Initiator effects in reactive extrusion of starch-polyacrylamide graft copolymers

Starch-polyacrylamide (PAAm) graft copolymers were prepared by reactive extrusion using ammonium persulfate (APS), ceric ammonium nitrate (CAN), or ferrous ammonium sulfate/hydrogen peroxide (FAS/H2O2) as initiator. The initiator contents, measured as anhydroglucose units per initiator radical (AGU/I), ranged from 70 to 280 AGU/I for CAN and FAS and 70 to 1140 for APS. CAN was not an effective initiator, giving low conversions, low graft content, low grafting efficiencies, and no detectable high molecular weight PAAm. FAS/H2O2 gave conversions of approximately 80%, graft efficiencies of approximately 50%. and PAAm molecular weights from 75,000 to 357,000, depending on the initiator content and starch/AAm ratio. APS gave conversions exceeding 90% with graft efficiencies of approximately 75%. PAAm molecular weights with APS were 575,000 and higher. As the AGU/I ratio increased above 280 for APS, the conversion and graft content decreased whereas the graft efficiency was essentially constant. Initiation with APS gave fewer PAAm grafts of higher molecular weight compared to FAS/H2O2. (c) 2005 Wiley Periodicals, Inc.