## 2 Covalent Interactions
### CNT-Based Nanocomposites
#### 2.1.1 Grafting-from through Surface-Initiated Polymerization
The authors showed that the grafting of dendrimer polymer to CNTs was key to achieving a uniform dispersion because without it, several micro-sized CNTs clusters formed in the EP matrix (Figure 5A) preventing suitable homogeneity of the SWCNTs. In addition, the increase in the branching degree of dendrimer enhances the solubility of the PAMAM/SWCNT nanocomposites in the epoxy matrix, given the higher number of amino groups which are likely to react with the matrix, as shown in Figure 5B,C. The longitudinal alignment of the SWCNTs created by spinning (Figure 5D) also contributed to the good dispersibility of the CNTs within the polymeric matrix, thus enhancing its mechanical properties. Figure 4: Transmission electron microscopy (TEM) micrographs of (**a**) pristine MWCNTs and (**b**) MWCNT-g-poly(2,2,6,6-tetramethyl-4-piperidyl methacrylate) (PTMPM) (MWCNT-g-PTMPM)—Scale bars: 100 nm (Republished with permission (2020) of the Royal Society of Chemistry from [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Grafting of a Redox Polymer onto Carbon Nanotubes for High Capacity Battery Materials. _J. Mater. Chem. A._**2015**, \(3\), 8832–8839 [5]. Permission conveyed through Copyright Clearance Center Inc.). The fabrication of nanocomposites involving vertically aligned (VA) CNTs as fillers has also been studied and has strong potential for future biochemical sensors and water treat membranes. [PERSON] et al. [16] reported an ultrasonically assisted \"grafting-from\" RAFT polymerization of the monomer styrene in the presence of VA-SWCNTs on a silicon substrate. This involved two main steps: the VA-carboxylated SWCNTs, obtained via sulfuric and nitric acid treatment, were bonded to the substrate surface by the formation of an ester linkage between the carboxyl and hydroxyl groups from the VA-SWCNTs and substrate, respectively. Then, the sidewalls of SWCNTs were covalently functionalized with bis(dithioester) groups acting as CTAs to initiate the \"grafting-from\" polymerization of the styrene. The vertical preservation of VA-SWCNTs within the polystyrene matrix on the substrate was confirmed by atomic microscopy force microscopy (AFM) analysis, as depicted in Figure 6. [PERSON] et al. [23] performed the grafting-from polymerization of the monomer aniline in the presence of nitrogen-doped VA-CNTs and showed the conservation of the vertical alignment of carbon nanotubes during the polymerization, as depicted in Figure 7. They showed that the nitrogen-doped sites present in the CNTs walls acted as nucleation sites for the initiation of the aniline polymerization. The incorporation of metal oxides such as manganese or ruthenium oxide in the previous nanocomposites allows them to be used as supercapacitor electrodes because of their synergetic proprieties. Figure 5: Microscopic images of (**A**) poly(amidoamine)-free single-walled carbon nanotube-based epoxy matrix, PAMAM/SWCNTs/EP, with (**B**) 1 and (**C**) 2 as number generation and (**D**) field emission scanning electron microscope (FESEM) images of PAMAM/SWCNTs/EP with grafting generation 2 (Reprinted (adapted) with permission from [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Epoxy Composite Fibers Reinforced with Aligned Single-Walled Carbon Nanotubes Functionalized with Generation 0\(-\)2 Dendritic Poly(Amidoamine). _Chem. Mater._**2009**, _21_, 1471-1479 [22]. Copyright (2020) American Chemical Society.). Besides enabling greater efficiency in achieving very homogenous CNT dispersion, ultrasonication also makes it possible to create highly reactive species in a medium, thus obviating the need for chemical initiators during the polymerization. [PERSON] et al. (2020) drew attention to defects on the SWCNT sidewalls in a monochlorobenzene (MCB) solution of poly(methyl methacrylate) (PMMA) during ultrasonication. In addition to the fact that these defects acted as reactive sites, other reactive groups were produced through the solvent and polymer decomposition, resulting in a covalent attachment of PMMA to the CNT surface.