Functionalization of carbon nanotubes by combination of controlled radical polymerization and “grafting to” method

This paper reviews the recent advances in non-covalent and covalent tethering of small molecules and polymer chains onto carbon nanotube (CNT) and its derivatives. The functionalized CNT has recently attracted great attention because of an increasing number of its potential applications. In non-covalent functionalization of CNT, the sp2-hybridized network plays a crucial role. The non-covalent grafting of small molecules and polymers can mainly be carried out through hydrogen bonding and π-stacking interactions. In covalent functionalization of CNT, condensation, cycloaddition, and addition reactions play a key role. Polymer modification has been reported by using three main methods of "grafting from", "grafting through", and also "grafting to". The "grafting from" and "grafting through" rely on propagation of polymer chains in the presence of CNT modified with initiator and double bond moieties, respectively. In "grafting to" method, which is the main aim of this review, the pre-fabricated polymer chains are mainly grafted onto the surface using coupling reactions. The coupling reactions are used for grafting pre-fabricated polymer chains and also small molecules onto CNT. Recent studies on grafting polymer chains onto CNT via "grafting to" method have focused on the pre-fabricated polymer chains by conventional and controlled radical polymerization (CRP) methods. CRP includes reversible activation, atom transfer, degenerative (exchange) chain transfer, and reversible chain transfer mechanisms, and could result in polymer-grafted CNT with narrow polydispersity index of the grafted polymer chains. Based on the mentioned mechanisms, nitroxide-mediated polymerization, atom transfer radical polymerization, and reversible addition-fragmentation chain transfer are known as the three commonly used CRP methods. Such polymer-modified CNT has lots of applications in batteries, biomedical fields, sensors, filtration, solar cells, etc.