New electroactive macromonomers and multi-responsive PEDOT graft copolymers

Poly(3,4-ethylenedioxithiophene) (PEDOT) is the conducting polymer with the biggest prospects in the field of organic electronics due to its high electrical conductivity and transparency as thin films. It is commonly used and commercialized in the form of aqueous dispersions stabilized by polystyrene sulfonate. However, new PEDOT (co)polymers are necessary with properties such as stimuli-responsiveness, biofunctionality or biocompatibility in emerging application areas such as bioelectronics. Herein, we report for the first time the synthetic pathway towards new propylenedioxythiophene (ProDOT) end-functional polymers or macromonomers and a new generation of multi-responsive PEDOT graft copolymers. First, the macromonomers were synthesized via reversible addition–fragmentation-transfer polymerization (RAFT) mediated by a novel ProDOT based chain transfer agent (CTA). To show its versatility, three different ProDOT end capped macromonomers were synthesized: α-ProDOT-poly(methyl methacrylate) (ProDOT-PMMA), α-ProDOT-poly(ethylene glycol methyl ether methacrylate) (ProDOT-POEGMA) and α-ProDOT-poly(N-isopropylacrylamide) (ProDOT-PNIPAM). Then, the homopolymerization of ProDOT-PMMA macromonomers was carried out by chemical oxidative polymerization obtaining polymacromonomers having a semi-conjugated polymer backbone. Finally, the macromonomers were copolymerized with the EDOT monomer in water by chemical oxidative polymerization to obtain new graft copolymers. As a result, new PEDOT-graft-POEGMA and PEDOT-graft-PNIPAM were obtained in the form of aqueous dispersions. The graft copolymers were characterized by UV-VIS, FTIR, TEM and AFM showing the typical features associated with electrically conductive PEDOT as well as the phase separation of graft copolymers. Furthermore, the PEDOT-graft-PNIPAM showed a thermoresponsive character showing a volume phase transition between 26 and 34 °C depending on the composition and the macromonomer length.