Metallocenes, ansa Norbornene

Within the family of cycloolefin co-polymers, the most important from a material properties standpoint, are the ethylene/norbornene co-polymers. These co-polymers, dubbed COC for cycloolefin co-polymers, are produced by Ticona and Mitsui under the tradenames Topas and Apel , respectively. An overview of properties and applications (for example, blisters for pills) can be found on Ticona s Topas homepage.607 Detailed ethylene/norbornene copolymerization studies with different 4/-symmetric and ansa-Cp-amido catalysts, with listing of co-polymerization parameters, have been published.608 611 NB is inserted exclusively in the cis-2,3-exo-modc (Scheme 25), and most of the metallocene catalysts tend to produce alternating co-polymers,609 612 due to the low reactivity of the M-NB intermediate toward further NB insertion. This mode of NB insertion prevents f3-H transfer, and thus ethylene/ norbornene co-polymers have increasing molecular masses at increasing NB content.611... 

Ansa-metallocenes with C2 and Cs symmetries generate random copolymers containing norbornene microblocks [43, 44, 61, 62, 64-68, 92]. Copolymers with norbomene content well above 50 mol% and Tg values as high as 220°C can be synthesized. Metallocene symmetry and ligand substituents dictate polymerizatiOTi activity, tacticity, and sequential distribution. The type of bridge has an influence oti polymerization activity, norbornene content, and molar masses (Fig. 5). 

Two trends common to almost all E-N copolymerizations by ansa-metallocenes are the following (1) increase in norbornene concentration in a polymerization feed results in a decrease in catalytic activity, likely due to the facility of coordination to the active sites, and in an increase of norbornene content in the copolymer up to a plateau, which depends on the catalyst structure and (2) molecular mass of the copolymer often increases with the increase of the norbornene content. 

Ansa-metallocenes with C2 and Cs symmetries (Figure 15) generate random copolymers containing norbornene micro-blocks. Copolymers with norbornene content well... 

---