Kumakazu Ohkita

The reaction of carbon black surface with 2,2-diphenyl-1-picrylhydrazyl

Abstract The reaction of carbon black surface with 2,2-diphenyl-1-picrylhydrazyl (DPPH) in carbon tetrachloride has been studied. It was found that DPPH abstracts hydrogen atoms from the surface of the carbon black and gives the corresponding hydrazine (DPPH 2 ), while hydrazyl radicals were found not to bind chemically to the surface of carbon black. The amounts of DPPH reacted with carbon blacks were determined. It was found that furnace blacks modified by oxidation with agents such as hydrogen peroxide are more reactive towards DPPH than the untreated carbons. It appears to be fairly conclusive that the reaction of DPPH with carbon black can be used for determination of the number of hydroquinone groups present on the surface of carbon blacks.

The free radical polymerization of vinyl monomers in the presence of carbon black

Abstract The polymerization of vinyl monomers has been carried out in the presence of furnace blacks using initiators such as 2,2′-azobisisobutyronitrile (AIBN) and benzoyl peroxide (Bz 2 O 2 ) in nitrogen or oxygen atmosphere. The results indicate that free radicals form by the decomposition of initiators reacting with carbon blacks to give active sites on their surface which then capture either the free radicals or the growing polymer radicals. Using the monomers with negative e values, such as styrene and vinyl acetate, a marked retardation was observed in Bz 2 O 2 -initiated polymerization in the presence of furnace blacks, while a moderate inhibition was found in the polymerization initiated by AIBN. The polymerization reaction using Bz 2 O 2 was found to be very sensitive to oxygen in the presence of furnace blacks and the involvement of oxygen was found to promote grafting onto the surface of carbon black by the growing polymer radicals, consequently giving polymer-grafted particles while hindering the formation of homopolymers. Furthermore, the reaction of Bz 2 O 2 with the surface of furnace blacks in oxygen atmosphere has been studied in carbon tetrachloride at 45°C. The resulting carbon blacks show an increase in the number of surface quinone groups with an increase in reaction time.

The competitive reactions of initiator fragments and growing polymer chains against the surface of carbon black

Abstract The reactivity of free radicals generated by the thermal decomposition of 2,2′-azobisisobutyronitrile (AIBN) is compared with that of the free radicals from 2,2′-azobis-2,4-dimethyl valeronitrile in nitrogen atmosphere at 60°C, and the reaction mode of the free radicals with carbon black surface is discussed. Also bulk polymerization of vinyl monomers such as styrene and methyl methacrylate was performed in the presence of furnace black in nitrogen at 60°C using AIBN as initiator. Typical retardation is found in the course of conversion of methyl methacrylate into the polymer, whereas inhibition is observed in the conversion of styrene which results in an induction period of the reaction. In addition, inhibition by carbon black is also found in the copolymerization of methyl methacrylate with a small amount of styrene. On the basis of the results of the conversions of different kinds of monomers, competitive reactions of 2-cyano-2-propyl radicals from AIBN and growing polymer radicals are suggested to occur preferentially on the surface of carbon black. The results are supported by the observation of the stability of the dispersion of the resulting carbon black in adequate solvents and also by gas chromatographic analysis of the pyrolysis products of the polymers bound to the surface of carbon black.

The polymerization of styrene catalyzed by n-butyllithium in the presence of carbon black

Abstract The polymerization of styrene catalyzed by n-butyllithium has been carried out in the presence of carbon black at 0°C in toluene. A large portion of the catalyst was consumed by the reaction with the carbon black surface and thus the growth of polystyrene anions on the surface was hindered to a considerable extent. The typical retardation of conversion of styrene monomer to polymer does not change even in the presence of carbon black pretreated with sodium borohydride solution. The intrinsic viscosities of the homopolymers formed in the presence of carbon black were found to be higher than those of the ones formed in the absence of carbon black. On the other hand, the addition of carbon black during the anionic polymerization of styrene was found to promote grafting the growing polymer anions onto the surface of carbon black, consequently giving polymer-grafted particles, while hindering the conversion of styrene into polymer. However, little grafting was observed when the carbon black pretreated with sodium borohydride solution was used. The phenomena indicate that quinonic groups present on the surface of carbon black may be responsible for the capture of growing polymer anions.