Synthesis, optical and electrochemical abilities of highly soluble poly(epoxy-ether)s bearing perylene bisimide units and their enhanced thermal properties by curing process

Abstract

Three highly fluorescent poly(epoxy-ether) containing three different units at two imide functionalities of perylene bisimide unit (PER-EP1, PER-EP2 and PER-EP3) could be efficiently synthesized in high yields, and were characterized by FT-IR, 1H NMR and 13C NMR spectroscopic techniques. Their optical properties were measured using UV–vis and emission spectroscopic methods, as well as cyclic voltammetry (CV) to analyze their electrochemical abilities. They all showed emission in the visible region. Additionally, one reversible one-electron oxidation and two reversible one-electron reductions in acetonitrile took place for the synthesized poly(epoxy-ether)s. Dihydroxy compounds containing perylene units exhibited three absorption maxima (λmax) values of 458, 489 and 524 nm in DMF owing to presence of perylene units and highly conjugated framework of π bonds. For poly(epoxy-ether)s, the functional groups influenced the conjugated systems, giving rise to the absorption peaks to shift to longer wavelengths. Fluorescence spectra of the synthesized poly(epoxy-ether)s in DMF showed emission peaks in the wavelength range of green light, and the highest value of fluorescence quantum yield was 8.2% for PER-EP1 in comparison to standard fluorescein solution. Furthermore, morphological analysis demonstrated that the synthesized poly(epoxy-ether)s possessed well-organized microstructure particles despite the linkage of the perylene bisimide core. The prepared epoxy resins were cured with p-phenylenediamine as aromatic hardener. The resulting cured epoxy resins were analyzed for their thermal properties such as thermal stability, char yield, glass transition temperature (Tg), and flame retardancy. The morphology behaviour was performed by SEM analysis on poly(epoxy-ether)s.