Direct observation of topological transition in vitrimers

In addition to the usual glass transition, vitrimers (polymer networks with associative crosslinks) show a transition from viscoelastic liquid to viscoelastic solid (topological transition). This is due to the freezing of the reversible network topology, caused by the slowing down of the bond exchange reactions upon cooling. The vitrimers investigated by us present clusters of linkers embedded in the polymer matrix. The T-dependence of the inter-cluster average distance reveals an increase in the expansion coefficient at the temperature where the viscosity reaches 1012Pa.s (defined as the topological transition Tv). We aim to follow the structural relaxation of the system at the inter-cluster level, to determine the T-dependence of its characteristic time and compare it with the activation energy of the bond exchange reaction. This study shall provide the definite microscopic observation of the topological transition by scattering techniques.