Compounds are attached to carbon nanotubes (CNT) by a process which comprises: subjecting surface treated CNTs which have been treated to induce negatively charged surface groups thereon, to nucleophilic substitution reaction with a compound carrying a functional group capable of reacting with the negatively charged groups on the CNT surface, whereby the compound chemically bonds to the CNT. The surface CNT treatment may be reduction. The compounds which are bonded to the CNT may be epoxy resins, bonded directly or through a spacer group. Bi-functional CNTs, grafted to both epoxy resins and other polymers such as polystyrene, are also made by this process.