Enhanced conductivity in polybenzoxazoles doped with carboxylated multi-walled carbon nanotubes

Two representative polybenzazoles, poly(p-phenylene benzobisoxazole) (PBO) and poly(2,5-benzoxazole) (ABPBO), have been used as matrix materials for fabricating electrically conducting nanocomposite films. In this strategy, pristine multi-walled carbon nanotubes (MWCNTs) were first treated with nitric acid to form carboxylated multi-walled carbon nanotubes (MWCNTs–COOH). Subsequently, MWCNTs–COOH were dispersed efficiently in the methanesulfonic acid (MSA) solution of polybenzazole, sonicated, and then processed into thin films. MWCNTs–COOH in MSA formed an isotropic regime at the concentration of ∼0.1 wt.%. Nanotubes could form net like structures and conductive channels in the polymer matrix to improve electrical conductivity, mechanical properties, and thermal stability. At the MWCNT–COOH composition of 5 wt.%, polybenzazole/MWCNT–COOH composite films exhibited a dramatic enhancement in electrical conductivity by 8 orders of magnitude from ∼10−12 to 1.6 × 10−4 S cm−1 without significantly sacrificing optical transparency.