Graft polymerization of vinyl monomers onto starch by use of tetravalent cerium

Grafting of acrylonitrile onto starch showed slightly higher yields when using soluble rather than insoluble starch, for reaction times < 1.5 hr. Beyond this time, the rate of grafting onto the soluble starch levels off, while that for grafting onto the insoluble starch proceeds leading to prograssive increase in the grafting yield. Momomer reactivity was in the following order: acrylonitrile > ethyl acrylate? methyl methacrylate. For the first two monomers, the order of reactivity is the reverse of that found for grafting onto cellulose; extremely low grafting yields resulted from grafting of ethyl acrylate rather than acrylonitrile onto starch. This result was attributed to the jelly nature of the polyethyl acrylate grafted starch, preventing diffusion of the monomer into the starch granules. This view was supported by the higher consumption of ceric ions at the start of the reaction, on grafting ethyl acrylate instead of acrylonitrile. As the reaction proceeds, the reverse takes place. Increase of ceric salt concentration, as well as the liquor to starch ratio, led to increased grafting yields.