Natural rubber with filler nanomatrix structure was prepared by forming chemical linkages between natural rubber particles and filler nanoparticles. The filler nanomatrix structure was formed by graft copolymerization of vinyltriethoxysilane (VTES) onto natural rubber particles in the latex stage followed by casting of the latex to prepare an as-cast film. The silica nanoparticles were produced during the graft copolymerization through hydrolysis and condensation, i.e., sol-gel reaction; hence, they linked to the natural rubber particles. The nanomatrix structure was observed by transmission electron microscopy, in which the natural rubber particles of about 1 μm in diameter were well dispersed in the filler nanomatrix. Tensile properties were significantly improved by forming filler nanomatrix structure. The loss modulus and loss tangent of the natural rubber with the filler nanomatrix structure were almost independent of deformation frequency in the rubbery plateau region, which was explained to be due to the energetic elasticity and entropic elasticity characteristic of the nanomatrix structure.

Fresh NR was adopted to prepare rubber with a nanomatrix structure. The nanomatrix structure was formed by graft-copolymerization of styrene onto deproteinized fresh NR (fresh DPNR) in the latex stage using tert-butyl hydroperoxide/tetraethylenepentamine as an initiator. Graft-copolymer consisting of fresh DPNR and polystyrene (fresh DPNR-graft-PS) was characterized by 1H-NMR spectroscopy and transmission electron microscopy. Under a suitable condition of the graft-copolymerization, conversion and grafting efficiency of styrene was 98 and 80 mol%, respectively. Morphology of fresh DPNR-graft-PS was observed by transmission electron microscopy. The rubber particles of about 1 μm in diameter were found to be dispersed in polystyrene matrix of 10–30 nm in thickness. Tensile properties of fresh DPNR were dramatically improved by forming the nanomatrix structure, compared with DPNR.

We prepared phenyl-modified natural rubber using a two-step process. In the first step, natural rubber was brominated using N-bromosuccinimide in a dichloromethane solution of natural rubber. The amount of N-bromosuccinimide controlled the bromine content. In the second step, a Suzuki-Miyaura cross-coupling reaction of the brominated natural rubber with phenyl boronic acid in the presence of a palladium catalyst replaced the bromine atoms with phenyl groups. 1 H-nuclear magnetic resonance and 13 C-nuclear magnetic resonance measurements characterized the products. The signals around 7 ppm in the 1 H-nuclear magnetic resonance spectra of the products were assigned to the phenyl protons, and based on the assigned signals, the estimated conversion of the cross-coupling reaction under mild conditions was more than 70 mol%. The amount of phenyl groups present affected both the loss tangent and the glass transition temperature of natural rubber, which increases from À62°C to À30°C.

An attempt to prepare hydrogenated natural rubber with hydroxyl groups was made by hydrogenation of epoxidized natural rubber (ENR) in latex stage after removal of proteins. The hydrogenation was carried out by reaction of deproteinized ENR (EDPNR) with hydrogen gas in latex stage with palladium black as the catalyst, in which EDPNR was prepared by epoxidation of natural rubber followed by deproteinization. Effects of dry rubber content, concentration of surfactant and feed of catalyst on the hydrogenation of EDPNR in latex stage were investigated to find the optimal condition for achieving the highest conversion. Characterization of the resulting hydrogenated EDPNR (HEDPNR) was carried out through NMR spectroscopy and size exclusion chromatography to prove introduction of hydroxyl groups into the rubber without chain scission. Mechanical properties, thermal aging properties and oil resistivity of HEDPNR were compared with those of natural rubber, deproteinized natural rubber and ethylenepropylene-diene rubber. It was found that tensile strength, permanent set, thermal resistance and oil resistance of natural rubber were rationally improved by hydrogenation of the rubber and introduction of the hydroxyl groups.

a b s t r a c tThe mechanism of proton transport of a polymer electrolyte membrane (PEM) with nanomatrix channel was investigated with respect to the activation energy of proton conductivity. The PEM with nanomatrix channel was prepared by graft-copolymerization of styrene onto deproteinized natural rubber (DPNR) followed by sulfonation with chlorosulfonic acid. The resulting sulfonated graft-copolymer (SDPNR-graft-PS) was characterized by FT-IR spectroscopy, solid-state 13 C CP/MAS NMR spectroscopy, elemental analysis, transmission electron microscopy (TEM) and impedance analysis. The PEM was found to form completely continuous nanomatrix channel consisting of natural rubber particle of about 1 μm in average diameter as a dispersoid and sulfonated polystyrene of about 60 nm in thickness as a matrix. The value of the activation energy of proton conductivity estimated from the slope of Arrhenius plot was 12 kJ/mol for SDPNR-graft-PS, suggesting that the proton transport occurred in a manner of Grotthuss mechanism.