**3. Grafting of polymers onto GO by ligand‐exchange reaction with ferrocene**

#### **3.1. Ligand‐exchange reaction of ferrocene with graphene structure of nanocarbons**

Morrison et al. reported that the *h*<sup>6</sup> -benzene-*h*<sup>5</sup> -cyclopentadienyliron cation could be readily prepared by the ligand-exchange reaction of ferrocene with benzene in the presence of AlCl3 and Al powders as the catalysts [31, 32]. Furthermore, Miyake et al. reported that the ligand-exchange reaction is successfully applied for the introduction of functional groups to graphene structure of various carbon materials [32]. We have reported the grafting of polymers by ligand-exchange reaction of ferrocene moieties of polymers with graphene structure of carbon black, carbon fiber, and carbon nanofibers [23, 24]. Therefore, we designed the grafting of poly(Vf-*co*‐MMA) onto GO surfaces by ligand‐exchange reaction between ferrocene moieties of poly(Vf-*co*‐MMA) and polycondensed aromatic rings of the GO surface, as shown in **Scheme 2**.

#### **3.2. Preparation of poly(Vf‐***co***‐vinyl monomer) and characterization**

Ferrocene containing copolymer of vinyl ferrocene (Vf) with methyl methacrylate (MMA) [poly(Vf-*co*‐MMA)] and styrene (St) [poly(Vf‐*co*-St)] was prepared by the copolymerization of the corresponding monomers, using 4,4'‐azobisisobutylonitrile (AIBN) as an initiator.

**Table 1** shows the number-average molecular weight (*M*<sup>n</sup> ) and molecular weight distribution (*M*w*/M*<sup>n</sup> ), which are determined by SEC, Vf contents of poly(Vf-*co*‐MMA), and poly(Vf‐*co*-St), which are determined by elemental analysis, and are also shown in **Table 1**. As shown in **Table 1**, it is found that *M*w*/M*<sup>n</sup> of these copolymers prepared by the conventional radical copolymerization by using AIBN as an initiator is considerably narrow. The content of vinyl ferrocene (Vf) moieties of poly(Vf-*co*‐MMA) and poly(Vf‐*co*-St) is estimated to be 9.3 and 6.3%, respectively. 1 H‐NMR and FT‐IR are used to confirm the structures of poly(Vf‐*co*‐MMA) and poly(Vf‐*co*-St).

#### **3.3. Grafting of poly(Vf‐***co***‐MMA) and poly(Vf‐***co***‐St) onto GO by ligand‐exchange reaction**

The results of the grafting reaction of poly(Vf-*co*‐MMA) with GO surface under several conditions are shown in **Table 2**. No grafting of the copolymer onto GO surface was hardly observed, even if, GO was reacted (heated) with poly(Vf-*co*‐MMA) in 1,4dioxane in the absence of AlCl<sup>3</sup> and Al powders as a catalyst at 80°C for 24 h (Run 1). In addition, no grafting of the copolymer onto GO proceeded in the presence of Al powder alone (Run 2).

**Scheme 2.** Grafting of poly(Vf-*co*‐MMA) and poly(Vf‐*co*-St) onto GO by ligand-exchange reaction of these copolymers with polycondensed aromatic rings of the surface.


**Table 1.** Molecular weight, molecular weight distribution, and Vf content of Vf copolymers.

decomposition of Azo-PEG, are successfully captured by GO surface, and PEG is grafted

**3. Grafting of polymers onto GO by ligand‐exchange reaction with** 

**Figure 4.** Mass spectra of decomposed gas of GO‐*g*-PEG and PEG at retention time 6.8 min.

**3.1. Ligand‐exchange reaction of ferrocene with graphene structure of nanocarbons**


ily prepared by the ligand-exchange reaction of ferrocene with benzene in the presence of

 and Al powders as the catalysts [31, 32]. Furthermore, Miyake et al. reported that the ligand-exchange reaction is successfully applied for the introduction of functional groups to graphene structure of various carbon materials [32]. We have reported the grafting of polymers by ligand-exchange reaction of ferrocene moieties of polymers with graphene structure of carbon black, carbon fiber, and carbon nanofibers [23, 24]. Therefore, we designed the grafting of poly(Vf-*co*‐MMA) onto GO surfaces by ligand‐exchange reaction between ferrocene moieties of poly(Vf-*co*‐MMA) and polycondensed aromatic rings of the


(chemically bonded) onto GO.

8 Graphene Materials - Structure, Properties and Modifications

Morrison et al. reported that the *h*<sup>6</sup>

GO surface, as shown in **Scheme 2**.

**ferrocene**

AlCl3

On the other hand, the grafting reaction successfully proceeded in the presence of AlCl3 alone (Run 3). In the coexistence of AlCl3 and Al powders, the grafting of poly(Vf-*co*‐MMA) successfully proceeded and the percentage of grafting reached 54.1% after 24 h (Run 4). These results indicate that AlCl3 receives cyclopentadien of ferrocene, and after the grafting of the copolymers onto GO, iron in ferrocene moiety exists in reduced form, because it is reported that Al powder prevents ferrocene from being oxidized to ferrocenium cation [32].

**Figure 5** shows the relationship between reaction time and percentage of grafting during the ligand-exchange reaction of GO with poly(Vf-*co*‐MMA) at 80°C. The percentage of poly(Vf-*co*‐MMA) grafting increased with progress of the reaction and reached 54.2% after 24 h, but no longer increased after 24 h. This may be due to the fact that GO surface was blocked by previously grafted poly(Vf-*co*‐MMA) chains.


*Note*: GO, 0.05 g; poly(Vf-*co*‐MMA), 0.05 g; 1,4‐dioxane, 10.0 mL, Temp., 80°C; 24 h.

**Table 2.** Effect of catalyst on the grafting of poly(Vf‐*co*‐MMA) onto GO by ligand‐exchange reaction.

**Figure 5.** Grafting of poly(Vf-*co*‐MMA) onto GO by ligand‐exchange reaction of poly(Vf‐*co*‐MMA) with GO. GO, 0.05 g; poly(Vf-*co*‐MMA), 0.05 g; AlCl<sup>3</sup> , 0.70 mmol; Al powder, 0.18 mmol; 1,4-dioxane, 10.0 mL; Temp., 80°C.

The grafting of poly(Vf-*co*-St) onto GO was also achieved by the ligand-exchange reaction of the corresponding copolymer with GO: the percentage of poly(Vf-*co*-St) grafting was determined to be 61.1%.

The mole number of grafted poly(Vf-*co*‐MMA) and poly(Vf‐*co*-St) on GO was estimated to be 4.2 × 10⁻ 5 and 3.0 × 10⁻ 5 mol/g, respectively. This may be due to the fact that the ferrocene content of poly(Vf-*co*-St) is smaller than that of poly(Vf-*co*‐MMA).

#### **3.4. Identification of poly(Vf‐***co***‐MMA)‐grafted GO by GC‐MS**

The GC of thermally decomposed gas of untreated GO, GO-*g*-poly(Vf-*co*‐MMA) and poly(Vf-*co*‐MMA) is shown in **Figure 6**. It was observed that the generation of same thermally decomposed gas was generated at retention time 5.8 min. However, the small difference in thermal decomposition GC between poly(Vf‐*co*‐MMA) and GO‐*g*-poly(Vf*co*‐MMA) was observed. The same results were reported in the case of poly(Vf‐*co*‐MMA)‐ grafted vapor grown carbon fiber and carbon black [17]. It can be presumed that that poly(Vf-*co*‐MMA) was grafted by coordinate bonds with graphene structure of GO, as shown in **Scheme 2**.

The MS of decomposed gas of GO‐*g*-poly(Vf-*co*‐MMA) and poly(Vf‐*co*‐MMA) at retention time 5.8 min is shown in **Figure 7**. As shown in **Figure 7**, the MS of decomposed gas of GO-*g*-poly(Vf-*co*‐MMA) was also in accord with that of poly(Vf‐*co*‐MMA): the structure of fragments at 56, 65, and 91 (m/z) estimated from MS database are also shown in **Figure 7**. These results clearly indicate that poly(Vf-*co*‐MMA) was successfully grafted onto GO, and poly(Vf-*co*‐MMA) was immobilized by coordinate bonds between the graphene structure of GO and the ferrocene moiety of poly(Vf-*co*‐MMA) as mentioned above.

**Figure 6.** Thermal decomposition gas chromatograms of poly(Vf-*co*‐MMA), GO‐*g*-poly(Vf-*co*‐MMA) and untreated GO.

**Figure 5.** Grafting of poly(Vf-*co*‐MMA) onto GO by ligand‐exchange reaction of poly(Vf‐*co*‐MMA) with GO. GO, 0.05 g;

On the other hand, the grafting reaction successfully proceeded in the presence of AlCl3

successfully proceeded and the percentage of grafting reached 54.1% after 24 h (Run 4). These

copolymers onto GO, iron in ferrocene moiety exists in reduced form, because it is reported

**Figure 5** shows the relationship between reaction time and percentage of grafting during the ligand-exchange reaction of GO with poly(Vf-*co*‐MMA) at 80°C. The percentage of poly(Vf-*co*‐MMA) grafting increased with progress of the reaction and reached 54.2% after 24 h, but no longer increased after 24 h. This may be due to the fact that GO surface was

that Al powder prevents ferrocene from being oxidized to ferrocenium cation [32].

**Run Catalyst Grafting (%)**

**Table 2.** Effect of catalyst on the grafting of poly(Vf‐*co*‐MMA) onto GO by ligand‐exchange reaction.

1 – – 0 2 – 1.8 0 3 7.0 – 21.0 4 7.0 1.8 54.1

*Note*: GO, 0.05 g; poly(Vf-*co*‐MMA), 0.05 g; 1,4‐dioxane, 10.0 mL, Temp., 80°C; 24 h.

 **(10‐4 mol) Al powder (10‐4 mol)**

and Al powders, the grafting of poly(Vf-*co*‐MMA)

receives cyclopentadien of ferrocene, and after the grafting of the

alone (Run 3). In the coexistence of AlCl3

10 Graphene Materials - Structure, Properties and Modifications

blocked by previously grafted poly(Vf-*co*‐MMA) chains.

**AlCl3**

results indicate that AlCl3

, 0.70 mmol; Al powder, 0.18 mmol; 1,4-dioxane, 10.0 mL; Temp., 80°C.

poly(Vf-*co*‐MMA), 0.05 g; AlCl<sup>3</sup>

**Figure 7.** Mass spectra of decomposed gas of poly(Vf‐*co*‐MMA) and GO‐*g*-poly(Vf-*co*‐MMA) at retention time 5.8 min.
