Effects of comonomer on active center distribution of TCl4/MgCl2–AlEt3 catalyst in ethylene/1-hexene copolymerization

• Ethylene/1-hexene copolymerization with supported Z-N catalyst conducted under different [1-hexene].
• Number of active centers and rate constants of ethylene and 1-hexene insertion in the active centers were determined.
• Polymerization activity and number of active centers were significantly enhanced by adding 1-hexene.
• The rate constant of ethylene insertion slightly changed with [1-hexene].
• The rate constant of 1-hexene insertion was markedly lowered by increasing [1-hexene].

Ethylene/1-hexene copolymerization with MgCl2/TiCl4–AlEt3 catalyst has been conducted under different initial 1-hexene concentration (0–0.5 mol/L). Number of polymerization active centers was determined by quenching the reaction with 2-thiophenecarbonyl chloride and measuring sulfur content of the quenched polymer. Each copolymer sample was fractionated into boiling n-heptane soluble and insoluble fractions, and active centers in these fractions were also counted. The rate constants of ethylene and 1-hexene insertion in the active centers were calculated, respectively. Molecular weight distribution (MWD) curves of the polymers were deconvoluted with 4–5 Flory components, and changes of activity of the Flory components with [1-hexene] were analyzed. The polymerization activity and the number of active centers were significantly enhanced by increasing [1-hexene]. Large number of active centers were revived by small amount of 1-hexene. With the increase of [1-hexene], the number of active centers producing polymer chains with lower molecular weight and higher 1-hexene content was increased more than those producing polymer chains with higher molecular weight and lower 1-hexene content, and the MWD curve continuously inclined to the low molecular weight side. The active centers with higher 1-hexene incorporation rate have relatively smaller rate constant of ethylene insertion. When [1-hexene] was increased, the rate constant of ethylene insertion was only slightly changed, but the rate constant of 1-hexene insertion was markedly lowered, meaning that the active centers revived by 1-hexene have relatively lower ability of incorporating 1-hexene.

Ethylene/1-hexene copolymerization with supported Z-N catalyst under different [1-hexene] was compared. [C*] and propagation rate constants of ethylene and 1-hexene insertion (kp) were determined. Polymerization activity and [C*] were significantly enhanced by adding 1-hexene. kp of ethylene insertion changed slightly with [1-hexene], meanwhile kp of 1-hexene insertion was markedly lowered.Figure optionsDownload as PowerPoint slide