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Laure Kayser1 Madeleine Russell1 Alexander Stein1 Daniel Rodriquez1 Darren Lipomi1

1, University of California, San Diego, San Diego, California, United States

The recent development of highly flexible and stretchable organic electronics has prompted novel applications in wearable and bio-integrated electronics where skin-like properties (stretchable, soft, self-healing) are desirable for an intimate contact with the human body. But, polymers which are conductive, mechanically compliant, biosafe and easily processable remain difficult to obtain. The commonly used conductive polyelectrolyte complex PEDOT:PSS suffers from poor mechanical properties and breaks at only 5% strain. While the use of additives (Zonyl, Triton X, ionic liquids) can improve the stretchability of PEDOT:PSS, concerns about the biocompatibility and toxicity of these additives have been raised. Another strategy to obtain stretchable conductive material is to blend PEDOT:PSS with elastomers (PDMS, polyurethane) but the poor or incompatible solubility of the elastomers makes the incorporation of the composites in electronic devices difficult. Alternatively, our approach is to use a water-soluble and intrinsically stretchable triblock copolymer comprised of polystyrene sulfonate (PSS) and poly(polyethylene glycol methyl ether acrylate) (PPEGMEA) as a matrix for the in situ oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT). While PSS-based elastomers are typically synthesized via the sulfonation of polystyrene triblock copolymers, this approach requires harsh reaction conditions and does not achieve complete sulfonation, ultimately leading to defects and poorly water-soluble polymers. Instead, we are using an aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization to obtain the well-defined copolymer PSS-b-PPEGMEA-b-PSS. This ionic triblock elastomer serves as a matrix for the polymerization of EDOT, ultimately providing a water-based formulation of stretchable, conductive polymer. After processing via casting, printing or spin-coating, the conductive films can be stretched up to 120%. We are currently investigating the use of the obtained biosafe, water-soluble and conductive elastomers in wearable strain sensors, stretchable organic solar cells and electrotactile devices.

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