ELASTIC PROPERTIES OF POLYMER NETWORKS

Many fundamental questions for the understanding of polymer melts and networks are more suitably addressed by current computer simulations t han by experiments. The reason is that simulations have simultaneous a ccess to the microscopic structure and the macroscopic behavior of wel l-defined model systems. The coarse-grained models used often bear lit tle relation to actual chemical species. This is justified by the expe rimentally established universality of polymer dynamics and no limitat ion for the test and development of theories which are directed at the se universal aspects. The difficulties already encountered on this lev el will be illustrated for entanglements between polymers which domina te the dynamic in dense systems. For practical purposes it would, of c oarse, be desirable to predict the characteristic length and time scal es of experimental systems from the chemical structure of the polymer chains. Due to the extremely long relaxation times it is impossible to achieve this in brute-force simulations of truely microscopic models. Systematic coarse-graining combined with a better theoretical underst anding seem to offer a practical alternative.