Synthesis of multifunctional PEDOT-block copolymers by combining controlled and chemical oxidative polymerization for bioelectronics

Abstract

Poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) is considered a conducting polymer with the biggest prospects in the field of organic (bio)electronics. However, it is necessary to develop new PEDOT (co)polymers with additional properties such as stimuli-responsiveness, functionality and biocompatibility to extend its applications. Herein, we report a synthetic pathway towards new 3,4-ethylenedioxythiophene (EDOT) end-functional macromonomers and a new generation of multifunctional PEDOT-block copolymers. The macromonomers were synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization mediated by a tailored EDOT functional RAFT chain transfer agent (CTA). To show the versatility of this approach, three types of EDOT macromonomers with controlled molecular weights were synthesized based on poly(methyl methacrylate) (α-EDOT-PMMA), poly(styrene sulfonate) (α-EDOT-PSS) and poly(N-isopropylacrylamide) (α-EDOT-PNIPAM). Then, the macromonomers were copolymerized with the EDOT monomer via chemical oxidative polymerization to obtain the corresponding new PEDOT-b-PMMA, PEDOT-b-PSS and PEDOT-b-PNIPAM block copolymers. The physicochemical and electrochemical properties of the PEDOT-block copolymers were characterized by FTIR, DSC, TGA, contact angle measurement, UV-Vis-NIR spectroscopy, AFM, TEM, CV and EIS, showing the typical features associated with PEDOT and the phase separation of the block copolymers. The PEDOT-b-PSS block copolymers were studied as channel materials in an organic electrochemical transistor (OECT) and shown to be comparable with the commercial PEDOT:PSS in terms of transconductance, stability and response time. Interestingly, owing to the presence of PEDOT-b-PSS, the OECT showed two orders of magnitude larger on/off ratios. Furthermore, the PEDOT-b-PNIPAM block copolymers showed a low critical solution temperature (LCST) of around 36.0 °C, above which their resistance increased dramatically. The integration of PEDOT-b-PNIPAM as the channel material in an OECT allowed the generation of bioelectronic devices with a response to temperature variations from 25 °C to 45 °C, together with high sensitivity of 0.02 °C⁻¹.