In-situ polymerization of 3-phenoxybenzoic acid in the presence of various amounts (1-30 wt%) of vapor-grown carbon nanofibers (VGCNF) was carried out in poly(phosphoric acid)/phosphorus pentoxide (PPA/P2O5; 1:4 w/w) medium. 3-Phenoxybenzoic acid polymerizes via Friedel-Crafts acylation in PPA to form poly(oxy-1,3-phenylenecarbonyl-1,4-phenylene) or mPEK. The resulting mPEK-g-VGCNF products that contained less than 10 wt% of VGCNF were soluble in N-methyl-2-pyrrolidinone and had intrinsic viscosity values ranging from 1 to 1.73 dL/g in methanesulfonic acid (MSA) at 30 +/- 0.1 degreesC. The overall evidence based on the data from elemental analysis (EA), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FT-IR) as well as scanning electron and transmission electron microscopies of the resulting materials implicates that VGCNF remained more or less structurally intact under the mildly acidic, relatively high-shearing and hot polymerization conditions. It is also evident that under these reaction conditions rnPEK was grafted onto the surface of VGCNF, resulting in the formation of "hairy tubes". The wide-angle X-ray diffraction result showed the growth of the 3.35 Angstrom peak characteristic of VGCNF that increased in intensity proportionately to the presence of VGCNF in the sample and correlated well with the EA and TGA results. The conductivity of the cast film (10 wt% VGCNF) is 0.25 S/cm (bottom of film) and 0.30 S/cm (top of film).