Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

In this research, the degradation effect of the low temperature polycrystalline silicon TFTs (LTPS TFTs) under dynamic stress was investigated. The experiment results revealed that the degenerate behaviors of n- and p-type poly-Si were different. In p-channel TFT, it was observed that the degradation of threshold-voltage (Vth) was closely associated with the stress frequency of ac stress. The degradation was more serious at low-frequency stress than that at high-frequency stress. The degradation of electrical characteristics of device is mainly dominated by the self-heating enhanced negative bias temperature instability effect. Moreover, the increased temperature around the environment could make the degradation of characteristics more serious, such as Vth shift (fixed charge), degraded S.S (dangling bonds). We suggest that the generation of deep states originated from bond broken at both of grain-boundary and interface state was explained the degradation mechanism of threshold-voltage. In n-channel TFT, the degradation characteristics may be attributed to both of the temperature effect and the hot carrier effect under the different stress frequency. At low-frequency stress, Vth shift (positively) and mobility are increased after 100 seconds stress because of the temperature effect. However, Vth shift (negatively) and mobility are decreased after 500 seconds stress because of the effect of the state creation near the drain regime. At high-frequency stress, the times of the switch is numerous, and result in the on-state current decreased because of the trap state generated.

Les copolymères à blocs amphiphiles s’auto-assemblent en solution aqueuse grâce à l’association de leurs segments hydrophobes. Les nanoparticules formées à partir de copolymères biocompatibles et biodégradables tels que les poly(hydroxyalkanoates) (PHAs) sont particulièrement attractives pour la conception de systèmes à libération prolongée de principes actifs. La relation entre la composition/structure chimique du copolymère, ses propriétés d’auto-assemblage et ses effets sur les cellules in-vitro doit être étudiée. Des copolymères à blocs poly(acide malique)-b-poly(3-hydroxybutyrate) (PMLA-b-PHB), PMLA-b-PHB-b-PMLA et poly(triméthylène carbonate)-b-poly(acide-malique) (PTMC-b-PMLA) ont été synthétisés par polymérisation par ouverture cycle (ROP) des monomères correspondants, suivie d’une hydrogénolyse. Une gamme de copolymères bien définis, caractérisés par spectroscopie RMN 1H, 13C{1H}, HSQC, HMBC, et DOSY, par analyses SEC, DSC, TGA, et mesure des angles de contact, présentant des balances hydrophile/hydrophobe modulables, a été obtenue grâce au control précis de la fraction hydrophile f (11-82%). Des auto-assemblages modulables ont été formés par nanoprécipitation des copolymères en l’absence d’agent tensio-actif. De larges agrégats ainsi que des micelles cœur-couronne (Rh = 16-335 nm) ont été obtenus en fonction du copolymère utilisé (dibloc vs. tribloc). Des micelles stables pendant 10 jours à 37 °C en solution aqueuse ont été obtenues pour les copolymères avec f allant jusqu’à 50%. Les copolymères PMLA-b-PHB et PTMC-b-PMLA n’ont pas révélé de toxicité aigüe in-vitro. De plus, l’utilisation du PHB a avantageusement permis de diminuer la captation des nano-objets par les macrophages et d’augmenter la captation par les cellules hépatiques. / Amphiphilic block copolymers are able to form self-assembled systems in aqueous solution by association of their hydrophobic segments. Nanoparticles formed from biodegradable and biocompatible polymers such as poly(hydroxyalkanoate) copolymers are particularly attractive for drug delivery applications. The relationship between the chemical structure/composition of the macromolecule, its self-assembly properties and its effect on cells in-vitro has to be studied.The synthesis of poly(-malic acid)-b-poly(3-hydroxybutyrate) (PMLA-b-PHB), PMLA-b-PHB-b-PMLA, and poly(trimethylene carbonate)-b-poly(-malic acid) (PTMC-b-PMLA) was established through the ring-opening polymerization (ROP) of the corresponding monomers followed by hydrogenolysis. A range of well-defined copolymers characterized by 1H, 13C{1H}, HSQC, HMBC, DOSY NMR spectroscopy, SEC, DSC, TGA, contact angle analyses, with tunable hydrophilic/hydrophobic balance were thus obtained through the precise control of the hydrophilic weight fraction f (11-82%). Tunable self-assembled systems were obtained by nanoprecipitation of the amphiphilic PHA-based copolymers without the use of a surfactant. Large aggregates and core-shell micelles (Rh = 16-335nm) were obtained depending on the polymer topology. PHB-based copolymers with f up to 50% formed highly stable micelles at 37 °C over a period of 10 days in aqueous solution. PMLA-b-PHB as well as PTMC-b-PMLA copolymers revealed no acute in-vitro cytotoxicity. The use of PHB as hydrophobic segment enabled to minimize the non-specific scavenging by macrophages cells while the cellular uptake by hepatocytes was favored.

Les poly(hydroxyalcanoate)s (PHAs) sont des polyesters biodégradables et biocompatibles d'intérêt pour leur application dans le domaine biomédical ou en substitution des plastiques dérivés de l'industrie pétrolière. La synthèse des PHAs par polymérisation par ouverture de cycle (ROP) de monomères cycliques, les β-lactones, permet un bon contrôle de la masse molaire, de la microstructure et de la fonctionnalité des polymères. Les propriétés des polyesters peuvent être modulées par l'utilisation de différents monomères. Depuis quelques décennies, différents PHAs ont été synthétisés, notamment le poly(hydroxybutyrate) (PHB) et les poly(malolactonate d'alkyle)s (PMLARs). Ces travaux ont été étendus à la ROP d'une nouvelle famille de β-lactones, les 4- alcoxyméthlylène-β-propiolatones (BPLORs). Ainsi, différents systèmes catalytiques à base d'yttrium offrent des (co)polymères de tacticité (syndiotactique, atactique ou isotactique) et de topologie (copolymères à blocs, alternés ou aléatoires) originales. La stéréosélectivité des systèmes catalytiques mis en œuvre est inédite dans le contexte scientifique actuel. En effet, la nature des substituants des ligands ancillaires des complexes d'yttrium permet de moduler la microstructure et donc les propriétés des PHAs obtenus. / Poly(hydroxyalkanoate)s (PHAs) are biodegradable and biocompatible polyesters of interest for their application in the biomedical field or as alternative to plastics derived from the petroleum industry. The synthesis of PHAs by ring-opening polymerization (ROP) of cyclic monomers, β-lactones, enables a good control of the molar mass, the microstructure and the functionality of the polymers. The properties of the polyesters can be tuned by the using different monomers. In recent decades, various PHAs have been synthesized, in particular poly(hydroxybutyrate) (PHB) and poly(alkyl malolactonate)s (PMLARs). This work has been extended to the ROP a new family of β-lactones, namely 4-alkoxymethlylene-β-propiolatones (BPLORs). Thus, various yttrium-based catalyst systems provide (co)polymers with original tacticity (syndiotactic, atactic or isotactic) and topology (block, alternating or random copolymers). The stereoselectivity of the catalytic systems implemented is unprecedented in the current scientific context. Indeed, the nature of the substituants on the ancillary ligand of the yttrium complexes enables to tune the microstructure and therefore the properties of the resulting PHAs.

In a push towards more environmentally friendly pyrotechnics, new greener pyrotechnic compositions need to be developed. A primary goal is to replace components such as lead, barium, and chromium in pyrotechnic compositions. Fused Deposition Modelling (FDM) is a 3D printing/additive manufacturing method whereby a thin filament is passed through a heated nozzle, and extruded onto a substrate in successive layers. This method of manufacturing could be used to produce pyrotechnic time delays based on suitable “green” polymer/fuel mixtures. Fluoropolymers are an attractive oxidising system for pyrotechnic use as fluorine is highly reactive and reacts relatively easily with common metallic fuels such as aluminium and magnesium to release a large amount of energy. Fluoropolymers are already in use as oxidisers and binders, especially in infrared decoy flares. PTFE has found wide use in the pyrotechnics industry, but is not melt-processible. A similar fluoropolymer, poly(chloro-trifluoroethylene) (PCTFE) was considered instead. PCTFE differs from PTFE in that one of the fluorine atoms in the TFE monomer has been replaced by a chlorine atom. The larger chlorine atom interferes with the packing of the polymer chains during polymerisation and, as such, may make it easier to process than PTFE. It was found that pure PCTFE degraded heavily during processing and was therefore precluded from any further study. Melt-processible copolymers containing PCTFE are available from industry. These copolymers contain vinylidene fluoride (VDF) in addition to the CTFE i.e. poly(CTFE-co-VDF). Two grades of copolymer were obtained from 3M: FK-800® resin and Dyneon® 31508 resin. These two polymers contain different ratios of CTFE to VDF. FK-800® resin was successfully extruded and showed minimal signs of degradation. Pyrotechnic films, containing aluminium powder as the fuel, were cast with both polymers using solvent techniques. Differential thermal analysis (DTA) was used to determine the ignition points of the compositions. All of the FK-800®-based compositions ignited at approximately 450 °C whilst all the Dyneon® 31508-based compositions ignited at approximately 400 °C. The energy output of the compositions was determined using bomb calorimetry. The experimental energy outputs of the FK-800®-based compositions correlated well with the predictions from the thermodynamic simulations. The maximum energy output, ~7.0 MJ∙kg1, occurred at a fuel loading between 30 – 35 wt.%. Except for one composition, the Dyneon® 31508-based compositions did not ignite in the bomb calorimeter. FK-800® was successfully extruded into a filament and showed minimal signs of degradation. In order to assess the impact of adding a solid filler on the mechanical properties and extrudability of the polymer, magnesium hydroxide was used as inactive model compound in place of aluminium. A filament of FK-800® and Mg(OH)2 was successfully compounded and produced using a filler loading of 30 wt.%. Compounding of the Dyneon 31508® with the magnesium hydroxide was unsuccessful. Addition of LFC-1® liquid fluoroelastomer improved the processibility of the Dyneon 31508® by lowering the melt viscosity. / Dissertation (MEng)--University of Pretoria, 2017. / Chemical Engineering / MEng / Unrestricted

Amphiphilic block copolymers consisting of poly(ethylene oxide) and poly(lactide) have great potential for formulating drug delivery systems. Our approach was to synthesize poly(ethylene oxide-b-D,L-lactide), (PEO-b-PDLLA), block copolymers with controlled molecular weights and good functionality on the poly(ethylene oxide) end for the design of potential core-shell delivery vehicles for HIV drugs. PEO-b-PDLLA block copolymer was used as a polymeric nanocarrier to encapsulate the HIV protease inhibitor, Ritonavir, within magnetite nanoparticles. Well-defined multifunctional polymeric nanoparticles with controlled sizes and size distributions were fabricated by rapid nanoprecipitation using blends of the PEO-b-PDLLA block copolymer with poly(L-lactide), (PLLA) homopolymer. Heterobifunctional PEO oligomers were directly prepared by initiating ethylene oxide with functional alcohols bearing vinylsilane, vinylether and maleimide moieties to provide appropriate end groups for conjugating targeting ligands. The polyethers with narrow molecular weight distributions were utilized as macroinitiators for the synthesis of poly(lactide) block. Heterobifunctional diblock copolymers possessing carboxylic acids were prepared from ene-thiol addition reaction of mercaptoacetic acid across the vinyl group on the PEO end, while preserving the hydroxyl functionality on the other end. Additionally, PDLLAs bearing maleimide functionality with controlled molecular weights were synthesized using maleimide functional initiator. End group modification was performed via  Michael addition using cysteamine hydrochloride to introduce an amino group over the vinyl bond. The resulting carboxylic acid functional PEO-b-PDLLA diblock copolymers, and amino functional PDLLAs are potential biocompatible polymers that can be utilized to encapsulate an array of bioactive molecules, targeting ligands. / Master of Science

Yes / A low concentration poly(acrylamide) sensor has been developed which uses the segmental mobility of another polymer probe with a covalently attached fluorescent marker. Interpolymer complexation with poly(acrylic acid) leads to reduced segmental mobility which can be used to determine the concentration of polymer in solution. This technique could be useful in detecting the runoff of polymer dispersants and flocculants in fresh water supplies following water purification processes. / Funding for the research was kindly provided by the Engineering and Physical Sciences Research Council (EPSRC).

La poly(ADP-ribosyl)ation est une modification post-traductionnelle créée par l'ajout successif d'unités ADP-ribose sur une protéine acceptrice pour former un polymère (pADPr) hétérogène branché. La caractérisation biochimique de tous les membres de la famille des PARPs est incomplète mais un constat important peut être dégagé par l'analyse de cette famille élargie : les PARPs présentent une grande diversité de domaines protéiques fonctionnels. Conséquemment, il est logique de croire que cette étonnante diversité sera responsable de fonctions variées dans plusieurs sentiers de signalisation ou événements cellulaires. La poly(ADP-ribosyl)ation, bien qu'étant une modification cruciale impliquée dans la régulation de l'intégrité génomique et la survie cellulaire, ne se limite plus aux seules fonctions nucléaires mais se présente de plus en plus comme un événement pouvant se dérouler dans un contexte physiologique extra-nucléaire. De plus, la liaison noncovalente de plusieurs protéines au pADPr libre ou à d'autres protéines poly(ADP-ribosyl)ées est un phénomène dont nous commençons à mieux mesurer les impacts fonctionnels. Contrairement aux PARPs, lesquelles sont exprimées par une superfamille de gènes apparentés, la majorité de l'activité de dégradation du pADPr est attribuable à l'expression d'un seul gène chez les mammifères : la poly(ADP-ribose) glycohydrolase (PARG). Un volet important de mon projet de recherche visait à identifier des partenaires de la PARG dans le but de reconnaître les sentiers biochimiques qui pourraient inclure une composante de poly(ADP-ribosylation) dans leur régulation et définir des interactions fonctionnellement pertinentes. Dans une optique complémentaire, les protéines associées au pADPr, que ce soit de manière covalente, noncovalente ou en association avec des complexes protéiques, ont été ciblées par des approches protéomiques. Enfin, des études protéomiques ont permis d'aborder l'état de phosphorylation de la PARP-1 et de la PARG

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