Description
Ureidopyrimidinone (UPy) derivatives are capable of forming dimers linked by four strong H-bonds. They have been widely used as polymer crosslinkers in self-healing supramolecular polymers and gels. In this work, a N,N-dimethyl-p-phenylenediamine redox couple is attached to the urea side of the UPy with the goal of adding a redox reactive dimension to self-repair. Cyclic voltammetry (CV) scans of the resulting UPy, UPyH, conducted in CH2Cl2, show two reversible redox waves at slower scan rates. Part of the goal of this project was to investigate the use of glassy carbon (GC) vs. platinum electrodes on the UPyH electrochemistry. In addition, further oxidation leads to proton transfer to another still reduced UPyH, resulting in break-up of the dimer. Since the protonated, reduced UPyH is electroinactive, this means that only half of the UPyH dimers can be fully oxidized and broken apart, with the other half simply acting as a base. The next goal for this project was to find an electro-inactive base that facilitates both full dimer break-up upon oxidation and proton transfer and dimer reformation by reduction and back proton transfer. The final goal was to see if the UPyH-base system can be used as a redox-controlled chain terminator to control the degree of polymerization in a UPy-based supramolecular polymer. However, full oxidation of UPyH by bulk electrolysis (BE) proved to be chemically irreversible over the longer time scale of BE. Nonetheless, UPyH could still prove useful as a single use on/off switch to control polymerization. To investigate this, UPyH plus base was added into a UPy supramolecular polymer solution. As expected, the solution viscosity dropped indicating UPyH was an effective chain terminator. Upon full oxidation, the UPyH should no longer be able to act as a chain terminator and the viscosity should increase as the polymer reforms. Unfortunately, these experiments were not able to be completed due to the malfunctioning of the viscometer. However, the completed base study does provide important insight into the overall mechanism for UPyH oxidation.
