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Precursor of polyimide, polyamic acid has been prepared sucessfully. Acid‐modified carbon nanotube (MWCNT) was grafted with soluble polyimide then was added to the polyamic acid and heated to 300 °C to form polyimide/carbon nanotube composite via imidation. Morphology, mechanical properties and electrical resistivity of the MWCNT/polyimide composites have been studied. Transmission electron microscope microphotographs show that the diameter of soluble polyimide‐grafted MWCNT was increased from 30–60 nm to 200 nm, that is a thickness of 70–85 nm of the soluble polyimide was grafted on the MWCNT surface. PI‐g‐MWCNT was well dispersed in the polymer matrix. Percolation threshold of MWCNT/polyimide composites has been investigated. PI‐g‐MWCNT/PI composites exhibit lower electrical resistivity than that of the acid‐modified MWCNT/PI composites. The surface resistivity of 5.0 phr MWCNT/polyimide composites was 2.82 × 108 Ω/cm2 (PI‐g‐MWCNT) and 2.53 × 109 Ω/cm2 (acid‐modified MWCNT). The volume resistivity of 5.0 phr MWCNT/polyimide composites was 8.77 × 106 Ω cm (PI‐g‐MWCNT) and 1.33 × 1013 Ω cm (acid‐modified MWCNT).Tensile strength and Young's modulus increased significantly with the increase of MWCNT content. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3349–3358, 2007

Multiwalled carbon nanotube (MWCNT)/ epoxy composites are prepared, and the characteristics and morphological properties are studied. Scanning electron microscopy microphotographs show that MWCNTs are dispersed on the nanoscale in the epoxy resin. The glass-transition temperature (T g ) of MWCNT/epoxy composites is dramatically increased with the addition of 0.5 wt % MWCNT. The T g increases from 1678C for neat epoxy to 1898C for 0.5 wt % CNT/epoxy. The surface resistivity and bulk resistivity are decreased when MWCNT is added to the epoxy resins. The surface resistivity of CNT/epoxy composites decreases from 4.92 Â 10 12 O for neat epoxy to 3.03 Â 10 9 O for 1 wt % MWCNT/epoxy. The bulk resistivity decreases from 8.21 Â 1016 O cm for neat epoxy to 6.72 Â 10 8 O cm for 1 wt % MWCNT/epoxy. The dielectric constant increases from 3.5 for neat epoxy to 5.5 for 1 wt % MWCNT/epoxy. However, the coefficient of thermal expansion is not affected when the MWCNT content is less than 0.5 wt %.