Polymeric Mixed Ionic/Electronic Conductors (MIECs) are receiving intense research interest due to their utility in applications such as organic electrochemical transistors, biosensors, and other electrochemical applications. State of the art polymers utilize an oligoethylene glycol (oEG) side chain attached to a conjugated backbone; however, little attention has been given to modifying the chemical identity of the oEG side chains to improve performance. To better understand the influence of oxygen content and positioning on performance of oEG-based MIECs, we have investigated a series of polythiophenes modeled around permutations of exchanging the oxygen atoms for carbon in a common oEG-based MIEC, poly(3-(methoxyethoxyethoxymethyl)thiophene) [P3MEEMT]. We targeted 8 permutations using molecular dynamics simulations to characterize the predicted performance and selected a subset of 4 polymers was selected for further study. To characterize the variations in polymer behavior with varying side chains, thin films of polymers doped with LiTFSI were made, and the ionic and electronic conductivities were measured. For the same oxygen content, the farther the oxygen atoms are from the polymer backbone along the side chain, the better the ionic and electronic conductivity become due to increased oxygen atom range of motion and improved π-stacking. Changing the oxygen content has counterbalancing effects on ionic and electronic conductivity. Increasing oxygen content leads to an improvement in ionic conductivity, but also a decrease in electronic conductivity. All polymers show a reduced LiTFSI solubility as compared against P3MEEMT. In spite of this, one polymer still demonstrated higher ionic conductivities than P3MEEMT, poly(3-(methoxyethoxybutyl)thiophene). This work highlights the importance of increasing the distance between coordinating atoms and the polymer backbone and maximizing the range of motion of the coordinating atoms in the side chain to produce the highest performance MIECs.

Controlling mixed conduction in oligoethylene glycol-substituted polythiophenes <i>via</i> side chain engineering

ACS Spring Meeting 2021

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Controlling mixed conduction in oligoethylene glycol-substituted polythiophenes via side chain engineering