Redox grafting

Thermoplasticization of Wood by Heterogeneous Graft Copolymerization (Redox Initiation). A redox grafting method using ferrous sulfate-hydrogene peroxide as the initiator was conducted to copolymerize MMA to wood meal. The results of grafting are shown in Table III. 

Table III. Redox Graft Copolymerization of MMA onto Wood Using Ferrous Sulfate - Hydrogen Peroxide as an Initiator...

Figure 6. Plots of the deformation vs. temperature for W-O, untreated wood and PW—2—PW—8, the wood-PMMA composites prepared by the redox grafting...

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. 

Chernyy, S., K. Torbensen, J. Iruthayaraj, S. U. Pedersen, and K. Daasbjerg. Elucidation of the mechanism of redox grafting of diazotated anthraquinone. Langmuir 28, 2012 9573-9582. 

Grafting by chain transfer other than redox system. 

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 ... 

Misra et al. have utilized the ceric-amine redox system for grafting MM A onto wool [60] and gelatin [61], The graft yield was explained in terms of basicity, nu-cleophilicity, and steric requirements of amines. A complex of ceric ion and amine (AH) decomposes to generate free radical species, which produce additional active sites onto the polymeric backbone where grafting can occur. 

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 ... 

In aqueous solutions the persulphate ion is known as a strong oxidizing agent, either alone or with activators. Thus, it has been extensively used as the initiator of vinyl polymerization [43-47]. However, only later, Kulkarni et al. [48] reported the graft copolymerization of AN onto cellulose using the Na2S203/K2S20s redox system. 

The presence of sulphonic and carboxylic groups enables the iron ions to be in the vicinity of the cellulose backbone chain. In this case, the radicals formed can easily attack the cellulose chain leading to the formation of a cellulose macroradical. Grafting of methyl methacrylate on tertiary aminized cotton using the bi-sulphite-hydrogen peroxide redox system was also investigated [58]. 

To sum up, the optimum conditions for methylmethacrylate grafting onto pulp by the ceric ion redox system can be summarized as follows the grafting is done at 30°C for a 1-h reaction time, using liquor ratio 40 1, acid concentration 1%, initiator concentration 0.1%, and monomer 1 mL/g pulp. 

D. Grafting of Cellulose by Using KBrOs or KMn04 Redox System... 

Graft Copolymerization of Vinyl Monomers Onto Macromolecules Having Active Pendant Group via Ceric Ion Redox or Photo-Induced Charge-Transfer Initiation... 

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