Catalytic Control of Crystallization in Dynamic Networks

Abstract

The effect of catalysts with varying nucleophilic strength on thiol−thioester bond exchange dynamics and concomitant crystallization was studied in a model semicrystalline polymer network. It was found that the characteristic time scale of covalent bond exchange, τ, could be tuned over a ∼10 1 −10 3 s range simply by changing the nucleophilicity of the catalyst. Using isothermal crystallization measurements via differential scanning calorimetry, thermodynamic and kinetic features of crystallization were considered. A depression in melting temperature was observed with increasing bond exchange rate, suggesting a dependence of crystalline organization on network dynamics. Furthermore, a systematic slowing of crystallization kinetics with faster covalent bond exchange rates was observed. Lauritzen−Hoffman analysis showed a near doubling in the barrier for secondary nucleation for dynamic networks, suggesting that that bond exchange slows crystallization by limiting secondary nucleation and further growth. Finally, longitudinal DSC studies reveal a long-term increase in melting temperature for samples held at ambient temperature with bond exchange activated at room temperature, indicating that while bond exchange slows crystallization on short time scales it facilitates isothermal long-term crystal rearrangement and growth on longer time scales.

Crystallinity and perfection in ethylene vitrimers probed by combined calorimetry, scattering, and time-domain NMR

“…These results may be of general relevance for systems in which alkyl nanodomains can crystallize. Both in a recent study of somewhat more complex C 10 -based vitrimers (Kuenstler and Bowman, 2023) and in a linear methacrylate polymer with C 18 side-chains (Hempel et al, 2006), similar T m increases were reported. In the latter case, the melting enthalpy change over time was also studied by DSC, and shown to increase along with T m , in the same way as in our ethylene vitrimers (Soman et al, 2022a).…”

“…In recent years, using the knowledge generated from numerous fundamental studies, functional vitrimers have been developed for wide-ranging applications such as solid polymer electrolytes, durable coatings, shape-memory materials, and additive manufacturing (Jing and Evans, 2019;Yan et al, 2020;Chen et al, 2021;Ma et al, 2021;Niu et al, 2021;Rossegger et al, 2021;Gu et al, 2022;Lin et al, 2022;Van Lijsebetten et al, 2022) Despite the advances in vitrimers design and processing, a good understanding of how an exchange event that takes place on an Angstrom scale influences macroscopic events such as crystallization, rheological flow and self-assembly is lacking. Little work has focused on how adding dynamic bonds will affect the ability of polymer chains to crystallize (Soman et al, 2022a;Kuenstler and Bowman, 2023), which is a key attribute of polyolefins and many commercial plastics.…”

“…Local rearrangements of the network strands facilitated by bond exchange are hypothesized to allow crystal perfection or an increase in crystallinity, and to enable a crystalcrystal transformation into a more stable polymorph. Even more recent work by Kuenstler and Bowman (2023) have also investigated crystallization in dynamic networks, where different catalysts allowed for control of bond exchange kinetics. A similar longtime evolution in T m was observed, and the actual T m values were found to be inversely correlated with the exchange kinetics.…”