Various factors have been investigated which affect the diffusion coefficient and oil absorbing rate of ethylene-prepylene rubber and natural rubber in contact with high viscous oils.
According to the results obtained, the diffusion coefficient is primarily determined by the viscosity of oil, if the constitutions of the segments of the oils used are the same. It has also been found that the diffusion coefficient is dependent on the cross-link density only, irrespective of the kind and quantity of filler. The oil absorbing rate of rubber depends on the viscosity of oil, the filler content and the cross-link density. Furthermore, the thearetical treatment of these phenomena has been made.

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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.

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Column fractionation for a small sample size or a large sample size of cis-polybutadiene has been studied. After optimizing fractionation conditions particularly suitable for a large sample size fractionation, one to 300 gramms of a sample of cis-polybutadiene were fractionated by a suitable column apparatus. A reversion of a degradation problem usually encountered in an incomplete column fractionation process was not observed in this experiment even at fractionation of larger sample sizes. Intrinsic viscosity distributions obtained from each fractionation experiment showed good agreement provided the maximum polymer concentration in the eluant was below 0.5 %. The breadths of molecular weight distributions of typical fractions thus obtained were fairly narrow (molecular weights ratio 1.1; measured by ultracentrifugation). The fractionation could be completed within several days for 300 gramms of the sample. The fractionation system offers a possibility of a supply of large quantity of narrow distribution polybutadienes to permit physical or technological studies as a function of molecular weight.

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In many cases of tensile tests of soft vulcanizates having large elongation, such as pure rubber compounds, using JIS No. 3 or ASTM-C type (shown in Fig. 6), the specimens break down outside the parrallel marked (narrow) part, resulting in a failure of the test.
The author examined and analized thoroughly many shapes of dumbbell type specimens, through cross check design (shown in Fig. 1), photo-elastic experiments, measurement of the dimension at the end of elongation (shown in Fig. 3), and obtained the following conclusions from the variation of their dimension, the appearance of the rupture or the section and the distribution of tensile stress.
(1) Observation of rupture : The main factor in the rupture of specimens is not always attribute to the largest flaw existing in the parrallel part. Depending on the shapes and clamping of specimens, tear and shear stresses together with tensile stress produce necking behavior, namely, the shrinkage of the sectional area, deviated elongation of curvature edge, enlarged flaw at the necking edge and unbalanced surrounding stress at this curved part; all these stresses concentrate on this enlarged flaw and cause instantaneous breakdown.
(2) Improvement : The author recommends to enlarge (3040 mm) this inner curvature radius, to do away with outer curvature and to make both ends more narrow (1520 mm).
When a specimen of the above mentioned new type is tested the outer parts (3035 mm) should be clamped from the bench marks in parrallel with the bench mark lines.
It is advisable to take special care so that no visible flaw may be produced at these curvature edges, and to dust talcum on all the surfaces of sticking specimen and clamping bar.
(3) Merit : Even in case of pure rubber compounds, almost all of the specimens break down inside the bench marks. As the result, the tensile strength, modulus and elongation of the specimens will be measured under proper condition to obtain the required true value. In other words, the distribution of the respective mean measurement data is approximately normal. Moreover, the size of the specimen becomes smaller and simpler than the JIS type, resulting in less cost.

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