This dissertation describes a study of the kinetics of formation of tethered polymer layers. Polymer chains diffuse from dilute solution to the surface a solid, to which they become attached by one end. Kinetics profiles composed of three distinct regimes are displayed by all tethering reactions studied in the absence of segmental adsorption, regardless of solvent quality, temperature, chemistry of polymer, architecture of polymer, and type of reactive site on the surface. The first regime, fast and predicted previously by theory, is controlled by diffusion of the polymer chains through solution to the bare surface. The second regime, slow and also predicted by theory, is controlled by diffusion of the polymer chains through the already tethered layer. The third regime, relatively fast and not predicted by theory, appears to be the consequence of cooperative interaction between incoming chains and tethered chains. During the tethering process, each tethered polymer chain changes from a random-coil-like configuration to a vertically stretched configuration. The end of the first regime corresponds to completion of a layer of nonoverlapping, coil-like tethered chains, called a mushroom layer. Cessation of tethering corresponds to a layer of vertically stretched chains, called a polymer brush. Transition from mushroom to brush mainly takes place in the third regime and develops in spatially nonuniform manner. The understanding gained about the kinetics of tethering was used to construct simply tethered layers, bi-component tethered layers, bidisperse (two molecular weights) tethered layers, and tethered layers of mixed architecture (linear and star-branched).

No description available.

No description available.

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Different click chemistry methods have been used together with Reversible Addition- Fragmentation chain Transfer (RAFT) mediated polymerization to synthesize macromolecular architectures. A new leaving group for RAFT was introduced. This triazole leaving group allows for easy conjugation of the RAFT agent to various substrates via the copperI catalyzed Huisgen 1,3-dipolar cycloaddition reaction. Subsequently monomer can be polymerized onto the substrate using the RAFT agent. This connects the polymer to the substrate via a hydrolytically stable 1,2,3-triazole. The Mitsunobu reaction was used to chain-end functionalize polymers. The Mitsunobu reaction allows for the substitution of primary and secondary alcohols with a nucleophile. The modification of polymer chain-ends was done in two ways. Firstly, thiol-functional chain-ends were used as the nucleophile in the Mitsunobu reaction using propargyl alcohol as the alcohol. This yielded alkyne-functional polymers. Thiol chain-end functional polymers were obtained by the aminolysis of polymers synthesized via RAFT. Secondly, alcohol-functional polymers were modified. In the case of poly(vinylpyrrolidone), the RAFT group was hydrolyzed and alcohols were obtained. Hydroxyl functional PEG was obtained commercially. The hydroxyl functionality was reacted in the Mitsunobu reaction using hydrazoic acid (HN3) as the nucleophile. Azide chain end functional polymers were obtained. These alkyne and azide chain end functional polymers were subsequently used in the copperI catalyzed Huisgen 1,3-dipolar cycloaddition reaction. Ultra Fast Hetero Diels-Alder click chemistry (UFHDA) was used to synthesizes norbornenelike structures (substituted 2-thiabicyclo[2.2.1]hept-5-ene moieties). Norbornene-like structures can be polymerized via Ring Opening Metathesis Polymerization (ROMP). Monomers were synthesized using phenethyl(diethoxyphosphoryl)dithioformate and cyclopentadiene. Macromonomers were obtained from the UFHDA of Polystyrene (PSTY) synthesized via RAFT, using phenethyl(diethoxyphosphoryl) dithioformate as the RAFT agent, and cyclopentadiene or cyclopentadienyl-terminated PEG as the dienes. The obtained (macro) monomers were homo- and copolymerized using Ring Opening Metathesis Polymerization (ROMP). For the ROMP, four different Grubbs type catalysts were tested.The ring-strain promoted Huisgen 1,3-dipolar cycloaddition reaction uses cyclooctynes as the alkyne. The ring-strain in this molecule allows for a fast reaction at room temperature. This reaction is potentially very interesting for biological applications because it doesn’t require the toxic copper catalyst. In this work three routes towards cyclooctynes are investigated. PEG was chain end functionalized with the obtained cyclooctyne derivatives. Overall, click chemistry methodologies were applied to synthesize different macromolecular architectures. Results include a new type of RAFT agent that allows for easy conjugation to substrates, reaction methods for chain end modification of polymers, and the synthesis of new monomers and polymers. / AFRIKAANSE OPSOMMING: Verskillende kliek chemie metodes, tesame met Omkeerbare Addisie Fragmentasie ketting Oordrag beheerde polimerisasie (OAFO), is gebruik vir die sintese van makromolekulêre argitekture. ʼn Nuwe verlatende groep vir OAFO was bekend gestel. Die triazool verlatende groep bied die moontlikheid vir gemaklike koppeling van die OAFO agente met ‘n verskeidenheid van substrate via die koperI gekataliseerde Huisgen 1,3-dipolêre siklo-addisie reaksie. Gevolglik kan monomere gepolimeriseer word op die substraat deur middel van die OAFO agent. Dit laat toe vir die koppeling van die polimeer op die substraat via a hidrolitiese stabiele 1,2,3-triazool. Die Mitsunobu reaksie was gebruik vir die funksionaliseering van die end groepe van die polimeer ketting. Die Mitsunobu reaksie laat toe vir die substitusie van primêre en sekondêre alkohole met ‘n nukleofiel. Die verandering van die polimeer ketting end groepe was uitgevoer op twee verskillende maniere. Eerstens is ketting end groepe met ‘n tiol funktionaliteit gebruik as a nukleofiel in die Mitsunobu reaksie deur gebruik te maak van propargiel alkohol as die alkohol. Dit het alkyn funktionele polimere opgelewer. Tiol ketting end funktionele polimere was verkry deur middel van aminolise van die polimere gesintetiseer via OAFA. Tweedens is alkohol funktionele polimere gemodifiseer. In die geval van poli(N-vinielpirolidoon) is die OAFA grope gehidroliseer en gevolglik is alkohole verkry op hierdie manier. Kommersiële funksionele PEG was gebruik. Die hidroksie funksionele groep was gereageer in die Mitsunobu reaksie deur gebruik te maak van waterstof asied (HN3) as die nukleofiel. Dit het asied funksionele ketting eindes opgelewer. Die alkyne en asied ketting end funksionele polimere was gevolglik gebruik in die koperI gekataliseerde Huisgen 1,3- dipolêre siklo-addisie reaksie. Ultra Vinnige Hetero Diels-Alder kliek chemie (UVHDA) was gebruik vir die sintese van norborneen agtige strukture (gesubstitueerde 2-tiabisiklo[2.2.1]hept-5-een groepe). Monomere was gesintetiseer deur gebruik te maak van fenieletiel(di-etoksifosforiel)di-tioformaat en siklopentadiëen of siklopentadiëen-getermineerde PEG. Die sintese van makromonomere is verkry via UVHDA deur gebruik te maak van polistireen, gesintetiseer deur middel van OAFO (waar fenieletiel(dietoksifosforiel) di-tioformaat gebruik is as OAFO agent), en siklopentadiëen of siklopentadiëengetermineerde PEG. Die makromonomere wat verkry is, is verder gebruik vir homo- en kopolimerisasie deur middel van Ring Opening Metatesis Polimerisasie, ROMP. Vir die ROMP is vier verskillende Grubbs tipe kataliste gebruik. Die ring-spanning bevorderde die Huisgen 1,3,-dipolêre siklo-addissie reaksie waar siklooketyne gebruik is as die alkyne. Die ring-spanning in die molekule laat toe vir vinninge reaksies by kamer temperatuur. Die reaksie het die potensiaal vir interessante biologiese toepassings aangesien dit nie ’n kopper katalis vereis nie wat toksies van aard is. In die studie word drie roetes ten einde to siko-oktyn ondersoek. PEG was geketting end gefunksionaliseerd met die gevolgde siko-oktyne afgeleides. Verskillende kliek chemie metodologiëe was toegepas vir die sintese van verskillende makromolekulêre argitekture. Resultate sluit in een nuwe tipe OAFO agent wat maklike konjugasie met substrate bewerkstellig, ketting einde modifikasie van polimere, nuwe monomere en polimere wat gesintetiseer is.

Ce travail porte sur les mouvements moléculaires dans les caoutchoucs composants les pneumatiques : les polybutadiènes (PB) et les copolymères de polystyrène et polybutadiène (SBR). L’intérêt de cette étude est double : Nous souhaitons à partir de résultat de spectroscopies mécanique et diélectrique, comprendre l’origine moléculaire des relaxations dans ces élastomères, mais aussi voir le rôle de la microstructure chimique dans la mobilité moléculaire. Nous travaillons donc sur des matériaux différents par leur microstructure chimique à travers leurs taux respectifs de butadiène 1,2 vinyle, de butadiène 1,4 cis/trans ou encore de styrène pour les SBR. L’étude de la modification de la microstructure passe aussi par l’ajout de diluants qui servent de perturbateurs à la mobilité. La gamme de température balayée est comprise entre 90K et 350K et permet ainsi l’étude systématique de toutes les relaxations présentent dans les polymères de l’étude : La relaxation β, à plus basse température, la relaxation α pour des températures proches de Tg mais aussi, à plus haute température, les relaxations de bouts de chaine et enfin les phénomènes de reptation de chaines libres pour des températures 90K supérieures à Tg. Les techniques de spectroscopie mécanique (1.10-4/1 Hz) et diélectrique (0,1/1.106Hz) permettent d’obtenir des résultats sur un large domaine fréquence /température. Par ailleurs, les couplages mécanique d'une part et électrique d'autre part étant de nature différente, les informations obtenues par les deux techniques sont complémentaires. Le développement d’un modèle nous permet de démontrer que les mouvements des groupements butadiène 1,2 (vinyle) sont responsables de la contribution haute température de la relaxation β alors que ceux des groupements butadiène 1,4 cis et trans sont responsables de la partie basse température. L’étude approfondie de la relaxation α à l’aide du modèle de Perez amène à penser que ces mêmes groupements butadiène 1,2 vinyles jouent aussi un rôle non négligeable dans cette relaxation α. La dilution par une huile polaire provoque la suppression de la partie haute température de la relaxation β et amène ainsi à une modification de sa mobilité basse température. Diminuer la réticulation dans un polymère entraine revient à augmenter la longueur des bouts de chaine. Ces bouts de chaines peuvent alors relaxer selon les lois de rétraction de bouts de chaine développées par Curro à partir des modèles de Pearson et Helfand. Enfin, les chaines libres introduites dans un polymère réticulé suivent la théorie de la reptation de De Gennes-Doi-Edwards. / This work deals with the study of the molecular mobility in rubbers used for pneumatic applications, namely, polybutadiene (PB) and styrene butadiene rubber (SBR). They exhibit relaxation processes, which are in fact responsible for their main behaviors (adhesion, energy consumption, etc.). From mechanical and dielectric spectroscopy data, we tried to understand the molecular origins of these elastomers relaxation, but, also the role of their chemical microstructure on molecular mobility. We studied materials with different chemicals microstructures, i.e., with different butadiene 1,2 vinyl, butadiene 1,4 cis and 1,4 trans and styrene (for SBR only) ratio. The impact of microstructure modification was also studied with addition of diluents, which modifies the molecular mobility. Experimental temperature range was between 90 and 350K, so all relaxations present in polymer can be studied: the β relaxation at low temperature, the α relaxation for temperature near Tg, the chain-end relaxation at higher temperature and free chain reptation phenomenon at Tg+90K. Mechanical (10-4 Hz to 1 Hz) and dielectric spectroscopy (0,1 Hz to 106 Hz) allow obtaining large frequency range. Besides that, mechanical and dielectric induced stresses are different so both methods are complementary. The β relaxation exhibits two main contributions, so-called here high and low temperature contributions. The use of modeling permits to show that movements responsible for the high temperature contribution are those of butadiene 1,2 vinyl, whereas butadiene 1,4 cis and trans are responsible from low temperature contribution. Perez model used for studying the α relaxation shows that 1,2 vinyl also impact it. High temperature contribution of the β relaxation disappears after dilution by polar oil. Decreasing the crosslinking density in polymers results in the increase of average chain-end length. These chain-ends relax, and it has been found that their relaxation processes follow the chain-end retraction model developed by Curro from Pearson and Helfand works. On the contrary, free chains motions, when introduced in the already cross-linked polymer network follow De Gennes-Doi-Edwards reptation theory.

The thesis constitutes investigations from two distinct areas of research. One part deals with controlling and modulating the conformation of linear polymer in solution. Folding of a polymer chain has been achieved by utilising weak non-covalent interactions interaction like metal ion binding, charge-transfer complex formation and solvophobic effect in tandem. The second part of the thesis deals with synthesis and characterization of end-functionalized polymers prepared by melt-transesterification. The thesis is divided into five chapters. Chapter 1 provides a general introduction on foldamers – a class of polymers that adopts an ordered conformation in solution and various approaches to obtain end-functionalized polymers. Chapter 2 describe the attempts to improve the association constant (based on earlier works reported by Ghosh and Ramakrishnan) between the external folding agent and the polymer repeat unit. The polymer used in this study constitutes an electron deficient pyromellitic dimide units (PDI) linked with a flexible oxyethylene glycol spacer. An electron rich dialkoxy naphthalene (DAN) serves as the folding agent which forms a charge-transfer (C-T) complexation with the electron deficient aromatic units (PDI) in the polymer backbone and effects the folding. The folding agent has the metal ion as its integral part and this aids the interaction between electron-deficient and electron-rich aromatic units by complexing with oxyethylene glycol spacer. Thus folding is due to the synergistic effect of C-T complex formation and metal ion binding. Further a new polymer with larger -surface area of electron acceptor units was prepared with naphthalene dimide (NDI) unit instead of PDI unit which is expected to show higher folding propensity. Chapter 3 explores the possibility of modulating the folding of the donor acceptor (D-A) polymer. A D-A polymer consist of adjacently placed DAN and PDI units linked by an oxyethylene glycol spacer. Folding of the D-A polymer is effected in the presence of suitable metal ion that binds to the oxyethyleneglycol spacer. Random copolymers with segments of alternately placed D-A pairs and segments that is devoid of D-A pairs were prepared. Depending on composition of the random copolymer, the stack length was shown to be modulated as evident from UV-visible and NMR titration experiments. Following a similar approach, a two step folding of the synthetic polymer was demonstrated. The synthesis and characterization of end functionalized polyesters by melt transesterification is discussed in chapter 4. Well defined linear polymer with propargyl group as the end functionalizable group is prepared by the polycondensation of AB type monomer whereas polycondensation of AB2 type monomer leads to peripherally functionalized hyperbranched polymer. Azide-alkyne ‘click’ reactions carried out at the chain end of linear polyester with fluorophores allowed the estimation of the molecular weight by UV-visible and fluorescence spectroscopic method which is compared with estimation from 1H-NMR. Similarly the glass-transistion temperature of hyperbranched polyester is modulated by the peripheral functionalization with various organic azides by ‘click’ reaction. Chapter 5 gives the conclusion and future directions based on the findings from the thesis work.

No description available.

No description available.

La Résonance Magnétique Nucléaire RMN DOSY (Diffusion Ordered SpectroscopY) 1H est une technique permettant de mesurer les coefficients de diffusion des espèces en solution. Elle permet ainsi d’obtenir des informations structurales de par sa dimension RMN conventionnelle mais également des informations physico-chimiques telles que la taille de la (macro)molécule ou encore la formation d’agrégats. L’objectif de ces travaux a été d’examiner comment les méthodes de RMN (RMN 1D ,2D et DOSY), permettent de fournir des informations sur la caractérisation des matériaux polymères. La première partie de ce travail souligne l’intérêt de la RMN pour la caractérisation de la microstructure de quelques matériaux polymères en s’attardant plus particulièrement sur l’exploration de leurs extrémités de chaînes. La RMN s’est en effet révélée très performante pour établir le lien entre extrémité de chaîne et méthode de polymérisation appliquée. Le deuxième volet de ces travaux concerne l’étude de quelques architectures complexes (type dibloc et tribloc) et la mise en évidence du caractère contrôlé d’une copolymérisation radicalaire grâce à la RMN diffusionnelle. Nous avons également vu comment déterminer la masse moyenne en poids (Mw) par une simple mesure du coefficient d’autodiffusion. Finalement, l’ensemble des travaux présentés dans ce manuscrit a été valorisé grâce à l’étude des interactions par RMN diffusionnelle. Plus particulièrement la RMN DOSY 1H a permis d’observer des phénomènes de micellisation, d’agrégation, d’encapsulation et de relargage de molécules de principe actif. / Diffusion Ordered Spectroscopic Nuclear Magnetic Resonance (DOSY NMR 1H) makes it possible to determine physicochemical data such diffusion coefficients. While typical NMR data on the structure of molecules can be obtained, this technique also permits determinations of the physicochemical characteristics, such as molecular sizes or aggregate formation. The objective of this work was to examine how various NMR methodologies, specifically, 1 and 2 dimensional DOSY NMR, can be applied to the characterization of polymers. The first part of the manuscript relates the NMR characterization of some polymeric materials with a special interest in chain-end groups. In particular, we demonstrate the relationships between chain-ends and the polymerization methods employed. In a second part, the potential of the DOSY technique is used to determine controlled features of a radical polymerization resulting in di- and triblock architectures. Molecular weights are also determined by self-diffusion coefficient measurements. The results presented herein demonstrate that diffusional NMR can be effectively employed to understand interactions in polymeric structures. Indeed, DOSY 1H-NMR provides new interesting results concerning micellization, aggregation, encapsulation phenomena and the release of active molecules.

In recent years, a compound N-nitrosodimethylamine (NDMA), a probable human carcinogen, has been identified as an emerging disinfection by-product (DBP) since its formation and detection were linked to chlorine-based disinfection processes in several water utilities in the U.S. and Canada. Numerous organic nitrogen compounds present in water may impact the formation of NDMA during disinfection. Amine-based water treatment polymers used as coagulants and flocculants have been suggested as potential NDMA precursors due to the presence of amine functional groups in their structures, as well as the possible presence of dimethylamine (DMA) residues in polymer products. To minimize the potential risk of NDMA associated with water treatment polymers, the mechanisms of how the polymers behave as NDMA precursors and their contribution to the overall NDMA formation under actual water treatment conditions need to be elucidated. This research involved a systematic investigation to determine whether amine-based water treatment polymers contribute to NDMA formation under drinking water and wastewater treatment conditions, to probe the involved reaction mechanisms, and to develop strategies to minimize the polymers NDMA formation potential. The investigation included five research tasks: (1) General screening of NDMA formation potential of commonly used amine-based water treatment polymers, (2) NDMA formation from amine-based water treatment polymers under relevant water treatment conditions, (3) Probing the mechanisms of NDMA formation from polyamine and PolyDADMAC, (4) Effect of water treatment processes on NDMA formation from amine-based water treatment polymers, and (5) Developing strategies to reduce polymers NDMA formation potential. Direct chloramination or chlorination of high doses of polymers in deionized water at longer than typical contact time was used in the general screening of the NDMA formation potential of water treatment polymers and in the studies to identify reaction mechanisms. On the other hand, realistic dosages of chloramines and polymers and contact time were used in simulating representative water treatment conditions to evaluate the contribution of polymers to the overall NDMA formation in real systems. On the basis of the study results, strategies were developed to reduce the NDMA formation potential of amine-based water treatment polymers, which include modification of polymer structures and treatment parameters.