Frontal Polymerization of Stereoisomers: Distinct Microstructures and Properties in <i>Endo-</i> and <i>Exo-</i>Dicyclopentadiene Thermosets
Hanlin M. Wang, Benjamin A. Suslick, Jacob J. Lessard, Christina Yu, Chaimongkol Saengow, Randy H. Ewoldt, Jeffrey S. Moore
Abstract
This study explores the relationship between monomer stereochemistry and the materials properties of thermosets generated by frontal ring-opening metathesis polymerization (FROMP). The exo- and endo- stereoisomers of dicyclopentadiene ( DCPD ) undergo rapid FROMP to fabricate robust thermosets within seconds. The exo -isomer provides significant benefits compared to the commonplace endo - DCPD resins; exo - DCPD supports faster fronts (≈3 times faster) than the endo -analogue and is an easier-to-handle liquid at room temperature. This work is among the first to explore the materials properties of p( exo - DCPD ) thermosets. Here, we demonstrate a significant decrease in T g for products derived from exo - DCPD, despite having a similar rubbery plateau compared to p( endo - DCPD ). Soluble oligomers were synthesized as models to probe the microstructural features affected by the monomer stereochemistry. Interestingly, hydrogenated oligomers of endo - DCPD exhibit slight differences in stereoregularity compared to their exo -counterparts. Lastly, we incorporated a bisnorbornenyl cross-linker in exo - DCPD resins to boost the polymer T g, while also maintaining fronts that propagate faster than endo - DCPD .