Effects of cumene hydroperoxide (CHPO)/tetraethylene pentarnine (TEPA), tert-butyl hydroperoxide (TBHPO)/TEPA, and potassium persulfate (K2S2O8)/Sodium thiosulfate (Na2S2O3) redox initiator on methyl methacrylate (MMA) grafted natural rubber by emulsion polymerization were investigated. The optimum reaction condition for each redox initiator on the grafting of natural rubber was studied. The grafted poly(methyl methacrylate) (PMMA) stays on the surface of rubber particles. CHPO dissolves very well in the oil phase and TBHPO dissolves moderately in the oil phase, and K2S2O8/Na2S2O3 initiation is water-soluble. Each can interact with TEPA in the aqueous phase. CHPO was found to give a higher grafting efficiency. To promote a greater grafting efficiency and yield a lower homopolymer content of PMMA, vinyl neo-decanoate (VneoD) was added. Percentages of grafting of MMA on natural rubber latex initiated by CHPO/TEPA, TBHPO/ TEPA, and K2S2O8/K2S2O3 of 84.4, 74.5, and 61.1, respectively, were in good agreement with percentages of PMMA in the aqueous phase as 7.2, 12.0, and 17.9 by CHPO, TBHPO, and K2S2O8. VneoD produces allylic radicals on polyisoprene chains, favoring the grafting reaction with other vinyl monomers. CHPO/TEPA is thus a better redox system for grafting of MMA monomer on natural rubber latex. (c) 2006 Wiley Periodicals, Inc.