C set temperature and 2rpm, 4rpm, and 7rpm screw rotation rate. Afterwards the PET´s properties were investigated by measuring their intrinsic viscosities, conducting a 1H NMR and a DSC measurement. Additionally, pre-experiments were conducted to explore the possibilities of feeding industrial scrap polyester fabrics into the extruder. The polymer characterization showed that the intrinsic viscosity and therefore the molecular weight of the processed samples decreased with the parameters chosen for this experiment. Samples processed at 285°C and 7 rpm showed in the average the highest intrinsic viscosities and therefore the highest molecular weight of all processed samples. Additionally, the results of the 1H NMR and the DSC indicated degradation reactions such as thermal degradation and hydrolysis. Thus, further research is necessary to find an easily accessible recycling method for polyester textiles and reduce the amount of polyester textile waste. However, it is possible to feed long textile stripes into the twin screw extruder and reprocess it to a strand which is an important step for further recycling.

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The initial purpose of this study was to determine if steric problems would account for the difference in the products obtained in the reaction of the N-(substituted)phthalimide with low and high molecular weight amines.

<p> Cationic polyelectrolytes have attracted growing attention in the field of non-viral oligonucleotides (ONs) deliveries because of their ability to bind ONs by electrostatic interactions for efficient cellular uptake. However the formation of electrostatic polymer/ONs complexes and their biological effects are still poorly understood. The relationships between polymer structure and complexation performance have not been well established. The objectives of this research are to synthesize and characterize well-defined and well-controlled cationic polyelectrolytes and to evaluate the effects of polyelectrolyte chain properties on ONs complexation. Poly(2-(dimethylamino) ethyl methacrylate) (polyDMAEMA) and its derivatives are used as the polymer candidate. A fluorescein-labeled oligonucleotide, 5 '-FGCGGAGCGTGGCAGG-3' (F: fluorescein), is used as the oligonucleotide candidate.</p> <p> Low-molecular-weight cationic polyDMAEMA samples having narrow molecular weight distribution were synthesized by living anionic polymerization (LAP) and atom transfer radical polymerization (ATRP) methods. Fully charged polyDMAEMA quats were prepared by sequential quaternization of polyDMAEMA samples, as well as by direct ATRP of the quaternized DMAEMA monomer. An aqueous GPC calibration method was first developed for the characterization of these cationic polyelectrolytes. It was found that the type of counter-ion has little effect on the hydrodynamic volume of polyDMAEMA quat. Therefore the dimethyl sulfate salt of polyDMAEMA provided a reliable calibration standard for other types of quaternized DMAEMA homopolymers.</p> <p> Cationic block copolymers of polyDMAEMA with 2-hydroxyethyl methacrylate (HEMA) and polyethylene glycol (PEG) were also prepared by ATRP. It was found that the order of monomer addition, solvent type, temperature, and molecular weight of macroinitiator have significant effects on the living feature of the polymerization. Well-controlled block copolymers were obtained when polyHEMA was used as the macro initiator.</p> <p> The complexation capability of the prepared polyelectrolytes with oligonucleotides (15 mer) was evaluated by a fluorescence technique. It was found that the complexation performance depends on polymer molecular weight, charge density, and counter-ion type, as well as polymer concentration and block composition. The polymer sample that has double molecular weight of the ONs gave the optimal complexation performance.</p> / Thesis / Master of Applied Science (MASc)

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