  Thermo-gelling polymers have been envisioned as promising smart biomaterials
but limited to their weak mechanical and thermodynamic stabilities. Here we
propose a new thermo-gelling vitrimer, which remains at a liquid state because
of the addition of protector molecules preventing the crosslinking, and with
increasing temperature, an entropy driven crosslinking occurs to induce the
sol-gel transition. Moreover, we find that the activation barrier in the
metathesis reaction of vitrimers plays an important role, and experimentally
one can use catalysts to tune the activation barrier to drive the vitrimer to
form an equilibrium gel at high temperature, which is not subject to any
thermodynamic instability. We formulate a mean field theory to describe the
entropy driven crosslinking of the vitrimer, which agrees quantitatively with
computer simulations, and paves the way for design and fabrication of novel
vitrimers for biomedical applications.
