Ethylene/propylene copolymerization with half-titanocene/mao catalyst II.¹³C-NMR analysis of ethylene-propylene copolymer

Stereo-structure and monomer sequence distribution of the ethylene-propylene copolymers obtained from half-titanocene catalytic system, (η₅-pentamethylcyclopentadienyl) titanium triallyloxide (Cp*Ti(OCH₂-CH=CH₂)₃) combined with methylalumiloxane (MAO) have been investigated by ¹³C-NMR spectra. The monomer reactivity ratios of the copolymerization with this catalyst were calculated from the monomer sequence distribution in ¹³C-NMR spectra, r₁ = 7.91 ± 0.06 for ethylene, r₂ = 0.135 ± 0.03 for propylene,and the products r₁r₂ for all runs in various feeding monomer ratio are almost equal to one (r₁r₂≈1). The monomer reactivity ratios were also determined according to Fineman-Ross method, the values of r₁ =7.74, r₂ = 0.134 and r₁r₂ = 1.04 are very close to those of calculating above by ¹³C-NMR analysis. These results indicated that the copolymers produced are random ones. The ethylene-propylene copolymers could be fractionated by successive solvent extraction and gave two fractions of ether-soluble and hexane-soluble. These two fractions showed slight differences in their monomer sequence distribution and monomer reactivity ratio. The ether-soluble fraction contained more propylene units, while more ethylene segments existed in the hexane-soluble fraction.