The effect of redox initiator on graft copolymerization of methyl methacrylate onto natural rubber

Abstract

This research investigated the effect of redox initiator on natural rubber graft methyl metacrylate by emulsion polymerization. Three different types of redox initiator namely cumene hydroperoxide (CHPO)/tetraethylene pentamine (TEPA), tert-butyl hydroperoxide (TBHPO)/TEPA, and potassium persulfate (K2S2O3)/sodium thiosulfate (Na2 S2 O3). The optimum reaction condition for each redox initiator on grafting of natural rubber was studied. Functional groups of grafted natural rubber by FT-IR and NMR, molecular weights and their distribution by GPC, thermal properties by DSC, and morphology by TEM were carried out. It was found that the polyZmethyl methacrylate) graft copolymerization resides on the surface of rubber particles. CHPO dissolves very well in the oil phase, and TBHPO dissolves moderately in the oil phase as well. Each can interact with TEPA in aqueous phase. CHPO was found to give a higher grafting efficiency. K2S2O8 /Na2S2O3 is water-soluble initiator. To promote a greater grafting efficiency and lower homopolymer content of poly (methy methacrylate) in the aqueous phase, vinyl neo-decanoate (VneoD), a grafting promoter was then added in the latter. It was found that the percentages of grafting on methyl methacrylate on natural rubber latex initiated by CHPO, TBHO, and K2 S2 O8 are 84.4, 74.5, and 61.1, respectively, which are in good agreement with percentages of poly(methyl methacrylate) formed in the aqueous phase as 7.2, 12.0, and 17.9 By CHPO, TBHPO, and K2 S2 O8.. The role of added VneoD is to produce allylic radicals on polyisoprene chains that favor the grafting reaction with other vinyl monomers. This research concludes that CHPO/TEPA is a good redox system for grafting of vinyl monomers on natural rubber latex. Additionally, this research also describes the reaction mechanism that promotes such a graft copolymerization.