Synthesis and properties of poly(thiourea-azo-naphthyl)/multi-walled carbon nanotube composites

Abstract

An aromatic azo-polymer, poly(thiourea-azo-naphthyl), has been synthesized using 1-(5-thiocarbamoylaminonaphthyl)thiourea and diazonium salt solution of 2,6-diaminopyridine. Poly(thiourea-azo-naphthyl) was easily processable using polar solvents and had high molar mass, 57 × 103 g/mol. Electrically conducting and mechanically and thermally stable polymer/multi-walled carbon nanotube nanocomposites were obtained via melt processing technique. Fine distribution of multi-walled carbon nanotubes in a polymer matrix played an essential role in the preparation of polymer/multi-walled carbon nanotube nanocomposites based on interfacial interaction between multi-walled carbon nanotubes and polymer matrix. Field emission-scanning electron microscopy images revealed good dispersion of filler and adhesion of matrix on the surface of multi-walled carbon nanotubes. Accordingly, increasing the amount of multi-walled carbon nanotubes from 1 to 5 wt% increased the electrical conductivity from 2.42 to 4.11 S cm−1. Percolation behavior of the composite was also studied. Tensile modulus for 1 wt% nanocomposite was 4.2 GPa, which increased up to 6.8 GPa on 5 wt% filler addition. A relationship between nanotube loading and thermal stability of the materials was also observed. Ten percent gravimetric loss increased from 502℃ to 538℃ in the presence of 1 wt% multi-walled carbon nanotube. Similarly, glass transition increased from 227℃ to 245℃ in the presence of 5 wt% multi-walled carbon nanotube. Enhancement of the physical properties of multi-walled carbon nanotube-reinforced polymer nanocomposites was accredited to the non-covalent interactions (π–π interactions and secondary bond forces).