  Vitrimers, an important subset of dynamically crosslinked polymer networks,
have many technological applications for their excellent properties, and the
ability to be re-processed through plastic flow above the so-called
vitrification temperature. We report a simple and efficient method of
generating such adaptive crosslinked networks relying on transesterification
for their bond exchange by utilising the `click' chemistry of epoxy and thiols,
which also has the advantage of a low glass transition temperature. We vary the
chemical structure of thiol spacers to probe the effects of concentration and
the local environment of ester groups on the macroscopic elastic-plastic
transition. The thermal activation energy of transesterification bond exchange
is determined for each chemical structure, and for a varying concentration of
catalyst, establishing the conditions for the optimal, and for the suppressed
bond exchange. However, we also discover that the temperature of
elastic-plastic transition is strongly affected by the stiffness (dynamic
rubber modulus) of the network, with softer networks having a much lower
vitrification temperature even when their bond-exchange activation energy is
higher. This combination of chemical and physical control factors should help
optimise the processability of vitrimer plastics.
