Thiol–Ene Networks with Tunable Dynamicity for Covalent Adaptation

Abstract

To be fully recyclable, covalent adaptable networks must ultimately be able to overcome all topological restrictions and flow. By using a statistically based method, it was shown that the extent of stress relaxation in disulfide-containing thiol−ene polymers is closely correlated to the fraction of permanent cross-links. Given sufficient disulfide content, the cured materials can be recycled at moderate temperatures with no apparent loss in tensile properties. Since the materials also feature ester bonds, even when the disulfide content is low, one can increase the reprocessing temperature to trigger transesterification reactions which ensure full stress relaxation and recyclability.

Structural Design of CANs with Fine-Tunable Relaxation Properties: A Theoretical Framework Based on Network Structure and Kinetics Modeling

“…This expression is more general than the one provided by Li et al . and is also consistent with the work of Konuray et al It is not surprising that , where r c is the critical ratio of reactive groups from static monomer S j with respect to reactive groups from A f monomer leading to network formation at the end of a polymerization process in off-stoichiometric A f S j step-wise systems…”

“…However, it is observed that, in fact, reaches a value almost equal to 0 before is reached. Therefore, quantitative or almost full stress relaxation can be achieved with an even lower r dyn than predicted using eq , as observed by Konuray et al An extremely weak permanent network structure may exist within this range below , but preventing unrestricted macroscopic flow all the same. It is also apparent that, while complete stress relaxation might be observed below , the fraction of network material would still be higher than 0.…”

“…Later, an original strategy was reported by Van Lijsebetten for the control of the undesired creep of low T g vinylogous urethane vitrimers, based on the release of blocked amines by high temperature reversible cyclization of dicarboxamide structures . Alternatively, Konuray et al combined two bond exchange reactions with distinct kinetics and obtained a material that relaxes stresses in a sequential manner . Similarly, El-Zaatari et al studied the effect of the intrinsic bond exchange kinetics of different crosslinkers on the relaxation behavior of crosslinked polydimethylsiloxane and showed that combinations of different crosslinkers led to intermediate relaxation behavior .…”

“…It is acknowledged that there are intrinsic reactivity effects that contribute to the reported results, such as the presence of hydroxyl groups in transesterification polyester vitrimers. − However, it is the authors’ belief that there are certain structural effects that have not been properly taken into consideration. The results from Li et al and Konuray et al suggest that some relaxation effects can be analyzed from a structural point of view. Other works describing the effect of monomer functionality on the relaxation kinetics , point in a similar direction.…”

Catalyst-Free, Mechanically Robust, and Ion-Conductive Vitrimers for Self-Healing Ionogel Electrolytes

“…Vitrimers, recognized as chemically cross-linked networks with dynamic topology, introduce remarkable properties to bulk cross-linked polymeric materials, such as self-healing, adhesion, and malleability. − These features are enabled by reversible covalent bonds that can exchange polymer chains while maintaining a constant cross-link density at lower temperatures. , Thus the polymer networks remain frozen at low temperatures, but flow when temperature increases. To impart such dynamic properties to materials, various dynamic covalent bonding motifs are typically incorporated into networks, such as disulfides, , olefin metathesis, , boronic ester exchange, , or transesterification reactions. − The resulting cross-linked polymers display properties not achievable by other covalent, nondynamic bonds, such as self-healing, thermoset recyclability, and reprocessing behavior. While significant efforts have been dedicated to the molecular design enabling these dynamic properties, the functional applications of vitrimers have been largely overlooked, requiring the proposition of novel scenarios to expand the use of vitrimers.…”