Marcel Enke

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.

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.

A translation of the structure of mussel byssal threads into synthetic materials by the utilization of histidine-rich block copolymers

Mussel byssal threads are well-known due to their self-healing ability after the mechanical stress caused by waves. The proposed mechanism demonstrates the importance of reversible histidine–metal interactions as well as the block copolymer-like hierarchical architecture of the underlying protein structure. Taking these two aspects as inspiration for the design of synthetic analogs, different histidine-rich block copolymers were synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. The hard domain was mimicked using polystyrene and the soft domain consists of n-butyl acrylate (BA) as well as histidine moieties as ligands. The block copolymers were crosslinked using different zinc(II) salts and the resulting metallopolymers were investigated with respect to their self-healing abilities. The observed two-step mechanism of the self-healing process was studied in detail. Furthermore, the mechanical properties were determined by nanoindentation and were correlated with other results.

Influence of Aspartate Moieties on the Self-Healing Behavior of Histidine-Rich Supramolecular Polymers

Aspartate incorporated into the protein structure of mussel byssal threads is believed to play an important role, besides the reversible histidine-zinc interactions, in the self-healing behavior of mussel byssal threads. Therefore, copolymers containing both aspartate and histidine moieties are synthesized in order to investigate the influence of aspartate on the complexation of zinc(II) as well as on the self-healing behavior and the mechanical properties of the resulting supramolecular networks. For this purpose, isothermal titration calorimetry measurements of a model aspartate compound as well as of these copolymers are performed and the thermodynamic parameters are utilized for the design of self-healing copolymers. For this purpose, n-lauryl methacrylate-based copolymers containing histidine and aspartate are synthesized and crosslinked with zinc(II) acetate. The self-healing behavior of the supramolecular networks is investigated using scratch healing tests and the mechanical properties by nanoindentation.