The stress‐optical behaviour of crosslinked trans‐1,5‐polypentenamer (TPR) in the unswollen and the swollen state was investigated and the results were compared with the data for other elastomers. The optical anisotropy of the statistical segment was found to be 5.6 × 10−24 cm3 at 50°C. The number of chemical bonds in the main chain per statistical segment, a measure of the chain stiffness, was 5.6. From the comparison of the data in the unswollen and swollen state an estimate for the short range orientational order in the bulk polymer was made. The mean aggregate size of 1.6 at 50°C is relatively high compared to natural rubber.

The elastic properties in simple elongation have been investigated under various aspects for a series of elastomers, which were crosslinked randomly in the bulk state. The results are compared with different theoretical concepts for explaining the deviations from predictions of the simple statistical theory of rubber elasticity. The results do not favour clearly any one of the theoretical concepts under discussion.0025-1 16X/84/$03.00 *) Systematic IUPAC nomenclature for polypentenamer: poly(1-pentenylene). **) Systematic IUPAC name: Bis(2-phenyl-2-propyl) peroxide.