A new chromium(III)/p-tert-butylcalix[4]arene/alkylaluminum catalyst system for the preparation of low molecular weight polyethylene

Abstract A new chromium(III)/ p-tert -butylcalix[4]arene/alkylaluminum catalyst system was applied to assist the ethylene polymerization. The catalyst system was found to be very active for the ethylene polymerization, and gave strictly linear polyethylene, with high crystallinity and low number average molecular weight ( M n ) ranging from 910 to 9740, without using molecular hydrogen as a molecular weight reducer. The effects of polymerization parameters such as temperature, ethylene pressure, chromium catalyst concentration, type of alkylaluminum compounds, and Al/Cr molar ratio on the catalytic activity and properties of the polyethylene were investigated. The formation of low molecular weight polyethylene using the chromium(III)/ p-tert -butylcalix[4]arene/alkylaluminum catalyst system was explained by the coordination effect of structurally hindered and less electron-donating p-tert -butylcalix[4]arene ( L H 4 ) anion ligand.