Effect of the pore architecture of Ziegler-Natta catalyst on its behavior in propylene/1-hexene copolymerization

Abstract

The role of the pore architecture of the Ziegler-Natta (ZN) catalysts in the propylene polymerizations is unveiled, towards the catalyst activity, H2– and comonomer-response, and final properties of the synthesized polymer. In this regard, two commercially available ZN catalysts (Cat-A and Cat-B belong to the 4th generation, containing diisobutyl phthalate as internal donor) with a similar composition but with different pore structures were employed in propylene/1-hexene copolymerizations in the presence of H2 as a chain transfer agent. Although pore diameter does not alter H2-response noticeably, it significantly affects the comonomer incorporation as well as the distribution of the isotactic sequence length in the copolymer backbone. Cat-A with a lower surface area, a larger pore diameter, and a wider inlet showed slightly higher activities in homopolymerization and copolymerization experiments. According to the self-nucleation and annealing (SSA) results, the copolymer produced from Cat-A demonstrated lower isotactic sequence length and lamellar thickness contents owing to its larger pore diameter with wider inlets. Moreover, Temperature Rising Elution Fractionation (TREF) profiles asserted SSA data in which the copolymer from Cat-A represented a higher content of low elution temperatures fractions, due to its higher comonomer content. These findings will lead to catalysts for different polypropylene grades.