Vitrimers: Associative dynamic covalent adaptive networks in thermoset polymers.

Krishnakumar, B., et al. Chemical Engineering Journal 2020,385, 123820,DOI: https://doi.org/10.1016/j.cej.2019.123820.

The vitrimer-thermoset concept represents an important contribution to improve the durability and recyclability of thermoset-systems. The concept of Associative Dynamic Covalent Adaptive Networks (ADCAN), based on thermosetting vitrimers,demonstrates a high level of stress relaxation, self-healing and shape memory properties. This review article describes the relevant associative dynamic covalent exchange reaction mechanisms for vitrimers within thermosetting polymers and summarizes the resulting material properties with a final focus on recent applications. Reproduced with permission. Copyright 2019© Elsevier B. V.

Catalyst free self-healable vitrimer/graphene oxide nanocomposites.

Krishnakumar, B., et al. Composites Part B: Engineering 2020, 184, 107647,DOI: https://doi.org/10.1016/j.compositesb.2019.107647.

Catalyst free graphene oxide (GO) promoted self-healing vitrimer nanocomposites are designed, where the synthesized vitrimer nanocomposites displays self-healing properties via disulfide exchange based covalent adaptive network behavior. This study found that GO based nanofiller enhance the self-healing properties, including the shape memory and flexural strength of the materials. The GO induced lower glass transition was helpful to achieve low temperature self-healing: when compared to epoxy vitrimers (73% and 60% self-healing) the vitrimeric nanocomposites demonstrates a 88% and 80% self-healing for the first and second cycle, respectively. Reproduced with permission. Copyright 2019© Elsevier B. V.

Functional structural nanocomposites with integrated self-healing ability.

Guadagno, L., et al. Materials Today: Proceedings 2020 DOI: https://doi.org/10.1016/j.matpr.2020.03.051.

The use of aeronautical thermosetting resins in the field of structural materials is still limited because of several drawbacks, such as the absence of electrical and thermal conductivity and the poor impact damage resistance. An important contribution for increasing the composite application in this field can be given by implementing a strategy of autonomous damage-repair and other specific functions integrated into the material structure. This work proposes a successful strategy based on the design of supramolecular self-healing systems. It is aimed at developing self-healing, load-bearing structures with all functionalities integrated into a single material able to fulfill important industrial requirements. Reproduced with permission. Copyright 2020© Elsevier B. V.

Biomimetic Elastin-Like Polypeptides as Materials for the Activation of Mechanophoric Catalysts.

Funtan, S., et al. Organic Materials 2020, 2, 116-128,DOI: https://doi.org/10.1055/s-0040-1702149.

Elastin-like polypeptides (ELPs) are well known for their elastic and thermoresponsive behaviors. Here, the synthesis of ELPs of varying chain lengths and their coupling to a mechanoresponsive catalyst are reported. Mechanochemical activation of the synthesized catalysts by an external applied force, showed conversions of the copper(I)-catalyzed alkyne-azide “click” reaction (CuAAC) up to 5.6% with an increasing chain length of the peptide. Reproduced with permission. Copyright 2020© Georg Thieme Verlag KG, Germany.

Synthesis of polymer-linked copper(i) bis(N-heterocyclic carbene) complexes of linear and chain extended architecture.

B iewend, M., et al. Polymer Chemistry 2019, 10 (9), 1078-1088, DOI: http://dx.doi.org/10.1039/C8PY01751D.

Here a novel synthetic approach towards poly(styrene) (PS)-based copper(i) bis(NHC) complexes with linear and chain extended different architectures and their defined activation for CuAAC by mechanical force is reported. A mechanochemical activation of these complexes is demonstrated in bulk quantifying the catalytic activity in a fluorogenic CuAAC click reaction with conversions up to 44%, which allows the use of these polymers as stress-sensors. Reproduced with permission of The Royal Society of Chemistry.

Mechanochemical Activation of Fluorogenic CuAAC “Click” Reactions for Stress-Sensing Applications.

Michael, P., et al. Macromolecular Rapid Communications 2018, 1800376, DOI: https://doi.org/10.1002/marc.201800376.

Strategies for visualizing stress within polymeric materials are of growing interest during the past decade. Stress-sensing materials, triggered by a mechanoresponsive catalytic system based on latent copper(I)bis(N-heterocyclic carbene) mechanophores, are reported. The activation for network-based mechanocatalysts, observing “click” conversions up to 44%, while chain-extended and linear mechanocatalysts activate is detected. The developed catalysts enable “irreversible” mechanochromic systems for stress-sensing devices. Reproduced with permission. Copyright 2018©, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-Healing in Supramolecular Polymers.

Campanella, A., et al. Macromolecular Rapid Communications 2018, 1700739, DOI: http://dx.doi.org/10.1002/marc.201700739.

Adaption and self-healing are two major principles in material science, often coupled with the placement of supramolecular moieties within a material. Basic physicochemical aspects as well as new material developments in the field are described, published after a recent review in Macromolecular Rapid Communications in 2013. Reproduced with permission. Copyright 2018©, WILEY-VCH Verlag GmbH & Co. KGaA,

Opposing Phase-Segregation and Hydrogen-Bonding Forces in Supramolecular Polymers.

Chen, S., et al. Angewandte Chemie International Edition 2017, 56 (42), 13016-13020, DOI: http://dx.doi.org/10.1002/anie.201707363.

We report significant changes in the association behavior of covalent H-bonds by the phase of attached polymer chains. Depending on the aggregation state, we observed either intact H-bonds despite segregation of the phases, or macrophase separation with a larger amount of H-bonding dissociation. Reproduced with permission. Copyright 2017©, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Supramolecular semifluorinated dendrons glued by weak hydrogen-bonds.

Chen, S., et al. Chemical Communications 2017, 53 (62), 8699-8702, DOI: http://dx.doi.org/10.1039/C7CC04683A

H-Bonded semifluorinated dendritic polymer networks are generated by association of macromolecules, driven by the weak diaminopyridine (DAP) and thymine (THY) couple. Reproduced with permission of The Royal Society of Chemistry.

Unveiling the molecular mechanism of self-healing in a telechelic, supramolecular polymer network.

Yan, T., et al. Scientific Reports 2016, 6, 32356, DOI: https://doi.org/10.1038/srep32356

Reversible polymeric networks can show self-healing properties due to their ability to reassemble after application of stress and fracture. A combination of linear and nonlinear rheological measurements clearly identifies the terminal relaxation process as being responsible for the process of self-healing. Reproduced with permission. Copyright© 2016, Springer Nature.