posted on 2024-03-05, 15:12authored byJacob J. Lessard, Edgar B. Mejia, Abbie J. Kim, Zhang Zhang, Mya G. Berkey, Zina S. Medina-Barreto, Randy H. Ewoldt, Nancy R. Sottos, Jeffrey S. Moore
In
this study, we explore the distinct reactivity patterns
between
frontal ring-opening metathesis polymerization (FROMP) and room-temperature
solventless ring-opening metathesis polymerization (ROMP). Despite
their shared mechanism, we find that FROMP is less sensitive to inhibitor
concentration than room-temperature ROMP. By increasing the initiator-to-monomer
ratio for a fixed inhibitor/initiator quantity, we find reduction
in the ROMP background reactivity at room temperature (i.e., increased
resin pot life). At elevated temperatures where inhibitor dissociation
prevails, accelerated frontal polymerization rates are observed because
of the concentrated presence of the initiator. Surprisingly, the strategy
of employing higher initiator loading enhances both pot life and front
speeds, which leads to FROMP rates exceeding prior reported values
by over 5 times. This counterintuitive behavior is attributed to an
increase in the proximity of the inhibitor to the initiator within
the bulk resin and to whether the temperature favors coordination
or dissociation of the inhibitor. A rapid method was developed for
assessing resin pot life, and a straightforward model for active initiator
behavior was established. Modified resin systems enabled direct ink
writing of robust thermoset structures at rates much faster than previously
possible.