Surface Grafting onto Barium Sulfate: Polymerization of Acrylamide Initiated by the System Consisting of Alcoholic Hydroxyl Groups on the Surface and Ceric Ion

Abstract

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 eerie ion and alcoholic hydroxyl groups on the surface was investigated. Barium sulfate modified by 12-hydroxystearate (BaSO₄-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 BaSO₄ 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 eerie ion and BaSO₄-HS to give poly (AAm)-grafted BaSO₄. This indicated that the grafted polymer chains are propagated from surface radicals formed by the redox reaction of eerie ion with 12-hydroxystearate groups on the surface. The polymerization rate (R _p) of AAm initiated by the redox system was given by R _p = kAAm]Ce(IV)]BaSO₄-HS] where k is constant, AAm] is AAm concentration, Ce(IV)] is cerie ion concentration, and BaSO₄-HS] is BaSO₄-HS concentration. The result suggested that in such an initiating system, the unimolecular termination of growing polymer radicals from the surface of BaSO₄ proceeds preferentially. Furthermore, by grafting of poly(AAm) onto the BaSO₄-HS surface, the wettability of the surface was found to turn from hydrophobic to hydrophilic.