Novel Anodic Polyelectrochromic Aromatic Polyamides Containing Pendent Dimethyltriphenylamine Moieties

Abstract

Two series of novel aromatic polyamides containing pendent dimethyltriphenylamine moieties were prepared based on N,N-bis(4-aminophenyl)-N′,N′-di(4-methylphenyl)-1,4-phenylenediamine (4) and N,N-bis(4-carboxyphenyl)-N′,N′-di(4-methylphenyl)-1,4-phenylenediamine (4′). These compounds with similar structures were successfully synthesized by amination reactions of 4-amino-4′,4′′-dimethyltriphenylamine with 4-fluoronitrobenzene and 4-fluorobenzonitrile, respectively; subsequent reduction and alkaline hydrolysis of the dinitro and dinitrile intermediates led to new triphenylamine-containing aromatic diamine and dicarboxylic acid monomers. These polyamides, with pendent 4,4′-dimethyl-substituted triphenylamine (TPA) units having inherent viscosities of 0.34−0.80 dL/g, were prepared via direct phosphorylation polycondensation. All the polymers were amorphous with good solubility in many organic solvents, such as N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc), and could be solution-cast into tough and flexible polymer films. These aromatic polyamides had useful levels of thermal stability associated with their relatively high glass transition temperature (236−288 °C), 10% weight-loss temperatures in excess of 505 °C, and char yields at 800 °C in nitrogen higher than 68%. The electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of polyamide IIc, prepared from the dicarboxylic acid monomer 4′ with the structurally similar diamine monomer 4, exhibited four reversible oxidation redox couples in acetonitrile solution at E1/2 = 0.58, 0.76, 0.96, and 1.12 V, respectively. All the polyamides exhibited excellent reversibility of electrochromic characteristics by continuous five cyclic scans between 0.0 to 1.30 V, with a color change from the original pale yellowish neutral form to the green and then to blue oxidized forms. Polyamide Ib not only showed excellent reversible electrochromic stability with good coloration efficiency of green (CE = 276 cm2/C) but also exhibited high contrast of optical transmittance change (ΔT, %) up to 52% at 423 nm and 67% at 1003 nm for green. After over 1600 cyclic switches, the polymer films still exhibited excellent stability of electrochromic characteristics.