Intramolecular Hydrogen-Bond-Based Latent Initiator for Olefin Metathesis Polymerization

Latent olefin metathesis polymerization catalysts have enormous potential, as they provide access to thermoset polymers. However, developing a novel latent catalyst is difficult because the catalyst must be inactive at room temperature and completely convert the starting material to the product upon activation. Herein, we report the synthesis of a series of novel initiators 1-4 bearing an additional hydrogen donor that can form a weak hydrogen bond with the metal-bound chloride anion of the active species of an alkylidene-containing N-heterocyclic carbene (NHC)-Ru-based initiator, and their latent catalytic behavior was examined in the ring-opening olefin metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) and cyclooctadiene (COD). The presence of intramolecular hydrogen bonds in initiators 1 and 2 facilitates latent polymerization, whereas the absence of intramolecular hydrogen bonds in initiators 3 and 4 allowed polymerization of DCPD at 30 degrees C. The TGA and DSC results for poly-DCPD (PDCPD) suggest that the intramolecular hydrogen bonding in initiators 1 and 2 did not alter the nature of the NHC-Ru-based initiator at 80 degrees C.

Automated summary

Latent olefin metathesis polymerization catalysts have great potential for producing thermoset polymers, but developing novel latent catalysts is challenging. A series of initiators bearing additional hydrogen donors were synthesized for examination of their latent catalytic behavior in ring-opening olefin metathesis polymerization. Intramolecular hydrogen bonding in initiators was found to impact the polymerization process.