  Liquid crystalline elastomers (LCE) undergo reversible shape changes in
response to stimuli, which may enable a wide range of smart applications, such
as soft robot, adhesive systems or implantable medical devices. Here we
introduce new dynamic covalent chemistry based on siloxane equilibrium exchange
into the LCE to enable processing (director alignment, remolding, and welding).
Unlike, the traditional siloxane-based LCE, which are produced by a other
reaction schemes with irreversible bonds (e.g. hydrosilylation), here we use a
much more robust reaction (thiol-acrylate/thiol-ene 'double-click' chemistry)
to obtain highly uniform dynamically crosslinked networks. Combining the
siloxane crosslinker with click chemistry produces LCEs with tunable
properties, low glass transition (-30C), controllable nematic to isotropic
transition (32 to 75C), and a very high vitrification temperature (250C).
Accordingly, this class of dynamically crosslinked LCE shows unprecedented
thermal stability within the working temperature range (-50 to 140C), over many
thermal actuation cycles without any creep. Finally, multiple materials sharing
the same siloxane exchangeable bonds can be welded into single structures to
allow for materials that sequentially and reversibly undergo multiple phase
transformations in different sections of the sample.
