Dynamic and reversible non‐covalent interactions endow synthetic systems and materials with smart adaptive functions that allow them to response to diverse stimuli, interact with external agents, or repair structural defects. Inspired by the outstanding performance and selectivity of DNA in living systems, scientists are increasingly employing Watson−Crick nucleobase pairing to control the structure and properties of self‐assembled materials. Two sets of complementary purine‐pyrimidine pairs (guanine:cytosine and adenine:thymine(uracil)) are available that provide selective and directional H‐bonding interactions, present multiple metal‐coordination sites, and exhibit rich redox chemistry. In this review, we highlight several recent examples that profit from these features and employ nucleobase interactions in functional systems and materials, covering the fields of energy/electron transfer, charge transport, adaptive nanoparticles, porous materials, macromolecule self‐assembly, or polymeric materials with adhesive or self‐healing ability.
The stimuli-responsiveness of supramolecular polymers has recently been exploited for the development of adhesives that can be (de)bonded on demand when heated or exposed to UV-light. However, it remains difficult to combine competitive solid-state mechanical properties and very low melt viscosity in one material. Here we report a new supramolecular polymer adhesives platform based on soybean oil as a multifunctional low-molecular weight monomer (~1500 g/mol) and isophthalic acid (IPA) groups that show hydrogen bonding and promote the formation of a reversible network. The polarity difference between the triglyceride backbone and the IPA groups leads to microphase separation, and the crystalline IPA domains act as physical cross-links. Heating the polymer above the melting temperature of the IPA-rich domains results in a dramatic viscosity reduction to 8 Pa·s at 120 ºC. Once cooled to room temperature, the material properties are fully recovered, as a result of the reassembly of the supramolecular network. Single lap joint adhesive tests performed at room temperature using glass and stainless steel substrates reveal shear strength values of 1.2 and 1.7 MPa, respectively, and heat and UV-light can be used as external stimuli to debond on command. In addition, composites were prepared by adding 5 or 10 wt%) microcrystalline cellulose (MCC), to the polymer and this led to an increase of strength and modulus below the glass transition by up to 80% and 170%, respectively. Because the introduction of MCC partially hinders the crystallization of the matrix, the the stiffness and tensile strength are reduced above the glass transition, while the elongation at break is significantly increased.
12 November 2018 in Macromolecular Rapid Communications
In the present paper, we describe the synthesis of novel monomers prepared by regioselective Michael addition to asymmetric divinylic compounds. This chemoselectivity was experimentally studied employing different reaction conditions and theoretically calculated using chemical global and local descriptors. The global reactivity data show that incoming nucleophilic secondary amines preferentially attack the acrylic derived units acrylate and acrylamide, while deactivated methacrylate and N-vinyl-pyrrolidone require harder reaction conditions, which leads to the formation of by-products. Moreover, it is demonstrated that the presence of two vinyl units within a studied divinylic agent leads to a significant increase in its global reactivity parameters. Besides, the local reactivity parameters of asymmetric divinyl compounds show a preference for an attack at the Cβ of activated units compared to the Cβ center of deactivated units. Based on these results, asymmetric divinyl compounds are very interesting starting materials for the preparation of new functionalized monomers.