Ethylene-norbornene terpolymerization experiments using 5-alkyl-substituted norbornenes (5-pentyl-2-norbornene (C₅N) and 5-octyl-2-norbornene (C₈N)) or dicyclopentadiene (DCPD) were conducted with two ansa-metallocenes, [Zr{(η⁵-C₉H₆)₂C₂H₄}Cl2] (1) and [Zr{(η⁵-2,5-Me₂C₅H₂)₂CHEt}Cl₂] (2), activated by methylaluminoxane (MAO). The terpolymers obtained were investigated in detail by determining the microstructure and termonomer contents by 13C NMR, molar masses and thermal properties. Results were compared to those of ethylene (E)-norbornene (N) terpolymerizations with 1-octene. 2, with lower steric hindrance and a shorter bridge, gave the best activities, termonomer incorporation and molar masses. The size of the substituent in 5-alkyl substituted norbornene also plays a role. C₈N gives the highest activities and molar masses, while DCPD terpolymers have the highest cycloolefin content. Terpolymers are random; their molar masses, much higher than those in 1-octene terpolymers, are in a range useful for industrial applications. Finally, Tg values up to 152 °C were obtained. For similar N content, poly(E-ter-N-ter-C₈N)s and poly(E-ter-N-ter-DCPD)s have the lowest and the highest Tg values, respectively. Thus, the presence of an eight-carbon atom pendant chain in C₈N increases the flexibility of the polymer chain more than a five-carbon atom pendant chain in C₅N. The higher rigidity of C₅N may lead to lower activities and to increasing probability of σ-bond metathesis and chain termination, as evidenced by chain-end group analysis.
Keywords: metallocenes; norbornene; substituted cycloolefin; terpolymerization.