Metal Coordination in Polyimine Covalent Adaptable Networks for Tunable Material Properties and Enhanced Creep Resistance

Abstract

Covalent adaptable networks (CANs) can replace classical thermosets, as their unique dynamic covalent bonds enable recyclable crosslinked polymers. Their creep susceptibility, however, hampers their application. Herein, an efficient strategy to enhance creep resistance of CANs via metal coordination to dynamic covalent imines is demonstrated. Crucially, the coordination bonds not only form additional crosslinks, but also affect the imine exchange. This dual effect results in enhanced glass transition temperature (Tg), elasticmodulus (G′) and creep resistance. The robustness of metal coordination is demonstrated by varying metal ion, counter anion, and coordinating imine ligand. All variations in metal or anion significantly enhance the material properties. The Tg and G′ of the CANs are correlated to the coordination bond strength, offering a tunable handle by which choice of metal can steer material properties. Additionally, large differences in Tg and G′ are observed for materials with different anions, which are mostly linked to the anion size. This serves as a reminder that for coordination chemistry in the bulk, not only the metal ion is to be considered, but also the accompanying anion. Finally, the reinforcing effect of metal coordination is proved insensitive to the metal–ligand ratio, emphasizing the robustness of the applied method.

Dual Reversible Network Nanoarchitectonics for Ultrafast Light-Controlled Healable and Tough Polydimethylsiloxane-Based Composite Elastomers

“…The FTIR spectra of Fe/FBA@ x % OHCNT composite elastomers shown in Figure c reflect that the amide I band at 1636 cm –1 and amide II band at 1572 cm –1 shifted to 1623 and 1575 cm –1 , respectively, suggesting the coordination between Fe­(III) and the urea group . According to hard–soft-acid/base theory in coordination chemistry and other previous studies, – the metal ion also can coordinate with the imine-N donor centers. Unfortunately, the absorption peak at 1628 cm –1 (CN vibration) was not observed in the spectrum of the Fe/FBA@ x % OHCNT composite elastomers.…”

Phase separation in supramolecular and covalent adaptable networks

“…149 To relieve the issue of creep in CANs, research has been focused on changing the reactivity and characteristics of the DC bonds, to tune the structural integrity and strength in the final materials. This has been done chemically, e.g., by changing local polarity 150 or sterics 144,151 near the DC bonds, by means of metal-coordination of dynamic covalent groups, 152,153 or by modifying the electronic behaviour of the DC bond, [154][155][156] . In addition, network characteristics have also been considered, such as the crosslinking density of the network, 157,158 or building in (a small degree of) permanent nondynamic crosslinks.…”

“…This has been done chemically, e.g. , by changing local polarity 150 or sterics 144,151 near the DC bonds, by means of metal-coordination of dynamic covalent groups, 152,153 or by modifying the electronic behaviour of the DC bond. 154–156 In addition, network characteristics have also been considered, such as the crosslinking density, 157,158 or building in (a small degree of) permanent non-dynamic crosslinks.…”

Coordination Adaptable Networks: Introducing Vitrimer Properties Using Dynamic Coordination Bonds

“…Further studies on similar polyimine vitrimers, made from either isophthalaldehyde or 2,6-pyridinedicarboxaldehyde and the bio-based Priamine 1071 (Figure 2) addressed the impact not only of the cation (Mn 2 + , Fe 2 + , Co 2 + , Ni 2 + , Cu 2 + , Zn 2 + ) but also of the corresponding anion (sulphate, nitrate, perchlorate, tetrafluroborate, triflate and triflimide) and of the polymeranchored ligand (iso-imine vs. pyr-imine) on the material properties (T g , creep resistance, elastic modulus). [13] The additional coordination bonds were shown to affect the imine exchange, in addition to increasing the crosslink density. The T g and the elastic modulus (G') are correlated to the strength of the coordination bonds.…”