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To modify the surface of barium sulfate, the grafting of polymers onto the surface by the polymerization of acrylamide (AAm) initiated by the system consisting of ceric ion and alcoholic hydroxyl groups on the surface was investigated. Barium sulfate modified by 12-hydroxystearate (BaS0,-HS) was prepared by the reaction of barium chloride with sodium sulfate containing a small amount of sodium 12-hydroxystearate. The presence of 12-hydroxystearate groups on the BaSO, surface was confirmed by XPS analysis and infrared spectra. It was found that the graft polymerization of AAm is initiated by the system consisting of ceric ion and BaS0,-HS to give poly(AAm)-grafted BaSO,. This indicated that the grafted polymer chains are propagated from surface radicals formed by the redox reaction of ceric ion with 12-hydroxystearate groups on the surface. The polymerization rate (R,) of AAm initiated by the redox system was given by R, = k[AAm] [Ce(IV)][BaSO,-HS] where k is constant, [ A h ] is AAm concentration, [Ce(IV)] is ceric ion concentration, and [BaSO,-HS] is BaS0,-HS concentration. The result suggested that in such an initiating system, the unimolecular termination 1135

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