Investigation of Chain Microstructure of Polypropylene Polymerized by Ziegler–Natta Catalysts with Diester and Diether Compound as Internal Donor via Hydrogen Chain Transfer

Two series of polypropylene samples (PP) were prepared with two MgCl₂/TiCl₄-type catalysts with diisobutyl phthalate and 9,9-bis­(methoxymethyl)fluorine as internal donors (named as cat1 and cat2), respectively, at different hydrogen dosages. The results show that the molecular weights and microstructures of polypropylene were affected by the dosages of hydrogen, which acted as a chain transfer agent in propylene polymerization. For the two catalysts, the molecular weights of polypropylene had an exponential relationship with the hydrogen dosages, to which the total defect contents and lamellar thicknesses (L_n) however showed a linear dependency, indicating that hydrogen exerted similar effects on the above polypropylene properties. However, there were differences in the linear relationships of mmmm contents and the hydrogen dosages for the two catalysts. Moreover, the linear relationship between the lamellar thickness (L₁) of PP prepared with the two catalysts and hydrogen content is also different. It was suggested that for different catalysts of different internal donors the hydrogen chain transfer followed different patterns in affecting polypropylene properties. Our results provide guidelines to obtain special quality polypropylene by hydrogen chain transfer.