High‐temperature and high‐pressure ethylene polymerization using a cationic activated metallocene catalytic system

Abstract

BACKGROUND: Normally, olefin polymerization via metallocene-based catalysis occurs under mild conditions. However, most technology developed for polyolefin production is designed for more severe temperature and pressure processes. Attaining more thermally stable metallocene systems for industrial applications is an important challenge for researchers. RESULTS:A systematic study of ethylene homopolymerization at higher temperatures and pressures, employing the ternary system Ph 2 C(Cp)(Flu)ZrCl 2 /PhNHMe 2 B(C 6 F 5 ) 4 /(i-Bu) 3 Al, is presented The optimal activity for this system is achieved with a Zr/B/Al molar ratio of 1/6/250 and a temperatures of around 130 • C. However, the amount of activator strongly affects the molecular weight and the polydispersity of the polymers produced. Polyethylene produced with Zr/B/Al molar ratios between 1/2/250 and 1/6/250 show no significant difference in their temperature of fusion (T m ) and their crystallinity (X c ). In contrast, in the presence of activator amounts higher than 1/6/250, both the temperature of fusion and polymer crystallinity undergo a steep decrease. All polymers presented lamellar morphology when the activator was present, and an amorphous aspect when the activator was not employed. CONCLUSION:The presence of the activator is essential for thermal stabilization of the catalytic system. Variation of the Zr/B/Al ratio leads to modifications of the catalytic activity as well as to the properties of the polymers synthesized.

Ethylene polymerization catalyzed by a cyclophane-diimine-based Ni(II) complex, a quantum/molecular mechanic study

“…This innovation expanded the number of applications of molecular Ziegler-Natta catalytic systems [5][6][7] for the development of new polyolefinic materials [8]. Chain walking occurs properly if the environment around the catalytic site, promoted by specific ligands, hinders termination polymerization reactions, such as ␤-hydride transfer from the growing chain to the monomer, and olefin change.…”

Regulating the polyethylene microstructure by increasing steric crowding in naphthoxy imine-ligated Ni(ii) complexes

“…[25][26][27][28][29] Furthermore, steric bulk has a significant influence on the thermal stability and polymerization activity of the catalyst. 16,30 Among several other sterically bulky groups, the dibenzhydryl moiety is commonly used to modify α-diimine ligated Ni(II) or Pd(II) complexes. 16,[31][32][33][34][35][36][37][38][39] The dibenzhydryl-substituted catalysts are robust and yield PE with a high molecular weight and low branch density.…”

Copolymerization of ethylene/α‐olefins using bis(2‐phenylindenyl)zirconium dichloride metallocene catalyst: structural study of comonomer distribution

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