RAFT Polymerization of an Intrinsically Stretchable Water-Soluble Block Copolymer Scaffold for PEDOT

Abstract

Despite the common association of π-conjugated polymers with flexible and stretchable electronics, these materials can be rigid and brittle unless they are designed otherwise. For example, low modulus, high extensibility, and high toughness are treated as prerequisites for integration with soft and biological structures. One of the most successful and commercially available organic electronic materials is the conductive and brittle polyelectrolyte complex poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). To make this material stretchable, additives such as ionic liquids must be used. These additives may render the composite incompatible with biological tissue. In this work, we describe the synthesis of an intrinsically stretchable variant of the conductive polymer PEDOT:PSS that is free of additives. The approach involves the synthesis of a block copolymer comprising soft segments of poly(polyethylene glycol methyl ether acrylate) (PPEGMEA) and hard segments of poly(styrene sulfonate) (PSS) using a reversible addition-fragmentation chain transfer (RAFT) polymerization. Subsequently, we used the newly synthesized ionic elastomer PSS-b-PPEGMEA as a matrix for the oxidative polymerization of EDOT. The resulting polyelectrolyte elastomer, PEDOT:PSS-b-PPEGMEA, can withstand elongations up to 128% and has a toughness up to 10.1 MJ m−3. While the polyelectrolyte elastomer is not as conductive as the commercial material, the toughness and extensibility are each more than an order of magnitude higher. Moreover, the electrical conductivity of the polyelectrolyte elastomer exhibits minimal decrease with strain within the elastic regime. We then compared the block copolymer to physical blends of PEDOT:PSS and PPEGMEA. The blend material had a much lower failure strain of only 38% and a maximum toughness of 4.9 MJ m−3. This approach thus emphasizes the importance of the covalent linking of the PSS and PPEGMEA blocks. Furthermore, we demonstrate that the conductivity of scratched films can be restored upon exposure to water.

Stretchable Conductive Polymers and Composites Based on PEDOT and PEDOT:PSS

“…We recently reported the use of a PSS‐based block copolymer to achieve stretchable PEDOT:PSS ( Figure ) . A block copolymer comprised of “hard” PSS and “soft” poly(polyethylene glycol methyl ether acrylate) (PPEGMEA) was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization (Figure a).…”

“…d) Strain at failure and toughness. Adapted with permission . Copyright 2018, American Chemical Society.…”

Self‐Healing and Stretchable 3D‐Printed Organic Thermoelectrics

“…As a result, π‐conjugated polymers lacking these specific bonding sites (mainly with relatively weak van der Waals interaction, <10 kcal mol −1 ) are generally unable to induce such healing characteristics . In contrast to this, the healing potential of a representative p‐type thermoelectric polymer, poly(3,4‐ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) has been demonstrated under the presence of water and high humidity conditions, and by incorporating polymer or capsule type of healing agents . Despite this step forward, the demonstration of a truly damage‐resistant TEG based on self‐healing materials, as well as in‐depth study on the healing effect on thermoelectric properties under mechanical stress, have not been reported to date.…”

Synthesis of Stretchable, Environmentally Stable, Conducting Polymer PEDOT Using a Modified Acid Template Random Copolymer

“…The Lipomi research group investigated a (poly(poly(ethylene glycol) methyl ether acrylate)‐based block copolymer (PPEGMEA) for PEDOT to address the flexibility and instability of PEDOT:PSS 12. The PPEGMEA component improved the flexibility and stability, while the block copolymer solved the intrinsic problem of the possible toxicity of the added components or incompatibility with the human body rendering them unsuitable for wearable and implantable applications.…”