Tricyclononenes and Tricyclononadienes as Efficient Monomers for ROMP: Understanding Structure–Propagation Rate Relationships and Enabling Facile Post-Polymerization Modification

Grubbs 3rd-generation (G3) pre-catalyst-initiated ring-opening metathesis polymerization (ROMP) remains an indispensable tool in the polymer chemist’s toolbox. Tricyclononenes (TCN) and tricyclononadienes (TCND) represent under-explored classes of monomers for ROMP—especially for G3-initiated ROMP—that have the potential to both advance fundamental knowledge (structure-polymerization kinetics relationships) and serve as practical tools for the polymer chemist (post-polymerization functionalization). In this work, a library of TCN and TCND imides, monoesters, and diesters, along with their exo-norbornene counterparts, were synthesized to compare their behavior in G3-initiated ROMP. Real-time 1H NMR was used to study their polymerization kinetics; propagation rates were extracted for each monomer. To understand the relationship between monomer structure and ROMP propagation rate, density functional theory methods were used to calculate a variety of electronic and steric parameters for the monomers. While electronic parameters (e.g., HOMO energy levels) correlated positively with the measured kp values, steric parameters generally gave improved correlations, which indicates that monomer size and shape are better predictors for kp than electronic parameters for this data set. Furthermore, the TCND diester—which contains an electron-deficient cyclobutene that is resistant to ROMP—and its polymer p(TCND) are shown to be highly reactive toward DBU-catalyzed conjugate addition with thiols, providing a protecting/activating-group free strategy for post-polymerization modification.