Polyurethanes prepared from isocyanates containing triphenylamine derivatives: synthesis and optical, electrochemical, electrochromic and memory properties

Abstract

Two novel series of triphenylamine (TPA)-containing aromatic polyurethanes (PUs) were synthesized via polymerization of N′,N′-bis(α-naphthyl)-N,N′-bis(4-phenylisocyanate) biphenyl (M1) and N,N′-diphenyl-N,N′-bis(4-phenylisocyanate) biphenyl (M2) with different dihydroxy compounds. The structures of the polymers were characterized by Fourier transform infrared (FT-IR) spectroscopy, hydrogen nuclear magnetic resonance (¹H-NMR) and carbon nuclear magnetic resonance (¹³C-NMR); and the thermostability and morphology were studied by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The molecular weights were measured to be from 1.02 × 10⁴ to 1.31 × 10⁴ by gel permeation chromatography (GPC). The polymers were coated onto indium tin oxide (ITO) and the electrochromic properties were investigated by using the ultraviolet visible (UV-vis) absorption spectra and cyclic voltammetry (CV). The energy gaps were in the range of 2.21–2.26 eV. The polymer films revealed good stability of the electrochromic characteristics by continuous cyclic scans, with the color changing from neutral yellowish to a blue doped form at applied potentials. Meanwhile, the PUs film exhibited non-volatile write-once-read-many-times (WORM) memory behavior in the device resulting from the non-isolated donor–acceptor (D–A).