  We built randomly cross-linked model PDMS networks and used Molecular
Dynamics Methods to obtain stress-strain curves. Mooney-Rivlin (MR) analysis
was used to estimate the shear moduli. We applied Primitive Path analysis (PPA)
and its variation, Phantom Primitive Path analysis (3PA), to estimate the
entanglement and the cross-link moduli, respectively. The MR moduli estimates
are in good agreement with the sum of the entanglement and the cross-link
moduli, and we observe that the stress-strain data collapse to a universal form
when reduced with the PPA and 3PA moduli. We studied how the MR parameters
$\mathrm{C}_1$, $\mathrm{C}_2$ vary from cross-link to entanglement dominated
networks. For the latter, we observed a $40\%$, $60\%$ contribution of
$2\,\mathrm{C}_1$, $2\,\mathrm{C}_2$ to the shear modulus, respectively.
Finally, we fitted several models to the data. While all fits are good, the
estimates for the entanglement and the cross-link moduli vary significantly
when compared to our PPA and 3PA benchmarks.
