Covalent Grafting of Cationic Polythiophene Nanowires onto a Polyurethane Interface via Surface-Assisted Polymerization

We report a robust and scalable approach for covalently grafting cationic polythiophene (CPT) nanowires onto polyurethane (PU)-functionalized gold surfaces using a surface-assisted (SurfAst) polymerization strategy. The methodology involves sequential incubations of hexamethylene diisocyanate (HDI) and 1,4-butanediol (1,4-BDO) on an 11-mercaptoundecanoic acid (MUA)-functionalized gold substrate, forming an OH-terminated PU interface. Subsequent functionalization with 2-isocyanatoethyl methacrylate yields a methacrylate-terminated PU interface, enabling the grafting of CPT nanowires through an UV-induced reaction between the methacrylate group on the PU interface and the allyl moieties of CPT. Atomic force microscopy (AFM) reveals the formation of highly elongated and well-defined CPT nanowires with stability. Electrostatic force microscopy (EFM) further confirms distinct phase shifts in the CPT-grafted regions. These findings demonstrate not only the successful immobilization of CPT on the PU-functionalized gold surface but also the preservation of accessible cationic functionalities, which ensure surface activity. A key aspect of this platform is the use of ethylene glycol (EG) as the solvent for CPT during the grafting process, which facilitates well-dissolved CPT chains and may provide the polymer in a dispersed state in solution, allowing effective interaction with the functionalized surface. These results establish a chemically robust and electrostatically tunable CPT-PU interphase, offering new opportunities for integration into next-generation electronic and sensing technologies.