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The enthalpy and entropy of micellization in water, AHmic and ASmic, respectively, of three linear amphiphilic BAB block copolymers consisting of either poly(methyl acrylate) (Mn similar to 1200 and 700 Da) or poly(ethyl acrylate) (Mn similar to 800 Da) as hydrophobic (B) segments and poly(ethylene oxide) (PEO) as the hydrophilic (A, Mn similar to 3000 Da) segment were determined by isothermal titration calorimetry (ITC). The AHmic and ASmic of the cyclic AB block copolymers obtained by cyclization of the linear triblock copolymers were determined under the same conditions. The AHmic value of the cyclic copolymers was smaller than that of their linear precursors. The ASmic value showed the same trend, but the relative difference between the cyclized and linear copolymers was less pronounced. The hydrodynamic diameter (Dh), critical micelle concentration (CMC), molecular weight (Mw-mic), and second virial coefficient (A2) of the micelles were determined. The Dh value of the cyclic copolymer micelles was smaller than the linear counterpart. On the other hand, the CMC value became larger, whereas the A2 value was comparable or increased by cyclization. Overall, the results suggest that, in the unimer state, the hydrophobic segments of the cyclized copolymers form a tightly coiled structure to minimize contact with water, resulting in the smaller AHmic value. Contrary to the linear copolymer micelles, the cyclic copolymer micelles have no "dangling chains", which may explain the topology-driven slight difference in the ASmic value.

The enthalpy and entropy of micellization in water, AHmic and ASmic, respectively, of three linear amphiphilic BAB block copolymers consisting of either poly(methyl acrylate) (Mn similar to 1200 and 700 Da) or poly(ethyl acrylate) (Mn similar to 800 Da) as hydrophobic (B) segments and poly(ethylene oxide) (PEO) as the hydrophilic (A, Mn similar to 3000 Da) segment were determined by isothermal titration calorimetry (ITC). The AHmic and ASmic of the cyclic AB block copolymers obtained by cyclization of the linear triblock copolymers were determined under the same conditions. The AHmic value of the cyclic copolymers was smaller than that of their linear precursors. The ASmic value showed the same trend, but the relative difference between the cyclized and linear copolymers was less pronounced. The hydrodynamic diameter (Dh), critical micelle concentration (CMC), molecular weight (Mw-mic), and second virial coefficient (A2) of the micelles were determined. The Dh value of the cyclic copolymer micelles was smaller than the linear counterpart. On the other hand, the CMC value became larger, whereas the A2 value was comparable or increased by cyclization. Overall, the results suggest that, in the unimer state, the hydrophobic segments of the cyclized copolymers form a tightly coiled structure to minimize contact with water, resulting in the smaller AHmic value. Contrary to the linear copolymer micelles, the cyclic copolymer micelles have no "dangling chains", which may explain the topology-driven slight difference in the ASmic value.

Thermoresponsive polymer layers on silica surfaces have been obtained by utilizing electrostatically driven adsorption of a cationic-nonionic diblock copolymer. The cationic block provides strong anchoring to the surface for the nonionic block of poly(2-isopropyl-2-oxazoline), referred to as PIPOZ. The PIPOZ chain interacts favorably with water at low temperatures, but above 46 degrees C aqueous solutions of PIPOZ phase separate as water becomes a poor solvent for the polymer. We explore how a change in solvent condition affects interactions between such adsorbed layers and report temperature effects on both normal forces and friction forces. To gain further insight, we utilize self-consistent lattice mean-field theory to follow how changes in temperature affect the polymer segment density distributions and to calculate surface force curves. We find that with worsening of the solvent condition an attraction develops between the adsorbed PIPOZ layers, and this observation is in good agreement with predictions of the mean-field theory. The modeling also demonstrates that the segment density profile and the degree of chain interpenetration under a given load between two PIPOZ-coated surfaces rise significantly with increasing temperature., QC 20150506

A nonionic-cationic diblock copolymer, poly(2-isopropyl-2-oxazoline)(60)-b-poly((3-acrylamidopropyl)- trimethylammonium chloride)(17), (PIPOZ(60)-b-PAMPTMA(17)), was utilized to electrostatically tether temperature-responsive PIPOZ chains to silica surfaces by physisorption. The effects of polymer concentration, pH, and temperature on adsorption were investigated using quartz crystal microbalance with dissipation monitoring and ellipsometry. The combination of these two techniques allows thorough characterization of the adsorbed layer in terms of surface excess, thickness, and water content. The high affinity of the cationic PAMPTMA(17) block to the negatively charged silica surface gives rise to a high affinity adsorption isotherm, leading to (nearly) irreversible adsorption with respect to dilution. An increase in solution pH lowers the affinity of PIPOZ to silica but enhances the adsorption of the cationic block due to increasing silica surface charge density, which leads to higher adsorption of the cationic diblock copolymer. Higher surface excess is also achieved at higher temperatures due to the worsening of the solvent quality of water for the PIPOZ block. Interestingly, a large hysteresis in adsorbed mass and other layer properties was observed when the temperature was cycled from 25 to 45 degrees C and then back to 25 degrees C. Possible causes for this temperature hysteresis are discussed., QC 20140604

Julio C Fernandes,1 Xingping Qiu,2 Francoise M Winnik,2 Mohamed Benderdour,1 Xiaoling Zhang,3 Kerong Dai,3 Qin Shi11Orthopaedics Research Laboratory, Research Centre, Sacré-Coeur Hospital, 2Department of Physical Chemistry and Polymer Science, Faculty of Pharmacy, University of Montreal, Montreal, Quebec, Canada; 3Orthopaedic Cellular and Molecular Biology Laboratories, Institute of Health Sciences, Chinese Academy of Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai, ChinaAbstract: The low transfection efficiency of chitosan is one of its drawbacks as a gene delivery carrier. Low molecular weight chitosan may help to form small-sized polymer-DNA or small interfering RNA (siRNA) complexes. Folate conjugation may improve gene transfection efficiency because of the promoted uptake of folate receptor-bearing cells. In the present study, chitosan was conjugated with folate and investigated for its efficacy as a delivery vector for siRNA in vitro. We demonstrate that the molecular weight of chitosan has a major influence on its biological and physicochemical properties, and very low molecular weight chitosan (below 10 kDa) has difficulty in forming stable complexes with siRNA. In this study, chitosan 25 kDa and 50 kDa completely absorbed siRNA and formed nanoparticles (≤220 nm) at a chitosan to siRNA weight ratio of 50:1. The introduction of a folate ligand onto chitosan decreased nanoparticle toxicity. Compared with chitosan-siRNA, folate-chitosan-siRNA nanoparticles improved gene silencing transfection efficiency. Therefore, folate-chitosan shows potential as a viable candidate vector for safe and efficient siRNA delivery.Keywords: nonviral vector, chitosan, gene delivery, folate-targeted, siRNA

If two good solvents become poor for a polymer when mixed, the solvent pair is called a cononsolvent pair. The sharp reentrant coil-to-globule-to-coil transition of a poly(N-isopropylacrylamide) chain observed in the mixed solvent of water and methanol is shown to be caused by the competitive hydrogen bonding by water and methanol molecules onto the polymer chain. On the basis of a new statistical-mechanical model for competitive hydrogen bonds, the mean square end-to-end distance is theoretically calculated and compared with experiment. The chain sharply collapses at the molar fraction xm0.2 of methanol, stays collapsed up to xm0.4, and finally recovers the swollen state at xm0.6. Such a reentrant coil-globule transition takes place because the total number of hydrogen bonds along the chain exhibits a similar square-well-type depression as a result of the competition.

This doctoral thesis has investigated various aspects of the solution properties of water-soluble amphiphilic polymers. The ultimate goal was to achieve a better understanding of the macroscopic phenomena demonstrated by these systems by elucidating the molecular interactions causing them. Two commercial cationic cellulose ethers were studied, the cationic derivative of hydroxyethyl cellulose, HEC-N+CH3 and its hydrophobically-modified analogue, HEC-N+C12 . Their interpolymeric associations and their interactions with surfactants were studied using photophysical techniques, such as UV-vis and fluorescence spectroscopy. Initial fluorescence probe experiments were directed at investigating the interactions between these cationic polymers and a series of cationic surfactants. No interaction was predicted to occur in systems where the polymer and surfactant were of the same charge due to electrostatic repulsions. However, the results obtained clearly indicated that polymer/surfactant complexes formed if the polymer contained hydrophobic groups. A more detailed picture of the interactions was then obtained by using polymers to which the dye was covalently attached via an ether linkage. Various pyrene labelled and naphthalene labelled analogues of the two cellulose ethers were synthesised and characterised by standard methods. The interpolymeric associations of cationic polymer solutions was studied using mixed solutions of naphthalene and pyrene labelled polymers using non-radiative energy transfer experiments. Fluorescence studies of these labelled polymers in the presence of cationic surfactants confirmed the results of the probe studies. Other fluorescence studies investigated the interactions of the pyrene labelled HEC-N+C12 with a series of anionic surfactants. A stronger interaction was observed due to the electrostatic attraction of the two species. Additionally, an unexpected feature of the fluorescence spectra led to the speculation of the presence of two pos, Doctor of Philosophy (PhD)

QS 2014