Polyacrylonitrile was grafted onto caesarweed fibers and on the allyldervative in aqueous media by ceric ion-2-mercaptoethanol redox pair. The allylfibre was obtained by treatment of caesarweed fibers with sodium hydroxide followed by allylchloride in diisoproylether to yield an average degree of substitution of 3.24 allyl moieties per anhydroglucose unit (AGU). The graft yield dependence on 2-mercaptoethanol concentration, in the range, 10.7-64.0 X 10(-4)M was characterized by a minimum followed by an enhanced yield. This suggested the existence of two initiating species, a thioglycol radical and mercaptoethoxyl radical. A fivefold increase in the concentration of 2-mercaptoethanol was accompanied by reduction in the frequency of graft, F. from 75.6-0.79 Ng/10(4) AGU and a concomitant increase, by two orders of magnitude, in the average molecular weight of grafted polymer M-upsilon, with values of up to 11.78 X 10(5). Infrared spectroscopy of allylfibre-g-polyacrylonitrile copolymer showed evidence of radical coupling reaction involving thioglycol radical species and allylic macroradicals of the allylfibre. The unmodified fiber was more reactive than the allylfibre by as much as a factor of 2, and was ascribed to resonance stabilization of allylic macro radicals derived from the latter. For the allyl fiber, a 150% increase in monomer concentration resulted in nominal increase in graft yield, not higher than 7%. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 2796-2801, 2008