Structure–Reactivity–Property Relationships in Covalent Adaptable Networks

Abstract

Polymer networks built out of dynamic covalent bonds offer the potential to translate the control and tunability of chemical reactions to macroscopic physical properties. Under conditions at which these reactions occur, the topology of covalent adaptable networks (CANs) can rearrange, meaning that they can flow, self-heal, be remolded, and respond to stimuli. Materials with these properties are necessary to fields ranging from sustainability to tissue engineering; thus the conditions and time scale of network rearrangement must be compatible with the intended use. The mechanical properties of CANs are based on the thermodynamics and kinetics of their constituent bonds. Therefore, strategies are needed that connect the molecular and macroscopic worlds. In this Perspective, we analyze structure−reactivity−property relationships for several classes of CANs, illustrating both general design principles and the predictive potential of linear free energy relationships (LFERs) applied to CANs. We discuss opportunities in the field to develop quantitative structure−reactivity−property relationships and open challenges.

Remolding and Deconstruction of Industrial Thermosets via Carboxylic Acid-Catalyzed Bifunctional Silyl Ether Exchange

“…Plots of relaxation time vs 1/ T revealed approximately Arrhenius relaxation behavior for both materials (Figure c) (Figures S37 and S38), providing estimated activation energies for stress relaxation of 49 and 30 kJ mol –1 for i PrSi7+ and EtSi7+ , respectively. While these values do not quantitatively agree with the barriers calculated using DFT due to fundamental differences between polymer network relaxation and vacuum calculations, respectively, the trends that describe the effects of i Pr- and Et-substituted BSEs agree well.…”

Phase separation in supramolecular and covalent adaptable networks

“…Because of these promising qualities, recent research has focused on tuning BERs through molecular architecture and chemistry. 50,[122][123][124]…”

“…The development of polymer networks with reversible bonds has received increased attention in the last decades. [43][44][45][46][47][48][49][50] We define reversible networks as networks containing either (1) supramolecular, non-covalent bonding motifs or (2) dynamic covalent bonding motifs. These bonding motifs provide reversibility by either freely dissociating and associating, or through bond exchange reactions.…”

Covalent Adaptable Polymethacrylate Networks by Hydrazide Crosslinking Via Isosorbide Levulinate Side Groups

“…Another strategy to enhance and vary the properties (e.g., increase hardness, T g , thermal stability, and solvent resistance) with the aim of widening the applicability is to transform a thermoplastic polymer into a thermoset by connecting the linear polymer chains via dynamic multifunctional crosslinkers . Such dynamic covalent polymer networks, also known as covalent adaptable networks (CANs), may provide chemical stability and mechanical strength equal to that provided by conventional non-dynamic crosslinked polymer networks . CANs have also been studied from different biobased sources, e.g., vegetable oils, lignin, and sugars .…”