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Composite materials made with polymer and carbon nanotubes (CNTs) are expected to have enhanced mechanical, thermal and electrical properties, due to extraordinary properties exhibited by carbon nanotubes themselves. However due to their insolubility in common solvents, homogeneous dispersion of CNTs in polymer matrix remains challenging. One way to overcome the problem is to functionalize their surface. In our work we used functionalization not only to modify solubility of nanotubes, but also to make covalent links between nanotubes surface and polymer by chemical reaction. Two kind of polymers have been used – thermoset (epoxy) and thermoplastic (PEEK) – and functionalization has been followed using different characterization techniques such as XRD, FT Raman, TEM, XPS and NEXAFS. Then mechanical and electrical tests have been performed. A functionalization method has been successfully applied to functionalize carbon nanotubes surface, then to graft polymer chains like SPEEK, making a composite material with covalent bond between the nanotubes and the polymer. Grafting has been evidenced using spectroscopy techniques such as NEXAFS, XPS or FT Raman. Nevertheless shaping of the PEEK/SPEEK-MWNTs composite sample in order to make mechanical or electrical measurements remains extremely difficult and so far no satisfying method has been found. However mechanical and electrical properties have been enhanced when mixing epoxy resin with functionalized carbon nanotubes. In particular it has been shown that conductivity increases drastically when nanotubes weight fraction increases.