Interfacial Properties of Amphiphilic Dendritic Polymers

The self-assembly behavior of arborescent polystyrene-graft-poly(ethylene oxide) copolymers (PS-g-PEO) at the air-water interface and the solubilization/release properties of arborescent polystyrene-graft-poly(2-vinylpyridine) (PS-g-P2VP) copolymers were investigated. These amphiphilic dendritic molecules are covalently bonded unimolecular micelles incorporating a highly branched hydrophobic polystyrene core surrounded by a hydrophilic poly(ethylene oxide) or poly(2-vinylpyridine) shell. Molecules of PS-g-PEO copolymers spontaneously formed supramolecular assemblies at the air-water interface. The type of superstructures formed was found to depend upon copolymer composition, while the level of association was more directly related to the branching density of the polymers. At low surface pressures the PEO segments apparently remained adsorbed on the water subphase, but desorbed into water at very high surface pressures, in the condensed monolayer state. Controlled degradation of the PEO chains with UV light greatly enhanced molecular association, resulting in the formation of either large clusters or long ribbon-like superstructures. The PS-g-P2VP copolymers were found to efficiently solubilize and release hydrophobic small molecules in aqueous media. The partition coefficient and solubilization capacity of the copolymers for hydrophobic polyaromatic hydrocarbons increased with the polystyrene content of the copolymers, while the rate of solubilization decreased with increasing branching functionality of the copolymers. The release profiles for two model drugs displayed an initial burst in release followed by gradual approach to equilibrium. The diffusion coefficients of the drugs in the micelles increased with the branching functionality and the generation number of the micelles, presumably due to increased electrostatic repulsions of the protonated vinylpyridine units

Interfacial Properties of Amphiphilic Dendritic Polymers

I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically to the public ii The self-assembly behavior of arborescent polystyrene-graft-poly(ethylene oxide) copolymers (PS-g-PEO) at the air-water interface and the solubilization/release properties of arborescent polystyrene-graft-poly(2-vinylpyridine) (PS-g-P2VP) copolymers were investigated. These amphiphilic dendritic molecules are covalently bonded unimolecular micelles incorporating a highly branched hydrophobic polystyrene core surrounded by a hydrophilic poly(ethylene oxide) or poly(2-vinylpyridine) shell. Molecules of PS-g-PEO copolymers spontaneously formed supramolecular assemblies at the air-water interface. The type of superstructures formed was found to depend upon copolymer composition, while the level of association was more directly related to the branching density of the polymers. At low surface pressures the PEO segments apparently remained adsorbed on the water subphase, but desorbed into water at very high surface pressures, in the condensed monolayer state. Controlled degradation of the PEO chains with UV light greatly enhanced molecular association, resulting in the formation of either large clusters or long ribbon-like superstructures. The PS-g-P2VP copolymers were found to efficiently solubilize and release hydrophobic small molecules in aqueous media. The partition coefficient and solubilization capacity of the copolymers for hydrophobic polyaromatic hydrocarbons increased with the polystyrene content of the copolymers, while the rate of solubilization decreased with increasing branching functionality of the copolymers. The release profiles for two model drugs displayed an initial burst in release followed by gradual approach to equilibrium. The diffusion coefficients of the drugs in the micelles increased with the branching functionality and the generation number of the micelles, presumably due to increased electrostatic repulsions of the protonated vinylpyridine units. ii

Chiral Imprinting of Diblock Copolymer Single-Chain Particles

This Article reports the molecular imprinting of polymer single-chain particles that have a radius ∼3.7 nm. For this, the template l-phenylalanine anilide or l-ΦAA and a diblock copolymer PtBA-b-P(CEMA-r-CA) were used. Here, PtBA denotes poly(tert-butyl acrylate), and P(CEMA-r-CA) denotes a random block consisting of cinnamoyloxyethyl methacrylate (CEMA) and carboxyl-bearing (CA) units. In CHCl3/cyclohexane (CHX) with 64 vol % of CHX or at fCHX = 64%, a block-selective solvent for PtBA, PtBA-b-P(CEMA-r-CA) formed spherical micelles. The core consisted of the insoluble P(CEMA-r-CA) block and l-ΦAA, which complexed with the CA groups. Pumping slowly this micellar solution into stirred CHCl3/(CHX) at fCHX = 64% triggered micelle dissociation into single-chain micelles, which comprised presumably a solubilized PtBA tail and a collapsed P(CEMA-r-CA)/l-ΦAA head. Because the solvent reservoir was under constant UV irradiation, the photo-cross-linkable units in the P(CEMA-r-CA) head cross-linked, and the single-chain micelles were converted into cross-linked single-chain micelles or tadpoles. Synchronizing the micelle addition and photoreaction rates allowed the preparation, from this protocol, of essentially pure tadpoles at high final polymer concentrations. Imprinted tadpoles were procured after l-ΦAA was extracted from the tadpole heads. Under optimized conditions, the produced imprinted tadpoles had exceptionally high binding capacity and high selectivity for l-ΦAA. In addition, the rates of l-ΦAA release from and rebinding by the particles were high

Tadpoles from the Intramolecular Photo-Cross-Linking of Diblock Copolymers

Preparation of tadpoles or globule−coil diblock copolymers from three coil−coil diblock copolymers is reported. The coil−coil copolymers consist of one poly(tert-butyl acrylate)-block-poly(2-cinnamoyloxyethyl methacrylate) or PtBA-b-PCEMA sample and two PtBA-b-P(CEMA-ran-hCEMA) samples. Here P(CEMA-ran-hCEMA) denotes poly[(2-cinnamoyloxyethyl methacrylate)-ran-(2-hydrocinnamoyloxyethyl methacrylate)]. The tadpoles are prepared by photo-cross-linking the PCEMA or P(CEMA-ran-hCEMA) blocks intramolecularly. Intramolecular cross-linking competes with intermolecular cross-linking. The former is encouraged by adding a diblock copolymer solution at a low pumping speed into a solvent under constant UV irradiation and stirring. The irradiation ensures that the newly added copolymer is immediately converted into tadpoles. The slow copolymer addition ensures that the copolymer concentration in the photoreactor remains low throughout the photolysis process. Factors affecting the purity, yield, and compactness of the tadpoles produced are examined