Ethylene- co -norbornene Copolymerization Using a Dual Catalyst System in the Presence of a Chain Transfer Agent

Ethylene- -norbornene copolymers were synthesized by a dual catalyst system at three concentrations of norbornene in the feed and variable amounts of ZnEt₂, as a possible chain transfer agent. The dual catalyst system consists of two -metallocenes, isopropyliden(η cyclopentadienyl)(η⁵-indenyl)zirconium dichloride ( ) and isopropyliden(η⁵-3-methylcyclopentadienyl)(η⁵-fluorenyl)zirconium dichloride ( ), activated with dimethylanilinium tetrakis(pentafluorophenyl)borate, in presence of TIBA. Values of norbornene content, molecular mass, glass transition temperature, and reactivity ratios and of copolymers prepared in the presence of + are intermediate between those of reference copolymers. The study of tensile and elastic properties of ethylene- -norbornene copolymers (poly(E- -N)s) gave evidence that copolymers were obtained in part through transfer of polymer chains between different transition metal sites. Mechanical properties are clearly different from those expected from a blend of the parent samples and reveal that copolymers obtained in the presence of + and ZnEt₂ consist of a reactor blend of segmented chains produced by exchange from to and to 2 acting as the ideal compatibilizer of chains produced by the chain transfer from to , and from to .