Synthesis, characterization, and thermal properties of ring-opening metathesis polynorbornenes and their hydrogenated derivatives bearing various ester and cyano groups

Doubly functionalized polar norbornenes 3a-3g substituted by both a variety of ester and cyano groups were polymerized by ring-opening metathesis polymerization (ROMP) with a Ru carbene complex 2 bearing 3-bromopyridine as a ligand (third generation Grubbs' catalyst) in a living manner. The successive hydrogenation of the main-chain double bond in the synthesized living ROMP polymers 4a-4g with a hydridoruthenium complex was exploited. The comparison of thermal properties of a series of ring-opening metathesis polymers 4a-4g with those of their hydrogenated derivatives 5a-5g revealed the decrease of glass transition temperatures (Tg) but little change of the 5% decomposition temperature (T_d⁵). In all cases examined in this study, a decrease of T_g by hydrogenation was around 20-40 °C, regardless of the ester substitutents. In the presence of the additional PCy₃, triethylamine, and methanol after complete consumption of monomer 3a under the living ROMP condition, the tandem ROMP-hydrogenation of the resulting polymer 4a generated in situ was attained under a H₂ (9.8 MPa) atmosphere at 80 °C to afford the hydrogenated polymer 5a, retaining the narrow polydispersity of 1.03.