Binaphthyl-containing electroactive polymer networks by ring-opening metathesis polymerization

Abstract

Conducting polymers (CPs), organic polymers that conduct electricity, have broad applications that include sensors, catalysis, electrochromism, anticorrosion, and modern (flexible) electronics. In particular, CPs have drawn wide attentions due to their applicability to energy storage and conversion devices, such as batteries, supercapacitors, organic photovoltaics, and fuel cells. However, the use of CPs is often hampered by low processibility and insufficient mechanical properties. To overcome such limitations, CPs have been combined with other polymers that play a complementary role. Poly(ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), a widely used conducting polymer system, is a good example; polystyrene sulfonate helps maintain the mechanical integrity of the resulting films as well as balance the charges. Combinations of conducting polymers with polymers range from simple blending, graft or block copolymers, to interpenetrating networks depending on the bonding between the polymers. Network polymer systems that contain conductive polymers are of particular interest due to their robustness, versatility, and high degree of controllability. Conductive polymer networks have been utilized in sensors, fuel cell membranes, electrochromics, and tissue engineering. Interest in binaphthyl-containing CPs has been growing due to the conformational flexibility and molecular recognition ability of binaphthyls. Electropolymerization on conducting substrates easily furnished thin films of binaphthyl-containing CPs, but their mechanical integrity was not satisfactory. Moreover, the molecular weights of CPs prepared by electrochemical methods were quite varied. We envisioned that a combination of binaphthyl-containing CPs with polymers of controlled molecular weight could render the product polymers more mechanically robust and might result in a variety of interesting properties. Among “living” polymerization methods that provide controlled molecular weights, we chose ring-opening metathesis polymerization (ROMP). ROMP has been widely utilized in materials synthesis because of a low polydispersity, functional group tolerance, and clean polymer end-capping. The driving force of the polymerization reaction is relief of ring strain in cyclic monomers such as norbornene and cycloalkenes. While oligothiophenederivatized norbornenes and ROMP polymers thereof have been reported by Sotzing and Swager, binaphthyl systems have not been previously studied. We report here the synthesis of electroactive polymer networks from binaphthyl containing CPs via ROMP. First, ROMP-capable thienylbinaphthyl monomers were synthesized. Polymerization resulted in highly processible and mechanically robust polymers with controlled molecular weights. Oxidative polymerization of the thiophene moieties was subsequently performed to produce electroactive polymer networks, and their electrochemical properties were investigated. We also tested the electrochromic properties of the electroactive binaphthyl-containing polymer networks.