The production of functionalized multiwall carbon nanotube/amino acid-based poly(amide–imide) composites containing a pendant dopamine moiety

The high compatibility of amino-acid based poly(amide–imide) (PAI) as a polymer matrix for acid-modified multi-walled carbon nanotubes (MWCNTs) is discussed. PAI was synthesized from the direct polycondensation reaction of N,N′-(pyromellitoyl)-bis-l-isoleucine with a dopamine-based diamine, 3,5-diamino-N-(3,4-dihydroxy-phenethyl)benzamide, in a medium consisting of a molten salt, tetrabutylammonium bromide, and triphenyl phosphite as the activator under microwave radiation. To obtain a homogeneous dispersion of MWCNTs in the PAI matrix, acid-functionalized MWCNTs were used. Composites containing 5, 10, and 15 wt.% MWCNT–COOH exhibited a relatively good dispersion on the macroscopic scale. MWCNT/PAI composite films have been prepared by casting a solution of precursor polymer containing MWCNTs into a thin film and its tensile properties examined. Incorporation of MWCNTs improved the mechanical properties significantly. Composites were also characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy, and thermal gravimetric analysis. The thermal stability of the composites containing the CNTs was improved due to the increased interfacial interaction between the PAI matrix and the modified CNTs and their good dispersion.