Carbonaceous sorbents for high‐temperature interactive liquid chromatography of polyolefins

Abstract

The elution behavior of polyethylene (PE) and the three stereoisomers of polypropylene (PP) was studied on porous graphite along with three other carbon-based sorbents, carbon-clad zirconia particles, activated carbon, and exfoliated graphite in a systematic way in this work. Decahydronaphthalene, 1,2,3,4-tetrahydronaphthalene, 1,3,5-trimethylbenzene, tetrachloroethylene, xylene and p-xylene were used as mobile phases. While PE is adsorbed to various extents on all the tested carbonaceous sorbents from the majority of the solvents, PP is fully adsorbed only in selected cases. Testing alcohols (C7-C9) as mobile phase with Hypercarb™ indicates that all stereoisomers of PP are selectively adsorbed and desorbed when a solvent gradient alcohol→1,2,4-trichlorobenzene is used at 160°C. The retention of all stereoisomers of PP increases with the polarity of the alcohol. Linear PE is retained on Hypercarb™ even from 1,2-dichloro- and 1,2,4-trichlorobenzene, when a temperature below 120°C is applied, while it is not retained from these solvents at higher temperatures. All stereoisomeric forms of PP are not adsorbed under the same conditions. Some of the tested new sorbent/solvent systems have potential to be applied in routine analysis of industrially synthesised polyolefins.

Characterization of the Chemical Composition Distribution of Ethylene/1‐Alkene Copolymers with HPLC and CRYSTAF—Comparison of Results

“…Full adsorption of PE is observed also at temperature as high as 160 °C from various polar and nonpolar solvents . PE is adsorbed on graphite at 100 °C even from ODCB and TCB, i.e., from thermodynamically very good solvents, which underlines that pronounced interactions exist between the PE and the sorbent surface. On the other hand, PE is fully desorbed by ODCB and TCB at 160 °C.…”

Separation of Ethylene‐Propylene Copolymers by Crystallization and Adsorption Mechanisms. A Journey Inside the Analytical Techniques

“…The chain regularity (related to the number of branches) is a common contributing factor for crystallizability (internal forces) as well as the adsorption potential on an ALFS substrate. In all crystallization and adsorption techniques there is an elution volume dependence on molar mass below a certain level, the lowest in CRYSTAF and TREF, followed by TGIC and SGIC . Above that molar mass level, elution volume is only dependent on composition for the ordered copolymer series.…”

Elution Behavior of Polypropylene with Different Tacticity – An Overview

“…The system 1‐decanol→TCB/Hypercarb™ has been widely applied for HPLC separations of polyolefins . In this system iPP is not retained, i.e., it elutes in SEC mode in 1‐decanol and aPP and sPP elute in the gradient (Figure a).…”

“…The adsorption of PP and PE on graphite forms the basis for the separation of polyolefins, not only in solvent gradient liquid chromatography, but also in temperature gradient liquid chromatography (TGIC) and in two‐dimensional liquid chromatography (2D‐LC) . Moreover, a transition modus between size exclusion and adsorption liquid chromatography, i.e., critical conditions, for PE was found with the porous graphite column packing.…”