IMPROVED SYNTHESIS OF POLY(MAA)-STARCH GRAFT-COPOLYMERS

Graft copolymerization of methacrylic acid (MAA) onto starch using a p otassium persulfate/sodium thiosulfate redox initiation system was inv estigated. Emphasis was placed on the promotion of graft formation whi le minimizing homopolymerization. This could be achieved through a tho rough investigation into the major factors affecting the polymerizatio n reaction such as the state of the starch, redox ratio of the initiat or, monomer and initiator concentrations, time and temperature of poly merization, and material-to-liquor ratio. The results obtained imply t hat the magnitude of the polymer yield including total conversion, gra ft yield, and homopolymer are determined by these factors. The yield i s favored under the influence of higher temperature, longer time, shor t liquor, and increased monomer and initiator concentrations. A poly(M AA)-starch graft copolymer is the main product of the polymerization r eactions only when starch was preswelled (through cooking prior to gra fting). Moreover, this grafted product could be precipitated by more d ilution with water and easily separated by filtration. Hence, the resu lts of the current work formed the basis of a novel method for the syn thesis of poly(MAA)-starch graft copolymers. The mechanisms involved i n the synthesis are reported. (C) 1998 John Wiley & Sons, Inc.