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aSilica-POC, 8.8 g, vinyl monomer, 0.025 mol; temperature, 100°C

aSilica-POC, 8.8 g, vinyl monomer, 0.025 mol; temperature, 100°C

It is well known that p-toluensulfonyl and methyl iodide are able to initiate the polymerization of 2-methyl-2-oxazoline (MeOZO) [36, 37]. Therefore, we designed the graft polymerization onto silica nanoparticle surface by cationic ring-opening polymerization of MeOZO initiated by silica nanoparticle having methylsulfonyl groups and 3-iodopropyl groupsand carried out in solvent-free dry-system [38] . It is considered that polyMeOZO is grown from methoxysulfonyl and iodopropyl groups on silica nanoparticle surface to give the corresponding polymer grafted silica (Scheme 2.6).

2.3.4.1 Experimental Methods

Introduction of Methoxysulfonyl and 3-Iodoropyl Groups onto Silica Nanoparticle in Solvent-Free Dry System

The introduction of methoxysulfonyl and 3-iodopropyl groups onto silica nanoparticle surface was achieved by the treatment of surface silanol groups with 2-(4-methox-ysulfonylphenyl)ethyltrimethoxysilane and 3-iodopropyltrimethoxysilane, respectively, in solvent-free dry-system [38].

These treatments were achieved in solvent-free dry-system by the same manner as mentioned above (2.3.2.1). The resulting silica nanoparticles having methoxysulfonyl and 3-iodopropyl groups are abbreviated as Silica-SO2OMe and Silica-(CH2)3I, respectively.

Cationic Ring-Opening Graft Polymerization in Solvent-Free Dry-System

Cationic ring-opening graft polymerization of MeOZO onto silica nanoparticle surface initiated by Silica-SO2OMe and Silica-(CH2)3I in solvent-free dry-system was achieved as follows. Into a 200-mL three-necked flask (shown in Fig. 2.3) containing 4.0 g of Silica-SO2OMe (Silica-(CH2)3I), MeOZO was sprayed and the silica nanoparticle was stirred at 100 rpm at 110°C (boiling point of MeOZO) under argon gas. After the reaction, unreacted MeOZO was removed under high vacuum.

Scheme 2.6 Cationic ring-opening graft polymerization of MeOZO initiated by methylsulfonyl groups and 3-iodopropyl groups on silica nanoparticle surface

2.3.4.2 Cationic Ring-Opening Graft Polymerization of MeOZO onto Silica Nanoparticle in Solvent-Free Dry-System

Table 2.10 shows the result of the cationic ring-opening graft polymerization of MeOZO in the presence of Silica-SO2OMe and Silica-(CH2)3I in solvent-free dry-system. It was found that Silica-SO2OMe and Silica-(CH2)3I were able to initiate the cationic ring-opening polymerization of MeOZO to give polyMeOZO-grafted silica nanoparticle. PolyMeOZO grafting onto silica nanoparticle surface initiated by 3-iodopropyl group increased to nearly 100% by increasing the MeOZO monomer concentration.

This may be due to the fact that in solvent-free dry-system, the polymerization occurs on silica nanoparticle surface. Consequently, the monomer concentration of silica surface became very high in solvent-free dry-system.

On the other hand, the percentage of grafting efficiency decreased with increase in the amount of MeOZO. The results suggest that chain transfer reaction increased with increase in MeOZO monomer concentration.

Figure 2.11 shows FT-IR spectrum of untreated silica nanoparticle, polyMeOZO-grafted silica nanoparticle, and polyMeOZO. The FT-IR spectra of polyMeOZO-grafted silica show new absorptions at 1,630 cm-1, 2,860 cm-1 and 2,930 cm-1. The absorptions at 2,860 cm-1 and 2,930 cm-1 are characteristic of methylene group of polyMeOZO. The absorption at 1,630 cm- 1 is characteristic of C = O bond of polyMeOZO. These results also suggest that polyMeOZO had been grafted onto silica nanoparticle surface.

The polymerization of MeOZO onto silica surface in solvent-free dry-system was compared with that in solution. The results are shown in Table 2.11. As shown in Table 2.11, the conversion, grafting, and grafting efficiency in solvent-free dry-system were larger than those in solution. In addition, the grafting efficiency in solvent-free dry-system did not decrease with the progress of polymerization. The result suggests that in solvent-free dry-system, chain transfer reaction was depressed, because the polymerization occurs on silica nanoparticle surface.

Table 2.10 Graft polymerization of MeOZO onto silica nanoparticle surface initiated by methoxysulfonyl group and 3-iodopropyl group in solvent-free dry-system

Silica

Conversion (%)

Grafting efficiency (%)

Silicaa Silica-R-

SO2OMeb Silica-R-(CH2)3Ic Silica-R-(CH2)3Ic Silica-R-(CH2)3Ic

0 0

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