9 Environmentally Friendly Synthesis of Polymer-Grafted Nanoparticles
Inorganic nanoparticles such as silica, and titanium oxide, are widely used industrially as fillers and pigments for polymer materials, because inorganic nanoparticles have excellent properties such as chemical, heat and weather resistance, lightweight, thermal conductivity and low thermal expansion. On the other hand, nanocarbons, such as carbon black, nanodiamond, and carbon nanotube, are well known as one of the industrially important carbon materials. Carbon materials also have outstanding properties such as electro-conductivity, heat-resistance, biocompatibility, and chemical-resistance. Carbon nanotubes in particular have attracted attention as nanotechnology related materials. In general, dispersing inorganic nanoparticle and nanocarbons uniformly into a polymer or an organic solvent is very difficult because of aggregation. In addition, the mechanical properties of polymer composite from nanoparticles and nanocarbons are considered to depend on not only the mechanical properties of the polymer matrix but also on the properties of interfacial regions between surface of nanoparticles and matrix polymers. The chemical and physical modifications of inorganic nanoparticle and nanocarbon surfaces, therefore, have been extensively studied. The chemical modification of surfaces is permanent, but physical modification is temporary. We have pointed out that the dispersibility of silica nanoparticles and nanocarbons is extremely improved by surface grafting of polymers, namely, chemical binding of polymers, onto nanoparticle and nanocarbon surfaces (Tsubokawa, 1999; Tsubokawa, 2002; Tsubokawa, 2007). In addition grafting of polymers onto these surfaces interests us for designing new functional composite materials which have the excellent properties both of nanoparticles as mentioned above and of grafted polymers, such as photosensitivity, biorepellent activity, antibacterial activity, and pharmacological activity (Tsubokawa, 2007). We have succeeded in the grafting of various polymers such as vinyl polymer (Tsubokawa et al., 1988a; Tsubokawa et al., 1990; Fujiki et al., 1990; Tsubokawa et al., 1992a), polyester (Tsubokawa et al., 1982; Tsubokawa et al., 1983), polyether (Tsubokawa et al., 1986; Tsubokawa et al., 1988b), poly(organophosphazene) (Tsubokawa et al., 1992b), and poly(dimethysiloxane) (Tsubokawa et al., 1992c) onto silica nanoparticle and carbon black surfaces using surface functional groups as grafting sites. Furthermore, many experimental attempts by other researchers also have been made to graft polymers onto silica nanoparticle and carbon black surfaces.
Radical Grafting from Carbon Black. Graft Polymerization of Vinyl Monomers Initiated by Peroxyester Groups Introduced onto Carbon Black Surface
AbstractCarbon blacks having tert-butyl peroxyester groups (1, 2, and 3) were prepared by the reaction of acyl chloride
 
 groups on carbon black with tert-butyl hydroperoxide. The introduction of acyl chloride groups onto carbon black was achieved by three methods: (1) reaction of a carboxyl group with thionyl chloride, (2) reaction of a phenolic hydroxyl group with adipoyl chloride, and (3) reaction of thionyl chloride with a carboxyl group introduced by the treatment of aromatic ring of carbon black with 4,4′-azobis(4-cyanovaleric acid). Carbon black 1 has no ability to initiate the graft polymerization of methyl methacrylate (MMA) because phenyl radical formed on the carbon black by decomposition of the peroxyester groups inhibited the polymerization. On the contrary, carbon blacks 2 and 3 were able to initiate the graft polymerization of MMA at 70–90°C and PMMA was effectively grafted onto the surface based on the propagation of the polymer from the alkyl radicals formed on the surface. The percentage of grafting of PMMA at 70°C by use of 3 as initiator increased to about 80% with progress of polymerization. Furthermore, the graft polymerization of several vinyl monomers initiated by 3 was investigated.
An Ultrasensitive Analytical Method Based on Chemiluminescence Sensing Electrochemical Parallel Catalytic Reaction Event
An ultrasensitive electrochemiluminescence (ECL) method on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed for improving ECL analytical characteristics using vanadate(V) as a representative. Vanadate(V) could be electrochemically reduced to generate vanadate(II) which could be chemically oxidized by potassium periodate to regenerate vanadate(V) and give parallel catalytic wave effect. Then, the reduced product of potassium periodate could react with butyl-rhodamine B to emit a sensitive chemiluminescence signal. The chemiluminescence intensity was correlative with vanadate(V) concentration. The investigation on the electrochemical reaction rate constant (k0) confirmed that the speed of electrochemical reaction was faster than that of the subsequent chemiluminescence reaction. The possibility of the combination of electrochemical parallel catalytic reaction with chemiluminescence signal sensing was proved. The similar ECL behaviors could be observed at zirconia nanowires-Nafion modified electrode. Because of the separation and enrichment effect of the modified electrode on vanadate(V), the selectivity and sensitivity was further improved greatly. Based on these findings, a new concept on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed and an ultrasensitive ECL method for the determination of vanadate(V) was developed at zirconia nanowires-Nafion modified electrode. Under the optimum experimental conditions, the ECL intensity was linear with the concentration of vanadate(V) in the range of 2.0×10−12 mol/L–2.0×10−10 mol/L. The detection limit was 8.0×10−13 mol/L, which was more than 6 orders of magnitude lower than that observed by electrochemical current transduction for electrochemical parallel catalytic reaction at zirconia nanowires-Nafion modified electrode.