Synthesis of Poly(Methacrylic Acid‐)Starch Graft Copolymers Using Mn‐IV‐Acid System

When starch was treated with KMnO 4 solution, MnO 2 was deposited overall the starch. The amount of MnO 2 deposited relied on the KMnO 4 concentration. Subjecting the MnO 2 ‐containing starch to a solution consisting of monomer (methacrylic acid, MAA) and acid (citric, tartaric, oxalic or sulphuric acid) resulted in formation of poly(MAA)‐starch graft copolymer. The magnitude of grafting, expressed as meq. ‐COOH/100 g starch, was determined by amount of MnO 2 deposited, MAA concentration, temperature and duration of polymerization as well as kind and concentration of the acid. Incorporation of cations such as Fe +3 , Cu +2 and Li +1 had a significant effect on grafting. The highest extent and rate of grafting were obtained with citric acid and the least with sulphuric acid; tartaric acid stood in‐mid‐way position. The magnitude of grafting increased as the acid concentration increased till a certain concentration beyond which grafting levelled off. Similar trend was observed when the magnitude of grafting was related to the amount of MnO 2 deposited. The extent and rate of grafting increased by raising the polymerization temperature from 30° to 50°C then decreased by raising the temperature further from 60° to 70°C. On the other hand, grafting enhanced significantly by addition of Fe +3 , Cu +2 or Li +1 and followed the order Fe +3 > Cu +2 > Li +1 . A tentative mechanism for grafting of starch with MAA using MnO 2 ‐acid system was elucidated.