Reuse and life-cycle-enhancement of polymers is among the most pressing societal needs. We address novel concepts for reusing thermoplastics and thermosets based on vitrimers1, self-healing materials2 and reusable rubbers, funded by the graduate school AGRIPOLY, DFG- and EU-projects. Both, chemical synthesis and enzymatic degradation are studied to generate polymers with improved life-cycle as modern, environmentally friendly materials3.
Self-healing is among the great desires in materials, especially if accomplished autonomous and at room temperature conditions – only then an application in everyday life, such as coatings, smartphones, electronics is possible. One focus is placed on the embedding of multiple hydrogen-bonds,4-6 able to introduce self-healing into any desired polymeric materials.2, 7-9 Based on our longstanding tradition in hydrogen-bonds,6 their assembly, their phase-behavior10 and strength in polymers,4, 11-13 we are able to adapt the required strength and properties for the effect needed.7, 14 Proper choice of the hydrogen bond6, 15-17 in relation to the polymer allows to tune the healing-response, the healing time, and the healing conditions.18-19
Multiple-H-bonds based on barbiturates and complex, chelate-type H-bonds13, 20 in particular are prone to reversible assembly, useful for room-temperature self-healing.18, 21-22 Different methodologies of synthetic (polymer) chemistry are used to address the incorporation of the H-bonds into the final polymers, such as RAFT, ATRP, NMP, living carbocationic polymerization (LCCP), or living anionic polymerization (LCP). Thermoplastic, elastomeric and also thermoset/composite-materials18, 21-25 are equipped with self-healing properties, the latter using dynamic disulfide-bonds, introducing vitrimeric properties26. We can achieve self-healing at ambient conditions, technologically important when transferred to structural materials and coatings.24-25, 27 Since in all cases the intrinsic dynamics of the hydrogen bond is important and often different from the solvated state,28 their dynamics4 within the solid material are studied via various physical methodologies, among them melt-rheology,29-31 X-ray scattering,19, 32-33 or solid state NMR-spectroscopy11 to reveal mechanistic details of such self-healing processes.29
Our second approach uses encapsulation methods, coupled to a triggered “click”-chemistry to sense and subsequently heal the material.34 Based on the enormous versatility of the CuAAc (copper-catalyzed-click-reaction)34-37 as developed by Meldal in 2001 and its extreme robustness mainly due to autoacceleration-effects38-39 and chelation-assistance,40 this chemistry can easily be used in stress-induced, catalytic systems. We still work on then improvement of this highly valued self-healing materials using modern multicomponent 3D-printing-technologies.
Embedding nanosized capsules into the polymers, wherein reactive components are stored, a stress-triggered signal releases the components and activates the catalyst.41-42 Various self-healing nanocomposites and thermoset-systems, able to heal cracks at ambient temperature within several minutes have been developed.39, 41-46Graphene–47 and CNT-based Cu-catalyst48-50 are specifically attractive for this purpose due to their high stability and excellent dispersibility. With specially designed bis-N-heterocyclic Cu(I)-complexes as mechanophores a direct activation by stress can be achieved,51-54 allowing to sense and quantify stress inside thermoplastic- and thermoset polymers and biomaterials such as elastin-like peptides.55-56
Current research activities in this area are using 3D-printed multicomponent materials57 to embed all types of self-healing and self-sensing properties58-59 in coatings, elastomers, biomaterials, together with the exact quantification of the molecular force required to activate the mechanophores60-61 via SFMS-methods.
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- Campanella, A., et al., Self-Healing in Supramolecular Polymers. Macromolecular Rapid Communications 2018, 1700739,DOI:http://dx.doi.org/10.1002/marc.201700739.
- Binder, W. H., The Past 40 Years of Macromolecular Sciences: Reflections on Challenges in Synthetic Polymer and Material Science. Macromolecular Rapid Communications 2019, 40 (1), 1800610,DOI:https://doi.org/10.1002/marc.201800610.
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- Herbst, F., et al., Self-healing polymers via supramolecular forces. Macromolecular Rapid Communications 2013, 34 (3), 203-220,DOI:http://dx.doi.org/10.1002/marc.201200675.
- Binder, W., et al., Supramolecular Polymers and Networks with Hydrogen Bonds in the Main- and Side-Chain. In Advanced Polymer Science: „Hydrogen Bonded Polymers“, Binder, W. H., Ed. 2007; pp 1-78,DOI:http://dx.doi.org/10.1007/12_2006_109.
- Herbst, F., et al., Self-healing polymers via supramolecular, hydrogen bonded networks. In Self Healing Polymers: from Principles to Application, Binder, W. H., Ed. Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2013; pp 275-300,DOI:https://doi.org/10.1002/9783527670185.ch11.
- Döhler, D., et al., Principles of Self Healing Polymers. In Self Healing Polymers: from Principle to Application, Binder, W. H., Ed. Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2013; pp 7-60,DOI:https://doi.org/10.1002/9783527670185.ch1.
- Binder, W. H., et al., Biomimetic Principles in Macromolecular Science. In Bioinspiration and Biomimicry in Chemistry, Swiegers, G., Ed. John Wiley and Sons: Hoboken, New Jersey, 2012; pp 323-366,DOI:https://doi.org/10.1002/9781118310083.ch11.
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- Binder, W. H., et al., Synthesis and Self-Assembly of Hydrogen-Bonded Supramolecular Polymers. In Complex Macromolecular Architectures, John Wiley & Sons (Asia) Pte Ltd: 2011; pp 53-95,DOI:http://dx.doi.org/10.1002/9780470825150.ch3.
- Enke, M., et al., Intrinsic Self-Healing Polymers Based on Supramolecular Interactions: State of the Art and Future Directions. Advances in Polymer Science 2016, 59-112,DOI:http://dx.doi.org/10.1007/12_2015_345.
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