ABSTRACT:The radical graft polymerization of vinyl monomers from inorganic ultrafine particles, such as silica, titanium oxide, and ferrite, by use of azo groups introduced onto their surface was investigated. The introduction of azo groups onto the ultrafine particles was achieved by the reaction of glycidyl groups, which were introduced by the reaction of hydroxyl groups on the surface with 3-glycidoxypropyltrimethoxysilane, with 4,4'-azobis(4-cyanopentanoic acid). The amounts of azo groups introduced onto silica, titanium oxide, and ferrite were determined to be 0.07, 0.05, and 0.03 mmol g ·· 1 , respectively. The polymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and N-vinylcarbazole (NVC), was found to be initiated by radicals formed by the decomposition of the azo groups. During the polymerization, the polymer was effectively grafted onto these surfaces through propagation from the surfaces; the percentage of grafting of polyMMA onto silica, titanium oxide, and ferrite reached to 45
ABSTRACT:Recent advances in surface grafting of polymers onto carbon nanotubes (CNT) and nanofibers, such as vapor grown carbon fiber (VGCF), are reviewed. The grafting of polymers onto these surfaces was achieved by (1) the ''grafting onto'' method, (2) ''polymer reaction'' method, (3) ''grafting from'' method, and (4) ''stepwise growth'' method by dendrimer synthesis methodology. For the grafting of polymers, surface functional groups, such as carboxyl and phenolic hydroxyl groups, previously introduced onto the surface by oxidation with nitric acid, were used as grafting sites. These functional groups were converted into various initiating groups and surface initiated graft polymerization was achieved. The graphene sheet (polycondensed aromatic rings) of CNT and VGCF were used as grafting sites by using ligand-exchange reaction with polymers containing ferrocene moieties. The radical trapping nature of CNT and VGCF surface was used for the grafting of polymers. Dispersibility in solvents for good solvents of grafted polymer was remarkably improved by the surface grafting of polymers onto CNT and VGCF surfaces. The response of electric resistance of the composite prepared from polymer-grafted CNT and VGCF to solvent vapor and temperature is discussed. [DOI 10.1295/polymj.37.637] KEY WORDS Carbon Nanotube / Vapor Grown Carbon Fiber / Graphene Sheet / Surface Grafting of Polymer / Dispersibility / Composite / Electric Property / Carbon nanotubes (CNTs) are of considerable interest for applications to fabricating new engineering materials, because they have unique chemical, physical, and structure properties. 1-4 Among many different applications, a composite of CNT with polymer has been extensively investigated.4-8 The important problem for preparation of composites with polymers is the dispersion, compatibilization, and stabilization of CNT in the polymer matrices. Especially, singlewalled CNT (SW-CNT) is a strikingly inert material and usually in the form of bundles. To solve the problem, surface modification of CNT has been widely investigated. The covalent attachment of polymers, grafting of polymers, onto CNT is very effective because grafted polymers on the surface prevent the aggregation of CNT. Therefore, modification of CNT surface by grafting of polymers has been widely investigated by many researchers.Vapor grown carbon fiber (VGCF) is a new class of carbon nanofiber different from carbon nano-tube in its method of production and lower cost. It is also different from the conventional pitch-based and poly-(acrylonitrile)-based carbon fiber in nano-sized diameter. 9 VGCF is generaly by the form of annular carbon layers arranged like a tree ring structure. The carbon rods have a high aspect ratio and nano-sized diameter ranging from 50 to 200 nm, which is between those of conventional carbon fibers (5-10 mm) and of carbon nanotubes (1-50 nm).10 Due to unique physical properties, such as excellent thermal and electrical conductivity, and good mechanical behavior, VGCF is of considerable interest. 11,12 ...
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