Abstract Further work has been carried out on a new method of studying polymer network theory in an effort to find an accurate way of determining prepolymer functionalities. Model polyester systems containing tri-, di-, mono-, and nonfunctional molecules have been studied. In the majority of cases the results agree very well with the theory. In other examples the discrepancies can be explained by side reactions or unequal reactivity of similar functional groups. Some experiments were carried out with commerical prepolymer mixtures and these indicate that accurate results can also be obtained with these materials.