The "Universal Polymer Backbone" Concept
Pollino, Joel Matthew
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This thesis begins with a brief analysis of the synthetic methodologies utilized in polymer science. A conclusion is drawn inferring that upper limits in molecular design are inevitable, arising as a direct consequence of the predominance of covalent strategies in the field. To address these concerns, the universal polymer backbone (UPB) concept has been hypothesized. A UPB has been defined as any copolymer, side-chain functionalized with multiple recognition elements that are individually capable of forming strong, directional, and reversible non-covalent bonds. Non-covalent functionalization of these scaffolds can lead to the formation of a multitude of new polymer structures, each stemming from a single parent or universal polymer backbone. To prepare such a UPB, isomerically pure exo-norbornene esters containing either a PdII SCS pincer complex or a diaminopyridine residue were synthesized, polymerized, and copolymerized via ROMP. All polymerizations were living under mild reaction conditions. Kinetic studies showed that the kp values are highly dependent upon the isomeric purity but completely independent of the terminal recognition units. Non-covalent functionalization of these copolymers was accomplished via 1) directed self-assembly, 2) multi-step self- assembly, and 3) one-step orthogonal self-assembly. This system shows complete specificity of each recognition motif for its complementary unit with no observable changes in the association constant upon functionalization. To explore potential applications of this UPB concept, random terpolymers possessing high concentrations of pendant alkyl chains and small amounts of recognition units were synthesized. Non-covalent crosslinking using a directed functionalization strategy resulted in dramatic increases in solution viscosities for metal crosslinked polymers with only minor changes in viscosity for hydrogen bonding motifs. The crosslinked materials were further functionalized via self-assembly by employing the second recognition motif, which gave rise to functionalized materials with tailored crosslinks. This non-covalent crosslinking/functionalization strategy could allow for rapid and tunable materials synthesis by overcoming many difficulties inherent to the preparation of covalently crosslinked polymers. Finally, the current status of the UPB concept is reviewed and methodological extensions of the concept are suggested. Evaluation of how UPBs may be used to optimize materials and their potential use in fabricating unique electro-optical materials, sensors, and drug delivery vesicles are explored.