Ring-opening metathesis polymerizations with norbornene carboxylate-substituted metal oxo clusters

The clusters Ti6O4(OPr)8(endo,exo-OOC–Norb)8, Zr6O4(OH)4(endo-OOC–Norb)12 and Zr6O4(OH)4(exo-OOC–Norb)12(BuOH) were prepared by the reaction of 5-norbornene-2-carboxylic acid (HOOC–Norb) with Ti(OPr)4 or Zr(OBu)4 and were characterized by X-ray structure analyses. Ring-opening metathesis polymerization was performed with Zr6O4(OH)4(OOC–Norb)12 either in the absence or in the presence of norbornene. Highly crosslinked polynorbornene was obtained in the latter reactions. The onset of thermal decomposition of the polynorbornene crosslinked by 1–5 mol% of the cluster was about 40–45° higher than that of pristine polynorbornene. Small-angle X-ray scattering investigations showed that the clusters are randomly distributed in the polymer.