Molecular Dynamics Simulation of the Glass Transition Temperature of Fullerene Filled Cis-1,4-polybutadiene Nanocomposites

In this work, the effect of the fullerene（C_（60）） weight fraction and PB-C_（60） interaction on the glass transition temperature（T_g） of polymer chains has been systemically investigated by adopting the united atom model of cis-1,4-poly（butadiene）（cis-PB）. Various chain dynamics properties, such as atom translational mobility, bond/segment reorientation dynamics, torsional dynamics, conformational transition rate and dynamic heterogeneity of the cis-PB chains, are analyzed in detail. It is found that T_g could be affected by the C_（60） weight fraction due to its inhibition effect on the mobility of the cis-PB chains. However, T_g is different, which depends on different dynamics scales. Among the chain dynamics properties, T_g is the lowest from atom translational mobility, while it is the highest from the dynamic heterogeneity. In addition, T_g can be more clearly distinguished from the dynamic heterogeneity; however, the conformational transition rate seems to be not very sensitive to the C_（60） weight fraction compared with others. For pure cis-PB chains, T_g and the activation energy in this work can be compared with those of other polymers. In addition, the temperature dependence of the dynamic properties has different Arrhenius behaviors above and below T_g. The activation energy below T_g is lower than that above T_g. This work can help to understand the effect of the C_（60） on the dynamic properties and glass transition temperature of the cis-PB chains from different scales.

Synthesis and Characterization of Trans-1,4-butadiene/Isoprene Copolymers: Determination of Sequence Distribution and Thermal Properties

Abstract Two series of trans-1,4-poly（butadiene-co-isoprene） copolymers （TBIR） were prepared using the catalyst system TiCl4/MgCl2-Al（i-Bu）3 at different reaction temperatures. All dyad and triads sequence distributions, the number-average sequence length and the sequence concentration of the copolymers were calculated according to 13C-NMR spectra. The influences of temperature and initial molar ratio of butadiene to isoprene （Bd to Ip） on the distribution of the chain segments in the TBIR copolymers were discussed. The correlation of copolymer compositions and thermal properties were also evaluated, which facilitated the understanding of controlling the degree of crystallinity and the transition tempera^re by changing Bd content and temperature.

Synthesis and Characterization of trans-1,4-Butadiene/Isoprene Copolymers: Determination of Monomer Reactivity Ratios and Temperature Dependence

A series of trans-1,4-butadiene/isoprene copolymers were prepared using the catalyst system TiCl4/MgCl2-Al（i- Bu）3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calculated based on the Kelen-Tiid6s （K-T） method and the Mao-Huglin （M-H） method. The influence of temperature on copolymer composition and polymerization rate was discussed in detail. The increase of reaction temperature brought the decrease of butadiene reactivity ratio rBd and supplied an effective adjustment on copolymers＇ composition distribution.

The Influence of Trans-1,4-poly(butadiene-co-isoprene) Copolymer Rubbers(TBIR) with Different Molecular Weights on the NR/TBIR Blends

The molecular weight of a polymer is of prime importance and greatly influences the processing and mechanical properties of the polymer. Trans-1,4-poly(butadiene-co-isoprene) multi-block copolymer rubbers(TBIR) exhibit outstanding fatigue resistance, low heat build-up and good abrasion resistance, and are expected to be desirable candidate for high performance tire. Study on the influence of TBIR with different molecular weights on the structure and properties of TBIR and natural rubber(NR)/TBIR blends is essential to understand its contribution to the greatly improved dynamic properties of the rubber vulcanizates. TBIR with different molecular weights characterized by 1H-NMR, 13C-NMR, GPC, and DSC were highly trans-1,4-copolymers with similar chain sequence distribution and crystalline trans-1,4-polyisoprene(TPI) blocks. The green strength and modulus of TBIR increased with the increasing molecular weight.The NR/TBIR compounds filled with 40 phr carbon black were chemically cured by sulfur for the preparation of NR/TBIR vulcanizates.The compatibility between NR and TBIR, filler distribution, crosslinking bond and density, and properties of NR/TBIR vulcanizates were studied. The NR/TBIR vulcanizates showed increasing tensile strength, hardness, modulus, rebound, abrasion resistance, and flexural fatigue properties with increasing molecular weight of TBIR. Furthermore, they presented significant improvement in flexural fatigue resistance when compared with that of NR vulcanizate. The contribution mechanism of TBIR on the NR/TBIR blends was discussed. The TBIR with a wide range of molecular weight are ideal rubbers for high performance tires.

Synthesis of Well-defined Telechelic Trans-1,4-polyisoprene by Oxidative Cleavage

Synthesis of telechelic trans-1,4-polyisoprenes（TPI： trans-structure ＆gt; 95%） was evaluated based on two different methods of oxidative cleavage（indirect cleavage： first epoxidation of TPI, then the selective cleavage of epoxidized units in epoxidized trans-1,4-polyisoprene（ETPI） and direct cleavage of isoprene units in TPI）. The influence of solvents and the ratio of oxidative agents was investigated by 1H-NMR and 13C-NMR. A series of well-defined telechelic TPI with double terminated functional groups and less side reaction（molecular weight distribution range： 1.96？2.26） were synthesized by indirect cleavage in chloroform. Telechelic TPI showed similar crystallization behavior with TPI and interesting cold crystallization behavior characterized by DSC.

CHEMICAL STRUCTURE DEPENDENCE OF THE INTERNAL ENERGY CONTRIBUTION IN RUBBER ELASTICITY

Conformational elasticity theory recently developed has been used to explore the internal energy contribution to the elastic force f(e)/f as a function of strain for poly(cis-1,4-isoprene) and poly(trans-1,4-isoprene). Calculated f(e)/f values are in good agreement with those obtained experimentally. Results show that behavior of f(e)/f is mainly contributed by chemical structure, or intramolecular interaction, supporting the experimental observations, and that the internal energy contribution is strain dependent.

Polymerization of 1,3-Butadiene Catalyzed by Cobalt(Ⅱ) and Nickel(Ⅱ) Complexes Bearing Pyridine-2-imidate Ligands

Cobalt and nickel complexes （la-ld and 2a-2d, respectively） supported by 2-imidate-pyridine ligands were synthesized and used for 1,3-butadiene polymerization. The complexes were characterized by IR and element analysis, and complex la was further characterized by single-crystal X-ray diffraction. The solid state structure of complex la displayed a distorted tetrahedral geometry. Upon activation with ethylaluminum sesquichloride （EASC）, all the complexes showed high activities toward 1,3-butadiene polymerization. The cobalt complexes produced polymers with high cis-1,4 contents and high molecular weights, while the nickel complexes displayed low cis-l,4 selectivity and the resulting polymers had low molecular weights. The catalytic activities of the complexes highly depended on the ligand structure. With the increment of polymerization temperature, the cis-1,4 content and the molecular weight of the resulting polymer decreased.

Fabrication and Chemical Crosslinking of Electrospun Trans-polyisoprene Nanofiber Nonwoven

In this work, the optimal electrospinning conditions of trans-polyisoprene （TPI） solutions were evaluated nevertheless its lower glass transition temperature than the room temperature. Subsequently, chemical crosslinking of TPI nonwovens was firstly investigated by vulcanizing at high temperatures in the case of the persistence of nanofiber structure. For this purpose, curing agents of TPI were embedded in TPI nanofibers by co-electrospinning, and then a protect layer was coated on TPI nanofibers by filtering gelatin solution going through TPI nonwoven before the vulcanization at 140-160 ℃. The results showed that the vulcanization of TPI fibrous nonwoven at high temperatures did not destroy the fiber morphology. Interestingly, TPI fibrous nonwovens after vulcanization showed excellent mechanical properties （N17 MPa of tensile strength） that could be comparable to or even higher than that of some bulk rubber materials.