Simultaneous electronic and ionic conduction in ionic liquid imbibed polyacetylene-like conjugated polymer films†
Polymer films composed of a polyacetylene-like conjugated polymer and 1-propyl-3-methylimidazolium iodide ionic liquid (IL) were synthesized using a ‘one-pot’ hydroiodic acid catalyzed thermal dehydration of poly(vinyl alcohol) (PVA) precursor polymer blended with the IL. The dehydration of the precursor polymer and the formation of polyene segments, in films reacted at temperatures in the range of 60 to 250 °C, were characterized using thermogravimetry and infrared spectroscopy. In reactions catalyzed by HI, infrared, 13C NMR, and Raman spectroscopies confirmed nearly complete elimination of the hydroxyl groups of PVA at 200 °C, which was below the decomposition temperature of the IL in the blend. In contrast, the synthesis of the polyene–IL blend was not feasible in the absence of the HI catalyst, because pure PVA exhibited peak mass loss at about 280 °C, a temperature at which the IL also showed significant thermal degradation. Electrochemical and mechanical properties of the polyene–IL blends synthesized at 200 °C were investigated. The films exhibited both electronic and ionic conductivities. The charge conduction pathways were identified and quantified using electrochemical impedance spectroscopy (EIS). The electronic and ionic conductivities increased by as much as four orders of magnitude over the temperature range of 25 to 115 °C. The storage and loss moduli of the films were measured using dynamic mechanical analysis (DMA), and elongation at break was determined by tensile testing. Addition of IL to the conjugated polymer not only imparted ionic conductivity to the polyene films, but also greatly improved their mechanical properties, including the elongation at break.