Improvement of semiconducting and thermomechanical properties of polymer materials based on polypyrrole and polyvinylpyrrolidone

Abstract

In this study, we investigate how the addition of polyvinylpyrrolidone (PVP), a thermoplastic polymer, contributes to enhance the processability, thermomechanical and semiconducting properties of a semiconducting polymer without side chains. Here, polypyrrole (PPy) is chosen as reference semiconducting polymer. Different blend ratio of polyvinylpyrrolidone/polypyrrole (PPy/PVP) is prepared by in situ polymerization in acidic solution. The pre-requisite for an effective gain in mechanical properties is to ensure an intimate mixing of both polymers. The miscibility of PPy with PVP is assessed preliminarily using thermodynamic approaches derived from the appropriate group contribution theory which is confirmed experimentally by thermal measurements using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. All PPy/PVP blend ratios exhibit a single glass transition temperature (T_g) characteristic of their appropriate miscibility in the solid state. The morphology and thermal behavior of PPy/PVP mixtures are investigated by DSC and TGA. The potential specific interactions between PPy and PVP moieties are investigated both qualitatively and quantitatively using Fourier transform infrared spectroscopy (FTIR). The FTIR study reveals specific interactions mainly hydrogen bonding between antagonist groups of PPy and PVP. The TGA showed an improved thermal stability. The optical gap of PPy in the mixture PPy/PVP (0.8–0.5 eV) determined by UV–Visible spectrophotometry is attributed to π → π* transition, while the electric conductivity measured by the four-point method revealed their semiconducting behavior (57–3960 µS cm⁻¹). Electrochemical impedance spectroscopy (EIS) exhibits semicircles attributed to bulk material, whose diameter decreases with increasing temperature, thus confirming the semiconducting behavior of PPy; the data obey to an Arrhenius law with an activation energy of 0.1 eV and the conduction occurs by electrons delocalization through alternating double bonds.