RESUMEN
Atom transfer radical polymerization with an activator regenerated by electron transfer (ATRP-ARGET) was performed for graft copolymerization of styrene onto natural rubber in the latex stage as a heterogeneous system. Deproteinized and subsequently brominated natural rubber particles in the latex stage were subjected to graft copolymerization of styrene on their surfaces in the presence of an activated ATRP catalyst. 1H NMR spectroscopy and size exclusion chromatography (SEC) characterized the particles. Ozonolysis was performed to deduct the polyisoprene contribution to SEC. Graft copolymerization in heterogeneous media by extraction with an acetone/2-butanone solution. Both the linear evolution of the molecular weight versus monomer conversion and the high grafting efficiency associated with a narrow molecular weight distribution of the resulting grafted polystyrene confirm a living radical behavior.
RESUMEN
The entropic and energetic elasticities of natural rubber with a nanomatrix structure are investigated by measuring the viscoelastic properties of deproteinized natural rubber (DPNR)-graft-polystyrene (PS). A nanomatrix structure is formed by graft copolymerization of styrene onto the surface of natural rubber particles, followed by coagulation. The morphology of the nanomatrix structure is observed with transmission electron microscopy. Natural rubber particles with about 1 µm diameter are well dispersed in a nanomatrix of PS. The horizontal shift factor (aT) and vertical shift factor (bT) are determined by superposition to create a master curve according to the time-temperature superposition principle. The positive slope of DPNR appears in the plot of bT versus temperature, suggesting that entropic elasticity occurs. In contrast, the slopes of DPNR-graft-PS are negative at lower temperatures but positive at higher temperatures. The negative slope, which suggests entropic elasticity, may be attributed to the formation of a nanomatrix structure. Natural rubber with a nanomatrix structure realizes both energetic elasticity and entropic elasticity.
