Highly Active FI Catalyst of Bis [N-(3,5-dicumylsalicylidene)cyclohexylaminato]-zirconium (IV) Dichloride for Polymerization of Ethylene

Ahighly active Zr-based FI catalyst of bis[N-(3,5-dicumylsalicylidene)cyclohexylaminato]zirconium(IV) dichloride was prepared and used for polymerization ofethylene. The catalyst displayed a very high activity of about 3.2×106 in ethylenepolymerization at the monomer pressure of 3 bar using triisobutylaluminium (TIBA) andmethylaluminoxane (MAO) as a scavenger and cocatalyst, respectively. The highestactivity of the catalyst was obtained at about 35°C. The polymerization activity wasincreased linearly with increased monomer pressure and [Al]:[Zr] ratio in the rangestudied. Introduction of bulky cumyl group on ortho position to the phenoxy oxygenprevents the catalyst from coordination to the cocatalyst following its easiercoordination of ethylene to the active centres. The existence of bulky substitutions onthe catalyst structure resulted in linear increase in its activity with increasing the MAOconcentration through ion separation which facilitates the monomer insertion. However,fouling of the reactor was strongly increased with monomer pressure and the amountof MAO used. Ethylene polymerization was carried out using different amounts ofhydrogen. The activity of the catalyst was slightly increased with addition of hydrogen;however, the viscosity average molecular weight (Mv) of the obtained polymer was notaffected. In order to study the catalyst lifetime service, ethylene polymerizationreactions were carried out at different reaction times while the temperature and [Al]/[Zr]molar ratio were kept constant. Despite the high activity, the catalyst showed a shortlifetime. Crystallinity and melting point of the obtained polymer were between 55-65%and 125-130°C, respectively. Mv Values of the obtained polymer were dropped aspolymerization temperature increased, while higher pressure increased both thecrystallinity and the Mv values of the resulting polymer. Meanwhile some specificationsof the obtained polymer were investigated.