Chemical Composition Separation of EP Copolymers by CEF and HT‐SGIC: Crystallization versus Adsorption

Abstract

Preparative temperature rising elution fractionation (prep TREF) suffers from co‐crystallization effects and, therefore, cannot provide reliable chemical composition distribution (CCD) information. This limitation can be overcome when prep TREF is combined with further fractionation methods such as crystallization elution fractionation (CEF) or high‐temperature solvent‐gradient‐interaction chromatography (HT‐SGIC) as a new approach. By CEF, significant amounts of (co‐crystallizing) amorphous ethylene‐propylene (EP) copolymer are identified in semicrystalline TREF fractions of a heterophasic ethylene/propylene copolymer (HEPC). Complete compositional fractionation with no influence of crystallization effects is accomplished by HT‐SGIC. Prep TREF–HT‐SGIC is found to be the most selective and suitable method for the fast and complete CCD analysis of such complex EP copolymers with CEF providing complementary information.

Molecular heterogeneity of ethylene-propylene rubbers: New insights through advanced crystallization-based and chromatographic techniques

“…A comprehensive solvent‐gradient chromatographic technique which permits separation and characterization to occur above the melting and crystallization temperatures of polyolefins has been used to avoid the problems of co‐crystallization effects that take place in DSC, TREF, and CRYSTAF . The recently developed high temperature–high performance liquid chromatography (HT‐HPLC) allows the analysis of both the amorphous and the crystalline fractions since the separation depends on the interaction or adsorption of the macromolecules with the stationary phase . For EPR copolymers it had been reported that on a graphitic stationary phase the separation depends mainly on the ethylene content of the sample .…”

Chemical Composition Fractionation of Olefin Plastomers/Elastomers by Solvent and Thermal Gradient Interaction Chromatography

“…Such methods are still able to separate plastomers with densities between 902 and 910 kg m −3 according to their comonomer contents but are not suitable for elastomers with densities from 900 to 857 kg m −3 . [2][3][4][5] The most significant contribution to the characterization of polyolefins with low crystallinities according to their CCDs has been achieved by interaction liquid chromatography at high temperatures (HTIC), which works at operating conditions above crystallization and melting temperatures and separates complex polyolefins regarding chemical composition, irrespec tive of crystallinity. [6][7][8][9][10] HTIC uses graphitized carbon black as stationary phase and the separation is based on the selective interaction of long uninterrupted ethylene sequences with the graphitic surface.…”

“…These techniques fractionate the macromolecules according to their crystallizability in solution and provide a predictable separation of the polymer fractions depending on the comonomer content, polymer chain irregularities, or tacticity differences. Such methods are still able to separate plastomers with densities between 902 and 910 kg m −3 according to their comonomer contents but are not suitable for elastomers with densities from 900 to 857 kg m −3 …”

Assessment of the Cocrystallization of Ethylene/1‐Octene Copolymer Blends by CRYSTAF and TREF

“…Well‐established techniques working in solution such as crystallization fractionation (CRYSTAF), [ 25,26 ] temperature rising elution fractionation (TREF) [ 27 ] and Crystallization Elution Fractionation (CEF) [ 28,29 ] provide chemical composition based on crystallizability. [ 30–32 ] Regularly folded single crystals are the most stable polyethylene crystallite state in solution, in contrast, spherulites with amorphous regions are expected from melt crystallization.…”