Propylene–ethylene copolymerization over titanium–magnesium catalysts: the effect of the composition of an internal stereoregulating electron donor on the molecular structure of the copolymer

Abstract

The data on the molecular structure of random propylene–ethylene copolymers containing 4–5 mol% ethylene, produced over supported titanium–magnesium catalysts (TMCs) with internal stereoregulating electron donors of different composition (di-n-butyl phthalate, 2-isopropyl-2-isopentyl 1,3-dimethoxypropane, and diethyl 2,3-diisobutyl succinate), are reported. Five fractions differing by molecular weight and isotacticity were isolated for these copolymers by preparative temperature rising elution fractionation procedure. The data on the composition of these fractions (ethylene content), their molecular weight, melting temperatures, and crystallinity were obtained. Ethylene content was found to be close for the three copolymer fractions characterized by high molecular weight (M_w = 210–660 kg/mol) and higher isotacticity and these data are independent of composition of the internal donor. Ethylene content increased abruptly in the case of the two lower-molecular-weight fractions (M_w = 90–180 kg/mol). The ¹³C NMR data on the content of ethylene monomeric units EEE and PEE ethylene segments for the low-molecular-weight copolymer fractions are reported. The composition of the internal donor has a noticeable effect on the proportion of EEE and PEE ethylene segments and isolated PEP ethylene segments in these low-molecular-weight copolymer fractions.