Multifunctional poly(2,5-benzimidazole)/carbon nanotube composite films

Abstract

The AB-monomer, 3,4-diaminobenzoic acid dihydrochloride, was recrystallized from an aqueous hydrochloric acid solution and used to synthesize high molecular weight poly(2,5-benzimidazole) (ABPBI). ABPBI/carbon nanotube (CNT) composites were prepared via in-situ polymerization of the AB-monomer in the presence of single-walled carbon nanotube (SWCNT) or multi-walled carbon nanotube (MWCNT) in a mildly acidic polyphosphoric acid (PPA). The morphology of these composite films was studied by x-ray diffraction and scanning electron microscopy. The results showed that both types of CNTs were uniformly dispersed into the ABPBI matrix. Tensile properties of the composite films were significantly improved as compared to ABPBI and their toughness (~200 MPa) was close to the nature’s toughest spider silk (~215 MPa). The electrical conductivities of ABPBI/SWCNT and ABPBI/MWCNT composite films were 9.10ⅹ10-5 and 2.53ⅹ10-1 S/cm, respectively, while that of ABPBI film was 4.81ⅹ10-6 S/cm. Finally, without acid impregnation, while the ABPBI film was non-conducting, the SWCNT and MWCNT based composites were proton-conducting with maximum conductivities of 0.018 and 0.017 S/cm, respectively.