Microphase Separation Controls the Dynamics of Associative Vitrimers

Vitrimers are a class of polymers characterized by dynamic covalent networks, where specific monomer units─stickers─form reversible cross-links that enable network rearrangement without loss of overall connectivity. The conventional wisdom is that the sticker dynamics control chain relaxation behavior and hence the mechanical properties of associative vitrimers where the number of cross-linked sticker pairs is precisely constant over time. Instead, here we show that the chemical differences between sticker groups and nonsticky chain monomers can cause them to microphase separate. Under these conditions, the slow exchange of a sticker from one microphase to an adjacent one controls the relaxation behavior. Controlling sticker aggregation is thus a key to tailoring the properties of these polymers, with immediate relevance to a circular polymer economy.