Abstract: ESR method has been used to study the active center states of high yield MgCl₂-n-BuOH-i-Bu₃Al-TiCl₄ catalyst for ethylene and propylene copolymerization. It has been shown that two kinds of coordination states with one and two vacant sites would exist in the alkylated Ti³⁺ ions. The variation of ESR spectra of the catalysts in the presence of ethylene or ethylene and propylene mixture gases show that the ESR signals with g=1.954 and g=1.941 were associated with active centers of Ti³⁺. Combining with the ¹³C NMR studies on the composition of copolymerization products and the reactivity ratios, a mechanism for ethylene and propylene simultaneous coordination with active centers of Ti³⁺ in the catalyst has been proposed.

Key words: ESR, ¹³C-NMR, Ethvlcne and propylcnc copolymcrization, Ti-Mg catalvst, Zicaler-Natta catalvst