Polymerization in a Ferromagnetic Spin Model with Threshold

We propose a spin model with a new kind of ferromagnetic interaction, which may be called {\it ferromagnetic coupling with threshold}. In this model the contribute of a given spin to the total energy has only two possible values and depends on the number of parallel spins among its nearest and next to the nearest neighbors. By mapping the model onto the Ising version of the isotropic eight vertex model, we obtain some evidence of a low temperature phase made of alternate parallel pluses and minuses polymers.