Elastic and photoelastic properties of polyisoprene networks — applicability and bounds of theories

Abstract

AbstractMeasurements of stress and birefringence of networks of natural rubber and cis‐1,4‐polyisoprene deformed by simple elongation are reported. The experimental results are compared with theoretical calculations. It is found that the stress‐strain relation is in accordance with the empirical Mooney‐Rivlin equation. The constants 2 C1 and 2 C2 increase linearly with temperature indicating that both reflect essentially entropic elasticity. From theories dealing with the origin of the Mooney‐Rivlin behaviour, neither the entanglement concept nor the fluctuation or packing concept alone may account for the elastic behaviour observed. The photoelastic investigations prove the well‐known proportionality of stress and birefringence.