Synthesis of Multifunctional PEDOT-block Copolymers by Combining Controlled RAFT and Chemical Oxidative Polymerizations for Bioelectronics

Poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) is the conducting polymer with the biggest prospects in the field of organic (bio)electronics. However, new PEDOT (co)polymers are necessary with additional properties such as stimuli-responsiveness, functionality or biocompatibility for extending 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. First, the macromonomers were synthetized via reversible addition-fragmentation chain transfer (RAFT) polymerization mediated by a tailored EDOT functional RAFT chain transfer agent (CTA). To show its versatility, three different types of EDOT macromonomer of controlled molecular weights were synthetized based on poly(methyl methacrylate) (EDOT-PMMA), poly(styrene sulfonate) (EDOT-PSS) and poly(N-isopropylacrylamide) (EDOT-PNIPAM). Then, the macromonomers were copolymerized with the EDOT monomer by chemical oxidative polymerization to obtain new PEDOT-b-PMMA, PEDOT-b-PSS and PEDOT-b-PNIPAM block copolymers. The physicochemical and electrochemical properties of PEDOT-block copolymers were characterized by FTIR, DSC, TGA, contact angle, UV-Vis-NIR spectroscopy, AFM, TEM, CV and EIS showing the typical features associated with PEDOT as well as the phase separation of block copolymers. PEDOT-b-PSS block copolymers were studied as channel material in an organic electrochemical transistor (OECT) and compared positively with commercial PEDOT:PSS in transconductance, stability and response time. Interestingly, PEDOT-b-PSS made OECT shows two orders of magnitude larger ON/OFF ratios. Furthermore, the PEDOT-b-PNIPAM block copolymers show a low critical solution temperature (LCST) around 36.0 °C, above which their resistance increases dramatically. The integration of PEDOT-b-PNIPAM as the channel material in an OECT allows generating bioelectronic devices with response to temperature variations from 25 to 45 °C, along with high sensitivity of 0.02 °C−1.