Hexacyclotetradecenes as polycyclic fused exo-norbornene monomers: synthesis of cyclic olefin copolymers via Ti-catalyzed controlled polymerization

Abstract

Polycyclic fused norbornenes (NBs) are important monomers for producing thermally stable cyclic olefin polymers and copolymers (COCs). However, the difficult addition polymerization of sterically demanding endo-substituted NBs limits the range of accessible COCs. Here, we explored the synthesis and polymerization of an isomeric mixture of hexacyclotetradecenes (1a and 1b) as new polycyclic fused exo-NB-based monomers. These monomers were readily prepared via a two-step catalysis process: norbornadiene dimerization followed by protic-acid-catalyzed isomerization. While ring-opening metathesis polymerization using conventional Ru carbene catalysts was not viable, addition polymerization and copolymerization with 1-octene, using a constrained geometry Ti catalyst, successfully proceeded in a controlled manner. Monomer 1 was consumed faster than 1-octene to form gradient copolymers. ¹³C nuclear magnetic resonance spectra exhibited reasonable signals that indicated a 1,2-addition polymer structure. X-ray diffraction and thermogravimetry analysis confirmed the amorphous nature and thermal stability of poly1, which showed no weight loss below 400 °C. Thus, this study demonstrates the synthesis and polymerization of new promising polycyclic olefin monomers suitable for producing COC materials.