The stress-strain behavior of polydisperse networks is investigated using the maximum entropy principle. The network is described as a gas of phantom chains, and the deformation is taken into account by macroscopic constraints. Thus, nonaffine deformation on a microscopic scale is allowed and occurs. The main experimental features are reproduced, without introducing parameters additional to the strand number. In addition, the length distribution of network strands in a polymerization reaction is calculated. An exponential distribution of chain lengths is found.