The essential role of network topology in rubber elasticity

This paper discusses various new aspects in the elasticity of rubbers and the statistics of elastomers. It is shown that the role of network topology is crucial in the statistics of rubbers. This is seen mostly on the influence of heterogeneities of crosslink density, which is also of practical interest. Strong heterogeneities lower the modulus, but do not change the stress‐strain behavior. It is also shown that if in a given network the flexible chains are replaced by rigid rods which are flexibly hinged the entropy is still of order of that of the flexible network and that the modulus is of the same order as the Gaussian one. This holds for lower functionalities, i.e. less than six. The phase behavior of crosslinked blends and interpenetrating networks is shown to be similar of the microphase transition of block copolymers. Semi IPNs demix at a critical crosslink density of the crosslinked part, or alternatively at a critical length of the free chains, even though if the chains are of the same chemical nature as the crosslink component.