  The classical theory of rubber elasticity fails in the regime of large
deformation. The un- derlying physical mechanism has been under debate for long
time. In this work, we test the recently proposed mechanism of thermal elastic
fluctuations by Xing, Goldbart and Radzi- hovsky1 against the biaxial
stress-strain data of three distinct polymer networks with very different
network structures, synthesized by Urayama2 and Kawabata3 respectively. We find
that both the two parameters version and the one-parameter version of the XGR
theory provide satisfactory description of the elasticity in whole deformation
range. For comparison, we also fit the same sets of data using the slip-link
model by Edwards and Vilgis with four parameters. The fitting qualities of two
theories are found to be comparable.
