Copolymerisation of Ethylene and Cycloolefins

Cycloolefins having rings with more than four carbon atoms do not homo-polymerise in the presence of Ziegler-Natta catalysts based on titanium or vanadium compounds as precursors and alkylaluminium activators. However, these cycloolefins may copolymerise with ethylene via the double bonds while preserving the cycloolefin ring ethylene is able to compensate the steric hindrance at the Ca atom of the growing chain after and before the 1,2-insertion of the cycloolefin [2], 

Alternating copolymers have been obtained by copolymerisation of ethylene and cycloolefins (using a large excess of cycloolefin) in the presence of vanadium-based Ziegler-Natta catalysts such as V(Acac)3-AlEt2Cl and VC14 AlEt2Cl  

Only cycloolefins with rings containing an odd number of carbon atoms, such as cyclopentene (x = 3) and cycloheptene (x = 5), yield crystalline copolymers with an erythro-diisotactic configuration. Cycloolefins with an even number of carbon atoms in the ring, such as cyclobutene (x = 2) and cyclooctene (x = 6), give amorphous copolymers [241]. 

The rate of copolymerisation of ethylene and odd-membered ring cycloolefins is higher than the rate of copolymerisation involving even-membered cycloolefins [467]. This indicates that both the polymerisation kinetics and the spatial configuration of the copolymer are influenced by steric factors [2]. 

While ethylene is vastly more reactive than cyclopentene in copolymerisation with the (IndCH2)2ZrCl2 [AI(Mc)0]x. catalyst (relative reactivity ratio of ethylene r = 80 300), norbornene is quite readily incorporated, with 

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