Synthesis, Characterization, Conductivity, Band Gap, and Thermal Analysis of Poly-[(2-mercaptophenyl)iminomethyl]-2-naphthol and Its Polymer–Metal Complexes

Abstract

Oxidative polycondensation reaction conditions of [(2-mercaptophenyl)iminomethyl]-2-naphthol (2-MPIM-2N) were studied using oxidants such as air and NaOCl in an aqueous alkaline medium between 40 °C and 90 °C. The structure of poly-[(2-mercaptophenyl)iminomethyl]-2-naphthol (P-2-MPIM-2N) was characterized by 1H- 13C NMR, FT-IR, and UV–Vis spectroscopy, size exclusion chromatography (SEC), and elemental analysis. At optimum reaction conditions, the yield of P-2-MPIM-2N was found to be 78 and 82% for air and NaOCl oxidants, respectively. From SEC measurements, the number-average molecular weight (Mn), weight-average molecular weight (Mw) and polydispersity index (PDI) of P-2-MPIM-2N are 2900, 3500 g mol−1 and 1.207; 2200, 2500 g mol−1 and 1.136, for air and NaOCl oxidants, respectively. Polymer–metal complexes were synthesized by the reaction of P-2-MPIM-2N with Co2+, Cu2+, Zn2+, Pb2+ and Cd2+ ions. The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and electrochemical band gaps (\( E^{\prime}_{g} \)) of 2-MPIM-2N and P-2-MPIM-2N were −5.97, −2.66 and 3.31 eV and −5.82, −2.68 and 3.14 eV, respectively. The conductivity of polymer and polymer–metal complexes were determined in the solid state. Conductivity measurements of doped and undoped Schiff base polymer and polymer–metal complexes were carried out at room temperature and atmospheric pressure by the four-point probe technique using an electrometer. The conductivities of the polymer and polymer–metal complexes increased when iodine was used as doping agent.