Graft copolymerization of methyl methacrylate and vinyltriethoxysilane binary monomers onto natural rubber

This work presents two different paths of graft-copolymerization of methyl methacrylate (MMA) and vinyltriethoxysilane (VTES) binary monomers onto natural rubber (NR) to prepare NR/PMMA/silica hybrid materials and investigates their properties. The first path was performed by adding VTES during graft copolymerization of MMA onto NR initiated by TBHP/TEPA initiators. The second path was carried out with two consecutive graft copolymerizations of MMA and VTES, in which VTES was grafted onto the gross NR-graft-PMMA latex. The products prepared by these two paths were denoted as NR-graft-PMMA-PVTES, NR-graft-PMMA-graft-PVTES, respectively. The formation of PMMA and silica particles were confirmed through structural characterization by NMR spectroscopy. The NR-graft-PMMA-graft-PVTES has lower MMA conversion, higher MMA grafting efficiency, and higher VTES conversion than NR-graft-PMMA-PVTES. And it has higher tensile strength, higher hardness but lower storage modulus than NR-graft-PMMA-PVTES. However, the frequency dependence of loss tangent for NR-graft-PMMA-graft-PVTES did not follow the ordinary rubber elasticity as NR and NR-graft-PMMA-PVTES did. These were due to the different morphology of PMMA and silica in the graft copolymers.