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Abstract |
During cooling, amorphous silica, the archetype glass-former gradually
increases its viscosity over a wide temperature range and it becomes so viscous
that for all practical purposes it behaves like a hard solid, the glass. In
striking contrast and without exception all organic glass-formers increase
their viscosity and rigidify very abruptly when cooled. Moreover, silica is not
soluble. We imagined, vitrimers, organic materials that undergo gradual glass
transition and are not soluble just like silica. Vitrimers are molecular
networks that through thermo-activated exchange reactions are able to change
their topology without changing the total number of bonds. Solid at low
temperatures and malleable when heated yet insoluble whatever the temperature,
vitrimers constitute the third class of polymers along with thermoplastics and
thermosets (elastomers). First vitrimers were made from epoxy resins. Today
most plastics and rubbers can be transformed into vitrimers. Since vitrimers
can be shaped, assembled, repaired and recycled while showing exquisite
chemical and thermomechanical resistance they should rapidly find applications
in electronics, automotive, airplane, and coatings industries. And as for
inorganic glass-formers, the question whether amorphous silica is a vitrimer
opens intriguing perspectives. |
