Conductive Inks Based on Methacrylate End-Capped Poly(3,4-Ethylenedioxythiophene) for Printed and Flexible Electronics

A new synthesis of methacrylate end-capped Poly(3,4-ethylenedioxythiophene) (PEDOT) was performed: the polymer is soluble in common organic solvents, thus overcoming the well-known technical problems related to the use of commercial PEDOT in different printing technologies, such as screen printing, due to its poor processability and compatibility in formulations with other resins and polymers. The new synthetic method developed is based on the direct oxidative polycondensation of 3,4-ethylenedioxythiophene (EDOT) in the presence of an oxidant species and a cross-linkable end-capper, i.e. methacrylate end-capped EDOT (mEDOT), prepared via Friedel Crafts acylation with methacryloyl chloride. The oxidative polycondensation between EDOT and mEDOT monomers in the presence of a new kind of doping agent, Sulfonated Polyarylethersulfone (SPES)—characterized by different degree of sulfonation (DS)—was conducted, leading to functional end-capped conducting PEDOT (mPEDOT_SPES), with conductivity of 210 S/cm, 50 S/cm higher than the one of commercial PEDOT. Thanks to the enhancement of solubility, leading to better processability, end-capped PEDOTs were formulated with a thermoplastic ink, PlastisolVR , and electronic circuits were successfully screen printed on flexible cotton substrates, to obtain printed cross-linkable electronic circuits. The conductive features of mPEDOT_SPESs were successfully compared with the ones of PEDOT and of not-doped end-capped PEDOTs.