Synthesis and Processing of Graft Copolymers from Cornstarch and Methyl Acrylate: Physical and Mechanical Properties

Starch‐g‐poly(methyl acrylate) (S‐g‐PMA), containing 40‐65% PMA, was prepared with ceric ammonium nitrate (CAN) initiation in a 2‐gallon reactor. CAN initiator was added either in one portion or portionwise. Graft copolymers were characterized with respect to % acetone‐extractable polymer (largely PMA homopolymer), PMA content of the graft copolymer, and Mw of PMA grafts. Normal cornstarch as well as waxy and high amylose cornstarches were used in the grafting reaction. Conversions of monomer to polymer were nearly quantitative. Continuous plastic ribbons for tensile testing were prepared by extrusion processing. Tensile properties varied with the method used for CAN addition (i. e., single portion vs. portion‐wise) and depended upon the particular starch variety used in the graft polymerization reaction. Since water acts as a plasticizer for starch, samples extruded at high moisture content exhibit higher % elongation (%E) values than the same polymers extruded at low moisture. Values for %E also increase with higher percentages of PMA in the graft copolymer.