Vitrimers in a nutshell - thermoplastic and thermoset dual behavior, a win-win situation?

Reversible covalent bonds containing polymers (RCBPs), also known as "covalent adaptable networks (CANs)" or "Reorganizable Polymers", are a novel class of polymers with interesting thermosetting/thermoplastic characteristics. Chemical crosslinks in known thermosets are usually thermally stable, but in this case exchangeable crosslink bonds form which lead to a dynamic crosslink network.

CANs can be classified by their exchange mechanism. Dissociative CANs exhibit a sudden significant reduction in viscosity when the crosslinks break under certain conditions (temperature, pH, UV-light) and re-form upon restoration of those conditions. Associative CANs exhibit dynamic bond exchange at rather constant crosslink density, usually driven by heat, yet the exchange rate allows for rheological properties typical of thermoplastics, such as shear thinning.

Apart from the glass transition temperature seen in amorphous thermosets, a "vitrification temperature" is shown that reflects the dynamic nature of the network and the transition from thermoset to thermoplastic behavior. The vitrification temperature in certain systems is low enough to allow processing by extrusion, injection molding and related processes.

The author will describe several vitrimer systems that can be processed at 200^oC, and their interaction with polyolefins, either virgin or recycled. As part of the CIRCLE Consortium, vitrimers are being considered as compatibilizers and tougheners of recycled polyolefins and polyolefin blends. Their thermoset nature may impart strength, while their processability makes them recyclable.

In the future, CANs may well be the key to new polymers designed for recyclability with better balance of properties such as creep, chemical resistance and dimensional stability.