Star polymers with norbornene/1-octene gradient copolymer arms synthesized by an ansa-fluorenylamidodimethyltitanium-[Ph3C][B(C6F5)4] catalyst system

Cyclic olefin copolymers (COCs), among which ethylene (E)/norbornene (NB) copolymer have been commercialized, are novel optical plastics but their brittleness narrows their application fields. In this research, star polymers with NB/1-octene (O) gradient copolymer arms and cross-linked cores were synthesized by adding norbornadiene (NBD)/E or 1,11-dodecadiene (DOD) after NB/O copolymerization using a (^tBuNSiMe₂Flu)TiMe₂ (I)-[Ph₃C][B(C₆F₅)₄] catalyst system with 2,6-di-tert-butyl-4-methylphenol-treated tri-n-octylaluminum (Oct₃Al/BHT) as a scavenger. The obtained star polymers possessed the O-rich soft segments close to the core and the NB-rich hard segments in the outer layer. The DOD-cored star polymers had a larger number of arms (15) and a higher star polymer content (68 wt%) than the NBD/E-cored ones (6 and 58 wt%, respectively). The films of the mixtures of the star and the corresponding arm polymers were molded by a melt-pressing procedure. The tensile properties of the films of the DOD-cored star polymer mixtures were significantly improved compared to those of the arm polymers. The Young's modulus, yield stress, strength, and strain at break were controlled by the NB content, the arm length, and the gradient structure of the arms. These results clarified the novelty of the star-shaped NB/α-olefin copolymers and would expand the application fields of COCs.