Catalytic Control of Crystallization in Dynamic Polymers

Associative interactions in macromolecules introduce significant opportunities to manipulate their static and dynamic behavior. While the influence of ‘sticky’ groups like hydrogen bonding and ionic groups on emergent mechanics, rheology, and morphology have been extensively explored, only recently has the effect of dynamic covalent bonds on such properties begun to be probed. When incorporated into polymer networks, dynamic covalent bonds undergo exchange reactions that introduce plasticity into the network, facilitating rearrangement of network strands. In this work, we explore how bond exchange can be used to control crystallization in polymer networks. We show that the kinetics of thiol-thioester exchange reactions with chemically-identical polymer networks can be controlled through the choice of nucleophilic catalysts. In this way, characteristic timescales of network relaxation can be controlled over three orders of magnitudes (t_R ≈ 10¹ – 10³ seconds). Using these materials as model systems, we find that as the rate of bond exchange increases, the rate of crystallization decreases for similar extents of undercooling, and that this can be controlled either through the judicious choice of catalytic species or catalyst loading. Finally, we present a rationale for these observations that provides insight into how manipulation of dynamic bonds can be used to control assembly in polymer systems.