Viscoelastic Properties of a Class of Carboxylated Rubbers: The Carboxylato-Telechelic Polydienes

Abstract

Abstract Halato telechelic polymers are well-characterized ion-containing polymers the investigation of which gives the scientist a clear insight into the role played by the ions in the modification of the base polymer properties. The end-neutralization of very short length, α,É-dicarboxylic acid polydienes by alkaline earth alcoholates triggers off the crosslinking of the rubber. In a nonpolar environment, the metal carboxylate bonds constitute ion pairs which associate into separate domains responsible for the vulcanization and the reinforcement of the rubber. For the very first time, the relaxation of these ionic domains has been observed and thoroughly investigated. Its mechanism obeys an Arrhenius-type of temperature dependence, whereas the activation energy strongly depends on the ion pair features. When entangled acid-ended polydienes are end-neutralized, an efficient crosslinking is again reported, whereas the relaxation of ionic domains is no longer observed. It means that the ion pair association is extended enough to stabilize a network of entangled chains, but that the size of the aggregates is too small to be accurately detected. In the series of alkaline earth metals, the higher the ionic radius, the less interacting the ion pairs. Nevertheless, the strength of the formed network increases with the ionic radius, which means that the functionality of the crosslinks, i.e., the mean size of the ionic aggregates, increases too. The extent of the ion pair association is therefore largely independent of their anchoring at the ends of macromolecules and is mainly related to the geometry of the metal carboxylates and to their mutual interaction.