Graft copolymerization onto starch. II. Grafting of acrylonitrile to granular native potato starch by manganic pyrophosphate initiation. Effect of reaction conditions on grafting parameters

Abstract

SynopsisThe effect of reaction conditions on the composition of native potato starch-polyacrylonitrile graft copolymers initiated by manganic pyrophosphate onto starch slurries at 30°C has been examined.In general, when the Mn3+ ion concentration was increased from 0.15 X 10-3M to 3.0 X 10-3M (other conditions kept constant), an increase in conversion of monomer to polymer and % add-on was observed, whereas frequency of grafts (anhydroglucose units, AGU, per grafted chain) decreased. Also, the average molecular weights of grafts showed a decrease from 2.2 X lo5 to 1.5 X lo5. Increasing the concentration ratio of starch to monomer during polymerization by a factor of 3 produced an increase in the conversion of monomer to polymer, whereas an increase in frequency of grafts (AGU/chain) was obtained. Values of % add-on and average molecular weights of the grafts showed, however, a decreasing tendency. It was observed that grafting onto starch took place readily even at acid additions as low as 10 X lO-3M H&04 (pH N 1.8). Selective solvent extraction of homopolymer and extremely low conversions of monomer to polymer (0.1%1.5%) in duplicate runs without addition of starch indicated that grafting efficiencies were high in all cases. An attempt has been made to interpret the results in terms of variations in factors such as initial ratio of (Mn3+)/(AGU), termination rate of acrylonitrile chain radicals by oxidation by Mn3+ ions, oxidation rate of radicals formed on anhydroglucose units by Mn3+ ions, and physical factors such as diffusion rate of Mn3+ ions through the polyacrylonitrile-grafted starch granules for terminating the radicals.

Graft copolymerization of acrylonitrile onto Cassia tora gum with ceric ammonium nitrate–nitric acid as a redox initiator

“…The decrease beyond the amount of 4 g could be attributed to the destruction of radical activity on the backbone soon after it was formed due to the termination between backbone–backbone and backbone–primary radicals. Similar results have also been reported in the literature 3, 45, 46…”

Ceric ammonium nitrate‐initiated graft copolymerization of acrylamide onto Cassia tora gum

“…The decrease beyond the amount of 4 g may be attributed to the destruction of radical activity on the backbone soon after it is formed due to the termination between backbone-backbone and backbone-primary radicals. This result is in agreement with the results obtained in the grafting of acrylonitrile onto starch 28 and grafting of poly(acrylonitrile) onto guar gum. …”

Morphological Studies of Potato Starch Modified by Grafting Using Mn3+ as Initiator and by Saponification

“…Acrylonitrile readily graft-polymerizes onto starch with Mn3+ ion initiation [2]. The grafting ratio can be varied by changing the starchlmonomer concentration ratio [3]. This was used to synthesize starch-polyacrylonitrile graft copolymers of different composition (Table 1).…”