In this article, a multiple-responsive polymer micelles system was constructed by using ionic bond to link the hydrophobic tetraphenylthiophene (TP) fluorophores, which possess the property of aggregation-induced emission enhancement (AIEE), with the hydrophilic poly(N-isopropyl acrylamide) (PNIPAM). The susceptibility of the ionic ammonium-sulfonate (Am-Sul) bonds towards metal ions, acid and base triggered the AIEE-operative fluorescence (FL) response. To exercise the idea, PNIPAM with sulfonate terminal was primarily prepared to react with TP-derivatives functionalized with ammonium groups to generate polymer complex of TP-PNIPAM. When in water, the polymer complex TP-PNIPAM formed micelles with the aggregated TP core interconnecting the hydrophilic PNIPAM shell by the ionic Am-Sul bonds. With the operative AIEE effect, the aggregated TP core of the micelles fluoresced but upon the additions of metal ions, acid and base, the ionic bonds dissociated to result in the collapse of the micelles and the FL quenching. A novel fluorogenic sensor capable to respond to multi-stimuli was therefore constructed. Amphiphilic micelle systems with the hydrophilic poly(N-isopropyl amide) (PNIPAM) shell and the hydrophobic tetraphenylthiophene (TP), which has the novel aggregation-induced emission enhancement (AIEE) feature, core inter-connected by ionic bonds were prepared in this study to explore the AIEE-operative emission response towards critical micelle concentration (CMC) and lower critical solution temperature (LCST). To exercise the idea, TP functionalized ammonium cations and PNIPAM with terminal sulfonate group were individually prepared and mixed together to yield three amphiphilic TP-PNIPAM complexes with different hydrophobic TP to the hydrophilic PNIPAM (x/y) ratios. When in aqueous solution, TP-PNIPAMs form micelles with the aggregated TP core, which emits strongly due to the operative AIEE effect, encompassed by the PNIPAM shell. The resultant CMC and LCST of the TP-PNIPAM micelles can be varied by changing the hydrophobic to the hydrophilic x/y ratio and can be monitored by the AIEE-dominant fluorescence responses towards concentration and temperature variables.

Thermoresponsive polymers such as poly(N-isopropylacrylamide) (PNIPAM) have lower critical solution temperature (LCST) in aqueous solutions. Below the LCST, these polymers are hydrophilic with an extended coil conformation. Above the LCST, they undergo a sharp phase transition to form a collapsed hydrophobic conformation. The LCSTs are also affected by cosolutes and the effects of anions on LCSTs follow the Hofmeister series. We successfully used a simple digital melting point apparatus to study the effects of heating rates, solvent compositions, cosolutes, and redox state, on the LCSTs of thermoresponsive polymers. Moreover, the temperature range of the apparatus allowed for analyses at much higher temperatures and provides a simple way to examine irregular clouding behavior in more complex systems. Meanwhile, stimuli-responsive surfaces grafted with thermoresponsive polymers can switch from hydrophilic to hydrophobic thermally. As the LCST can be subsequently changed with the addition of salts, the salt effects on the wettability of these thermoresponsive surfaces will dramatically impact the surface performance. In this dissertation, I prepared PNIPAM/SiO2 nanocomposite surfaces by a covalent layer-by- layer assembly procedure and such surfaces were then used in studies of salts effects on surface wettability. Both the effects of anions and cations on the changes of advancing angles (Delta Theta a) of the PNIPAM/SiO2 nanocomposite surfaces were significant (Delta Theta a up to 90 degrees). The anion effects on the surface wettability followed the Hofmeister effect as expected. Parallel studies on solution showed that variation of cations had a large effect on the LCST of PNIPAM too. Moreover, analyses of the Theta a and LCST data using activity instead of using concentration showed different orders for the cation effects which were readily grouped by the cation charge numbers. No difference was seen for the anion effects in similar studies. AFM studies showed that surface morphology changes were correlated with the Delta Theta a.

Poly(N-vinylcaprolactam), PNVCL, is a nonionic, nontoxic, water soluble, thermally sensitive and biocompatible polymer. It contains hydrophilic carboxylic and amide groups with hydrophobic carbon-carbon backbone chain so its hydrolysis does not produce small amide compounds which are often not desired for biomedical applications. Moreover PNVCL possesses lower critical solution temperature, (LCST) in the range of physiological temperature (32-34 oC). These properties make the polymer suitable for use in some biotechnology applications such as implantation of artificial organs and tissues, purification of enzymes, proteins and living cells, and in drug release systems. In this study PNVCL was synthesized by free radical polymerization with solution technique. Polymerization was done at different temperatures for different time periods in an oil bath. The activation energy for polymerization was found from Arrhenius plot as 108.4 kJ/mol. Polymer was characterized by FT-IR, 1H-NMR and 13C-NMR, DSC, TGA and XRD techniques. FT-IR and NMR measurements confirmed that the polymerization proceeded through the vinyl group.

About half a century ago, Főrster and Kasper discovered that traditional organic chromophore such as pyrene was weakened with an increase in its solution concentration. It was soon recognized that this was a general phenomenon for many aromatic compounds. This concentration-quenching effect was found to be caused by the formation of sandwich-shaped (disc-like) excimers and exciplexes aided by the collisional interactions between the aromatic molecules in the excited and ground states. In 2001, Tang¡¦group discovered such a system, in which luminogen aggregation played a constructive, instead of a destructive, role in the light-emitting process: a series of silole molecules were found to be non-luminescent in the solution state but emissive in the aggregated state. They coined the term ¡¥¡¥aggregation-induced emission¡¦¡¦ (AIE) or ¡§AIE enhancement¡¨ (AIEE) for this novel phenomenon which originated from the restricted intramolecular rotation (RIR) inherent from the chemical structures of the luminescent materials. To verify the effect of molecular structure on the AIE properties of organic and polymeric materials, four approaches were attempted in this research. (I) Aggregation-Induced Emission in Tetraphenylthiophene-Derived Organic Molecules and Vinyl Polymer Organic molecules of tetraphenylthiophene (TP) and the derived model compound of TP-Qu and vinyl polymer of PS-Qu with the pendant group of TP-Qu were prepared and characterized to identify their photoluminescent responses toward the effect of AIE. During aggregate formation, the corresponding TP solutions greatly gained the emission intensity. In contrast, TP-Qu and PS-Qu in isolated or aggregated states emitted strongly with nearly the same emission intensity. RIR is the key factor deciding the AIE effect in different states. With four small phenyl rotors around the central thiophene stator, the RIR of the TP molecules in dilute solution is low but increases upon aggregate formations. In contrast, the bulky C-2 quinoline rotor of the TP-Qu molecule enhances the RIR in isolated state. With the inherent TP-Qu pendant groups, the emissive behavior of vinyl polymer PS-Qu is similar to the TP-Qu molecule. (II) Aggregation-Induced Emission Enhancement of Diblock Copolymer Containing Tetraphenylthiophene-Quinoline Pendant Fluorphores by Selective Solvent Pairs In this study, diblock copolymer of PSQu-PBS containing 25 mol% of fluorescent PSQu segments was synthesized and its aggregation-induced emission enhancement (AIEE) behavior was characterized and compared to PSQu homopolymer with 100 mol% of fluorescent units. With fewer (25 %) fluorescent units, solutions of diblock PSQu-PBS copolymer actually have higher (or comparable) emission intensities than the homopolymer PSQu solutions. Solutions of PSQu-PBS in THF/H2O of varied compositions emit essentially with the same intensity but in contrast, emissions of PSQu-PBS in THF/hexane increase with the increasing hexane content. Copolymer micelles formed in THF/hexane mixtures are supposed to have higher extent of aggregation, leading to more pronounced AIEE effect than micelles formed in THF/H2O. (III) Tetraphenylthiophene-Functionalized Poly(N-isopropylacrylamide): Probing LCST with Aggregation-Induced Emission A hydrophobic TP center with novel AIE property was chemically linked to two poly(N-isopropylacrylamide) (PNIPAM) chains to obtain thermoresponsive polymers to study the relationships between the lower critical solution transitions (LCSTs) and the AIE-operative fluorenscence emission. Three ethynyl-terminated PNIPAMs with different molecular weights were synthesized via controlled atom transfer radical polymerization (ATRP) using ethynyl-functionalized initiator. The PNIPAMs were then coupled with diazide-funtionalized TP (TPN3) via click reaction to obtain the desired TP-embedded polymers of Px (x = 1, 2, and 3). All three polymers show AIE-property from their solution fluorescence behavior in THF/hexane mixtures. In the aqueous solution, the TP-center served as a fluorogenic probe that reveals the LCSTs of polymers and its relation to the degree of TP labeling in terms of polymer concentration. The thermoresponsiveness of Px was demonstrated by the complete emission quench when heated at temperatures above LCST. Dissociation of the TP aggregates above LCST is responsible for the emission quench. (IV) Influence of Molecular Weight on the Aggregation-Induced Emission of Vinyl Polymers Containing the Fluorescent 2,4,6-Triphenylpyridine Pendant Groups Molecular weight effect on the AIEE property of vinyl polymers containing fluorescent 2,4,6-triphenylpyridine (TPP) pendant groups was evaluated in the fourth topic. The high and low Mw vinyl polymers of PDMPS¡VL and ¡VH were prepared through Click chemistry between azide¡VTPP derivative and acetylene¡Vfunctionalized polystyrenes. Solutions of the low Mw PDMPS¡VL exhibited the normal AIEE effect with continuous emission gains with increasing extent of aggregation upon nonsolvent inclusion. On the contrast, the high Mw PDMPS¡VH solutions emitted with constant intensity on all solutions with different extent of aggregation. Despite the varied solution behavior, the solid PDMPS-L and ¡VH films are all strong deep-blue emitter with high quantum yields of 84 and 82.5%, respectively. The emission behavior was explained by the conformational difference between the PDMPS¡VL and ¡VH chains, which were approached by computer simulation in this topic.

Several analytical mean field models are presented for the class of stimuli responsive polymers that are driven by the lower critical solution temperature (LCST) transition. For solutions above the polymer crossover concentration, a hybrid model combines lattice-fluid excluded volume and van-der-Waals interactions with a combinatorial approach for the statistics of hydrogen bonding, hydration, and ionic bonding. This approach yields models for the LCST of both neutral polymers and lightly charged polyelectrolytes in aqueous salt solution. The results are shown to be in semi-quantitative agreement with experimental data for the cloud point of polyethylene oxide (PEO) in aqueous solution with various salts, and some aspects of the lyotropic series are reproduced. Results for lightly charged polyelectrolytes are compared to and shown to be in qualitative agreement with aspects of experimentally observed behavior. Finally, a framework is established for extension of these models to further aspects of the lyotropic series and polyelectrolyte behavior. At the nanoscale, lattice fluid (LF) and scaled particle theory (SPT) approaches are employed to model the LCST-related coil-globule-transition (CGT) of isolated polymer chains in highly dilute solution. The predicted CGT behavior semi-quantitatively correlates with experimental results for several polymer-solvent systems and over a range of pressures. Both the LF and SPT models exhibit a heating induced coil-to-globule transition (HCGT) temperature that increases with pressure until it merges with a cooling induced coil-to-globule transition (CCGT). The point at which the CCGT and HCGT meet is a hypercritical point that also corresponds to a merging of the lower critical and upper critical solution temperatures. Theoretical results are discussed in terms of a generalized polymer/solvent phase diagram that possesses three hypercritical points. Within the lattice model, a dimensionless transition temperature [author gives mathematical symbol] is given for a long chain simply by the equation [author gives mathematical equation], where [part of the equation] is the bulk solvent occupied volume fraction at the transition temperature. Furthermore, there is a critical value of the ratio of polymer to solvent S-L characteristic temperature below which no HCGT transition is predicted for an infinite chain. / text

This thesis reports the results of light-scattering measurements and visual investigations of critical phenomena in the complex mixture 1-propanol (1P) + water (W) + potassium chloride (KCl) which has a special critical point (or a special thermodynamic state) known as the double critical point (DCP). The main theme of the thesis is the critical behavior on approaching a special critical point (i.e., the DCP) in a complex or associating mixture in contrast with that in simple, nonassociating mixtures. The asymptotic critical behavior in complex or associating fluids, such as polymer solutions and blends, ionic and nonionic micellar solutions, microemulsions, aqueous and nonaqueous electrolyte solutions, protein solutions, etc., is now commonly accepted to belong to the 3D-Ising universality class. However, the temperature range of the asymptotic regime in these fluids, with universal behavior, has a nonuniversal width and is, in general, smaller than that in simple or nonassociating fluids. In complex mixtures, which are made up of relatively large molecules or particle clusters of mesoscopic range, the coupling between the conventional correlation length of the critical fluctuations ( ξ) and an additional length scale associated with the mesoscale structures (ξD) is known to modify the approach towards the universal nonclassical critical behavior near their critical points. Nevertheless, the generality of this approach needs to be confirmed. There are also instances of a pure classical or close to classical behavior being observed in the critical domain of complex mixtures, although recent experimental results contradict the earlier observations. Therefore, further experimental evidences than that presently available are necessary before one can say how far the analogy between simple and complex fluids can be pushed. Variations in the effective dielectric constant of a mixture have been known to affect the critical behavior. Furthermore, we anticipate the presence of special critical points in complex mixtures to cause nontrivial modifications in the approach towards the universal asymptotic critical behavior. Special thermodynamic states are characterized by critical fluctuations with exceptionally large correlation length, and are displayed by multicomponent liquid mixtures, in which there are a multitude of thermodynamic paths by which a critical point can be approached, and offers rich information about the critical phenomena. These issues are being addressed in this research work. This thesis is organized into 7 Chapters. Chapter 1 begins with an account of the historical development of the field of critical point phenomena with a brief introduction to critical phenomena in simple fluids. Critical phenomena observed in various complex systems such as aqueous and nonaqueous ionic fluids, polymer solutions and blends, micellar and microemulsion systems, etc., are discussed, with particular attention to investigations into crossover from Ising to mean-field critical behavior observed in these systems, which are relevant to the present work. Theoretical attempts at modeling ionic criticality are cited and summarized. This is followed by a discussion of re-entrant phase transitions in multicomponent liquid systems. An account of the various types of special critical points, such as double critical point, critical double point, critical inflection point, quadruple critical point, etc., highlighting the critical behavior on approaching these special critical points, and some of the models of reentrant miscibility are briefly given. The Chapter ends with a statement on the goals of the present research work. Chapter 2 describes the instrumentation developed and the data acquisition procedures adopted for the study. Details of the thermostats and precision temperature controllers used for visual and light-scattering measurements are provided. The important design considerations relating to the achievement of a high degree of temperature stability (~ ±1 mK in the range 293-383 K) are elucidated clearly. The temperature sensors used in the present experiments and their calibration procedures are discussed. The light-scattering instrumentation is discussed in depth. The problems associated with the light-scattering techniques when it is used to study critical point phenomena, and the strategies adopted to overcome them are discussed. The sample cells used for visual investigations and light- scattering experiments, along with the procedure adopted for cleaning and filling of sample cells are also described. Chapter 3 essentially deals with the characterization of the system 1P + W + KCl. It begins with a brief introduction to the critical behavior in complex mixtures, and the motivation behind choosing the present system. The phase behavior in the present mixture, the generation of the coexistence curves and the line of critical points in the mixture, and the method used for preparation of the samples are described. The criticality of the samples is judged by the equal volume phase separation criterion through visual investigations. Addition of a small amount of salt (i.e., KCl) to the 1P + W solution induces phase separation in the mixture as a result of a salting-out process. Decreasing the salt concentration has the same effect as that of increasing pressure on the liquid-liquid demixing of this mixture. Therefore, KCl may be considered as an appropriate field variable analogous to pressure in this mixture. The mixture 1P + W + KCl exhibits reentrant phase transitions and has an array of lower (TL) and upper (TU) critical solution temperatures. It is found that the line of TL’s and TU’s, known as the line of critical points, merge (TU - TL = ΔT → 0) to form a special thermodynamic state known as the DCP. The DCP is approached as close as 509 mK (i.e., ΔT ~ 509 mK) in this work. An analysis of the critical line shows that it is roughly parabolic in shape, which is in consonance with the predictions of the lattice models and the Landau-Ginzburg theory of phase transition. In addition to the presence of a special critical point, various structure probing techniques like small angle X-ray scattering (SAXS), small angle neutron scattering (SANS), etc., indicate the presence of large-scale density inhomogeneities or clusters in 1P + W solution and its augmentation on adding small amount of KCl. Therefore, the present mixture provides a unique possibility to investigate the combined effects of molecular structuring as well as a special critical point on the critical behavior. Only a section of the coexistence surface of the mixture could be generated, owing to various experimental limitations and other problems inherent to the system. This limited further studies on the coexistence curves in the mixture. Chapter 4 reports the critical behavior of osmotic susceptibility in the present mixture. The behavior of the susceptibility exponent is deduced from static light-scattering measurements, on approaching the lower critical solution temperatures (TL’s) along different experimental paths by varying t [ =| (T - T TL)/ TL|] from the lower one-phase region. The light-scattering data analysis emphasizes the need for correction-to-scaling terms for a proper description of the data over the investigated t range. Renormalization of the critical exponents is observed as the critical line is approached along certain special paths. Experimental evidence for the doubling of the extended scaling exponent Δ1 near the DCP is shown. There is no signature of Fisher renormalization in the values of the critical exponents. The data analysis yields very large magnitudes for the correction amplitudes A1 and A2, with the first-correction amplitude A1 being negative, signifying a nonmonotonic crossover behavior of the susceptibility exponent in the mixture. The magnitudes of the correction amplitudes are observed to increase gradually as TL approaches the DCP. The increasing need for extended scaling in the neighborhood of special critical points has been noted earlier in several aqueous electrolyte solutions, in polymer-solvent systems, etc. However, the magnitudes of the correction amplitudes were not as large as that in the present case. Analysis of the effective susceptibility exponent γeff in terms of t indicate that, for the TL far away from the DCP, γeff displays a nonmonotonic crossover from its single limit 3D Ising value (~ 1.24) towards its mean-field value with increase in t. While for that closest to the DCP, γeff displays a sharp, nonmonotonic crossover from its nearly doubled 3D-Ising value (~ 2.39) towards its nearly doubled mean-field value (~ 1.84) with increase in t. For the in-between TL’s, the limiting value of γeff in the asymptotic as well as nonasymptotic regimes gradually increases towards the DCP. The renormalized Ising regime extends over a relatively larger t range for the TL closest to the DCP, and a trend towards shrinkage in the renormalized Ising regime is observed as TL shifts away from the DCP. Nevertheless, the crossover behavior to the mean-field limit extends well beyond t > 10¯2 for the TL’s studied. The crossover behavior is discussed in terms of the emergence of a new lengthscale ξD associated with the enhanced ion-induced clustering seen in the mixture, as revealed by various structure probing techniques, while the observed unique trend in the crossover is discussed in terms of the varying influence of the DCP on the critical behavior along the TL line. The discussion is extended to explain the observed critical behavior in various re-entrant systems having other special critical points. The extended renormalized Ising regime towards the DCP is also reflected in a decrease in the correlation length amplitude (ξ0) as TL approaches the DCP. It is observed that the first-correction amplitude A1 corresponding to fit using two correction terms becomes more negative as TL approaches the DCP, implying an increase in the value of the parameter ū of the crossover model [by Anisimov et al., Phys. Rev. Lett. 75, 3146 (1995)] as the DCP is approached. This increase in reflected in a trend towards a relatively sharp crossover behavior of γeff as TL shifts towards the DCP, i.e., towards the high temperature critical points. The significance of the field variable tUL in understanding different aspects of reentrant phase transitions is manifested in the present system as well. Analysis of the data in terms of tUL led to the retrieval of universal values of the exponents for all TL’s. The effective susceptibility exponent as a function of tUL displays a nonmonotonic crossover from its asymptotic 3D-Ising value towards a value slightly lower than its nonasymptotic mean-field value of 1. The limited (TL _ T) range restricted such a behavior of the effective exponent (in terms of t as well as tUL) for the lowest TL. This feature of the effective susceptibility exponent is interpreted in terms of the possibility of a nonmonotonic crossover to the mean-field value from lower values in the nonasymptotic, high tUL region, as foreseen earlier in micellar systems. The effective susceptibility exponent in terms of tUL also indicates an increase in the sharpness of crossover towards the high temperature TL’s. An increase in the sharpness of crossover with polymer chain length has been observed in polymer solutions. Therefore, our results suggest the need for further composition and temperature-dependent study of molecular structuring in the present mixture. There is also a large decrease in the dielectric constant of the mixture towards the high temperature TL’s. In Chapter 5 the light-scattering measurements are performed on approaching the DCP along the line of the upper critical solution temperatures (i.e., TU’s), by varying t [ = (T - TU )/ TU ] from the high temperature one-phase region in the mixture. A trend towards shrinkage in the simple scaling region is observed as TU shifts away from the DCP. Such a trend was not visible in the data analysis of the TL’s using the correction terms, due to the varying (TL - T) ranges. The light-scattering data analysis substantiates the existence of a nonmonotonic crossover behavior of the susceptibility exponent in the mixture. As with the TL’s, for the TU closest to the DCP, γeff displays a nonmonotonic crossover from its 3D-Ising value towards its nearly doubled mean-field value with increase in t. While for that far away from the DCP, γeff displays a nonmonotonic crossover from its single limit Ising value towards a value slightly lower than its mean-field value of 1 with increase in t. The limited (TL – T) range restricted such a behavior of γeff for the TL far away from the DCP, This feature of γeff in the nonasymptotic, high t region is yet again interpreted in terms of the possibility of a nonmonotonic crossover to the mean-field value from below. Unlike TL’s, the crossover behavior in the present case is pronounced and more sharp for all TU’s. However, the variation in the width of the renormalized Ising regime on approaching the DCP along the TU line is quite similar to that observed along the TL line. The crossover behavior is attributed to the strong ion-induced structuring seen in the mixture, while the observed trend in the crossover as TU shifts towards/away from the DCP is attributed to the varying influence of the DCP. The influence of the DCP on the critical behavior along the TU (or TL) line decreases as TU (or TL) shifts away from the DCP. Our observations indicate an increase in the sharpness of crossover as the critical temperature shifts from TL towards TU, or in other words, as the critical point shifts towards higher temperatures. SANS measurements on the present mixture indicate no difference in the growth of mesoscale clusters in the lower and upper one-phase regions in the mixture. Hence, the observed increase in the sharpness of crossover towards the TU’s is very puzzling. The dielectric constant of the major constituent (i.e., water, ~ 62 %) of the present mixture decreases from around 80 to 63 as the critical temperature shifts from TL towards TU. Therefore, our results suggest the need to look at the crossover phenomena probably from two perspectives, namely, the solvent or dielectric effect and the clustering effect. The increase in the sharpness of the crossover behavior on approaching the high temperature critical points is probably related to the macroscopic property of the mixture, i.e., to the decrease in the dielectric constant of the mixture, while the actual nonmonotonic character of the crossover behavior is related to the microscopic property of the mixture, i.e., to the clustering effects, the extent of which determines the width of the asymptotic critical domain. However, this conclusion is somewhat subtle and calls for rigorous theoretical and experimental efforts to unravel the exact dependence of the crossover behavior on the dielectric constant. Analysis using the field variable tUL in lieu of the conventional variable t led to the retrieval of unique, universal exponents for all TU’s irrespective of the ΔT value. For all TU’s, the effective susceptibility exponent in terms of tUL displays a nonmonotonic crossover from its asymptotic 3D-Ising value towards a value slightly lower than its nonasymptotic mean-field value of 1, as that observed in the t analysis of the effective exponent for the TU far away from the DCP. Like with the TL’s, the crossover behavior extends over nearly the same tUL range for the TU’s studied. However, the crossover is again sharper when compared to the TL’s. Chapter 6 reports light-scattering measurements (by heating as well as cooling) on a non phase-separating 1P + W + KCl mixture in the vicinity of the DCP. The results indicate that despite the lack of phase-separation or critical points, critical-phenomena-like fluctuations can still occur in homogeneous mixtures if they reside in some other direction than temperature or composition (like, pressure or salt concentration) of the phase diagram. Unlike earlier studies on non phase-separating mixtures, our results indicate a crossover behavior of the effective susceptibility exponent, in addition to the power-law behavior. Chapter 7 sums up the major findings of the work reported in this thesis. It also presents a range of open problems that need to be explored further in order to fully understand the results that are reported in this thesis, especially, regarding the exact dependence of dielectric constant of the mixture on the character of the crossover behavior.

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Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

R??sum?? : Les copolym??res ?? blocs sensibles aux stimuli (SR-BCPs) et leurs assemblages, tels que les micelles, les v??sicules et les hydrogels, peuvent subir des changements physiques ou chimiques en r??ponse ?? l'??volution des conditions environnementales. Pour un excellent SR-BCP, habituellement, de l??g??res modifications de l'environnement sont suffisantes pour induire des modifications relativement drastiques dans la conformation, la structure ou les propri??t??s du polym??re. Ces polym??res sont aussi appel??s polym??res stimuli-r??actifs ou polym??res intelligents et ils ont un grand potentiel d'application dans de nombreux domaines. Au cours des deux derni??res d??cennies, un int??r??t de recherche et d??veloppement particulier a ??t?? port?? sur l'exploitation des SR-BCPs pour utilisation comme syst??mes de relargage de m??dicaments. Dans de nombreux cas, les changements induits par des stimuli dans la structure ou la morphologie des assemblages de BCPs peuvent entra??ner la lib??ration de l'esp??ce encapsul??e, parfois d'une mani??re contr??lable spatialement et temporellement par le choix d'un stimulus appropri?? et en ajustant les param??tres de la m??thode de stimulation utilis??e. De fa??on g??n??rale, le fait d???avoir un certain type de groupements r??actifs ?? un stimulus donn?? dans la structure permet aux SR-BCPs de reconna??tre et r??agir ?? ce stimulus. Malgr?? les ??normes progr??s r??alis??s sur les SR-BCPs, un certain nombre de questions fondamentales restent ?? r??soudre afin de leur permettre de se trouver dans des applications pratiques. Pour y arriver, la cl?? ou le d??fi r??side dans l???am??lioration du niveau et de la complexit?? de contr??le sur les SR-BCPs ainsi que la sensibilit?? avec laquelle ces polym??res r??agissent ?? des stimuli. G??n??ralement, il est souhaitable d'obtenir une r??action rapide sous l'action d'une stimulation mod??r??e. A cette fin, il est n??cessaire d???effectuer des recherches fondamentales sur la conception rationnelle de nouveaux SR-BCPs ainsi que sur le d??veloppement de m??thodes de stimulation qui peuvent amplifier l'effet d'un stimulus. Les travaux de recherche pr??sent??s dans cette th??se s'inscrivent dans ce domaine de recherche. Plus sp??cifiquement, nous avons ??tudi?? des micelles de BCPs qui r??pondent ?? deux types de stimuli. D'une part, nous avons ??tudi?? un m??canisme d'amplification bas?? sur l???effet des ultrasons combin?? ?? la thermosensibilit?? de BCPs. D'autre part, nous avons d??velopp?? une nouvelle conception de BCPs qui permet aux micelles d?????tre d??truites soit de mani??re photochimique, soit par des r??actions d'oxydo-r??duction, tout en ayant le nombre minimum des groupes stimuli-r??actifs dans la structure du polym??re. Notre recherche a g??n??r?? de nouvelles connaissances dans ce domaine et sugg??re de nouveaux moyens sur la fa??on dont les questions de sensibilit?? et de contr??le complexe des micelles SR-BCPs peuvent ??tre abord??es, contribuant ainsi ?? l'avancement des connaissances fondamentales. Le c??ur de cette th??se est compos?? de trois publications r??sultant des projets r??alis??s. Dans le premier projet, afin de coupler la sensibilit?? aux ultrasons et la thermosensibilit??, nous avons men?? une ??tude ayant pour but de trouver des structures possibles de polym??res qui sont susceptibles d'??tre affect??es par les ultrasons. Nous avons effectu?? une ??tude comparative sur la destruction des micelles form??es par divers BCPs et la lib??ration concomitante d'un colorant hydrophobe encapsul?? (rouge du Nil) par les ultrasons focalis??s de haute intensit?? (HIFU). Nous avons constat?? que toutes les micelles form??es par les quatre copolym??res diblocs synth??tis??s, ??tant constitu??s d'un m??me bloc du polyoxyde d'??thyl??ne (PEO) hydrophile et d???un bloc de polym??thacrylate hydrophobe diff??rent, peuvent ??tre perturb??es par les ultrasons. Toutefois, l'ampleur de la perturbation et la lib??ration du colorant encapsul?? dans la micelle est influenc??e par la structure chimique du block hydrophobe. En particulier, les micelles du PEO-b-PIBMA (poly(1-isobutoxym??thacrylate d'??thyle)) et du PEO-b-PTHPMA (poly(m??thacrylate de 2-t??trahydropyrannyle)), qui poss??dent une unit?? ac??tal labile dans le groupe lat??ral, subissent des perturbations plus importantes en raison, probablement, d???une r??action d???hydrolyse de l???ester induite par les ultrasons, donnant lieu ?? une lib??ration plus rapide du colorant. En revanche, les micelles du PEO-b-PMMA (poly(m??thacrylate de m??thyle)), dont le bloc polym??thacrylate est plus stable, sont plus r??sistantes aux ultrasons et pr??sentent une cin??tique de lib??ration du colorant plus lente que les autres micelles. De plus, l???analyse des spectres infrarouges des solutions micellaires, enregistr??s avant et apr??s l???exposition aux ultrasons, sugg??re une r??action d???hydrolyses pour le PEO-b-PIBMA et le PEO-b-PTHPMA, mais montre l'absence d???une quelconque r??action chimique pour le PEO-b-PMMA. L'effet de la structure de copolym??re ?? blocs sur la r??activit?? des micelles ?? l'irradiation HIFU ?? hautes fr??quences permet de mieux comprendre comment des micelles de BCPs sensibles aux ultrasons peuvent ??tre con??ues. Sur la base du premier projet, dans le deuxi??me projet, nous avons d??montr?? une nouvelle approche pouvant amplifier l'effet de HIFU sur la destruction des micelles de BCPs en solution aqueuse. L???id??e est d???introduire une petite quantit?? des unit??s comonom??res sensibles aux ultrasons dans le bloc thermosensible et initialement hydrophobe. On peut alors former une micelle dont le noyau est compos?? du polym??re sensible aux ultrasons. Si la r??action induite par les ultrasons sur le noyau permet d???augmenter la temp??rature de solution critique inf??rieure (LCST) du polym??re thermosensible au-dessus de la temp??rature de la solution micellaire, la micelle doit ??tre dissolue car tout le BCP est devenu soluble dans l???eau. Pour tester la validit?? de ce nouveau m??canisme, nous avons synth??tis?? et ??tudi?? un copolym??re dibloc de PEO-b-P(MEO[indice inf??rieur 2]MA-co-THPMA) (MEO[indice inf??rieur 2]MA repr??sente 2-(2-m??thoxy??thoxy) m??thacrylate d'??thyle), dans lequel le bloc thermosensible P(MEO[indice inf??rieur 2]MA-co-THPMA) est hydrophobe ?? T>LCST. Le THPMA a ??t?? choisi en raison de sa plus grande r??activit?? vis-??-vis des faisceaux HIFU que les autres monom??res ??tudi??s dans le premier projet. Les r??sultats montrent que les HIFU peuvent effectivement augmenter la LCST du bloc P(MEO[indice inf??rieur 2]MA-co-THPMA) et, par cons??quent, induire la dissociation des micelles ?? une temp??rature constante de la solution. Une analyse spectrale en RMN [indice sup??rieur 13]C a fourni des preuves montrant que l'hydrolyse des groupes THPMA se produit sous l???irradiation HIFU et que la destruction des micelles provient d'une augmentation de la LCST en raison de la conversion des motifs hydrophobes THPMA en motifs acides m??thacryliques (MAA) hydrophiles. Cette m??thode de modifier la LCST par une irradiation des ultrasons est g??n??rale et peut ??tre appliqu??e aux autres groupements sensibles aux ultrasons dans la conception de ce type de SR-BCPs. Cette ??tude a ainsi d??montr?? un nouveau m??canisme d'amplification et de contr??le des micelles de BCPs via la modification induite par les ultrasons de la temp??rature de transition de phase (LCST) du bloc constituant le noyau micellaire. Le troisi??me projet pr??sent?? dans cette th??se portait sur une conception rationnelle de BCPs ayant un but pr??cis: permettre aux micelles d?????tre perturb??es par deux types de stimuli en utilisant le nombre minimal des unit??s sensibles ?? des stimuli dans la structure de BCPs. Pour ce faire, nous avons con??u et synth??tis?? un nouveau copolym??re tribloc amphiphile de type ABC, soit le poly(oxyde d'??thyl??ne) - disulfure ??? polystyrene - o-nitrobenzyle - poly(2-(dim??thylamino) ??thylm??thacrylate) (PEO-S-S-PS-ONB-PDMAEMA). Il dispose d'une liaison disulfure redox-clivable entre les blocs PEO et PS ainsi que d'un groupe o-nitrobenzyle (ONB) photoclivable ?? la jonction des blocs PS et PDMAEMA. Nous avons montr?? que ce mod??le est une strat??gie utile pour permettre aux micelles de BCPs de r??pondre soit ?? un agent r??ducteur comme le dithiothr??itol (DTT) dans une solution, soit ?? l'exposition ?? la lumi??re UV, tout en ayant le nombre minimum des groups stimuli-r??actifs dans la structure du copolym??re (deux unit??s par cha??ne). Nos investigations ont r??v??l?? que les micelles de ce copolym??re tribloc peuvent ??tre perturb??es de diff??rentes fa??ons. Lorsqu'un seul stimulus est appliqu??, l'enl??vement d'un type des cha??nes de polym??re hydrophile ?? partir de la couronne de micelles, soit le PEO par clivage par oxydo-r??duction ou le PDMAEMA par photoclivage, entra??ne un effet limit?? de d??stabilisation sur la dispersion des micelles. L'agglom??ration de quelques micelles appara??t mais la dispersion reste essentiellement stable. En revanche, en cas d'utilisation combin??e des deux stimuli qui clivent ?? la fois le PEO et le PDMAEMA, une agr??gation importante du polym??re se produit ?? la suite de l'??limination de l'amphiphilicit?? du polym??re. // Abstract : Stimuli-responsive block copolymers (SR-BCPs) and their assemblies, such as micelles, vesicles and hydrogels, can undergo physical or chemical changes in response to changing environmental conditions. For an excellent SR-BCP, usually, slight changes in the environment are sufficient to induce relatively drastic changes in either the conformation or structure or properties of the polymer. Stimuli-reactive polymers are often referred to as smart polymers and they have great application potential in many fields. Over the past two decades, particular research and development interest has been focused on exploiting SR-BCP assemblies as drug delivery systems (DDSs). In many cases, stimuli-induced changes in the structure or morphology of BCP assemblies (drug carriers) can result in the release of loaded species, sometimes in a spatially and temporally controllable manner by choosing an appropriate stimulus and adjusting the parameters of the used stimulating method. Generally speaking, by having a certain type of stimuli-reactive moieties in the structure, SR-BCP assemblies have an ability to recognize a specific stimulus and react to its presence accordingly. Despite the tremendous progress achieved on SR-BCPs, a number of fundamental issues remain to be addressed in order to enable real-life applications of these smart polymers. Of them, an increasing level and complexity of control on SR-BCPs as well as the sensitivity with which these polymers react to stimuli are key and challenging. It is highly desirable to obtain a fast reaction under the action of a modest stimulation. To this end, fundamental research is necessary on rational and creative BCP structural design as well as on development of stimulation methods that can amplify the effect of a stimulus. The research work presented in this thesis falls into this important topic. More specifically, we studied BCP micelles that are responsive to two types of stimuli. On the one hand, we investigated an amplification mechanism based on coupling the ultrasound reactivity with the thermosensitivity of BCPs. On the other hand, we developed a BCP structural design that allows micelles to be disrupted by either light or redox agents while having the minimum number of stimuli-reactive moieties in the polymer structure. Our research provided new insights into and suggested new means on how the issues of sensitivity and complex control of SR-BCP micelles can be tackled, thus contributing to the advancement of fundamental knowledge. The core of this thesis is comprised of three publications resulting from the projects realized in our research work. In order to couple the ultrasound sensitivity and thermosensitivity, in the first project, we carried out studies to find possible polymer structures that are susceptible to be affected by ultrasound. We conducted a comparative study on the disruption of the micelles formed by various BCPs and the concomitant release of an encapsulated hydrophobic dye (Nile Red) by high-intensity focused ultrasound (HIFU). It was found that all micelles formed by the four synthesized diblock copolymers, being composed of a hydrophilic poly(ethylene oxide) (PEO) block and a different polymethacrylate hydrophobic block, could be disrupted by ultrasound. However, the extent of the micellar disruption and dye release was found to be influenced by the chemical structure of the micelle-core-forming hydrophobic polymethacrylate. In particular, micelles of PEO-b-PIBMA (poly(1-(isobutoxy)ethyl methacrylate)) and PEO-b-PTHPMA (poly(2-tetrahydropyranyl methacrylate)), whose hydrophobic blocks have a labile acetal unit in the side group and are more likely to undergo ester hydrolysis, could be disrupted more severely by ultrasound, giving rise to a faster release of Nile Red. By contrast, micelles of PEO-b-PMMA (poly(methyl methacrylate)), whose polymethacrylate block is more stable, appear to be more resistant to ultrasound irradiation and exhibit a slower rate of dye release than other BCPs. Moreover, infrared spectra recorded with micelles before and after ultrasound irradiation of the aqueous solution of the micelles give evidence for the occurrence of chemical reactions, most likely hydrolysis, for PEO-b-PIBMA and PEO-b-PTHPMA, but absence of chemical reactions for PEO-b-PMMA. The effect of BCP chemical structure on the reaction of micelles to high-frequency HIFU irradiation shows the perspective of designing and developing ultrasound-sensitive BCP micelles for ultrasound-based delivery applications. On the basis of the first project, in the second project, we demonstrated a new approach that could amplify the effect of HIFU on the disassembly of BCP micelles in aqueous solution. By introducing a small amount of ultrasound-labile comonomer units into the micelle core-forming thermosensitive polymer, the ultrasound-induced reaction of the comonomer could increase the lower critical solution temperature (LCST) of the thermosensitive polymer due to a polarity change, which renders the BCP soluble in water without changing the solution temperature and, consequently, results in disassembly of BCP micelles. To prove the validity of this new mechanism, we synthesized and investigated a diblock copolymer of PEO-b-P(MEO[subscript 2]MA-co-THPMA) (MEO[subscript 2]MA stands for 2-(2-methoxyethoxy)ethyl methacrylate). In the thermosensitive random copolymer block P(MEO[subscript 2]MA-co-THPMA), which is hydrophobic at T>LCST, THPMA was chosen due to its greater reactivity under HIFU than other monomer structures investigated in the first project. We found that HIFU could indeed increase the LCST of the P(MEO[subscript 2]MA-co-THPMA) block and, as a result, dissociate the BCP micelles at a constant temperature. A [superscript 13]C NMR spectral analysis provided critical evidence that hydrolysis of the THPMA groups occurs under HIFU irradiation and the micellar disassembly originates from an increase in the LCST due to the ultrasound-induced conversion of hydrophobic comonomer units of THPMA onto hydrophilic methacrylic acid (MAA). This ultrasound-changeable-LCST approach is general and can be applied by exploring other ultrasound-labile moieties in the BCP design. By transducing an ultrasound-induced effect into a changing thermosensitivity of the micelle core-forming block, this study demonstrated a new amplification and control mechanism for SR-BCP micelles. The third project presented in this thesis dealt with a rational BCP design that had a specific purpose: allowing BCP micelles to be disrupted by two types of stimuli while using the minimum number of stimuli-reactive moieties in the BCP structure. The unveiling of such BCP structures provides insight into how to make BCP micelles sensitive to stimuli. To do this, we designed and synthesized a new amphiphilic ABC-type triblock copolymer, namely, poly(ethylene oxide)-disulfide-polystyrene- o-nitrobenzyl-poly(2-(dimethylamino)ethylmethacrylate) (PEO-S-S-PS-ONB-PDMAEMA), which features a redox-cleavable disulfide linkage between the PEO and PS blocks as well as a photocleavable ONB group as the junction of the PS and PDMAEMA blocks. We demonstrated that this design is a useful strategy to allow BCP micelles to respond to both a reducing agent like dithiothreitol (DTT) in solution and exposure to UV light while having the minimum number of stimuli-reactive moieties in the block copolymer structure (two units per chain). Our investigations found that the micelles of this triblock copolymer could be disrupted in different ways. When only one stimulus is applied, the removal of one type of hydrophilic polymer chains from the micelle corona, either PEO by redox-cleavage or PDMAEMA by photocleavage, results in a limited destabilization effect on the dispersion of the micelles. The agglomeration between a few micelles appears but the dispersion remains essentially stable. By contrast, under combined use of the two stimuli that cleaves both PEO and PDMAEMA, severe polymer aggregation occurs as a result of elimination of the polymer amphiphilicity. Moreover, by loading the hydrophobic Nile Red in the micelles, the fluorescence quenching of the dye by aqueous medium under the different uses of the two stimuli appears to correlate with the different extents of the micellar disruption. // ?????? : ??????????????????????????????SR-BCPs???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????SR-BCP???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????-??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????SR-BCP?????????????????????????????????DDSs???????????????????????????????????????BCP?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????-????????????????????????SR-BCP??????????????????????????????????????????????????????????????????????????? ??????SR-BCPs?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????SR-BCPs?????????????????????????????????????????????????????????????????????SR-BCPs???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????BCP???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????BCP???????????????????????????BCPs???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????-???????????????BCP???????????????????????????????????????????????????????????????????????????????????????SR-BCP???????????????????????????????????????????????????????????????????????????????????????????????????????????? ??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????BCPs????????????????????????????????????????????????HIFU?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????PEO-b-PIBMA????????? 1-????????????????????????????????????????????? ??????PEO-b-PTHPMA?????????2-???????????????????????????????????? ??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ??????????????????????????????????????????????????????????????????PEO-b-PMMA?????????????????????????????????????????????????????????????????????????????????????????????????????????PEO-b-PMMA????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????PEO-b-PIBMA???PEO-b-PTHPMA????????????????????????????????????????????????PEO-b-PMMA???????????????????????????????????????HIFU????????????BCP???????????????????????????????????????????????????????????????????????????-??????BCP????????????????????? ??????????????????????????????????????????????????????????????????????????????????????????????????????HIFU??????????????????BCP???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????LCST?????????????????????????????????????????????????????????BCP??????????????????????????????BCP??????????????????????????????????????????????????????????????????????????????????????????????????????PEO-b-P(MEO2MA-co-THPMA) ???MEO2MA ??????2-???2-??????????????????????????????????????????????????????T > LCST????????????????????????????????????P(MEO2MA-co-THPMA)?????????????????????THPMA?????????????????????????????????????????????????????????????????????????????????HIFU?????????????????????????????????????????????????????????????????? ??????HIFU???????????????????????????P(MEO2MA-co-THPMA)?????????LCST?????????BCP??????????????????????????????????????????13C NMR ???????????????????????????THPMA?????????????????????????????????????????????THPMA??????????????????????????????MAA?????????LCST?????????????????????????????????????????????????????????????????????LCST??????????????????????????????????????????????????????BCP???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????SR-BCP????????????????????????????????? ????????????????????????????????????????????????????????????????????????????????????????????????BCP????????????????????????????????????????????????????????????????????????BCP?????????????????????????????????????????????BCP?????????????????????????????????????????????????????????BCP????????????????????????????????????????????????????????????????????????ABC???????????????????????????????????????????????? - ???????????? - ???????????? - ??? - ???????????? - ?????? 2 - ???????????????????????????????????????????????? (PEO-S-S-PS-ONB-PDMAEMA)?????????PEO???PS???????????????????????????????????????????????????PS???PDMAEMA?????????????????????????????????ONB????????????????????????????????????????????????????????????-??????????????????????????????????????????????????????BCP????????????????????????????????????????????? ???DDT????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????PEO????????????????????????PDMAEMA?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????PEO???PDMAEMA?????????????????????????????????????????????????????????????????????????????????????????????????????? ????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal