**2. Grafting of polymers onto GO by polymer radical trapping**

#### **2.1. Radical reactivity against aromatic compounds and nanocarbons**

It has been reported that reactivity of methyl radical to aromatic compounds increases with the increasing number of aromatic rings: the relative reactivity of methyl radical against to carbon black is ten million times of that of benzene [29]. Therefore, nanocarbons, such as carbon black, fullerene, and carbon nanotube, are known as a strong radical-trapping agent.

It is well known that radical polymerization of vinyl monomers is dramatically retarded (or inhibited) in the presence of nanocarbons, such as carbon black and carbon nanotubes. These results indicate that during the radical polymerization in the presence of nanocarbons, initiator radicals and growing polymer radicals are readily trapped by nanocarbons [29].

#### **2.2. Confirmation of radical trapping ability of GO**

mechanical, gas barrier, optical, and antibacterial properties. Therefore, a polymer composite with GO has recently attracted much interest in the materials field due to its outstanding properties [1–8]. Especially, many researchers have reported the preparation and properties of GO/chitin and GO/biopolymer composites [9–15]. For example, Travlou et al. have reported the synthesis and applications of GO/chitosan and GO/polysaccharides nanocomposites [9, 14]. It is well known that in comparison with GO/chitin nanocomposite, we can obtain GO having an excellent dispersibility into organic solvents and various polymer matrices by grafting of conventional polymers onto GO and readily obtain thermosetting, thermoplastic, and thermoelastic polymer nanocomposite thin films having electro and thermal conductivity. The surface modifications of graphene oxide (GO) by grafting of polymers via atom transfer radical polymerization (ATRP) [4–6, 16, 17] and reverse addition fragmentation chain transfer polymerization (RAFT) have been reported by many researchers [7, 8, 18]. According to the above-mentioned

However, the above graft polymerization needs the complicated treatment for the introduction of surface-initiating groups. Therefore, it is desired to develop a simple and an easy method for the grafting of polymers onto GO without complicated procedures for the intro-

On the other hand, we have also achieved the grafting of various polymers onto various nanocarbons such as carbon black, carbon nanotubes, fullerene, and nanodiamond, by "grafting from" and "grafting onto" methods [19, 20]. We have designed a simple surface grafting of various polymers onto these nanocarbons by polymer radical trapping [21, 22], ligand-exchange reaction [23, 24], surface-initiated cationic [25], and anionic graft polymerization [26]. According to the above processes, they do not require complicated process for the introduction of initiating

In this chapter, a novel and an easy grafting of polymers onto GO without complicated pretreatment by trapping of polymer radicals [27], ligand-exchange reaction of ferrocenecontaining polymer with GO [27], and simple cationic and anionic graft polymerization initiated by carboxyl groups on GO [28] are reviewed. In addition, the dispersibility of various polymer-grafted GO in several organic solvents and easy preparation of conductive

It has been reported that reactivity of methyl radical to aromatic compounds increases with the increasing number of aromatic rings: the relative reactivity of methyl radical against to carbon black is ten million times of that of benzene [29]. Therefore, nanocarbons, such as carbon black, fullerene, and carbon nanotube, are known as a strong radical-trapping agent. It is well known that radical polymerization of vinyl monomers is dramatically retarded (or inhibited) in the presence of nanocarbons, such as carbon black and carbon nanotubes.

composite gel consisting of reduced GO and polyaniline will be discussed.

**2. Grafting of polymers onto GO by polymer radical trapping**

**2.1. Radical reactivity against aromatic compounds and nanocarbons**

method, polymer brush grafted onto GO can be obtained.

groups onto nanocarbons for the graft polymerization.

duction of the initiating groups onto GO.

4 Graphene Materials - Structure, Properties and Modifications

To make sure the radical trapping activity of GO, the effect of GO on thermally initiated radical polymerization of styrene (St) at 80°C was investigated. **Figure 1** shows the result of the thermally initiated radical polymerization of St in the absence (blank) and in the presence of GO at 80°C.

As shown in **Figure 1**, it is found that the thermal radical polymerization of St is remarkably retarded in the presence of GO. It was confirmed that during polymerization, a part of polySt formed was grafted onto GO to give polySt-grafted GO (GO-*g*-polySt), although the formation of ungrafted polySt preferentially proceeded: the grafting of polySt onto GO was confirmed by GC‐MS: the percentage of polySt grafting was less than few percentage. Based on the above results, it is concluded that GO has a strong radical-trapping activity.

**Figure 1.** Thermally initiated radical polymerization of St in the absence (blank) and in the presence of GO (GO). GO, 0.10 g; St, 10.0 mL; Temp., 80°C.

#### **2.3. Grafting of PEG by radical trapping**

The grafting of poly(ethylene glycol) (PEG) onto the GO surface by trapping of PEG radicals produced by the thermal decomposition of PEG macroazo initiator (Azo-PEG) was investigated (**Scheme 1**). We used commercially available Azo-PEG [30].

**Scheme 1.** Grafting of PEG onto GO by the trapping of PEG radicals formed by thermal decomposition of Azo-PEG.

**Figure 2** shows the effect of polymerization time on the percentage of PEG grafting (percentage of grafted polymer on GO) onto the GO surface. It is found that the percentage of PEG grafting increased with the passage of the polymerization and reached over 15% after 24 h.

The grafting of PEG onto GO, on the contrary, was hardly observed when GO was reacted at room temperature, because of no decomposition of Azo-PEG for the generation of PEG radicals.

#### **2.4. Identification of PEG grafting onto GO by GC‐MS**

Identification of PEG grafting onto GO was achieved by using gas chromatogram and mass spectra (GC‐MS) of thermally decomposed gas of GO‐*g*‐PEG. The GC‐MS of PEG, GO-*g*-PEG, and untreated GO is shown in **Figures 3** and **4**. **Figure 3** clearly shows that the GC of GO-*g*-PEG agreed with that of PEG.

Furthermore, as shown in **Figure 4**, the MS of thermally decomposed gas of GO‐*g*-PEG at retention time 6.8 min was also in accord with that of PEG: the structures of fragment at 45, 59, 73, and 89 (m/z) estimated from MS database are shown in **Figure 4**.

The MS of thermally decomposed gas of GO‐*g*-PEG at other retention time was also in accord with that of PEG. These results suggested that PEG radicals, formed by the thermal

**Figure 2.** Grafting of PEG onto GO by the reaction of PEG with Azo-PEG. GO, 0.10 g; Azo-PEG, 2.00 g; toluene, 20.0 mL; Temp., 80°C.

**Figure 2** shows the effect of polymerization time on the percentage of PEG grafting (percentage of grafted polymer on GO) onto the GO surface. It is found that the percentage of PEG grafting increased with the passage of the polymerization and reached over 15% after

**Scheme 1.** Grafting of PEG onto GO by the trapping of PEG radicals formed by thermal decomposition of Azo-PEG.

The grafting of PEG onto GO, on the contrary, was hardly observed when GO was reacted at room temperature, because of no decomposition of Azo-PEG for the generation of PEG

Identification of PEG grafting onto GO was achieved by using gas chromatogram and mass spectra (GC‐MS) of thermally decomposed gas of GO‐*g*‐PEG. The GC‐MS of PEG, GO-*g*-PEG, and untreated GO is shown in **Figures 3** and **4**. **Figure 3** clearly shows that the

Furthermore, as shown in **Figure 4**, the MS of thermally decomposed gas of GO‐*g*-PEG at retention time 6.8 min was also in accord with that of PEG: the structures of fragment at 45,

The MS of thermally decomposed gas of GO‐*g*-PEG at other retention time was also in accord with that of PEG. These results suggested that PEG radicals, formed by the thermal

59, 73, and 89 (m/z) estimated from MS database are shown in **Figure 4**.

**2.4. Identification of PEG grafting onto GO by GC‐MS**

GC of GO-*g*-PEG agreed with that of PEG.

6 Graphene Materials - Structure, Properties and Modifications

24 h.

radicals.

**Figures 3.** Thermal decomposition gas chromatograms of untreated GO, GO-*g*-PEG, and PEG.

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

decomposition of Azo-PEG, are successfully captured by GO surface, and PEG is grafted (chemically bonded) onto GO.
