The unexpected fast polymerization during the synthesis of a glycolated polythiophene

Conjugated polymers with ethylene glycol side chains are emerging as ideal materials for bioelectronics, particularly for application in organic electrochemical transistors (OECTs). To improve the OECT device performance, it is important to develop an efficient synthetic strategy that will provide access to novel high-performing materials besides focusing on molecular design. While a lot of efforts are being devoted to designing of new polymers by modifying the glycol side chains, understanding how their nature affects the polymerization kinetics and eventually the polymer structure and properties is not known. In this work, we have studied the influence of the content of the ethylene glycol side chain and its linkage on the formation of the active Grignard monomer species upon Grignard metathesis in three thiophene derivatives. A strong dependence of the monomer's concentration on polymerization was noted in our study indicating that for synthesizing P3MEEMT, a high-performing OECT material, by Kumada catalyst transfer polymerization (KCTP) a minimum of 0.15 M monomer is needed. Furthermore, kinetic studies by GPC show uncontrolled polymerization behavior contrary to the controlled chain growth characteristics of the KCTP.