Hybrid polymer-network gels built by both physical and covalent polymer crosslinking combine the advantages of both these crosslinking types: they exhibit high mechanical strength along with excellent fracture toughness and extensibility. If these materials are extensively deformed, their physical crosslinks can break such that strain energy is dissipated and irreversible fracturing is restricted to high strain only. This mechanism of energy dissipation is determined by the kinetics and thermodynamics of the physical crosslinking contribution. In this paper, we present a poly(ethylene glycol) (PEG) based material toolkit to control these contributions in a rational and custom fashion. We form well-defined covalent polymer-network gels with regularly distributed additional supramolecular mechanical fuse links, whose strength of connectivity can be tuned without affecting the primary polymer-network composition. This is possible because the supramolecular fuse links are based on terpyridine-metal complexation, such that the mere choice of the fuse-linking metal ion adjusts their kinetics and thermodynamics of complexation-decomplexation, which directly affects the mechanical properties of the hybrid gels. We use oscillatory shear rheology to demonstrate this rational control and enhancement of the mechanical properties of the hybrid gels. In addition, static light scattering reveals their highly regular and well-defined polymer-network structures. As a result of both, the present approach provides an easy and reliable concept for preparing hybrid polymer-network gels with rationally designed properties.

Supramolecular polymer networks exhibit twofold dynamics: that of their polymer chains and that of the transient bonds between them, which is further complexed when irregular network structures lead to local variation of both. A typical irregularity is imperfect network-chain connectivity. To assess the impact of that, we study the diffusion of three different types of tracer polymers in supramolecular model networks of four-arm star-shaped poly(ethylene glycol). First, we focus on tracers that carry three stickers and one fluorescent label at their four arms, thereby creating an inherent network connectivity defect in their vicinity. Second, we embed tracers that carry four stickers and four labels and that do not intrinsically create network defects. Third, we embed non-sticky tracers with a larger size than the network meshes, thereby sterically obstructing their connectivity. These studies reveal that the first tracers can rapidly walk within the networks by sequential arm detachment above c*, whereas below c*, they are subject to a dynamic equilibrium of liberated and gel-cluster-bound portions. By contrast, the second tracers are efficiently incorporated into the network, which dramatically hinders their motion. Opposed to that, the third tracers can diffuse almost as unhindered as if they were embedded within an uncrosslinked matrix.FIGURE 1 Concept of this study. Supramolecular model-network gels are prepared from four-arm star-shaped poly(ethylene glycol) (pEG) building blocks transiently interlinked by complexation of end-capping terpyridine sticky groups to transition metal ions. Within these networks, 2% fractions of three different green-fluorescent labeled tracer polymers are embedded, targeted at observation of their diffusive motion by fluorescence recovery after photobleaching. (A) Tracers that have three of their arms capped with terpyridine and one arm capped with a fluorophore inherently create a connectivity defect adjacent to their unsticky arm. (B) Tracers that have all their four arms capped with terpyridine plus each arm labeled with a fluorophore are expected to perfectly match with the network matrix to become part of it without defect creation. (C) Tracers that are not sticky but larger than the ideal network meshsize sterically obstruct the network connectivity around them.

Hybrid silicon-based organic/inorganic (multi)block copolymers are promising polymeric precursors to create robust nano-objects and nanomaterials due to their sol-gel active moieties via self-assembly in solution or in bulk. Such nano-objects and nanomaterials have great potential in biomedicine as nanocarriers or scaffolds for bone regeneration as well as in materials science as Pickering emulsifiers, photonic crystals or coatings/films with antibiofouling, antibacterial or water- and oil-repellent properties. Thus, this Review outlines recent synthetic efforts in the preparation of these hybrid inorganic/organic block copolymers, gives an overview of their self-assembled structures and finally presents recent examples of their use in the biomedical field and material science.

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Hybrid silicon‐based organic/inorganic (multi)block copolymers are promising polymeric precursors to create robust nano‐objects and nanomaterials due to their sol–gel active moieties via self‐assembly in solution or in bulk. Such nano‐objects and nanomaterials have great potential in biomedicine as nanocarriers or scaffolds for bone regeneration as well as in material science as Pickering emulsifiers, photonic crystals or coatings/films with antibiofouling, antibacterial or water‐ and oil‐repellent properties. In their Review on page 3354 ff., S. Czarnecki and A. Bertin outline recent synthetic efforts in the preparation of these hybrid inorganic/organic block copolymers, give an overview of these self‐assembled structures and finally present recent examples of their use in the biomedical field and material science.