Reversible polymer networks containing covalent and hydrogen bonding interactions

• Hydrogen bonding and Diels–Alder active groups have been inserted on aliphatic polyketones.
• Thermally reversible polymers have been prepared.
• Thermal and mechanical properties are a clear function of chemical structure.

Thermally reversible polymers with relatively high glass transition temperatures (Tg) are difficult to prepare but very interesting from an application point of view. In this work we present a novel reversible thermoset with tunable Tg based on chemical modification of aliphatic polyketones (PK) into the corresponding derivatives containing furan (PK–FA) and/or amine (PK–DAP) groups along the backbone. The furan moieties allow thermal setting of the polymer by the Diels–Alder (DA) and retro-DA sequence with bis-maleimide (bis-Ma), while amine moieties allow tuning the hydrogen bonding density. By this combined approach, it is possible to synthesize well-defined thermosets with a wider Tg window with respect to PK–FA alone. Indeed, after several heating cycles, the material showed essentially the mechanical properties of the original even after the samples were broken and thermally reshaped. The incorporation of amine moieties at 20–60% conversion of the 1,4-dicarbonyl units along the PK-backbone significantly increased the Tg window from 100 °C to 185 °C. However, after each heating cycle the Tg of the material, detected as tan (δ) in DMTA measurements, continued to increase probably due to imine group formation between unreacted carbonyl and amine groups. Despite this limitation, the studied system still displays re-workability up to three thermal cycles and constitutes a proof of principle for the proposed approach, i.e. combination of Diels–Alder and hydrogen bonding groups towards higher Tg materials.

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