Study On The Roles Of External Electron Donors On Olefin Polymerization With Z-N Catalyst

As an important component of the supported Ziegler-Natta catalyst,external electron donors(ED)play great roles in influencing the catalytic activity of olefins and the stereoregularity of polyolefins.The influences of four kinds of silanes as ED with different structure and electron density(denoted as D1,D2,D3,D4 respectively)on propylene homopolymerization and propylene(first stage)-butene(Second stage)sequential polymerization were investigated.The results showed that ED had significant effects on the catalytic activity(CA),[C*]/[Ti]and the stereoregularity of active centers in olefin polymerization.Density functional theory(DFT)simulations showed that with the increase of steric hindrance and electron density of ED,the adsorption energy of ED on the surface of Mg Cl₂decreased,and the adsorption stability decreased.The increase in steric hindrance and electron density of ED was conducive to improve the stereoregularity of the active centers.When Dicyclopentyl dimethoxysilane(D4)/Ti was 20,the content of isotactic polypropylene(i PP)fractions in polypropoylene(PP)reached as high as 92.8%.When ED/Ti=15,The rate constant for chain propagation(k_p)of propylene polymerization reached the maximum value.The ED with greater steric hindrance and electron density enabled the active center of the sequential polymerization of propylene-butene with greater stereoregularity,ED had a more significant effect on the polymerization activity of butene(second stage)and the T_mof the isotactic polybutene(i PB)fractions in alloy PBA.