The Bio-based Polymers Group at the Ningbo Institute of Materials and Engineering (NIMTE) of the Chinese Academy of Sciences (CAS) has developed polyimine vitrimers with significantly enhanced creep resistance and thermal and mechanical properties via metal coordination. The study was published in Macromolecules.

Thermosets have been widely used as structural materials in lightweight vehicles, aircraft, electronics, etc., due to their excellent thermal and mechanical properties, chemical resistance and dimensional stability. Nevertheless, owing to their chemically cross-linked three-dimensional (3-D) networks, thermosets are difficult to recycle.

Vitrimers undergoing dynamic bond exchange enable reprocessing and recycle of thermosets. However, vitrimers easily creep, leading to their poor dimensional stability, thus limiting their application in structural materials.

Led by Prof. MA Songqi, the researchers at NIMTE developed a facile method via integration of metal complexes to address this issue.

Through a one-pot preparation involving the formation of metal complexes and cross-linking of polyimine, three metal complexes were introduced into polyimine vitrimers based on a Schiff base. The initial creep temperature was increased from 60 °C to about 100 °C by loading 5 mol% Cu²⁺.

The ability of different metal complexes to restrain creep followed the order of Fe³⁺ > Cu²⁺ > Mg²⁺. Meanwhile, the polyimine-metal complex vitrimers still exhibited excellent reprocessing recyclability. In addition, the introduction of coordination structures contributed to enhance the thermal and mechanical properties, solvent and acid resistance.

The study provided an efficient approach, i.e., metal coordination, to fabricate vitrimers based on a Schiff base with excellent high-temperature creep resistance, thermal and mechanical properties, as well as chemical stability.

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