On the Epimerization of endo-Dicyclopentadiene during Terpolymerization with Ethylene and Propylene

The isomerization of endo-DCP (I) to exo-DCP (II) during the synthesis of EPDM with several Ziegler-Natta catalysts has been investigated by means of IR spectroscopy and by reference to EPDM containing different levels of true exo-DCP. The I - II epimerization was absent for ail the catalysts examined. Only with the systems VC1₄-Et₂AlCl was a trace of isomerization observed, and then only at the limit of sensitivity of the analytical method. No isomerization was detected via gas-chromatographic analysis in monomeric DCP recovered from the polymerization mixture. Ziegler-Natta catalysts having acidic character can homopolymerize I, but epimerization was observed only with the system voc1₃-Et₃Al₂Cl₃. The results obtained have been interpreted in terms of a terpolymerization mechanism having a prevalent coordinated character. The poly functionality of Ziegler-Natta catalysts is sometimes responsible of the secondary isomerization process.