Grafting with cerium ions, initiation

A perspective method for the production of HCP was proposed by Labarre et al 92-94) [t invo]ves radical graft-copolymerization of methyl methacrylate onto heparin effected by cerium salts (Ce4+). As well as other hydroxyl-containing polymers, heparin may react with cerium ions producing free radicals which may initiate graft-copolymerization of unsaturated compounds ... 

Partial carboxymethylation of wood pulp significantly increases its susceptibility toward grafting with acrylonitrile using the ceric ion as the initiator 146]. Studies dealing with grafting of various vinyl monomers, such as acrylonitrile, methylmethacrylate, and acrylamide, onto partially carboxymethylated cotton cellulose using tetravalent cerium as the initiator have been reported [47]. 

Several natural polymers as chitin, cellulose, functionalized cellulose and natural fibers are some of most studied natural polymers in graft copolymerization using redox system as initiator, being cerium ion one with more reports. 

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. ... 

Different inorganic oxidants can react with organic molecules to generate radicals. An example of the reaction between cerium (IV) ions and an alcohol is given in Equation 3.9. Such a reaction has been used to initiate polymerisation of monomers on polysaccharides to obtain mainly graft copolymers and sometimes block copolymers (see Section 3.8). 

Cerium(I V) ions in acidic solution form chelates with the hydroxyl groups on carbons C-2 and C-3 of the anhydroglucose unit of cellulose. Transfer of electrons from cellulose to cerium(IV) gives cerium(III) which dissociates from the chelate. The anhydroglucose ring is scissioned between carbons C-2 and C-3 and a short-lived radical is formed. In the presence of monomer, grafting reactions are initiated. 

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