Influence of the Ethanol Content of Adduct on the Comonomer Incorporation of Related Ziegler–Natta Catalysts in Propylene (Co)polymerizations

Abstract

The aim of this work is to investigate the influence of the ethanol content of adducts on the catalytic behavior of related Ziegler–Natta (ZN) catalysts in propylene homo- and copolymerizations (with 1-hexene comonomer) in terms of activity, isotacticity, H2 response, and comonomer incorporation. For this purpose, three MgCl2.nEtOH adducts with n values of 0.7, 1.2, and 2.8 were synthesized and used in the synthesis of related ZN catalysts. The catalysts were thoroughly characterized using XRD, BET, SEM, EDX, N2 adsorption–desorption, and DFT techniques. Additionally, the microstructure of the synthesized (co)polymers was distinguished via DSC, SSA, and TREF techniques. Their activity was found to enhance with the adduct’s ethanol content in both homo- and copolymerization experiments, and the increase was more pronounced in homopolymerization reactions in the absence of H2. Furthermore, the catalyst with the highest ethanol content provided a copolymer with a lower isotacticity index, a shorter meso sequence length, and a more uniform distribution of comonomer within the chains. These results were attributed to the higher total surface area and Ti content of the corresponding catalyst, as well as its lower average pore diameter, a larger proportion of large pores compared to the other two catalysts, and its spherical open bud morphology. It affirms the importance of catalyst/support ethanol-content control during the preparation process. Then, molecular simulation was employed to shed light on the iso-specificity of the polypropylene produced via synthesized catalysts.

Keywords

• polypropylene
• Ziegler–Natta
• adduct
• ethanol
• comonomer
• structure properties relationship