Other Grafting Reactions

Metal ions of transition and other elements of variable valency, e.g. Ce, Co, Fe, V, Mn, etc., are known to oxidize polysaccharides rather selectively, producing macroradicals as intermediates which are capable of adding vinyl monomers and form graft copolymers. These initiators are redox systems which differ from those previously described by not producing free radicals of low molecular weight. Only macroradicals on the substrate are formed in the redox reaction. Some homopolymer may still be formed in the process, e.g. due to oxidation of monomer or other side reactions. ... 

Both Odian and Silverman models satisfactorily explain most of the observed results in all solvents (Tables I-III, VI) used in the present study, however there are some exceptions especially when solvents other than the alcohols are used (Table VI). Thus the Odian mechanism is not consistent with the DMF data nor can the Silverman model account for the acetone results. In addition, in further preliminary studies with grafting of styrene to polyethylene (10) in solvents other than those reported here both Odian and Silverman mechanisms are deficient. The problem is that possible contributions from the radiation chemistry of the components in the grafting reaction need to be considered in formulating a complete mechanism for the overall process. 

Grafted Polymers. Due to the special chain structure ABS terpoly-mers have been widely modified by grafting vinyl monomers onto the main chain. We emphasize that the method how ABS itself is obtained is addressed sometimes as grafting styrene and acrylonitrile onto a butadiene rubber. Here we focus on grafting reactions on the ABS itself. Some examples of ABS grafted polymers are shown in Table 8.7. The pending acid functionalities may be allowed to react with amines and other compounds (45). 

The samples of functionalized MTS show XRD patterns similar to those of the parent MTS, i.e., the lattice parameter a of the hexagonal array determined from dioo is unaffected by the grafting reaction and the other modifications. 

By substituting a-methyl styrene for styrene, true grafting conditions can be closely simulated without actual grafting since the radical affinity and other features of the two monomers are rather similar. In this way an approximate measure of the chain scission accompanying the grafting reaction can be made. This has been carried out (102) for the same conditions as the grafting experiments and the results are included in Table 2. It can be clearly seen that considerable chain scission occurs... 

In addition, the clear distinction between the grafting approach on one hand and co-condensation on the other hand becomes more and more blurred, because the products of co-condensation reactions are used frequently as the basis for subsequent grafting reactions or the integrated bridged organic components of PMOs are chemically modified afterwards. 

In like manner, inclusion of mineral acid in the photo-sensitised grafting of styrene in methanol to cellulose enhances the polymerisation yields significantly (Figure 2). The results obtained with phosphoric and sulfuric acids were consistent with earlier data (13,14). Dioxan is also a useful solvent for these reactions when uranyl ion is used as sensitiser. However dioxan is not as efficient as methanol for the grafting reaction. The grafting in dioxan exhibits a Trommsdorff peak at 60% monomer concentration. The results in Figure 2 also show that the unsensitised process does occur in dioxan as in other solvents, but... 

Cellulose can be replaced by starch or even proteins (Bhattacharya et al, 1997). Of course, it is possible to carry out other graft-polymerisation reactions on cellulose or starch, for instance with acrylic monomers. The obtained material is useful, but it lacks biodegradability due to the synthetic side chains. 

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