As polymers and polymeric materials are "the" smart invention and technological driving force of the 20th century, the quest for self-healing or self-repairing polymers is strong. The concept of supramolecular self-healing materials relies on the use of noncovalent, transient bonds to generate networks, which are able to heal the damaged site, putting aspects of reversibility and dynamics of a network as crucial factors for the understanding and design of such self-healing materials. This Review describes recent examples and concepts of supramolecular polymers based on hydrogen bonding, π-π interactions, ionomers, and coordinative bonds, thus convincingly discussing the advantages and versatility of these supramolecular forces for the design and realization of self-healing polymers.

Supramolecular polyisobutylenes (PIB) bearing mono- and bifunctional chain ends with hydrogen-bonding units were prepared, and their association behavior in the melt state was investigated by dynamic rheology and compared to aggregation in solution, aiming at determining association dynamics in the solid state. A preparation combining living cationic polymerization with either azide/alkyne “click” reactions or nucleophilic substitution reactions enabled a full end group transformation to the final PIB polymers, modified with either thymine or 2,6-diaminotriazine end groups as proven by NMR and MALDI methods with molecular weights of ∼3500 and ∼10 000 g/mol. Stoichiometric mixtures of these polymers bearing specifically interacting thymine/triazine moieties were prepared by solution blending and the temperature-dependent dynamics investigated by rheological measurements. At temperatures of 20−60 °C all samples display strongly thermoreversible aggregation with sheet-type or partially cross-linked structures, which deaggregate at temperatures of ∼80 °C. More complex aggregates with bridged micellar structure were formed from the respective bifunctional PIB’s bearing thymine and 2,6-diaminotriazine moieties. Thus, in addition to specific linear aggregates, the formation of clusters and aggregates of different architecture has to be taken into account to understand and control structure and mechanical properties of supramolecular chains in the melt.

Polymers with hydrogen-bonding groups in the melt state often combine the ability to form specific supramolecular bonds with a tendency for unspecific aggregation and microphase separation. Using a combination of small-angle X-ray scattering and shear spectroscopy, we present a study of structure formation and rheological properties of such a case, an exemplary series of telechelic polyisobutylenes, functionalized with hydrogen-bonding end groups. Unspecific interaction between hydrogen-bonding groups leads to the formation of micelles. For monofunctional samples, we observe ordering at lower temperatures, induced by a temperature dependent concentration of the micelles. The rheological properties of these systems can be mapped to the behavior of a concentrated colloidal fluid or solid. For bifunctional polymers with complementary hydrogen-bonding groups, interaction between micellar aggregates leads to network formation and solidlike properties at lower temperatures induced by gelation without ordering. Only in this case the supramolecular bonds directly determine the rheological properties.

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Reversible polymeric networks can show self-healing properties due to their ability to reassemble after application of stress and fracture, but typically the relation between equilibrium molecular dynamics and self-healing kinetics has been difficult to disentangle. Here we present a well-characterized, self-assembled bulk network based on supramolecular assemblies, that allows a clear distinction between chain dynamics and network relaxation. Small angle x-ray scattering and rheological measurements provide evidence for a structurally well-defined, dense network of interconnected aggregates giving mechanical strength to the material. Different from a covalent network, the dynamic character of the supramolecular bonds enables macroscopic flow on a longer time scale and the establishment of an equilibrium structure. A combination of linear and nonlinear rheological measurements clearly identifies the terminal relaxation process as being responsible for the process of self-healing.