From N to P: Examining Structure-Property Relationships of Ammonium- and Phosphonium-Containing Macromolecules
Hemp, Sean Taylor
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An unprecedented comprehensive study of ammonium and phosphonium polyelectrolytes probed and examined structure-property relationships with a focus on different macromolecular properties. Conventional free radical polymerization readily generated a large library of ammonium- and phosphonium-containing polyelectrolytes. Along with the two different cationic atoms, the alkyl substituent lengths and counterions were varied to generate a thorough structure-property relationship analysis. Phosphonium macromolecules displayed improved thermal stabilities and improved ionic conductivities compared to ammonium analogs. Longer alkyl substituent lengths systematically decreased the glass transition temperatures of all polyelectrolytes; the larger, bulkier counterions also resulted in lower glass transition temperatures. Counterion also impacted the thermal stability of the polymerized ionic liquids with less basic counterions leading to improved thermal stability. For the first time, the efficacy of phosphonium macromolecules for nonviral nucleic acid delivery was examined. Phosphonium macromolecules more efficiently complexed nucleic acids than ammonium analogs and butyl-containing phosphonium macromolecules delivered nucleic acids more effectively than the ammonium analog. Controlled radical polymerization generated unprecedented phosphonium-containing diblock copolymers and these diblock copolymers displayed enhanced colloidal stability and lower cytotoxicity compared to the phosphonium homopolymer for nucleic acid delivery. Step-growth polymerization techniques enabled the synthesis of well-defined, high molecular weight phosphonium ionenes for the first time. Phosphonium ionenes exhibited higher thermal stability and alkaline stability compared to ammonium ionenes. Due to their high thermal stability and relatively low glass transition temperatures, unprecedented melt rheology studies on polyelectrolytes probed the melt flow characteristics of phosphonium ionenes. Novel phosphonium gemini surfactants displayed interesting solution properties in aqueous and chloroform solutions. Electrospinning of the phosphonium gemini surfactants created uniform fibers. The synthesis and characterization of sulfonium polyelectrolytes enabled the first examination of sulfonium macromolecules for nonviral nucleic acid delivery. Sulfonium polyelectrolytes successfully bound nucleic acids and delivered them in vitro. Controlled radical polymerization generated innovative AB diblock and ABA triblock copolymers that displayed salt- and temperature-responsive properties suitable for biological applications such as drug delivery vehicles and hydrogels. Finally, adenine-containing polyelectrolytes were synthesized and they were successfully electrospun to generate adenine-decorated nanofibers appropriate for filtration and nonwoven applications.
- Doctoral Dissertations