Redox grafting reactions

In grafting reactions initiated by redox processes, there is an interaction of the intermediate products with the substrate polymer chains. There may also be a chain transfer reaction involved. It is sometimes difficult to make a clear distinction between a direct redox reaction and a chain transfer process. Three redox systems have been studied extensively in grafting onto cellulose persulfate ions 1, hydroperoxide/ferrous ions 2> 3 and cerium (IV) ions. ... 

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. 

Redox catalyzed polymerizations using ferrous ion and peroxidative compound have been reported to be usefiil for grafting reaction of natural fiber such as chitosan (79). Ascorbic acid is also used instead of the ferrous ion 80). Ascorbic acid is reported to produce activated oxygen under mild condition, and recently it is used for linear polymer synthesis of sugar alcohol derivatives containing vinyl group 81). These catalysts, which promote the reaction under... 

Grafting reactions are conventionally carried out by using the ceric ion induced redox initiation method [51, 52]. The details of the synthesis and the reaction conditions are as follows ... 

In conventional grafting procedures redox initiators are commonly used to initiate the grafting reactions. These initiators produce ions in the reaction medium which may be adsorbed at the copolymer surface to some extent. To avoid this, there has been recent interest in the use of microwave induced grafting reactions. Using microwave irradiation, methylmethacrylate (MMA) has been efficiently grafted onto Cassia marginata seed gum in the absence of... 

Redox polymerizations are among the most popular techniques for grafting reactions, and of the possible initiator systems, ferrous ion oxidation and those based on ceric ion reduction are widely used. In a redox polymerization, a hydroperoxide or similar group is reduced to a free radical plus an anion, while the metal ion is oxidized to a higher valency state, and at the same time a... 

Grafting reactions are carried out conventionally through free radical addition copolymerization mechanism, where free radicals are generated on a polymeric backbone by direct oxidation of certain transition metal ions (e.g., Ce ", Cr +, Co ). The redox... 

A typical redox system used to initiate grafting reactions is iron(II) ammonium sulfate and hydrogen peroxide. Cellulose is wetted with a solution of the iron(II) salt and dried. A hydrogen peroxide solution of monomer is brought into contact with the cellulosic product and stirred to generate radicals and grafting. The following reactions have been determined by ESR spectroscopy. 

Hritcu et al. [149] synthesized first cationic PS latexes covered with a shell-containing poly(styrene-co-2-hydroxyethyl acrylate) by a seed copolymerization procedure using an azo initiator. In the second step, grafted chains anchored to the surface were produced by polymerization of fV-(2-methoxyethyl) acrylamide (MEA), in the presence of Ce(lV) as a redox initiator. However, the percentage of MEA found covalently attached to the surface was very low because bulk MEA polymerization forming soluble polymers occurred to a much greater extent than the actual grafting reaction on the particles. 

Following the findings of Mino and Kaizerman [51] that ceric ion can form a redox system with cellulose, grafting onto various natural polymers has been carried out by the ceric ion method. In the case of cellulose, the reaction between ceric ion and cellulose occurs to produce active sites on cellulose in the following manner ... 

Metal chelates afford a better initiating system as compared to other redox systems since the reactions can be carried out at low temperatures, thus avoiding wastage reactions due to chain transfer. Homopolymer formation is also minimum in these systems. It was observed by Misra et al. [66,67] that the maximum percentage of grafting occurs at a temperature much below the decomposition temperature of the various metal chelates indicating that the chelate instead of undergoing spontaneous decomposition receives some assistance either from the solvent or monomer or from both for the facile decomposition at lower temperature. The solvent or monomer assisted decomposition can be described as ... 

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