Carbon nanotubes (CNTs), having excellent electrical and extraordinary mechanical properties, are suitable to serve as a conductive filler or a strengthening material in polymer composites; however, their chemical inertia and smooth surface result in their lack of solubility and poor compatibility with polymers. In addition, the CNTs have high aspect ratio and easily attract or tangle to each other due to the van der Waals force interaction. Furthermore, CNTs are inherently lightweight, occupy a lot of space, and are easily blown, thereby increasing the trouble in handling and the difficulty in processing and application.
To obtain good dispersion of CNTs in polymers, we can prepare the CNT masterbatch by mixing CNTs and carriers first, and then the masterbatch are diluted with thermoplastics to produce the CNT/polymer composites. There are three kinds of methods to prepare the CNT masterbatch. The first method is so-called in situ polymerization method ‐: the monomers and CNTs are mixed well in a solution. Then, the monomers are polymerized, and therefore, the CNTs can disperse in the polymer polymerized from the monomers. However, this method usually needs the chemical modification of CNTs for well-dispersed CNTs in the solution, and it could damage the structure of CNTs and reduce their conductivity. The second method is the solution process ‐: the CNTs and the polymer solution are mixed well, and the CNT/polymer composites are obtained by re-precipitation or removing the solvent from the mixture. This method can easily disperse the CNTs in the polymer; however, it is not suitable for mass production due to its high cost, toxicity of the solvent, and solubility limitations of the polymer in the solvent. The third method is the melt-mixing [5, 8]: the CNTs and polymer are directly mixed at high temperature (usually above the glass transition temperature of the polymer) by mechanical mixing. The melt-mixing is also an easy way to produce the CNT masterbatch, but the CNTs are difficult to disperse well in the polymer.
Non-covalent functionalization of CNTs by polymer wrapping is a feasible process to disperse CNTs in the solvent and that could not cause dramatic changes in the electronic properties of CNTs. It has been reported that a molecular structure containing functional groups can effectively absorb on the surface of CNTs and provide the dispersion of CNTs in a solution ‐. However, preparing the polymer-wrapped CNTs by in situ polymerization is not suitable to be used in CNT/polymer composites due to the residual catalysts and impurities ‐. The surface modification of CNTs with strong acids is usually used to improve the dispersion of CNTs in polar solvents (such as H2O, ethanol, and DMF), but that could also disrupt the sp2 structure and conjugation of the CNTs ‐. The CNTs functionalized with hydrophilic molecules can disperse in polar solvents, but they could not disperse well in less polar solvents (such as toluene and n-hexane) and have poor compatibility with aliphatic polymers ‐.
In this study, we reported an easy way to disperse CNTs in solvent and polymer. The surface functionalization of CNTs with a polymer dispersant, containing both aromatic group and amine group, can disperse CNTs in less polar solvents. The powder of polymer-wrapped CNTs can also re-disperse in organic solvents and be easily used in producing the CNT/polyethylene (PE) composites by melt-mixing.