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

Abstract

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 ( t BuNSiMe 2 Flu)TiMe 2 ( I )-[Ph 3 C][B(C 6 F 5 ) 4 ] catalyst system with 2,6-di- tert -butyl-4-methylphenol-treated tri- n -octylaluminum (Oct 3 Al/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. • Star-shaped polymers with norbornene/1-octene gradient copolymer arms were synthesized by an “arm-first” strategy. • The star-shaped polymers showed two T g values assignable to an octene-rich soft core and a norbornene-rich hard sphere. • Transparent films were obtained from the blend of the star and the arm polymers by melt processing. • The of mechanical properties of the blend films were improved compared with those of the arm polymer films. • The thermal and the star polymers were controlled by the arm length and the norbornene content.