From the equilibrium theory to the analysis of dynamics Since the early days of polymer science crosslinked polymer networks have enjoyed a special interest because of the remarkable success of the equilibrium theory of rubber elasticity l'=. No such easy reference point exists for the investigation of the mechanical properties of uncrosslinked systems: any such investigation has to be dynamical from the beginning. The complexity of multiple entanglement constraints often suggests mean field treatments, in which each chain is constrained to 'reptate' within a temporary 'tube '2a, whose slow renewal accounts for the high viscosity usually observed in uncrosslinked systems. Entanglements are present also in crosslinked rubbers 3 and the tube concept can certainly be extended to these systems. However, recent improvements in the equilibrium theory of rubber elasticity 4-7, show that junction chain entanglements play a dominant role in accounting for the experimentally observed departures from the ideal law of rubber elasticity. Such entanglements impose deformation dependent constraints on the motion of the junctions. These constraints are more effective on unswollen systems at very small deformations, whereas swollen and highly stretched networks obey the ideal phantom network elastic equation s . Junction chain entanglements naturally account for the experimentally observed features of the reduced stress strain curve, which shows a maximum in the vicinity of the undeformed state. The complete analysis of the dynamics of a rubber network poses problems which, in general, are no less difficult than those connected with a dynamical analysis of uncrosslinked systems. Nevertheless, the remarkable success of the equilibrium theory formulated in terms of chain~unction entanglements 6s, suggests some specific considerations. Because of their ability to form entanglements, junctions in a crosslinked network must have very high effective friction coefficients, which implies that the relaxation times associated with the diffusive motion of the junctions might be substantially longer, on the average, than those associated with intrachain motions. An early recognition of this special feature is due to Mooney 9, who, in his high frequency treatment of the dynamics of a crosslinked network, considers both ends of the general chain to be fixed in space. If the observation time is longer, we are able to resolve the collective motions of the junctions, but in these conditions the intrachain degrees of freedom are very likely to show an equilibrium behaviour. To this extent, in this time range junctions behave as 'heavy Langevin particles' interacting with one another through Gaussian potentials. Over convenient observation times (typically, ~> 10 4 s for highly swollen networks and >~ I 0ls for unswollen systems) the dynamics of a rubber network can therefore be described in terms of a many body Langevin equation coupling together the motion of large sets of junctions. We shall only consider highly swollen systems, in which no deformation dependence of the constraints on the mobility of the junctions is to be expected.