Supramolecular block copolymers composed of discrete blocks have promising properties for nanotechnology resulting from their ability to combine well-defined morphologies with good bulk material properties. Here, we present the impact of a well-defined siloxane block in either the main-chain or present as pendant grafts on the properties of supramolecular block copolymers that form ordered nanostructures with sub-5 nm domains. For this, two types of supramolecular block copolymers were synthesized based on the ureidopyrimidinone–urethane (UPy-UT) motif. In the first, oligodimethyl­siloxanes (oDMS) of discrete length were end-capped with the UPy-UT motif, affording main-chain UPy-UT-Si n . In the second, the UPy-UT motif was grafted with discrete oDMS affording grafted UPy-UT- g -Si 7 . For the two systems, the compositions are similar; only the molecular architecture differs. In both cases, crystallization of the UPy-UT block is in synergy with phase segregation of the oDMS, resulting in the formation of lamellar morphologies. The grafted UPy-UT- g -Si 7 can form long-range ordered lamellae, resulting in the formation of micrometer-sized 2D sheets of supramolecular polymers which show brittle properties. In contrast, UPy-UT-Si n forms a ductile material. As the compositions of both BCOs are similar, the differences in morphology and mechanical properties are a direct consequence of the molecular architecture. These results showcase how molecular design of the building block capable of forming block copolymers translates into controlled nanostructures and material properties as a result of the supramolecular nature of the interactions.

Polymer networks crosslinked via non-covalent interactions afford interesting materials for a wide range of applications due to their self-healing capability, recyclability, and tunable material properties. However, when strong non-covalent binding motifs in combination with high crosslink density are used, processing of the materials becomes troublesome because of high viscosities and the formation of insoluble gels. Here, we present an approach to control the processability of grafted polymers containing strong non-covalent interactions by balancing the interplay of intra- and intermolecular hydrogen bonding. A library of copolymers with different degrees of polymerization and content of protected ureido-pyrimidinone-urea (UPy-urea) grafts was prepared. Photo-deprotection in a good solvent like tetrahydrofuran (THF) at low concentrations (≤1 mg mL –1 ) created intramolecularly assembled nanoparticles. Remarkably, the intrinsic viscosity of these nanoparticle solutions was an order of magnitude lower compared to solutions of the intermolecularly assembled analogues, highlighting the crucial role of intra- versus intermolecular interactions. Due to the strong hydrogen bonds between UPy dimers, the intramolecularly assembled structures were kinetically trapped. As a result, the polymer nanoparticles were readily processed into a bulk material, without causing major changes in the morphology as verified by atomic force microscopy. Subsequent intermolecular crosslinking of the nanoparticle film, by heating to temperatures where the hydrogen-bond exchange becomes fast, resulted in a crosslinked network. The reversibility of the hereby obtained polymer networks was shown by retrieving the intramolecularly assembled nanoparticles via redissolution and sonication of the intermolecularly crosslinked film in THF with a small amount of acid. Our results highlight that the stability and processability of highly supramolecularly crosslinked polymers can be controlled both in solution and in bulk by using the interplay of intra- and intermolecular non-covalent interactions in grafted polymers.

Epithelial cysts and organoids are multicellular hollow structures formed by correctly polarized epithelial cells. Important in steering these cysts from single cells is the dynamic regulation of extracellular matrix presented ligands, and matrix dynamics. Here, control over the effective ligand concentration is introduced, decoupled from bulk and local mechanical properties, in synthetic dynamic supramolecular hydrogels formed through noncovalent crosslinking of supramolecular fibers. Control over the effective ligand concentration is realized by 1) keeping the ligand concentration constant, but changing the concentration of nonfunctionalized molecules or by 2) varying the ligand concentration, while keeping the concentration of non‐functionalized molecules constant. The results show that in 2D, the effective ligand concentration within the supramolecular fibers rather than gel stiffness (from 0.1 to 8 kPa) regulates epithelial polarity. In 3D, increasing the effective ligand concentration from 0.5 × 10−3 to 2 × 10−3 m strengthens the effect of increased gel stiffness from 0.1 to 2 kPa, to synergistically yield more correctly polarized cysts. Through integrin manipulation, it is shown that epithelial polarity is regulated by tension‐based homeostasis between cells and matrix. The results reveal the effective ligand concentration as influential factor in regulating epithelial polarity and provide insights on engineering of synthetic biomaterials for cell and organoid culture.

Dynamic covalent networks (DCNs) use chemical bonds that break and reform at appropriate processing conditions to allow reconfiguration of the networks. Recently, the acylsemicarbazide (ASC) motif has been added to the repertoire of such dynamic covalent bonds, which is capable of hydrogen bonding as well as dynamic bond exchange. In this study, we show that its sulfur congener, thioacylsemicarbazide (TASC), also acts as a dynamic covalent bond, but exchanges at a slower rate than the ASC moiety. In addition, siloxane‐based DCNs comprising either ASC or TASC motifs or a varying composition of both show tunable relaxation dynamics, which slow down with an increasing amount of TASC motifs. The reduction in stress relaxation goes hand in hand with a reduction of creep in the network and can be tuned by the ASC/TASC ratio. All networks are readily processed using compression molding and dissolve when treated with excess hydrazide in solution. The ability to control network properties and creep in dynamic covalent polymeric networks by small changes in the molecular structure of the dynamic bond allows a generalized synthetic approach while accommodating a wide temperature window for application.

Having external control over fundamental properties of polymers, such as their physical state, is a crucial yet challenging design criterion for smart materials. Liquifying polymers through photochemical events has significantly advanced various research lines. However, the opposite process of solidifying a polymer that is intrinsically in a liquid state reversibly with light is unattained. Herein, the light‐controlled liquid‐to‐solid transition of polysiloxanes is reported, which are decorated with a small number of azobenzene‐functionalized ureidopyrimidinone (Azo‐UPy) pendants. The UPy moieties toggle between intra‐ and intermolecular hydrogen bonding via trans→cis photoisomerization of the azobenzene. This transformation on the molecular level leads to the formation of strong supramolecular cross‐links, which, in turn, results in the macroscopic solidification of the material. The photoswitching event enables the post‐synthetic tailoring of the polymers’ mechanical properties, thus providing an alternative to the addition of plasticizers or hardeners. Moreover, the adhesion strength of the photochromic material increases by a factor of 6 upon exposure to UV light. In situ illumination during rheological measurements reveals the delicate interplay between wavelength dependent penetration depth and photoswitching efficiency. This conceptually new (de)bonding on demand strategy paves the way for creating light‐responsive materials with exciting applications in temporal adhesion, recycling, lithography, and material processing.