Electrochemically Controlled Polymerization through the Use of Redox-Responsive Ureidopyrimidinones for Supramolecular Polymers

摘要

Supramolecular polymers are constructed along weaker, non-covalent interactions such as hydrogenbonding. Compared to conventional polymers where monomer units react to form covalent bonds, non-covalent interactions of monomer units grant these supramolecular polymers dynamic behavior. One example of these systems that utilizes non-covalent interactions to construct supramolecular polymers are the well-investigated ureidopyrimidinones, UPy. UPy's dimerize along their 4 strong directional hydrogen bonds in non-polar organic solvents. UPy's have been covalently linked at the ends of smaller monomer chains so as to function as chain-linkers in the construction of larger polymer structures under favorable dimerization conditions. One interest in the use of these systems in supramolecular applications is their inherent ability of self-healing. Applying heat or mechanical stress to these systems will prevent polymerization at the H-bonds. However, upon relief of these external stimuli, H-bonding resumes. In this study, the use of electron transfer as an external stimulus to perturb dimerization and affect UPy chain polymerization will be explored. In order to exemplify the aims of this study, previously studied electroactive UPy's will be investigated as redox-responsive chain terminators with regards to linear polymer chains that are functionalized with UPy units at their terminal ends, allowing for long-chain polymerization indicated by an increase in solution viscosity. In this study, a decrease in solution viscosity should be observed once these long chain bifunctionalized UPy polymers are in the presence of redox-responsive mono-functional UPy. Upon electrochemical oxidation/reduction of the mono-functional electroactive UPy units, an increase in viscosity is expected. The weakened H-bonding of the mono-functional UPy units will prevent chain termination and long-chain polymerization between bi-functional long chain UPy's is expected to resume.