Study on electron donors for Ziegler-natta catalyst systems in propylene polymerization

Abstract

The role of two different internal donors [a phthalate (diisobutylphthalate) and a 1,3-diether (2,2-diisobutyl-1,3-dimethoxypropane)] on the formation of surface structure in MgCl2-supported Ziegler-Natta catalysts and their catalytic performance of propylene polymerization was investigated by comparing and correlating the catalyst structures and the polymerization characteristics. In the catalyst formation, the 1,3-diether had better affinity for the MgCl2 surface than the phthalate and the 1,3-diether generated the (110) surface rather than the (104) surface while the phthalate generated both the (110) and (104) surfaces of MgCl2. With both donors introduced, the (110) and (104) surfaces were generated simultaneously, although the (110) surface was dominant due to the higher affinity via the 1,3-diether. In addition, it seemed probable that the active sites formed on the (110) plane showed isospecific characteristics in the presence of a donor while those formed on the (104) plane could be isospecific regardless of a donor. Copolymerization of propylene and ethylene and terpolymerization of propylene, ethylene, and 1-butene were carried out to compare the characteristics of 1,3-diether- and phthalate-based Ziegler-Natta catalysts in a reaction system of pilot scale. The ethylene incorporation with the 1,3-diether-based catalyst was higher but the 1-butene incorporation was lower compared with those of the phthalate-based catalyst. In the case of copolymers from the 1,3-diether-based catalyst, melting behavior, determined through differential scanning calorimetry (DSC), showed a distinct shoulder peak and lots of nuclei were formed during crystalli-zation. The 1,3-diether-based catalyst led to polymers having blockier ethylene sequences compared with those of the phthalate-based catalyst; the highly crystallizable fraction (HIS) containing blockier ethylene sequences was produced with the 1,3-diether-based catalyst. These results seem to be the result of regi...