Covalent Adaptable Networks with Tailorable Material Properties Based on Divanillin Polyimines.

Covalent adaptable networks (CANs) are being developed as future replacements for thermosets as they can retain the high mechanical and chemical robustness inherent to thermosets but also integrate the possibility of reprocessing after material use. Here, covalent adaptable polyimine-based networks were designed with methoxy and allyloxy-substituted divanillin as a core component together with long flexible aliphatic fatty acid-based amines and a short rigid chain triamine, yielding CANs with a high renewable content. The designed series of CANs with reversible imine functionality allowed for fast stress relaxation and tailorability of the thermomechanical properties, as a result of the ratio between long flexible and short rigid amines, with tensile strength (σb) ranging 1.07-18.7 MPa and glass transition temperatures ranging 16-61 °C. The CANs were subsequently successfully reprocessed up to three times without determinantal structure alterations and retained mechanical performance. The CANs were also successfully chemically recycled under acidic conditions, where the starting divanillin monomer was recovered and utilized for the synthesis of a recycled CAN with similar thermal and mechanical properties. This promising class of thermosets bearing sustainable dynamic functionalities opens a window of opportunity for the progressive replacement of fossil-based thermosets.

Crystallization-Induced Gelling as a Method to 4D Print Low-Water-Content Non-isocyanate Polyurethane Hydrogels.

The use of three-dimensional (3D) printable hydrogels for biomedical applications has attracted considerable attention as a consequence of the ability to precisely define the morphology of the printed object, allowing patients' needs to be targeted. However, the majority of hydrogels do not possess suitable mechanical properties to fulfill an adequate rheological profile for printability, and hence, 3D printing of cross-linked networks is challenging and normally requires postprinting modifications to obtain the desired scaffolds. In this work, we took advantage of the crystallization process of poly(ethylene glycol) to print non-isocyanate poly(hydroxyurethane) hydrogels with tunable mechanical properties. As a consequence of the crystallization process, the hydrogel modulus can be tuned up to 3 orders of magnitude upon heating up to 40 °C, offering an interesting strategy to directly 3D-print hydrogels without the need of postprinting cross-linking. Moreover, the absence of any toxicity makes these materials ideal candidates for biomedical applications.

Broadening the Scope of Steroidal Scaffolds: The Umpolung of a Bis-Primary Amine Precatalyst for the Insertion of CO2 into Epoxides.

A cholic acid-based bis-primary amine is capable of promoting the insertion of CO2 into epoxides with the cooperative aid of an iodide anion. This framework is transformed in situ into a bis-carbamic acid. The latter is the active catalytic species, operating through H-bonding interactions. Our system works with complete atom economy, under solvent-free, metal-free, and mild conditions. Also, it can be recycled.

Mimicking Enzymes: Asymmetric Induction inside a Carbamate-Based Steroidal Cleft.

Cholic acid has been elaborated into a carbamate-based tripodal architecture, which is able to promote an asymmetric organic transformation inside its chiral cavity. The nature of this steroidal catalyst has been disclosed by quantum-chemical calculations. It comprises the preorganization and confinement of the reagents within the cavity of the steroid to form a supramolecular complex held together by means of cooperative H-bond contacts. This operational mode resembles that of some enzymes.

l-Isoleucine in a Choline Chloride/Ethylene Glycol Deep Eutectic Solvent: A Reusable Reaction Kit for the Asymmetric Cross-Aldol Carboligation.

l-Isoleucine is able to catalyze the cross-aldol reaction between cyclohexanone and aromatic aldehydes in a deep eutectic solvent consisting in choline chloride and ethylene glycol, rendering products with high diatereo- and enantioselectivity. This protocol is straightforward and green: the organocatalyst and the reaction medium can be recycled up to five times, allowing the preparation of different substrates with a single load of solvent and catalyst.