Epoxidized natural rubber-graphene (ENR-GE) composites with segregated GE networks were successfully fabricated using the latex mixing combined in situ reduced technology. The rheological behavior and electrical conductivity of ENR-GE composites were investigated. At low frequencies, the storage modulus (G') became frequency-independent suggesting a solid-like rheological behavior and the formation of GE networks. According to the percolation theory, the rheological threshold of ENR-GE composites was calculated to be 0.17 vol%, which was lower than the electrical threshold of 0.23 vol%. Both percolation thresholds depended on the evolution of the GE networks in the composites. At low GE concentrations (<0.17 vol%), GE existed as individual units, while a "polymer-bridged GE network" was constructed in the composites when GE concentrations exceeded 0.17 vol%. Finally, a "three-dimensional GE network" with percolation conductive paths was formed with a GE concentration of 0.23 vol%, where a remarkable increase in the conductivity of ENR-GE composites was observed. The effect of GE on the atom scale free-volume properties of composites was further studied by positron annihilation lifetime spectroscopy and positron age momentum correlation measurements. The motion of ENR chains was retarded by the geometric confinement of "GE networks", producing a high-density interfacial region in the vicinity of GE nanoplatelets, which led to a lower ortho-positronium lifetime intensity and smaller free-volume hole size.

Mechanical strength and toughness are usually mutually exclusive, but they can both appear in natural rubber (NR). Previous studies ascribe such excellent properties to highly cis stereoregularity of NR. To our surprise, after the removal of non-rubber components (NRC) by centrifugation, the strength and toughness of NR decrease dramatically. It is still a challenge for us to make out for the problem of how NRC affect the properties of NR. Our group ascribes the superior mechanical robustness of NR to NRC. To further verify such a viewpoint, we add phospholipids (phosphatidylcholines) into NR without NRC. Phosphatidylcholines construct a sacrificial network, which ruptures preferentially upon deformation to dissipate energy. Moreover, some of phosphatidylcholines participate in the vulcanization reaction, which further improves the mechanical strength and energy dissipation. As a result, the mechanical strength and toughness of samples are as high as 21.1 MPa and 49.6 kJ/m2, respectively, which have reached the same level as that of NR. Therefore, this work not only imitates the excellent mechanical robustness of NR but also further provides a rational design for elastomers with excellent mechanical robustness.

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Ti-based Ziegler-Natta catalysts supported on MgCl 2 doped with AlCl 3 were prepared by the reaction of MgCl 2 /AlCl 3 -ethanol adduct with TiCl 4 . No AlCl 3 crystallites were found in the AlCl 3 -doped catalysts by WAXD analysis, suggesting that AlCl 3 /MgCl 2 solid solution was formed. The effect of doping on the catalyst performance in ethylene polymerization was investigated. The results showed that the catalysts based on AlCl 3 -doped MgCl 2 support exhibited a slightly higher activity than did the MgCl 2 -supported catalyst and the molecular weight distribution (MWD) of polyethylene (PE) markedly increased (from 10.8 to 47.9) with the increase of AlCl 3 content in catalysts. The changes in catalyst's active center distribution were studied based on nonlinear fitting of the polymer GPC curves by multiple Flory functions. It was found that increase of types of active centers by introducing AlCl 3 into the support should be responsible for the broadening of MWD of PE.