New Methods in Chain-Growth Condensation Polymerization for Functional Aromatic Polyamides
Open Access DepositedThe rise of living polymerization mechanisms has transformed the field of polymer chemistry and allowed for the synthesis of well-defined polymer structures with remarkable precision and specificity. With recent discoveries in controlled radical polymerizations, this ‘living’ process has been made remarkably versatile and robust through mechanisms with limited termination reactions and seemingly limitless functionalities. Among others, these controlled radical polymerizations have enabled numerous advances in complex polymer architectures, such as polymer brushes. Surface-initiated polymer brushes have specifically produced organized structures with tunable thickness, grafting density, and chemical functionality, reaching applications in fields such as stimuli-responsive materials and membrane separations, to name a few. While side chain modifications to the polymer brush structure have enabled a diversity of functions, the sp3-hybridized polymer backbone produced via radical polymerization mechanisms is fundamentally limited in structure: the propagating radical species on the polymer chain end will only react with vinyl monomers to yield a new carbon-carbon bond. To introduce more rigid, aromatic or conjugated backbones into the polymer brush architecture, other chain-growth mechanisms (i.e. without radical propagation) are required.By converting common ‘step-growth’ monomers to ‘chain-growth’ ones, chain-growth condensation polymerization (CGC) enabled the controlled polymerization of a diverse set of rigid aromatic and conjugated polymers, such as aromatic polyamides, polyesters, or polyethers with narrow molecular weight distributions indicating living behavior with no termination. Aromatic polyamides specifically serve as attractive candidates for surface-initiated polymer brush architectures with high mechanical strength, chemical resilience, and excellent thermal stability. Previously, surface-initiated aromatic polyamide brushes have shown significant advancements in anti-fouling coatings and high strength thin-films. With further functionalization to the aromatic backbone and side chain, new functionalities can be introduced into the synthesis of well-defined aromatic polyamides with photoresponsive and fouling-release capabilities. The investigation of new functionalities in the aromatic polyamide backbone was first begun with the addition of new linkages between benzene rings in the polyamide structure, such as an aryl ether or azo linkage for increased solubility and photoresponsive behavior, respectively. In Chapter 3, the aryl ether aminobenzoate monomer was first functionalized with a solubilizing side chain to investigate the chain-growth behavior of the flexible polyamide, followed by modification with a protecting group to enable post-polymerization deprotection for more functional unsubstituted poly(amide-ether)s. In Chapter 4, the azobenzene chromophore was then introduced into the aromatic polyamide backbone for the synthesis of well-defined photoresponsive azobenzene polyamides with low polydispersity. A series of copolymerizations with flexible comonomers was then performed to increase the polymer free volume and promote more efficient photoresponsive isomerization. In Chapter 5, side chain modification was then performed to yield aromatic polyamides showing fouling-release behavior. The aminobenzoate monomer was functionalized with three side chain lengths with various fluorine functionalization to investigate the anti-fouling performance of the aromatic polyamide brush structure with low surface energy components. Relevant fouling studies were conducted with polymer brush-modified quartz crystal microbalance sensors, which revealed excellent fouling release behavior when compared to two control surfaces.
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Dickhudt_gwu_0075A_16709.pdf | 2024-10-02 | Open Access |
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