Ureidopyrimidinone (UPy) derivatives, introduced by Meijer and co-workers, 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. Previous studies with this UPy, UPyH, showed that the dimer remained intact down to at least 105 M concentrations upon one electron oxidation in CH2Cl2. However, further oxidation led 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 initial 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. Cyclic voltammetric (CV) studies with UPyH and several 4-substituted pyridines, indicate that 4-trifluoromethylpyridine should work. The next goal is to see if the UPyH plus base system can be used as a redox-controlled chain terminator that can control the degree of polymerization in a UPy-based supramolecular polymer. To do this, UPyH plus base will be titrated into a UPy supramolecular polymer solution until the viscosity drops below that observed at the critical polymerization concentration. The UPyH will then be oxidized electrochemically. In the oxidized state, the UPyH should no longer be able to act as a chain terminator and the viscosity should increase as the polymer reforms. The synthesis of a suitable UPy monomer is currently underway. Results from studies with this polymer and the UPyH plus base system will be reported.

Use of a redox-responsive 4 H-bond ureidopyrimidone (UPy) array to control polymerization in a UPy-Based supramolecular polymer

2019 Fall National Meeting

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