The starch-derived isohexides, with their unique structures of two fused tetrahydrofuran rings in a cis conformation, have been exploited to prepare covalent adaptable networks (CANs) and to tailor and understand their structure–property relationships, in pursuit of replacing oil-based thermosets. Here, dynamicity was achieved through vinylogous urethane chemistry, rigidity via the use of the starch-derived isomeric building blocks isosorbide, isomannide, and isoidide, and flexibility through the amines utilized. Similar to what is known for thermoplastics, depending on the isomer chosen, thermal stability and mechanical properties could be tailored to some extent. The distance between cross-links was ruled by the amines employed, and when this distance was long enough to allow sufficient chain mobility, stereochemical effects on mechanical performance were observed. The CAN structures all display thermoset properties, and as a consequence of the incorporated dynamic bonds, they were mechanically reprocessable. Based on the CANs structural design, i.e., isohexide isomer and amine structure, tensile strengths (σ<inf>b</inf>) ranging from 1.57 to 19.1 MPa, glass transition temperatures (T<inf>g</inf>) ranging from 20 to 114 °C, and thermal stabilities (T<inf>d,5%</inf>) between 200 and 305 °C were achievable. Mechanical reprocessing was proven, and no mechanical performance decay was observed after two reprocessing cycles. This provides important information on the structure–property relationship of CANs from starch-derived building blocks, and consequently, how material properties can be tailored depending on the targeted application.

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 (σ_b) 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.

Defined macromolecular architecture using anionic ring-opening copolymerization (ROcP) of lactones and cyclic carbonates offers facile routes toward copolymers with unique material properties, ranging from thermoplastic to elastomeric. However, monomers with a slow ROP rate are hampered by competing backbiting reactions, scrambling the macromolecular sequence, and, thereby, a loss of material properties occurs. We here solve this issue by controlling the rate of backbiting. Through our approach, we show how block structures previously inaccessible can be synthesized from monomers with vastly different ROP rates, covering small lactones and even including macrolactones. This control can also be extended beyond block structures to include random and gradient architectures by tuning monomer concentration to the relative ROP and backbiting rate.

Selective, active, stable, and general catalysts for the controlled ring-opening polymerization of (macro)lactones are central in our pursuit of a more benign material economy. Within, we explore the formation of an activated lactone initiator (ALI) based on ZnEt2-1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as an air-stable and selective initiator/catalyst, yielding linear polymers with one ß-keto ester and one alcohol end-group. Ring-opening polymerization (ROP) with high activity and control was found for unsubstituted (macro)lactones (ω-pentadecalactone (PDL), hexadecanolide (HDL), δ-valerolactone (δVL), and ε-caprolactone (εCL)) and cyclic carbonate trimethylene carbonate (TMC). A particular focus was placed on studying the ALI for the polymerization of strainless PDL and strained εCL. In contrast, ALI-ROP could not polymerize lactones containing substituents on the terminal carbon, indicative of the coordination insertion features of the polymerization. This work explores selective catalysts with high control, fast kinetics, and superb air stability towards the next generation of greener materials.

Zwitterionic Lewis pair (LP) catalysis is potent towards the polymerization of lactone monomers to form cyclic polymers. In pursuit of faster polymerization kinetics, the use of weaker Lewis acids, such as diethylzinc (ZnEt2), has hitherto been suggested. However, the strong Brønsted base character of ZnEt2 brings the question of the actual initiation mechanism. Here, the ZnEt2-1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) LP was studied as catalyst for the initiation and polymerization reactions of ω-pentadecalactone (PDL), ϵ-caprolactone, δ-valerolactone, and γ-butyrolactone. Collective MALDI-ToF MS, NMR, FT-IR, and Ubbelhode viscometry studies revealed a polymerization mechanism proceeding through deprotonation of the α-protons on the lactone and not zwitterionic ring-opening, yielding an anionic propagation mechanism and linear polymers. The polymerization kinetics display an initiation period that correlates to ethyl decomposition on ZnEt2 and the initiation period is shortened by increasing the reaction temperature, Lewis base equivalents, and the lactones, e.g. ϵ-caprolactone, δ-valerolactone, and γ-butyrolactone in the system.