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Conformational Entropy as a Means to Control the Behavior of Poly(diketonenamine) Vitrimers In and Out of Equilibrium
preprintsubmitted on 07.06.2019, 20:25 and posted on 10.06.2019, 18:59 by Changfei He, Peter Christensen, Trevor Seguin, Brandon Wood, Kristin Persson, Thomas Russell, Brett Helms
Here we show how to control the thermomechanical behavior of vitrimers, both in and out of equilibrium, by incorporating into the dynamic covalent network linear polymer segments varying in both molecular weight (MW = 0–12 kg mol–1) and conformational degrees of freedom. While increasing MW of linear segments predictably yields a lower storage modulus (E’) at the rubbery plateau after softening above the glass transition (Tg), due to the lower network density, we further find that both Tg and the characteristic time (t*) of stress-relaxation when deformed are independently governed by the conformational entropy of the embodied linear segments. We also find that activation energies (Ea) for vitrimer bond exchange in the solid-state are lower, by as much as 19 kJ mol−1, for networks incorporating flexible chains, and that the network’s topology freezing temperature (Tv) decreases with increasing MW of flexible linear segments, but increases with increasing MW of stiff linear segments. Therefore, the dynamics of vitrimer reconfigurability are influenced not only by the energetics of associative bond exchange for a given network density, but also foundationally by the entropy of polymer chains within the network.