Ring‐Opening Metathesis Polymerization of endo‐ and exo‐Norbornene Lactones

Abstract

New ester-functionalized bicyclic aliphatic polymers are synthesized through the ring-opening metathesis polymerization (ROMP) of endo- and exo-norbornene lactones (endo-NBL and exo-NBL) and their oxa-norbornene analogue (exo-oxa-NBL) followed by hydrogenation. The polymerizability between endo- and exo-NBLs, and the thermal properties between the six types of polymers before and after hydrogenation are compared and discussed. The ROMP of all three monomers proceeded in a living fashion under optimized conditions, which is confirmed by chain extension experiments. Endo-NBL shows a much lower homo- and copolymerizability than exo-NBL probably owing to six-membered chelation to the Ru center and steric hindrance in the ruthenacyclobutane intermediate. Stereo-block and stereo-gradient copolymers of poly(endo-NBL) and poly(exo-NBL) are also synthesized. The hydrogenation catalyzed by RuHCl(CO)(PPh3 )3 in the mixed solvents of o-xylene and N,N-dimethyl acetamide (DMAc) results in more than 95% conversion. The obtained hydrogenated polymers, H-poly(endo-NBL) and H-poly(exo-NBL), are amorphous, soluble in chlorinated aliphatic solvents, and thermally stable until 400 °C without a weight loss. Their glass transition temperatures are 163 and 131 °C, respectively; the values are appropriate in terms of both thermal stability and processing deformation for the application of transparent resin materials.