## 2 Covalent Interactions
### CNT-Based Nanocomposites
#### 2.1.1 Grafting-from through Surface-Initiated Polymerization
The surface-initiated atom transfer radical polymerization (SI-ATRP) of the monomer, 2,2,6,6-tetramethylpiperidin-4-yl methacrylate (TMPM) in the presence of the acidic-treated MWCNTs (MWCNT-initiator) took place at 60 \({}^{\circ}\)C for 16 h, followed by chemical oxidation resulting in MWCNT-g-poly(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl methacrylate) (PTMA) (MWCNT-g-PTMA). The main steps to producing MWCNT-g-PTMA can be seen in Figure 3. The thermogravimetric analysis (TGA) results confirmed the presence of initiator groups (the brominated groups were confirmed by X-ray photoelectron spectroscopy, XPS) on the surface of the nanotubes by a weight loss of 10% in the MWCNT-initiator. One of the main advantages of the SI-ATRP technique combined with the grafting-from method is the higher polymer grafting density on the MWCNTs [19]. To characterize this structure, a series of tests were performed on the MWCNT-g-poly(2,2,6,6-tetramethyl-4-piperidyl methacrylate) (PTMPM) (MWCNT-g-PTMPM). Transmission electron microscopy (TEM) images (Figure 4) revealed the formation of a core-shell structure. The MWCNT-g-PTMPM diameter was greater than the neat MWCNTs (17 nm and 11 nm respectively), which confirmed the presence of an organic layer (shell) wrapping the MWCNTs (core). Moreover, the PTMPM covering was found to be uniform: the XPS graph of MWCNT-g-PTMPM was similar to the neat PTMPM but different from the MWCNT-initiator (a shoulder was not present). After the oxidation step converting MWCNT-g-PTMPM to MWCNT-g-PTMA, the core-shell structure remained, as well as the thermal properties. [PERSON] et al., also successfully proved that the MWCNT-g-PTMPM was an efficient cathodic electrode by showing that it presents both high cycling stability (87% of the initial capacity retention maintained after 200 charge/discharge cycles) and good specific capacity (85% of the theoretical capacity). Figure 3: Preparation of poly(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl methacrylate) (PTMA) covalently grafted from MWCNTs by grafting-from polymerization (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.). [PERSON] et al. [21] discussed the challenges related to the dispersibility of acrylate-based polymer/single-walled carbon nanotube (SWCNT) nanocomposites within different organic solvents such as tetrahydrofuran (THF), acetone, or \(N\),_N_-dimethylformamide (DMF). They showed that methyl methacrylate (MMA)/SWCNT composites were not soluble, but by replacing the former monomer by tert-butyl acrylate (tBuA), the nanocomposite's solubility was clearly enhanced. These two composites were synthesized by the same method: a \"grafting-from\" ATRP polymerization of the monomers initiated by alkyl bromide-based chain transfer agents (CTAs) grafted onto the CNT surfaces prior to the growth-chain polymerization, assisted by sonication. This resulted in a covalent attachment of the polymers onto the sidewalls of the CNTs. The authors showed that this solubility difference was due to the appearance of crosslinking reactions between the two chain ends of the MMA polymers derived either from a single CNTs or two different nanotubes. In this study, [PERSON] et al. [22] greatly enhanced the dispersibility of aligned SWCNTs within the epoxy (EP) matrix by grafting-from a dendritic poly(amidoamine) (PAMAM) onto the CNT surface. The prior acidic-treated and isocyanate group-functionalized SWCNTs underwent a two-step reaction performed twice successively under sonication to achieve a four-branched dendrimer. This involved the formation of amino groups via the amidation reaction by the ethylenediamine (EDA) then conversion into ester groups by the addition of methyl acrylate.