  In many industrial processes, pieces of the same polymer material are brought
into contact at a temperature above the glass transition. Interdiffusion then
takes place across the interface and leads to a strengthening of the junction.
Often, a crosslinker agent is also added in order to improve the global
mechanical properties of the material, as in the formation of latex films from
dispersed solutions of polymer particles. In these systems, the interdiffusion
process and the crosslinking reaction couple strongly, and, in practice, may
sometimes interfere in a way that proves unfavorable to the tenacity of the
film. We studied theoretically the competition between interdiffusion and
crosslinking, and found a control parameter tuning the balance between these
two processes, in terms of simple physical quantities. The case of practical
interest occurs when this parameter is much smaller than unity: the reaction
locks the interfacial chains once a significant mixing has developed, resulting
in films with good mechanical properties.
