The modeling of network properties of copolyurethane systems of varying compositions based on hydroxy-terminated polybutadiene and poly( 12-hydroxy stearic acid-co-TMP) ester polyol (PEP), a copolyester polyol derived from 12-hydroxy stearic acid and trimethylol propane, crosslinked by different triols, and cured by various isocyanate compounds, has been carried out by the a-model developed by Marsh et al. The network parameters such as crosslink density, effective chain length, sol content, and mechanical properties of these systems have been evaluated. The functionality distribution of PEP has been derived from "Si nuclear magnetic resonance spectroscopy of the silyl derivative of P E P and chemical analysis. The extent of cure reaction (p) has been estimated by the use of a n empirical relationship of the type: p = a -b(Aa X F J , where A3 is the mole fraction of the trifunctional component of the OH group and F, is the fraction of secondary hydroxyls in the system. A method for evaluating the constants a and b is presented. The calculated network parameters by the a-model are found to be in good agreement with the observed values. Excellent linear correlations between the calculated network parameters and the mechanical properties of the urethane elastomers confirm the utility of the approach presented here in arriving at formulations with desired properties.