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This article reports the results of a study comparing commercially available high-cis polybutadiene rubbers (BRs) proceeding from different production technologies and bearing distinct structural characteristics. The microstructure of these polymers was characterized by Fourier transform infrared spectroscopy; molecular weight and polydispersity values were characterized by size exclusion chromatography (SEC). The degree of branching was characterized by SEC and dynamic mechanical rheological testing (RPA 2000). Glass-transition temperature was characterized by differential scanning calorimetry, and rheological properties were characterized with an oscillating rheometer rubber process analyzer (RPA 2000). Tire tread formulations were prepared with carbon black HAF N-339 as a reinforcement filler, and we compared the mechanical properties and performance of the different elastomer compositions. The compositions were characterized by their rheological properties, tensile resistance, resistance to abrasion, resistance to tearing, permanent deformation, resilience, and fatigue properties. The tested compositions obtained from BRs with distinct structural characteristics showed different performances. Neodymium-salt-based catalysts produced BRs with higher cis-1,4 levels and higher linearities. These polymer compositions also showed higher performances in abrasion resistance, fatigue resistance, and resilience tests.

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Abstract. The high temperature conductivity of polycrystalline Sr~.xTiO3_~ samples in air was found to be lower than the conductivity of SrTiO 3 samples. However, the dependence of the electrical conductivity on the oxygen partial pressure showed that this trend can be reverted under reducing conditions. Both trends contradict the expected effects of A-site deficiency on the defect chemistry. Differences in average grain sizes give a plausible explanation for these findings. The dependence of the conductivity on the oxygen partial pressure suggests that p-type conductivity is dominant in air, for every sample, and one can thus assume that the number of grain boundaries plays a negative role on this contribution. Electrochemical permeability measurements confirmed that the ionic transport number of strontium titanate in air remains small.