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

摘要

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 Ph2C(Cp)(Flu)ZrCl2/PhNHMe2B(C6F5)4/(i-Bu)3Al, 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.