On the Homogeneity of Metallocene Ethylene–Propylene Copolymers as Investigated by Multiple Fractionation Techniques

Abstract

The chemical heterogeneity of ethylene–propylene copolymers by multiple fractionation techniques is addressed. Three metallocene copolymer samples with different ethylene contents, ranging from 30 to 50 mol% are analyzed using bulk methods to confirm their molecular heterogeneity. In a second step, the samples are fractionated by temperature rising elution fractionation (TREF) to obtain fractions at 30, 60, 90, and 130 °C. These fractions are subsequently analyzed regarding their thermal and molecular properties. Differential scanning calorimetry, crystallization analysis fractionation, and high‐temperature high performance liquid chromatography (HT‐HPLC) results reveal that the TREF fractions collected at 130 °C are mainly due to polypropylene homopolymer, which is rather unexpected considering the high ethylene contents of the bulk samples. Most importantly, HT‐HPLC reveals a remarkably high chemical heterogeneity of the fractions and thus the bulk samples. Solution 13C NMR provides the comonomer contents and sequence distributions of the fractions. These indicate that the same TREF fractions from different samples have distinctively different chemical compositions.

Exploring the Compositional Heterogeneity of Vis‐Broken Impact Poly(propylene) Copolymers by Advanced Fractionation Methods

“…In agreement with the assumption, the DSC melting curves of the 30 °C fractions show no melting events thus confirming that these fractions are completely amorphous (see Figure ). At the same time, the 130 °C fractions exhibit very similar melting peaks at about 160 °C that can be assigned to it ‐PP being the components with the highest crystallinity …”

“…At the same time, the 130 °C fractions exhibit very similar melting peaks at about 160 °C that can be assigned to it -PP being the components with the highest crystallinity. [ 33 ] The most distinct differences between the samples can be seen for the 60 and 90 °C fractions. These contain EP copolymer molecules with different ethylene and propylene sequence lengths.…”

“…The dwell and void volumes of 1.7 and 1.1 mL, respectively, were measured according to the method described by Ginzburg et al. This reflects that there is an isocratic elution of 1‐decanol (1.7 mL) before the gradient hits the column . Samples were injected at a concentration of 1–1.2 mg mL −1 , with 20 μL of each sample being injected.…”

“…This refl ects that there is an isocratic elution of 1-decanol (1.7 mL) before the gradient hits the column. [ 17,33 ] Samples were injected at a concentration of 1-1.2 mg mL −1 , with 20 μL of each sample being injected.…”