Caesarweed fiber, Urena lobata, was modified by successive treatment with sodium hydroxide and allylchloride in diethylether to yield an average degree of substitution of 2.73 allyl moieties per anhydroglucose unit. The presence of allyl moieties on the fiber was confirmed by infrared spectroscopy. Graft copolymerization of acrylonitrile onto the unmodified and allyl-modified fibers was initiated by potassium permanganate -N,N'-dimethylacetamide redox pair in aqueous medium. The allyl fiber was markedly less reactive than the unmodified fiber with graft yields for the latter a factor of 2.3 higher than those of the former. This was attributed to resonance stabilization of allylic macroradicals of the fiber. The graft yield showed positive dependence on N,N'-dimethylacetamide concentration in the range, 9.0-45.0 x 10(-4)M with P-g/P-go of up to 1.39 at the highest concentration. The conversion in graft yield was however characterized by a plateau at the latter concentration and was ascribed to termination of grafted polymer chains by methylacetylaminomethyl radical initiating species. Spectroscopic evidence in support of the latter was the absorption peak at 1680 cm(-1) for the graft copolymers, characteristic of C=O stretching vibration for tertiary amide. Acetic acid, at concentrations in the range 0.28-2.22M, was inimical to grafting of acrylonitrile onto allylfibre with P-g/P-go, of less than one. Grafting onto allylfiber showed positive temperature dependence in the range, 30-50 degrees C with calculated activation energy of 12.3 kcal mol(-1) for the graft polymerization reaction. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 2671-2675, 2008