# Fabrication of Self-Healable Magnetic Nanocomposites via Diels - Alder Click Chemistry
## 3 Results and Discussion  
The ring opening polymerization (ROP) strategy has been widely used to facilely synthesize cyclic esters based polymers. In the current study, PCL diol which served as a macroinitiator was first mixed with TBD catalyst, followed by the addition of a mixture of CL and FGE monomers to synthesize PCLF copolymer with high yield. To monitor the polymerization progress of the reaction system, the molecular weight characterizations of the macroinitiator and polymer product were both analyzed by using GPC. On the basis of the GPC profiles, we could observe that the PCL diol macroinitiator exhibited a number-average molecular weight of 2600 g mol\({}^{-1}\) and a polydispersity value of 2.04. After the addition of CL/FGE mixing monomers, we could further observe that there was a molecular weight increase in the GPC trace from the original 2600 g mol\({}^{-1}\) toward a higher molecular weight of 5700 g mol\({}^{-1}\). This result clearly demonstrated the successful synthesis of the PCLF copolymer. All the molecular parameters of the polymerization system in the current study are listed in Table 1. The molecular structure of the synthesized PCLF copolymer was further characterized by using \({}^{1}\)H-NMR measurement. From the obtained spectrum shown in Figure 2, we could clearly identify the structural features of the sample. The characteristic peaks at 7.4 and 6.3 ppm could be assigned to the protons of stran rings and the peak at 3.7-3.3 ppm could be assigned to the protons of opened moiety of FGE. Additionally, the proton signals associated with methylene groups of CL were also assigned. According to the integrated area ratio between the protons of furan groups (6.3 ppm) and the protons of methylene groups adjacent to carbonyl groups of CL (2.3 ppm), the molar fraction of FGE in the PCLF copolymer was calculated to be \(\sim\) 15%. Additionally, the complete disappearance of the hydrogen signals from methylene of \(\varepsilon\)-caprolactone monomers (2.6 ppm) and the epoxy methylene of FGE monomers confirmed the high conversion from the ROP reaction. \begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **M\({}_{\mathbf{n}}\) (g/mol)** & **Mw (g/mol)** & **PDI** & **FGE/CL Ratio 1** \\ \hline PCL diol & 2600 & 5300 & 2.04 & – \\ PCLF & 5700 & 10,900 & 1.91 & 0.15 \\ \hline \end{tabular} \({}^{1}\) Based on the \({}^{1}\)H-NMR results shown in Figure 2.  
\end{table} 
Table 1: Molecular characteristics of PCL diol and PCLF copolymer samples. Figure 2: \({}^{1}\)H NMR spectrum of the PCLF copolymer sample in CDCl\({}_{3}\). In the current study, the combination of MWCNTs and monodispersed IONPs was prepared by using co-precipitation method [41; 42; 43], in which the acid-treated MWCNTs were used as structure-directing templates and the IONPs were subsequently in situ grown on the surfaces of the MWCNTs via a co-precipitation process. Figure 3a shows the TEM image of the acid-treated pristine MWCNTs prepared by drop coating MWCNTs/THF solution onto a carbon-coated copper grid. Figure 3b shows the TEM image of IONPs-MWCNTs hybrid sample. It could be observed that IONPs preferentially located along the MWCNTs templates to form a one-dimensional nanofibril structured hybrid system rather than located in the empty space without the presence of MWCNTs, indicating an intimate contact between IONPs and MWCNTs that resulted from the in situ synthesis process. A higher-magnification image of the IONPs-MWCNTs hybrid sample is also shown in Figure 3c. Based on the atomic ratio between the iron and carbon signals in the EDX spectrum (Figure 3e), the loading fraction of IONPs in the IONPs-MWCNTs hybrid is found to be \(\sim\)56%. Figure 3d further shows the morphology of the PCLF/ IONPs-MWCNTs hybrid with 10 wt% IONPs-MWCNTs. From the TEM image, we could observe an uniform distribution of IONPs-MWCNTs in the PCLF copolymer matrix, and no serious aggregations were found.