Water/Alcohol‐Processable Low‐Cost Dihydropyrazine‐Based Polymers for Highly Sensitive, Stable and Flexible Temperature Sensors

Abstract Flexible temperature sensors based on π–conjugated polymers are well‐suited for diverse applications, including food packaging and human health monitoring. Herein, novel dihydropyrazine (DHP)‐based polymers designed for the development of flexible temperature sensors are introduced. The DHP‐based polymers are synthesized via direct arylation polymerization, eliminating toxic byproducts. Polymers with carboxylate potassium salt side chains, which exhibit high solubility in green solvents like water and alcohol are obtained via post‐polymerization hydrolysis of carboxylate ester chains. Furthermore, a post‐deposition treatment converts the carboxylate potassium salt side chains into carboxylic acid side chains, resulting in highly solvent‐resistant polymers. Notably, these DHP‐based polymers exhibit moderate electrical conductivity in the range of ≈10⁻⁴ to 10⁻¹ S cm⁻¹ without the need for additional dopants. Resistor‐type temperature sensors based on the self‐doped DHP‐based polymers, processed with ethylene glycol (EG) on flexible polyethylene terephthalate (PET) substrates via blade coating, demonstrate an impressive temperature coefficient of resistance (TCR) of up to −1.5% °C⁻¹ (20–60 °C) and outstanding long‐term stability under ambient conditions. This work presents a well‐founded design of π–conjugated polymers that simultaneously fulfill performance, stability, processability, and cost criteria, paving the way for practical applications of flexible and printable temperature sensors.