Graft copolymers of natural rubber and poly (methyl methacrylate) (NR-g-PMMA) were prepared in a laboratory scale, and then extended to a pilot scale production. Reaction. conditions were first assessed based on a preparation in the laboratory scale with a reactor capacity of 1.51. An optimum grafting efficiency was obtained when cumene hydroperoxide/tetraethylenepentamine (CHP/TEPA) redox initiator was used at the reaction temperature and time of 50 degrees C and 3 h, respectively. MMA monomer was used without purification in the polymerization process comparing with the purified one by means of extraction. It was found that only a slight decrease of grafting efficiency was observed when the nonpurified monomer was used in the reaction. The nonpurified monomer was therefore used to prepare the NR-g-PMMA in a pilot scale production with a reactor capacity of 260 L. Various weight ratios of NR/MMA at 50/50, 60/40, 70/30, and 85/15 were studied. The resulting graft copolymers were characterized by FTIR and H-1-NMR techniques. It was found that increasing concentration of MMA caused an increase of free PMMA (i.e., homopolymer) but a decrease of free NR (i.e., ungrafted NR) and grafting efficiency. Quantity of grafted PMMA on the NR backbone was estimated using the integrated peak areas of 1H-NMR spectra and quantitative analysis by extraction method. The results were found to be in good agreement. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 587-597, 2009