Polymerizations from the Backbone Polymers

High degrees of grafting by the free-radical mechanism can be attained when polymerizations are initiated from the backbones of the polymer. One way this can be done is to form peroxides on the backbone structures. Decompositions of such peroxides can yield initiating radicals. Half of them will be attached to the backbones. An example is the preparation of graft copolymers of polysty- 

Thermal cleavage of the above peroxides results in macromolecules with free-radicals sites. Hydroxy radicals also form and initiate formations of homopolymers. Decompositions of the peroxides by redox mechanisms, however, increase the yields of graft copolymers, but do not stop all formations of hydroxy radicals  

Air oxidation of polypropylene can result in the formation of hydroperoxide units at the sites of the tertiary hydrogens. The polymer can also be oxidized when dissolved in cumene that contains some cumene hydroperoxide at 70-80 °C. A product containing 0.8% oxygen by weight as a hydroperoxide can be formed and can subsequently be reacted to form graft copolymers. Various monomers can be used, such as vinyl acetate or 2-vinyl pyrrolidone. 

Many other hydroperoxidations of polymers were reported in the literature. The materials are used in formations of graft copolymers. One example is hydroperoxidation of poly(ethylene terephthalate) and poly(fi-caproamide). The products yield graft copolymers with various acrylic and methacrylic esters and acrylic and methacrylic acids.  

Ozone treatment of polymers can also cause hydroperoxidation of labile hydrogens. It can, however, also cause extensive degradation of the backbone polymers, because attacks by ozone on double bonds in the backbones converts them to unstable ozonides. Starch can be ozonized to form graft copolymers. The same is true of cellulose, poly(vinyl chloride), and polyethyl-ene. Hydroperoxides form without noticeable degradation. This allows subsequent preparations of graft copolymers. 

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