Composition and rheology of polyamide-6 obtained by using bi- and tri-functional coupling agents

A statistical approach is developed, based on a Monte Carlo method, in order to determine the statistical composition of a polyamide-6 sample composed of caprolactam (an AB-type monomer) and of a di-acid (A2 type) or a triacid (A3 type) as coupling agents. For this composition, the linear rheological behavior of these systems is predicted using a tube-based theory. This allows us to show that while coupling agents of type A2 can be seen as flow improver, the effect of branching agents of type A3, depending on the synthesis recipe and the conversion level, can lead either to an increase or to a decrease of the viscosity. By adding specific amount of these agents, we also show that it is possible to obtain materials with the same zero-shear viscosity but with different shear thinning behavior. Furthermore, the polydispersity of linear samples of the same average number molecular weight, M n, is discussed in function of the amount of A2 monomers they contain. Ranging from 2 to 1.5, this difference in polydispersity is expected to have a significant influence on the processing behavior of such materials. Invited lecture presented at the International Symposium on Polymer Physics, 2012, Chengdu, Chin