The grafting of polymers onto a carbon black surface based on the trapping of polymer radicals by polycondensed aromatic rings of the surface was investigated. It was found that polymer radicals formed by the thermal decomposition of azo-polymer, peroxy-polymer and 2,2,6,6-tetramethylpiperidinyl-1-oxy-terminated polymer are successfully captured by a carbon black surface to give the corresponding polymer-grafted carbon blacks. The grafting of polymers onto carbon black was also achieved by the trapping of polymer radicals formed by the redox reaction of ceric ions with polymers having hydroxyl groups. It was concluded that surface grafting of polymers onto carbon black is effective when there are few functional groups. The electrical resistance of poly(ethylene oxide) (PEO)-grafted carbon black thus obtained is increased drastically to about 10 4-10 5 times the initial resistance at the melting point of PEO. This may be due to a widening of the gaps between the carbon black particles by melting of PEO. In addition, it was found that the electrical resistance of a crystalline poly(ethylene imine) (PEI)-grafted carbon black drastically increased to 10 3-10 4 times the initial resistance in methanol, ethanol and water vapor, but hardly any change in electrical resistance was observed in nhexane or toluene vapor. These results suggest the possibility of detecting a slight change in the crystalline structure of PEI upon absorption of solvent vapor as a large increase in the electrical resistance of the polymer-grafted carbon black.

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Grafting of Polymers onto a CarbonBlack Surface by the Trapping of Polymer Radicals. --(HAYASHI, S.; NAITOH, A.; MACHIDA, S.; OKAZAKI, M.; MARUYAMA, K.; TSUBOKAWA, N.; Appl. Organomet.

For the surface treatment of carbon black having few functional groups, the grafting of polymers through the trapping of polymer radicals by carbon black surface was investigated.Carbon black was reacted with polymers having hydroxyl groups such as poly(ethylene glycol) (PEG) in the presence of Ce(IV) in water at 25.0°C. It was found that polymer radicals formed by the redox reaction with Ce(IV) were successfully trapped by polycondensed aromatic rings of carbon black surface to give the corresponding polymer-grafted carbon black: the percentages of grafting of PEG was determined to be 49.7%. The percentage of PEG grafting tended to increase with increasing molecular weight of PEG, but the number of moles of grafted chain decreased, because of steric hindrance of grafted chains. The surface of carbon black turned from hydrophobic to hydrophilic by grafting of PEG onto the surface.