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A diblock copolymer of Poly (Styrene-b- [ethylene-co-propylene]) has been used as a stabilizer in non-aqueous dispersion polymerizations of methyl methacrylate and vinyl acetate in n-heptane. The particles thus produced were stabilized by well defined surface layers of ethylene-propylene copolymer chains. The dependence of the particle size on the stabilizer, monomer and initiator concentrations was studied. Both seeded and one-shot polymerization techniques were investigated. Polymer particles were characterized by transmission electron microscopy to determine particle shape and size. The long term stability of both types of polymer particles suggests that the anchoring efficiency in both systems was good. Rheological studies confirmed the sphericity of the particles and showed the particles to be non-flocculated under shear. The thickness of the surface layer was determined from viscosity studies of the dispersions at 298, 308 and 318K. Solution viscosities dispersions at of a narrow distribution standard of ethylene-propylene copolymer in n-heptane and in a binary liquid mixture of n-heptane and n-propanol (79:21, v/v) at 298, 308 and 318K were obtained in order to estimate the root-mean-square end-to-end distance of free ethylene-propylene copolymer chains. The thickness of the surface layer was observed to increase on raising the temperature and to decrease on changing the solvency of the dispersion medium from a good solvent to almost a theta solvent for the ethylene-propylene copolymer chains. The dimensions of the surface layer were slightly larger than the dimensions of the free ethylene-propylene copolymer chains in solution suggesting that long ethylene-propylene chains terminally anchored at the interface are only slightly extended over random coil dimensions. Calculations of the mean separation distance between adjacent stabilizing ethylene-propylene copolymer chains indicated close-packing of ethylene-propylene copolymer chains at the particle-liquid interface which may contribute to the slight extension of the ethylene-propylene copolymer chain conformation. The theta-conditions for ethylene-propylene copolymer in a mixture of n-heptane and n-propanol were determined using samples obtained by hydrogenating polyisoprene standards. The solvency of the dispersion medium for the stabilizing ethylene-propylene copolymer chain on the polymer particles was reduced until flocculation occurred, and this was achieved by cooling the dispersion system to find the critical flocculation temperature or by adding a non-solvent (n-propanol) for the ethylene-propylene copolymer chains at constant temperature to find the critical flocculation volume. The polymer dispersions just retained stability at theta conditions and started to lose stability when the dispersion medium was changed to slightly worse than a theta system for the ethylene-propylene chains. The close correspondence of the flocculation conditions to the theta conditions for free ethylene-propylene copolymer chains confirms that the steric stabilization mechanism is operative for these dispersions.

Research Doctorate - Doctor of Philosophy (PhD) / The adsorption characteristics of pH responsive tertiary amine methacrylate-based diblock copolymers have been investigated. The main focus of this work is on poly(2-(dimethylamino)ethyl methacrylate-b-poly(2-(diethylamino)ethyl methacrylate (PDMA-b-PDEA) adsorption to the silica/aqueous solution interface at pH 9. Differing degrees of polymerisation and quaternisation were investigated with some attention given to variation of the block hydrophobicity utilising poly(2-(dimethylamino)ethyl methacrylate-b-poly(2-(diisopropylamino)ethyl methacrylate (PDMA-b-PDPA). Principally, optical reflectometry (OR) and atomic force microscopy (AFM) have been employed to monitor the adsorption in terms of adsorbed mass and layer morphology. A variety of other techniques have been utilised to provide ancillary information, including quartz crystal microbalance, zeta potential, dynamic light scattering and contact angle measurements. The combined results have provided a comprehensive understanding of the adsorption characteristics for the copolymers studied. Micelles of the tertiary amine methacrylate-based copolymers adsorbed readily to silica from aqueous solution at pH 9. The adsorption isotherms were determined, exhibiting a high affinity Langmuirian shape where the CMC did not appear to impact on the adsorbed mass. The adsorption was rationalised by the interaction between the cationic PDMA corona of the micelles with the negatively charged substrate. The more hydrophobic PDEA core block increased the level of adsorption above that observed for the PDMA homopolymer. It was shown that the adsorbed layers were robust to rinsing with electrolyte at high pH, although reduction of the pH to 4 yielded significant desorption. The adsorbed layer morphology observed by in situ AFM exhibited distinct micellar structures. The combined adsorbed mass and AFM images showed a significantly higher surface aggregation number than the measured solution aggregation number, indicating a more complex adsorption process than simple direct micelle adsorption. The adsorption kinetics were studied to elucidate the adsorption mechanism and revealed complex dynamic processes. Particular focus was given to the adsorption of 0q PDMA93-b-PDEA24 where the impact of concentration was evident and three mechanistic regimes could be defined; below the CMC, just above the CMC and far above the CMC. Interestingly, the adsorption process just above the CMC indicates a surface aggregation mechanism, while well above the CMC, the adsorption proceeds via a process that includes both direct micelle and unimer adsorption. On longer timescales, the adsorption at higher concentrations revealed an additional induction period of micelle relaxation on the surface that allowed for further adsorption. Increasing the PDMA quaternisation was found to reduce post adsorption rearrangement and as result equilibrium was reached more quickly for the highly quaternised analogues. The response of the adsorbed PDMA-b-PDEA copolymer films to multiple changes in solution pH (9 and 4) was monitored. After the initial desorption of copolymer with rinsing at pH 9 and then at pH 4, the adsorbed mass of copolymer was found to be constant with multiple cycles of pH. The remaining robust adsorbed layers, then exhibited reversible uptake and release of water with multiple pH cycles as measured by QCM. This observation was readily rationalised by the observed changes in copolymer charge (and hence hydrophobicity) affecting the interaction of the copolymer chains with the surrounding solution. While these characteristics were found to be reversible with pH cycling it was found that the initial micelle structure of the adsorbed film was lost upon the first rinse to pH 4. Finally, the first low Tg micelle-micelle multilayers of up to six layers were constructed using alternating layers of cationic and anionic tertiary amine methacrylate-based copolymers at pH 9. The existence of true micellar structures within each layer was proven using in situ AFM imaging where the alternating layer characteristics were supported by measured force curves. The construction of the individual micelle layers was also monitored by OR, where clear evidence of layer build-up was shown. In addition, each layer was robust to rinsing with electrolyte at the adsorbing pH, although, the stability of the formed multilayer was found to be limited to six layers. Upon reduction of the pH, almost all the adsorbed material was instantaneously removed from the surface. The stimulus-responsive nature of such multilayer films augurs well for potential controlled uptake/release applications. These findings should greatly encourage a larger research focus on micelle-micelle multilayers.

<P> Polymers are one of the most prevalent types of molecules in modern life. These long macromolecules make up everything from DNA to plastics to Jell-0™. An interesting class of polymers are block copolymers, which are composed of two (or more) chains, or blocks, of chemically distinct monomers covalently bonded end-to-end to form a single polymer. Different types of polymers tend to avoid each other, but since block copolymers are joined together the polymer species can not macroscopically phase separate. Instead, they separate on the scale of the size of the polymers, forming nanostructures. For a diblock copolymer melt, which is made from two types of polymers, these nanostructures can be, depending on the ratio of the length of one block to the other, spheres, cylinders, lamellae, or the more bizarre gyroid phase. </p> <P> Self-consistent field theory (SCFT) as formulated by Helfand in 1975 has in recent years been successfully applied to the study of the phase behaviour of diblock copolymers. However, most of the studies assume that the polymers are monodisperse, while almost all polymer melts are polydisperse. This work examines the effect of polydispersity in the block lengths on phase behaviour of diblock copolymer melts, by developing the SCFT for polydisperse block copolymers. The theory is examined using a perturbation method, as well as the random-phase approximation (RPA). The perturbation parameter is the ratio K of the weight-averaged molecular weight and the number-averaged molecular weight, which is a common measure of polydispersity. </p> <P> The results show polydispersity shifts the transition from a disordered phase to an ordered phase to a higher temperature, and increases the period of the nanostructures. It is also observed that polydispersity leads to larger non-lamellar phase regions in the phase diagrams. Results from the RPA also suggest that macrophase separation occurs for large polydispersities. </p> / Thesis / Master of Science (MSc)

The principal goal of this research is to achieve the chemical labeling and surface modification of block copolymer vesicles (polymersomes) made from amphiphilic diblock copolymer Poly(butadiene-b-ethylene oxide) (PBd120- PEO89, MW 10400 g/mol) with the aim of developing possible drug carrier vehicles for controlled release of molecules triggered by stimuli-responsive environments. The terminal hydroxyl group of poly(ethylene oxide) (PEO), or poly(ethylene glycol) is converted into its corresponding carboxylic acid by a novel one-pot two-phase oxidation reaction. This regioselective and catalytic reaction assures the preservation of important structural characteristic of the block copolymers. Vesicles formed by a mixture of the carboxylate and unmodified block copolymer exhibit an increment in the critical aggregation concentration (CAC) value while the averaged vesicle size decreases demonstrating that the negative charges in the modified diblock copolymer disrupt the vesicle formation process. The carboxylated reactive intermediates are subsequently subjected to a covalent coupling reaction in organic solvent to replace the terminal hydroxyl of the PEO block. The obtained functionalized diblock copolymers are effectively incorporated into the vesicle bilayer. Also, surface density control in polymersomes of fluorescently modified diblock copolymers, synthesized by the amination reaction, is achieved. To demonstrate the ability of this polymersomes as carrier vehicles, a Noradrenaline functionalized vesicle is placed in closed contact with rat aortic smooth muscle cells (RASMC) using the micropipette aspiration technique. A distinctive increase in fluorescent intensity of cells is observed. It indicates that the drug molecule has been transported by the polymersome and internalized by the cell. In addition, diblock copolymers containing a disulfide moiety and a fluorophore are synthesized and studied through fluorescent microscopy. Vesicles are formed with this polymer and a decrease in fluorescent intensity is observed in the vesicle's bilayer after its exposure to a reductive environment. These results indicate that fluorophore molecules are successfully released into solution.

In block-selective solvent, the rod-coil block copolymers can form various micellar structures. With block copolymers that contain a conjugated polymer block, the conformation of the conjugated polymer can be reflected by spectral changes in the solution. Therefore, it is of interest to study the relationship between the spectral changes and the nature of the conjugated polymer. The fundamental physical properties of poly(3-hexyl thiophene) (P3HT) were studied. Five P3HT samples with different molecular weights were used. We have determined the relationship between physical and spectral properties of this polymer and its molecular weight. In particular, we have found that the refractive index increments, the maximum absorbance wavelength, extinction coefficients, and the emission wavelengths, increase with molecular weight. Diblock copolymers of poly(3-hexyl thiophene)-block-poly(2-hydroxyethyl methacrylate) (P3HT-b-PHEMA) were also studied. The morphological and spectral changes of these block copolymers were studied at various stages of micelle formation in block selective solvents. The relationship between the volume fraction of the P3HT block and their physical and spectral properties were also discussed. / Thesis (Master, Chemistry) -- Queen's University, 2010-03-31 11:30:44.539

Thesis (Ph. D.)--Rutgers University, 2010. / "Graduate Program in Chemistry." Includes bibliographical references.

Thesis (Ph. D.)--University of Massachusetts Amherst, 2009. / Includes bibliographical references (p. 101-110). Print copy also available.

In this dissertation, experiments are described which elucidate how the ordering of symmetric diblock copolymers affects the dynamics within various geometries. In all studies presented herein, experimental techniques are used to probe the dynamics of symmetric diblock copolymer systems as they progress toward equilibrium and to study the role that nanoscale ordering plays in these processes. In the majority of work presented herein, experiments were performed on symmetric diblock copolymer thin films. This work focuses on the effect of various sample preparation techniques on the equilibration kinetics of lamellar forming films. Films are prepared with varying thicknesses in the homogeneous, disordered state and annealed to form islands and holes as the surface decomposes to form commensurate thicknesses. Both nucleated and spinodal growth patterns were observed for this surface decomposition dependent on the initial thickness and intermediate morphologies formed upon ordering. We also prepare equilibrium commensurate films and induce a step change in surface interactions, switching from asymmetric to symmetric wetting boundaries. Upon equilibration, a perforated lamella forms at the free surface to mediate the order-order transition, inducing hole growth with a ramified shape. In the final project, the effect that lamellar order has on dynamics is studied within unstable polymer melt bridges. Liquid bridges are what is formed when a droplet is stretched between two surfaces, like spit between two fingers. Disordered diblock bridges are shown to evolve similar to their homopolymer counterparts. However, ordered diblock copolymer exhibits an enhanced stability with an inhibition of flow proposed to be induced by the isotropic orientational order within the bridge. As well, shear thinning is observed that is believed to be caused by an alignment of ordered domains along the bridge axis due to shear strain rates, providing pathways for flow of diblock copolymer out of the unstable bridge. / Thesis / Doctor of Philosophy (PhD)

Diblock copolymers like poly(styrene)-block-poly(2-vinylpyridine) pave the way for controllable self-assembled monolayers of nanoparticles. Using particular polymer weights and concentration, spherical micelles of PS-b-P2VP can be constructed with a non-polar PS corona and a polar P2VP core. Various precursor salts can be loaded into the core of the micelles due to interactions with the polar core which forms as the active site for nanoparticle growth. The PS corona protects the core from the atmosphere and non-polar solvents. The micelles can then act as nanobeakers for aqueous chemistry in two ways; spontaneous reactions between precursors result in nanoparticles or the trapping of precursor salts can be oxidized or reduced using polymer removal techniques like gas plasmas. In this way, reverse micelles are a facile method of growing metal, metal oxide or dielectric nanoparticles. Process parameters, such as concentration, molecular weights, nature of solvents and type of precursor salt, offer control over the periodicity and size of the monolayer of nanoparticles. Reverse micelle templating is a potentially useful nanofabrication method for tailor-made nanoparticles for use in electrical and optical devices which is not limited to form-factor of substrates. In this thesis, obstacles are identified that hinder the utility of PS-b-P2VP templated nanoparticles in device fabrication. The polymer is insulating which is detrimental to electrical applications. Additionally, the characterization of a monolayer of polymers, thus far, is limited to structural techniques such as SEM and AFM. This thesis sheds light on the mechanism of precursor loading in the micelle core, discusses the efficiency of different polymer removal techniques and uses vibrational spectroscopy for the characterization of monolayers of polymer, loaded polymer and nanoparticles. We have tested enhanced Raman methods using AFM probes to extend the resolution of normal Raman to view monolayers of empty polymers as well. Moreover, using FeCl3-loaded polymer micelles, the control offered by PS-b-P2VP templated growth on the crystal structure of nanoparticles is laid bare. The usefulness of the technique is further divulged by using ordered gamma-Fe2O3 nanoparticles in water-splitting photoanodes where they show an increased efficiency with the inclusion of nanoparticles and their periodicity. This is just an example of devices using reverse micelle templated nanoparticles, paving the way for future applications. The flexibility of this method is further revealed by constructing self-assembled Au/SnO2 nanojunctions within the PS-b-P2VP micelle cores. This was done by exploiting the spontaneous redox reaction between HAuCl4 and SnCl2 in an aqueous environment, and so can be replicated for other metals and metal oxides like Pt, Pd, Ag, TiO2 and ZnO2. The composite nanoparticles formed exhibit a tunable size and dispersion as typically seen with PS-b-P2VP micelles and so, can be used for various applications which require metal/metal oxide junctions. / Thesis / Doctor of Philosophy (PhD)