To efficiently reinforce polymer matrix composites with carbon nanotubes, issues of dispersion and nanotube−matrix compatibility should be optimized. Sidewall chemical functionalization was shown to be effective in improving both the dispersion and interaction between the nanotube and the matrix. This work evaluates the affect of sidewall functional group on dispersing the fluorinated single-walled carbon nanotubes (F−SWNTs) in a thermoplastic matrix (polyethylene) and on the mechanical properties of the F−SWNT composites fabricated. These studies demonstrate that in comparison with polyethylene composites, filled with purified nanotubes, improved dispersion and interfacial and mechanical properties are achieved for F−SWNT-loaded matrixes due to chemical functionalization. In addition, the observed partial removal of functional groups from the F−SWNTs during melt processing with polyethylene by shear mixing suggests a possibility of in situ direct covalent bonding between the nanotubes and the matrix whic...