Graft copolymers are compounds where synthetic polymers are covalently bonded to starch molecules. These are typically produced by generating free radicals from hydroxyl groups found in native or hydroxyalkylated starch molecules, followed by reaction with an unsaturated monomer. Different methods of producing starch free radicals, varying types of vinyl and acrylic monomers, mixtures of monomers, and different starches and modified starch products have been used to make a wide range of starch graft copolymers (Willett, 2008).
For instance, one commercial product is a graft copolymer of hydroxyethyl starch and styrene–butadiene latex (Nguyen, Martin, and Pauley, 1990). Other examples of products that have been produced include starch graft-polyacrylamide, -poly(acrylic acid), -polyacrylonitrile, -poly(butyl acrylate), -poly(methyl acrylate), -poly(methyl methacrylate), -polystyrene, and -poly(vinyl acetate) (Willett, 2008). Reactive extrusion is sometimes employed in the synthesis of starch graft copolymers. The uses and potential applications of some of the starch graft copolymers have been reviewed by Fanta and Doane (1986).