Graft Copolymerization of Methyl Methacrylate on to Natural Rubber: Effect of Polymerization Conditions on Particle Morphology

This article describes the graft copolymerization of methyl methacrylate (MMA) on to natural rubber (NR) by emulsion polymerization using cumene hydroperoxide and tetraethylene pentamine as redox initiators in NR latex. The effect of surfactants, cross-link density of NR, NR/MMA ratio, and mode of addition of monomer on particle morphology is investigated by a transmission electron microscope (TEM). The percent grafting increases with the increasing MMA content while the grafting efficiency decreases. Secondary nucleation of poly(methyl methacrylate) (PMMA) is observed when oleic acid is used as a surfactant, while sodium dioctyl sulphosuccinate (SDSS) and nonionic nonyl phenol poly(ethylene oxide), give core-shell morphology. In all the samples, the smaller rubber particles are heavily coated with PMMA while the larger particles are coated only at higher MMA content. At a given feed rate of the monomer, higher cross-link density of NR results in a more uniform shell. Ultramicrotomed sections of the latex particles show an interpenetrating network-like structure.