Dipentaerythritol‐Derived Hyperbranched Polyurethane Elastomers and Their Applications in Flexible Strain Sensors

Abstract Polyurethane (PU) elastomers have great potential to work as flexible substrates in electronic materials. In this work, hyperbranched PU elastomers are designed and prepared utilizing dipentaerythritol, isophorone diisocyanate, and polytetrahydrofuran as the monomers. The mechanical properties and transparency of the PU elastomers are regulated by the molar ratio of hydroxyl group to isocyanate group (OH/NCO). High tensile strength (26 MPa) and elongation at break (>600%) are achieved. Furthermore, PU elastomer composites are developed by introducing graphene into the surface of PU elastomers. PU elastomer composites are further utilized in assembling flexible strain sensors, which achieve a gauge factor (GF) of 170 in the strain range of 0–75% and a GF of 549 in the strain range of 75–225%. The response time is as low as 140 ms and at least 1000 reversible sensing cycles are successfully conducted. Utilizing such flexible sensors, monitoring of various human motions, including biceps motion, finger bending, knee joint bending, elbow bending, and vocal cord vibration, are demonstrated. Overall, this work not only develops a new kind of PU elastomer with hyperbranched structure but also provides candidate materials for flexible sensors and other flexible electronic devices.