**4. Cationic polymerization of vinyl monomers initiated by carboxyl groups on GO**

#### **4.1. Acidity of carboxyl groups on nanocarbons**

We have pointed out that carboxyl (COOH) groups on nanocarbons, such as carbon black and vapor grown carbon fiber, have strong acidity, because of the effect of neighboring hydroxyl groups (*ortho*‐effect) and have an ability to initiate the cationic polymerization of vinyl monomers to give the corresponding polymer-grafted nanocarbons.

For example, COOH groups on nanocarbons, such as carbon black and vapor grown carbon fiber, have strong acidity to initiate the cationic polymerization of vinyl monomers, such as vinyl ethers and *N*‐vinylcarbazole (NVC) [25]. During the polymerization, the corresponding polymers were grafted onto these nanocarbon surfaces, based on the termination of growing polymer cation with surface carboxylate groups on GO as a counter anion.

#### **4.2. COOH initiated cationic polymerization and grafting**

The content of COOH and hydroxyl groups of GO used was determined to be 4.0 and 0.5 mmol/g, respectively. The content of COOH groups on GO used is much larger than those of acidic carbon black; for example, the content of COOH groups on channel black FW 200 (Deggusa AG.) is 0.61 mmol/g [28]. Therefore, it is expected that COOH groups on GO act as an effective initiator of the cationic polymerization of NVC, as shown in **Scheme 3**.

**Figure 8** shows the relationship between conversion of NVC and reaction time during the polymerization of NVC in the presence of GO. As shown in **Figure 8**, the polymerization of NVC is successfully initiated even at 0°C and conversion of NVC increased with increasing reaction time and reached 95% after 12 h.

**Figure 9** shows the FT‐IR spectra of (A) polyNVC, (B) GO obtained from the cationic polymerization in the presence of GO, and (C) ungrafted GO. The FT-IR spectra of GO obtained from the polymerization in the presence of GO show characteristic absorptions of polyNVC. The result shows the grafting of polyNVC onto GO during the GO‐initiated cationic polymerization of NVC.

**Figure 10** shows the relationship between the percentage of polyNVC grafting onto GO and reaction time during the above-cationic polymerization. It was found that polyNVC was grafted onto GO, during the polymerization, and the percentage of grafting increased with increasing reaction time: the percentage of polyNVC grafting reached 14% after 12 h.

**Figure 11** shows the relationship between conversion of isobutyl vinyl ether (IBVE) and reaction time during the GO‐initiated cationic polymerization of IBVE. The conversion of IBVE increased with increasing reaction time and reached 78% after 1.5 h. The result indicates that GO also has an ability to initiate the cationic polymerization of IBVE.

**Scheme 3.** Cationic polymerization of vinyl monomers initiated by COOH groups on GO.

**4. Cationic polymerization of vinyl monomers initiated by carboxyl** 

**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.

vinyl monomers to give the corresponding polymer-grafted nanocarbons.

polymer cation with surface carboxylate groups on GO as a counter anion.

**4.2. COOH initiated cationic polymerization and grafting**

We have pointed out that carboxyl (COOH) groups on nanocarbons, such as carbon black and vapor grown carbon fiber, have strong acidity, because of the effect of neighboring hydroxyl groups (*ortho*‐effect) and have an ability to initiate the cationic polymerization of

For example, COOH groups on nanocarbons, such as carbon black and vapor grown carbon fiber, have strong acidity to initiate the cationic polymerization of vinyl monomers, such as vinyl ethers and *N*‐vinylcarbazole (NVC) [25]. During the polymerization, the corresponding polymers were grafted onto these nanocarbon surfaces, based on the termination of growing

The content of COOH and hydroxyl groups of GO used was determined to be 4.0 and 0.5 mmol/g, respectively. The content of COOH groups on GO used is much larger than

**groups on GO**

**4.1. Acidity of carboxyl groups on nanocarbons**

12 Graphene Materials - Structure, Properties and Modifications

**Figure 8.** The relationship between conversion and polymerization time during the cationic polymerization of NVC initiated by COOH groups on GO. GO, 0.10 g; NVC, 1.0 g; toluene, 10 mL; Temp., 0°C.

**Figure 9.** FT‐IR spectra of (A) polyNVC obtained from the conventional cationic initiator, (B) GO obtained from the cationic polymerization of NVC in the presence of GO, and (C) ungrafted GO.

**Figure 10.** Relationship between percentage of polyNVC grafting onto GO and reaction time. Reaction conditions are shown in **Figure 8**.

**Figure 11.** Cationic polymerization of IBVE initiated by COOH groups on GO. GO, 0.10 g; IBVE, 1.0 mL; toluene, 9.0 mL; Temp., 0°C.

**Figure 9.** FT‐IR spectra of (A) polyNVC obtained from the conventional cationic initiator, (B) GO obtained from the

**Figure 8.** The relationship between conversion and polymerization time during the cationic polymerization of NVC

initiated by COOH groups on GO. GO, 0.10 g; NVC, 1.0 g; toluene, 10 mL; Temp., 0°C.

14 Graphene Materials - Structure, Properties and Modifications

cationic polymerization of NVC in the presence of GO, and (C) ungrafted GO.

#### **4.3. Identification of polyIBVE grafting onto GO by GC‐MS**

The thermal decomposition GC of GO-*g*‐polyIBVE, polyIBVE, and ungrafted GO is shown in **Figure 12(A)**. The thermal decomposition gas of GO-*g*‐polyIBVE at retention time 1.2 min agreed with that of polyIBVE. On the other hand, the MS of thermally decomposed gas of polyIBVE and GO‐*g*‐polyIBVE at retention time 1.2 min is shown in **Figure 12(B)**. **Figure 12(B)** clearly shows that the MS of decomposed gas of GO‐*g*‐polyIBVE at retention time 1.2 min was in accord with that of polyIBVE: the parent peak at 74 (m/z) is considered to be isobutyl alcohol formed by the thermal decomposition of IBVE. The above results clearly indicate the grafting of polyIBVE onto GO during the GO‐initiated cationic polymerization.

In addition, the GO‐initiated polymerization of NVC and IBVE was completely inhibited by the addition of base, such as amines, indicating the initiation and propagation of the polymerization proceeded cationic polymerization mechanism.

#### **4.4. Initiation and grafting mechanism**

It is presumed that the cationic polymerization was initiated by proton addition of COOH groups on GO to vinyl monomer, as shown in **Scheme 4** (1) and then polymer chains propagated from carboxylate (COO- ) groups on GO as a counter anion, as shown in **Scheme 4** (2). The grafting of the corresponding polymer onto GO is considered to be termination (neutralization) grafting reaction of propagating polymer cation with carboxylate anion (counter ion) on GO, as shown in **Scheme 4** [25, 28].

**Figure 12.** (A) Thermal decomposition GC of GO-*g*‐polyIBVE, polyIBVE, and GO. (B) MS of thermal decomposition gas of GO-*g*‐polyIBVE and polyIBVE at retention time 1.2 min.

**4.3. Identification of polyIBVE grafting onto GO by GC‐MS**

16 Graphene Materials - Structure, Properties and Modifications

erization proceeded cationic polymerization mechanism.

**4.4. Initiation and grafting mechanism**

of GO-*g*‐polyIBVE and polyIBVE at retention time 1.2 min.

polymerization.

carboxylate (COO-

in **Scheme 4** [25, 28].

The thermal decomposition GC of GO-*g*‐polyIBVE, polyIBVE, and ungrafted GO is shown in **Figure 12(A)**. The thermal decomposition gas of GO-*g*‐polyIBVE at retention time 1.2 min agreed with that of polyIBVE. On the other hand, the MS of thermally decomposed gas of polyIBVE and GO‐*g*‐polyIBVE at retention time 1.2 min is shown in **Figure 12(B)**. **Figure 12(B)** clearly shows that the MS of decomposed gas of GO‐*g*‐polyIBVE at retention time 1.2 min was in accord with that of polyIBVE: the parent peak at 74 (m/z) is considered to be isobutyl alcohol formed by the thermal decomposition of IBVE. The above results clearly indicate the grafting of polyIBVE onto GO during the GO‐initiated cationic

In addition, the GO‐initiated polymerization of NVC and IBVE was completely inhibited by the addition of base, such as amines, indicating the initiation and propagation of the polym-

It is presumed that the cationic polymerization was initiated by proton addition of COOH groups on GO to vinyl monomer, as shown in **Scheme 4** (1) and then polymer chains propagated from

of the corresponding polymer onto GO is considered to be termination (neutralization) grafting reaction of propagating polymer cation with carboxylate anion (counter ion) on GO, as shown

**Figure 12.** (A) Thermal decomposition GC of GO-*g*‐polyIBVE, polyIBVE, and GO. (B) MS of thermal decomposition gas

) groups on GO as a counter anion, as shown in **Scheme 4** (2). The grafting


**Scheme 4.** Initiating and grafting mechanism of cationic polymerization of vinyl monomers initiated by COOH groups on GO.
