Stefan Bode

Self‐Healing Polymer Coatings Based on Crosslinked Metallosupramolecular Copolymers

Self-healing coating based on metallopolymers are prepared and fully characterized. Iron bisterpyridine complexes are incorporated into a polymer network based on methacrylates, resulting in self-healing properties of these materials. Moreover, the influence of the comonomers on the thermal properties is studied in detail.

Self-healing metallopolymers based on cadmium bis(terpyridine) complex containing polymer networks

The utilization of metal–ligand interactions within polymers generates materials which are of interest for several applications, including self-healing materials. In this work we use methacrylate copolymers containing terpyridine moieties in the side chain for the formation of self-healing metallopolymer networks. The materials were synthesized using the reversible addition–fragmentation chain transfer (RAFT) polymerization technique and subsequent crosslinking by the addition of a metal salt, here cadmium(II) salts, with different counter-ions. The influence of the counter-ions on the self-healing process within these structures was analyzed. The research resulted in a new polymeric material featuring a high (intrinsic) healing efficiency at relatively low temperatures (<75 °C).

Correlation between scratch healing and rheological behavior for terpyridine complex based metallopolymers

Certain metallopolymers possess the ability to close scratches by a simple thermal treatment. The present study comprehensively explores the structure–property relationship of these materials by variation of the corresponding metal salts. The scratch-healing properties are studied in detail and correlated to the rheological behavior. Rheological measurements are utilized to determine the supramolecular bond life time (τb). A crossover of G′ and G′′ is found for the scratch healing metallopolymers, whereas this is absent in materials displaying no healing under the investigated conditions. Thus, this study provides a first step for the fundamental understanding of the dynamic behavior of metallopolymers and the impact on the self-healing properties. Furthermore, the effect of the chosen cation and anion on the self-healing behavior is illustrated and studied in detail.

Self-healing mechanism of metallopolymers investigated by QM/MM simulations and Raman spectroscopy

The thermally induced self-healing mechanisms in metallopolymers based on bisterpyridine complexes of iron(II) sulfate and cadmium(II) bromide, respectively, were studied by means of combined quantum mechanical/molecular mechanical (QM/MM) simulations and Raman spectroscopy. Two possible healing schemes, one based on a decomplexation of the cross-linking complexes and a second one relying on the dissociation of ionic clusters, have been addressed. Temperature-dependent Raman spectroscopy displayed bathochromic shifts of the Raman intensity pattern upon heating. QM/MM simulations on the polymer models assign these alterations to a partial decomplexation of the metal terpyridine complexes, i.e. signals originating from free terpyridine ligands increase upon heating. Thus, a healing mechanisms based on partial decomplexation of the cross-linking complexes is suggested. The possibility that the dissociation of ionic clusters, which are assumed to be present in this class of self-healing polymers, is also responsible for the self-healing process was investigated as well. However, such calculations on model clusters revealed relatively strong binding of the clusters, which renders reversible cluster breaking and reformation upon temperature cycling in the range up to 100 °C unlikely.

Metallopolymers as an Emerging Class of Self-Healing Materials

Metallopolymers are highly interesting materials with properties combining typical polymeric features with the properties of metal–ligand complexes. Thereby, the incorporation of different metal complexes into the polymeric material enables the tuning of the resulting material’s properties. In particular, ionic interactions between charged metal complexes and the corresponding counterions as well as reversible (switchable) metal–ligand interactions make these materials potentially interesting as self-healing materials. Compared to other self-healing polymers, the research on these materials is still in its infancy. This review summarizes the latest trends in the research regarding this class of materials.

Polymeric Halogen‐Bond‐Based Donor Systems Showing Self‐Healing Behavior in Thin Films

The synthesis and comprehensive characterization of a systematic series of cleft-type anion receptors imbedded into a polymeric architecture is presented. For the first time, isothermal calorimetric titrations on polymeric halogen-bond-based donors were exploited to evaluate the dependence of the anion affinity on different key parameters (i.e. monomeric versus polymeric receptor, halogen versus hydrogen bonding, charge assistance). The combination of these donor systems with a copolymer bearing accepting carboxylate groups led to supramolecular cross-linked polymer networks showing excellent intrinsic self-healing behavior. FT-Raman spectroscopy and nano-indentation measurements were utilized to clarify the thermally induced self-healing mechanism based on the formation of halogen bonds. These first self-healing materials based on halogen bonds pave the way for new applications of halogen-bond donors in polymer and material science.

Characterization of self-healing polymers : From macroscopic healing tests to the molecular mechanism

Over the last few years, several testing methods have been introduced for the detection and quantification of autonomous and thermally stimulated healing in polymers. This review summarizes some of the most prominent state-of-the-art techniques for the characterization of polymer healing occurring at the microscopic and macroscopic levels during the repair of damage such as scratches, cracks, or ballistic perforations. In addition to phenomenological investigation of the self-healing process, a range of physical characterization techniques have been explored for elucidation of the underlying healing mechanism at the molecular or polymer network level. The present state of visual methods, spectroscopic techniques, scattering techniques, and dynamic methods is described. A short outlook is provided, discussing the future challenges and expected new trends in the characterization of self-healing polymers.

Intrinsic Self-Healing Polymers Based on Supramolecular Interactions: State of the Art and Future Directions

Supramolecular polymers are an intriguing class of materials with dynamic behavior as a result of the presence of non-covalent bonds. These bonds include hydrogen bonds, metallopolymers, ionomers, host–guest as well as π–π interactions. The strength of these supramolecular bonds can be tuned by varying the binding motifs. Their reversible and dynamic character can be utilized to engineer self-healing polymers. This review briefly presents the preconditions for design of self-healing polymers and summarizes the development of supramolecular self-healing polymers based on various non-covalent interactions. Furthermore, challenges and perspectives for the understanding of self-healing mechanisms and the preparation of novel materials with enhanced properties are discussed.

Blocked isocyanates: an efficient tool for post-polymerization modification of polymers

The utilization of blocked isocyanates for efficient post-polymerization functionalization of different polymers is presented. For this purpose, well-defined polymers obtained by the RAFT polymerization procedure are modified by conversion of the end groups to blocked isocyanates. Furthermore, α,ω-carboxy-terminated polystyrene and poly(phenylene ethynylene) are functionalized with blocked isocyanates. The utilization of these end groups could be shown by functionalization with anthracene moieties. The blocked isocyanates offer improved stability of functional polymers compared to isocyanate functionalized polymers. Their handling is much easier and it is possible to precipitate these polymers in methanol. On the other hand, an efficient reaction with an amine or an alcohol at 130 °C could be demonstrated. Thus, the versatility of this approach is shown, which offers a wide range of possibilities for potential applications, e.g., as soft segments in polyurethanes or for further functionalization towards tailor-made polymers.

Self-Healing Polymers Based on Reversible Covalent Bonds

Starting with reversible polymer networks based on the Diels–Alder reaction of furan and maleimide, a large variety of different self-healing polymers based on reversible covalent interactions have been developed in the last decade. These intrinsic self-healing polymers are mainly based on reversible addition reactions, exchange reactions, and condensations. The most prominent examples of such materials are based on Diels–Alder chemistry, photocycloadditions, disulfide reactions, acylhydrazones, and reversible radical reactions.