Using Thiol-Thioester Bond Exchange to Elucidate the Interplay Between Crystallinity and Dynamic Bond Exchange in Semi-Crystalline Polymer Networks

While crosslinks impart mechanical strength and solvent resistance to polymer networks, they preclude reprocessing and recycling. One way to make such networks reprocessable – and thus more sustainable – is through the incorporation of dynamic covalent bonds (DCBs) to form covalent adaptable networks (CANS). In CANS, bond exchange reactions in response to specific stimuli enable plasticity, allowing for materials to be reconfigured over their lifetime. In recent years, significant efforts have been made to incorporate various species of DCBs within polymeric materials of various backbones, architectures, and morphology to elucidate the effects of bond exchange on rheological properties. However, much less work has been undertaken to understand how bond exchange processes influence the self-assembly and morphology of polymers which are critical to realizing high performance reprocessable materials. In this work, we explore the effect of bond exchange on the crystallization of semi-crystalline polymer networks. By exploiting control over thiol-thioester exchange kinetics using different catalysts, we systematically probe how bond exchange kinetics in chemically-identical systems influences crystallization kinetics and crystalline assembly. We find that as bond exchange kinetics increase, the melting temperature of semi-crystalline networks is systematically depressed and crystallization kinetics are drastically slowed. Coupled with microscopy and x-ray scattering, we present a rationale for these observations and how dynamic bonds can be harnessed in polymer networks to control both rheology and structure. Finally, we show how semi-crystallinity and DCBs can be combined toward high-performance recyclable materials by applying these systems to additive manufacturing.