Encapsulated Transition Metal Catalysts Enable Long-term Stability in Frontal Polymerization Resins

Frontal polymerization involves the propagation of a
thermally
driven polymerization wave through a monomer solution to rapidly generate
high-performance polymeric materials with little energy input. The
balance between latent catalyst activation and sufficient reactivity
to sustain a front can be difficult to achieve and often results in
systems with poor storage lives. This is of particular concern for
frontal ring-opening metathesis polymerization (FROMP) where gelation
occurs within a single day of resin preparation due to the highly
reactive nature of Grubbs-type catalysts. Here, we demonstrate the
use of encapsulated catalysts to provide remarkable latency to frontal
polymerization systems, specifically using the highly active dicyclopentadiene
monomer system. Negligible differences were observed in the frontal
velocities or thermomechanical properties of the resulting polymeric
materials. FROMP systems with encapsulated catalyst particles are
shown with storage lives exceeding 12 months and front rates that
increase over a well-characterized 2 month period. Moreover, the modularity
of this encapsulation method is demonstrated by encapsulating a platinum
catalyst for the frontal polymerization of silicones by using hydrosilylation
chemistry.