Segmental and Chain Dynamics of Polyisoprene-Based Model Vitrimers.

Polymer vitrimers are a new class of materials that combine the advantages of thermoplastics and thermosets. This is due to the dynamic nature of the chemical bonds linking different chains. However, how this property affects the polymer dynamics at different length scales is still an open question. Here, we investigate the dynamics of model vitrimers based on well-defined polyisoprene (PI) chains using broadband dielectric spectroscopy. In this way, we study the polymer dynamics from the segmental to the whole chain scale, taking advantage of the fact that PI belongs to the class of molecules that exhibit a net dipole moment associated with the end-to-end vector. Three distinct relaxation phenomena are identified. The fastest relaxation is attributed to the segmental PI dynamics with a small influence of the cross-linking. An intermediate relaxation attributed to the dipolar character of the cross-linker is also observed. The slower identified relaxation component, corresponding to limited fluctuations of the end-to-end PI chains, is found to be determined by the dynamics of the clusters formed by the cross-linkers with an average time scale orders of magnitude faster than that of the terminal relaxation as inferred from the viscous flow.