Dynamic reaction-induced phase separation in tunable, adaptive covalent networks

Abstract

Dynamic covalent networks comprised of tunable thia-Michael bonds result in phase separated networks with tailorable mechanical and adaptive properties.

Controlling the Morphology of Dynamic Thia-Michael Networks to Target Pressure-Sensitive and Hot Melt Adhesives

“…Additionally, the incorporation of more electron-donating cross-linkers ( 1H and 1M ) with strongly withdrawing cross-linkers ( 1N ) effectively lowers the glass transition temperature ( T g ) and plateau modulus as compared to a parent film composed completely of the stronger acceptor, yielding materials more suitable for pressure-sensitive adhesion (Figure S1). …”

“…Characteristic of bond dissociation in dynamic networks, the changes to moduli for all systems are accompanied by an increase in the loss modulus (Figure S5) before the samples begin to readily flow. Further thermal characterization of the films via differential scanning calorimetry (DSC) showed the presence of a second higher thermal transition (>150 °C) characteristic of a “hard phase” formed via DRIPS process (Figure b) …”

“…The ditopic compounds were synthesized in two steps as previously described. , In the first step, the bis­(cyanoacetate) core, triethylene glycol (TEG, 20.0 g, 0.13 mol, 0.78 M), and cyanoacetic acid (23.2 g, 0.27 mol) were combined in a 500 mL round-bottom flask with 0.12 M equivalents of catalytic p -toluenesulfonic acid monohydrate (3.0 g, 0.016 mol) in toluene (166.7 mL). The setup was equipped with a waterless condenser and a Dean–Stark trap, heated to 105 °C under a nitrogen atmosphere, and stirred using a magnetic stir bar for ca.…”

“…Recent work by Bowman and co-workers has shown that (catalyzed) room-temperature thiol–thioester exchange can promote pressure-sensitive adhesion in thiol–ene adhesives, with further enhancement through pairing with hard filler particles . The catalyst-free, room-temperature dynamic behavior of the thia-Michael (tM) bond (Figure b) based on benzalcyanoacetate (BCA) Michael acceptors makes it a promising candidate for dynamic covalent adhesives targeting applications at or near room temperature. − Recent studies have demonstrated the utility of the tM motif in polymeric networks toward creating responsive, reprocessible materials. − An interesting aspect of the BCA Michael acceptor structures is that the equilibrium constant with thiols can be directly tuned by controlling the electronic nature of the β-phenyl group. Importantly, neat dynamic networks based on the BCA structures demonstrated a dynamic reaction-induced phase separation (DRIPS) phenomenon, giving rise to materials with tunable amounts of a spontaneously formed, high thermal transition (>150 °C) hard phase .…”

“…The catalyst-free, room-temperature dynamic behavior of the thia-Michael (tM) bond (Figure b) based on benzalcyanoacetate (BCA) Michael acceptors makes it a promising candidate for dynamic covalent adhesives targeting applications at or near room temperature. − Recent studies have demonstrated the utility of the tM motif in polymeric networks toward creating responsive, reprocessible materials. − An interesting aspect of the BCA Michael acceptor structures is that the equilibrium constant with thiols can be directly tuned by controlling the electronic nature of the β-phenyl group. Importantly, neat dynamic networks based on the BCA structures demonstrated a dynamic reaction-induced phase separation (DRIPS) phenomenon, giving rise to materials with tunable amounts of a spontaneously formed, high thermal transition (>150 °C) hard phase . Such materials were shown to have interesting stimuli responses (such as shape memory) and tunable mechanical properties that could be controlled based on thermal quenching from the melt, highlighting the ability to engineer material response by controlling the extent of phase separation.…”