Abstract
To investigate the tensile mechanism of rubber vulcanizates, in particular to determine the relationship between the tensile properties and polymer structure, styrene-butadiene copolymers (SBR) with various styrene contents were studied in this paper. The following conclusions were obtained from the results of tensile and physical properties measurements.
1) Failure of these SBR vulcanizates (carbon black filled) occurred mainly at the site of the main chain, not between rubber molecule and carbon black.
2) If the number average molecular weight, network chain density and the type of combined sulfur are considered nearly same, the same molecular motional region (which is regarded as the glass transition temperature in general) is shifted to the higher temperature side with an increase of styrene content in SBR, and the characteristic temperature for the failure properties is also shifted by the same quantity.
3) Shifting the tensile data in the same quantity as the transition temperature, only one master curve is obtained for the tensile strength, even if the styrene contents are changed. For the ultimate elongation, however, the master curves are not same for the various contents of styrene, but the value of the ultimate elongation after shifting is decreased with increasing styrene contents. This result was successfully interpreted on the hypothesis that the elongation of polymer molecule depends on the carbon atm in butadiene monomer unit, not on the carbon atm in styrene unit.
