Nanowire poly (3,4-dihydro-2H-thieno [3,4-b] [l,4]dioxepin-3-yl)methanol (PProDTM) free-supporting films with conductivities around 1.92 S cm(-1) were prepared using a template-free electro-polymerization method. The structure, morphology, mechanical properties, and thermal stability of the PProDTM films were characterized by Fourier transform infrared spectroscopy, UV-vis spectroscopy, scanning electron microscopy, dynamic mechanical analysis and thermogravimetric analysis. Moreover, the capacitance performances of PProDTM films were investigated in aqueous and organic electrolytes (acetonitrile (ACN) and dichloromethane (DCM)). In 0.1 M H2SO4, a symmetrical supercapacitor based on PProDTM exhibited specific capacitance of 89.2 F g(-1) at a current density of 1.0 A g(-1), an energy density of 3.1 Wh kg(-1) at power density of 0.5 kW kg(-1) and the cycling capacitance retention was 74.8% after 5000 cycles. As the scan rate and current density increased, the specific capacitance of PProDTM films clearly decreased in DCM, but no obvious changes occurred in water and ACN. In ACN containing 0.1 M BU4NBF4, a symmetrical supercapacitor based on PProDTM exhibited specific capacitance of 99.6 F g(-1) at a current density of 1.0 A g(-1), an energy density of 3.5 Wh kg(-1) at power density of 0.5 kW kg(-1) and the cycling capacitance retention was 82.2% after 5000 cycles. These results imply that our flexible free-supporting PProDTM films are promising for future use in supercapacitors. (C) 2018 Elsevier Ltd. All rights reserved.