  Frontal polymerization is a promising energy-saving method for rapid
fabrication of polymer components with good mechanical properties. In these
systems, a small energy input is sufficient to convert monomers, from a liquid
or soft solid state, into a stiff polymer component. Once the reaction is
initiated, it propagates as a self-sustaining front that is driven by the heat
released from the reaction itself. While several studies have been proposed to
capture the coupling between thermodynamics and extreme chemical kinetics in
these systems, and can explain experimentally observed thermo-chemical
instabilities, only few have considered the potential influence of mechanical
forces that develop in these systems during fabrication. Nonetheless, some
experiments do indicate that local volume changes induced by the competing
effects of thermal expansion and chemical shrinkage, can lead to significant
deformation or even failure in the resulting component. In this work, we
present a unique experimental approach to elucidate the effect of mechanics on
the propagation. Our experiments reveal that residual stresses that arise in
frontal polymerization are not only a potential cause of undesired deformations
in polymer products, but can also quench the reaction front. This
thermo-chemo-mechanically coupled effect is captured by our theoretical model,
which explains the mechanical limitations on frontal polymerization and can
guide future fabrication. Overall, the findings of this work suggest that
mechanical coupling needs to be taken into consideration to enable industrial
applications of frontal polymerization at large scales.
