Synthesis of Complex Polymer Topologies and Their Self-Assembly in Water

Daria Eden Lonsdale (2011). Synthesis of Complex Polymer Topologies and Their Self-Assembly in Water PhD Thesis, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland.

       
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Author Daria Eden Lonsdale
Thesis Title Synthesis of Complex Polymer Topologies and Their Self-Assembly in Water
School, Centre or Institute Australian Institute for Bioengineering and Nanotechnology
Institution The University of Queensland
Publication date 2011-09
Thesis type PhD Thesis
Supervisor Prof. Michael Monteiro
Dr. Joanne Blanchfield
Total pages 202
Total colour pages 55
Total black and white pages 147
Language eng
Subjects 10 Technology
Abstract/Summary The demand for more complex, tailor-made macromolecules has increased, based on the everrising number of applications for synthetic polymers in biomedical fields and materials science. Recent advances in living radical polymerization (LRP) techniques have allowed for the synthesis of well-defined polymers and complex polymer architectures, especially when combined with coupling techniques such as the copper-catalyzed azide/alkyne cycloaddition (CuAAC). This ability has opened an investigative opportunity for controlling macromolecular self-assembly in solution by means of architectural design. Therefore, the main focus of this thesis was to synthesize polymers with complex architectures and to examine their self-association properties in water. Initially, five polymeric architectures with a systematic increase in architectural complexity were synthesized utilizing the CuAAC reactions from a toolbox of functional linear polymers and low molecular weight linkers. The amphiphilic architectures ranged from a simple 3-miktoarm star block copolymer to the more complex third generation dendrimer-like block copolymer, consisting of polystyrene (PSTY) and polyacrylic acid (PAA). Subsequent micellization of these structures in water and characterization of the resultant spherical micelles provided insights into the effect of polymer architectural parameters on the self-assembly process. The next step was to investigate the influence of cyclic topology on the associative properties of polymers in water. The synthesis of cyclic polymers by coupling the end-groups of a linear polymer together using the CuAAC reaction has been used for many polymer systems. However, the strategy based on the CuAAC methodology has not been guided by theory and involved a very slow feed of polymer into a highly dilute reaction mixture of solvent and Cu catalyst. Therefore, as a first step, the Jacobson−Stockmayer theory was used to predict the percentage of monocyclic polystyrene (c-PSTY) in a one-pot reaction at 25 °C and a more appropriate empirical relationship based on experimental diffusion-controlled rate coefficients for cyclization and condensation of α,ω-polymer for the CuAAC reaction. Given this quantitative knowledge, the effect of l-PSTY concentration, temperature, feed rate, Cu(I)Br concentration and linear-PSTY molecular weight was investigated to find the optimum conditions for the synthesis of highly-pure monocyclic polymers. Strategies were also developed to produce high percentage of monocyclic polystyrene from parent l-PSTY with higher molecular weights. The kinetic simulations were then conducted to examine the effects of various experimental conditions on cyclization during the feed of α,ω-telechelic polymers into a reaction mixture. The simulations showed that the interplay between the feed rate and rate coefficients for cyclization and multiblock formation were the dominant and controlling parameters. The simulations were in good agreement with experimental results on cyclization of α,ω-telechelic polystyrene with different molecular vii weights by the CuAAC reaction. They also showed that high dilution was not a necessary condition for cyclization and that high percentages of monocyclic could be rapidly produced in solutions that are more concentrated. The theoretical and practical knowledge acquired for producing monocyclic polymers in high purity was utilized to develop a methodology for the synthesis of more complex architectures from functional linear and cyclic PSTY polymeric building blocks. Various topologies (from paddle-like to 3-arm stars) could be produced with high conversion at 25 oC in short reaction times. Remarkably, this approach overcame significant steric hindrance, linking polymeric cyclic structures with high coupling efficiency. Finally, the synthesis of AB, AB2 and A2B type block and miktoarm star copolymers was demonstrated, in which block A consisted of linear poly(tert-butyl acrylate) PtBA and block B consisted of cyclic polystyrene c-PSTY. These structures were produced using the atom transfer radical polymerization (ATRP) to make telechelic polymers that, after modification, were further coupled together by copper catalyzed ‘click’ reactions with high coupling efficiency. Deprotection of PtBA to poly(acrylic acid) PAA afforded amphiphilic miktoarm structures that when micellized in water gave vesicle morphologies when the block length of PAA was 21 units. Increasing the PAA block length to 46 units produced spherical core-shell micelles. Analysis of AB2 miktoarm star by AFFF showed that the packing density of the c-PSTY in the core was 4 times greater than that of its linear counterpart (a 4 times greater aggregation number for relatively similar micelle hydrodynamic diameter), the PAA corona arms extended into the water phase beyond the normal Gaussian chain conformation and were more compact on the surface. These results provided insights into the effect of a hydrophobic cyclic polymer attached to a hydrophilic linear block on the self-assembly process in water.
Keyword polymer synthesis,
'living' radical polymerization
CuAAC “Click” Chemistry
self-assembly
micelle
cyclic polymer
Additional Notes Colour: 27, 33, 36, 38, 46, 49, 69, 75, 80, 88, 91, 92, 94, 96, 99, 103, 105, 106, 108, 109, 110, 113-115, 125-127, 129, 132, 134, 135, 151-153, 155, 169, 175-181, 183, 185, 186, 188-194, 196, 199 Landscape: 173, 174

 
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Created: Tue, 06 Dec 2011, 18:39:13 EST by Miss Daria Lonsdale on behalf of Library - Information Access Service