Fractionation and characterization of an ethylene–propylene copolymer produced with a MgCl₂/SiO₂/TiCl₄/diester‐type ziegler–natta catalyst

Abstract

An ethylene-propylene copolymer synthesized with a Ziegler-Natta catalyst was fractionated by a combination of dissolution/precipitation and temperaturegradient extraction fractionation. The fractions were characterized with 13 C-NMR, differential scanning calorimetry, and wide-angle X-ray diffraction. The fractionation was carried out mainly with respect to the content of ethylene, but the crystallizable propylene sequences could also exert an influence on the fractionation. The copolymer contained a series of components with wide variations in the compositions. With an increase in the ethylene content, the structure of the fractions became blockier and blockier, and the fraction extracted at 1118C had the blockiest structure. A further increase in the ethylene content led to a decrease in the length and number of the propylene sequences. Differential scanning calorimetry results showed that the composition distribution in single fractions was not homogeneous, and multiple melting peaks were observed. Wideangle X-ray diffraction results revealed both polyethylene and polypropylene crystals in most of the fractions. Short propylene sequences could be included in the polyethylene crystals, and short ethylene sequences could also be incorporated into the polypropylene crystals. The incorporation of propylene sequences into polyethylene crystals strongly depended on the sequence distribution and crystallization conditions.

Copolymerization of ethylene and propylene catalyzed by novel magnesium chloride supported, vanadium‐based catalysts

“…For EP copolymers with high ethylene contents, such as those obtained in this work, it is also possible to observe the crystallinity. It was found that the crystallinity increased with the E/P molar ratio, and this is consistent with the results reported by Dong et al25 It is expected that the crystallinity of an EP copolymer with a higher comonomer composition will be smaller. In this work, the copolymers were practically amorphous (the crystallinity was below 20%).…”

Investigation of diene addition on ethylene–propylene (EP) copolymerization with a zirconocene catalyst: Effects of diene types and E/P ratios

“…Wang et al (2004) found that the long-chain branching (LCB) in EP copolymers was the determining factor in controlling rheological properties of the polymer. An EP copolymer synthesized with a Ziegler-Natta catalyst was studied by Dong et al (2008). They found that an increase in ethylene content made the * Corresponding author.…”

Kinetics of short‐duration ethylene–propylene copolymerization with MgCl2‐supported Ziegler–Natta catalyst: Differentiation of active centers on the external and internal surfaces of the catalyst particles

“…28,29,36 Two types of active centers are responsible for formations of these two fractions. 28,29,36 Two types of active centers are responsible for formations of these two fractions.…”

“…In ethylene copolymerization with aolefin (propylene, 1-butene, and so on), strong activation effects of the a-olefin have been reported in many ZN catalytic systems. 16,17,[27][28][29][30] The active centers producing these two copolymer fractions could have quite different chemical structure and stereochemical environments. 27 On the other hand, differences between the multiple active center types in supported ZN catalysts can be more easily studied in the copolymerization.…”