Redox initiators with ceric ions

Redox initiation is often an efficient method for graft polymerization. Hydroxyl-containing polymers such as cellulose and poly(vinyl alcohol) undergo redox reaction with ceric ion or other oxidizing agents to form polymer radicals capable of initiating polymerization... 

This paper summarizes chemical grafting techniques explored in this laboratory that have potential biomedical application. These reactions, initiated by ceric ions, persulfate-bisulfite redox systems, or the presence of comonomers forming donor-acceptor complexes, were carried out in an aqueous environment under conditions which, with suitable modifications, might be tolerated in vivo. Grafting onto tissue surfaces by means of ionizing radiation will not be discussed since techniques for avoiding undesirable side reactions have not yet been developed. 

There is no redox couple in solution at the start of the ferrous-ceric titration because the solution contains only Fe ". The oxidation of ferrous to ferric occurs as soon as an aliquot of ceric ions enter the solution to effect the redox reaction shown in equation (4.1). The bulk of the initially present ferrous ions remain, with the ferric products of the redox reaction residing in the same solution, i.e. a Fe " ", Fe + redox couple is formed. This couple has the electrode potential Epf + pg2+. 

The hydroxyl radicals can react with cellulose, initiating graft copolymerization, or react with monomer, resulting in homopolymerization. A similar redox system is based on the use of ceric ions, which produce radicals by direct oxidation of the cellulose chains and thus initiate graft polymerization ... 

A number of studies to determine the mechanisms of grafting onto collagen initiated by CAN, including characterization of the reaction products, have been reported (5, 8, 9, 53, 62). Ceric ammonium nitrate forms an effective redox system with alcohols, aldehydes, amines, and thiols. Alcohols form a ceric ion-alcohol complex, and the dissociation of this complex is the rate-determining step 63) ... 

Surface grafting of barium sulfate is interesting Ifom the point of view of the kinetics of such reactions. Barium sulfate like calcium carbonate, is an inert filler. So it is necessary to modify its surface. First, barium chloride is reacted with sodium sulfate in the presence of a small amount of sodium 12-hydroxystearate. This introduces a controlled number of hydroxyl stearate sites onto the barium sulfate surface. The reaction is followed by a redox graft polymerization of acrylamide initiated by the hydroxyl stearate groups and ceric ion as a catalyst. Figures 6.9 to 6.11 show the effect of reaction substrates concentrations on polymerization rate. 

Only a few of the initiators suitable for polymerizations in aqueous systems have been fully investigated recently described initiators for such systems include new redox combinations, e.g. the ceric ion with thiourea, lithium peroxydiphosphate, and various azo compounds. <... 

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