Liquid Chromatographic Separation of Olefin Oligomers and its Relation to Separation of Polyolefins – an Overview

Abstract

Linear and branched alkanes are oligomers of polyethylene. Alkanes with higher molar masses are called waxes. These substances are widely used as fuels, oils, lubricants, etc. and for these reasons many groups have tried to analyse, separate and characterise alkanes by various methods, including liquid chromatography. Alkanes may be separated according to their size in solution by SEC. In addition to chromatographic systems separating in the SEC mode, various sorbent-solvent systems have been published, where alkanes have been separated one from another by adsorption and/or precipitation mechanism. The mobile phase is either a nonpolar solvent or a polar solvent or a mixture of a solvent and a non-solvent for alkanes. Even near critical conditions, which have several advantages for applications of HPLC in polymer analysis, have been identified for alkanes. Moreover, selective separations of branched alkanes according to their structure have been published. In the majority of these published studies, solvents with low boiling points have been used as the mobile phases, which do not allow dissolution of crystalline polyolefins at atmospheric pressure. However, taking into account experiences with the separation of alkanes, new HPLC systems for the separation of polyolefins may be developed. This is a major challenge and first results are presented in this contribution.

A review on the development of liquid chromatography systems for polyolefins

“…Realization of 2-D LC for polyolefins was announced as late as in 2010 by groups working in Freeport [104] and in Darmstadt [105]. Roy et al [104] applied the same separation system, as described by Macko et al [77,79,83] to characterize ethylene/1-octene copolymers, whereas Ginzburg et al [105] realized HPLC Â SEC on-line to separate blends of PP stereoisomers, ethylene/propylene rubbers, ethylene/norbornene copolymers and ethylene/1-hexene copolymers with homopolymers, all at 1601C, using Hypercarb/1-decanol-TCB. The 2-D (composition versus molecular weight) distributions were obtained for the blends of polymers.…”

“…Porous graphite Hypercarb was originally developed by Knox and coworkers [80] and has been used in HPLC analysis of small molecules; it was, however, never applied to separate synthetic polymers [81]. Macko et al found that porous carbon Hypercarb adsorbed linear PE from the mobile phase 1-decanol at 1601C [77,79,82]. The retained polymer could be desorbed from the column using a linear gradient starting from 1-decanol and ending with TCB.…”

Recent Advances in High-Temperature Fractionation of Polyolefins

“…Roy et al [178] applied a separation system that was previously described by Macko et al [158,159,162]. This system was applied to the separation of ethylene/1-octene copolymers regarding chemical composition and molar mass.…”

“…28a). Isotactic PP chains or iPP blocks do not adsorb on graphite surface from 1-decanol [158][159][160]. The introduction of adsorbing 1-alkene groups (i.e., branches containing more that 11 carbons) leads to an increase in the retention volumes of the propene/1-alkene copolymers (Fig.…”

“…Hypercarb was originally developed by Knox and coworkers [157] and had been used in HPLC analysis of small molecules; it was, however, never applied to separate synthetic polymers. Macko et al found that porous carbon Hypercarb adsorbs linear PE from 1-decanol as the mobile phase at 160 C [158][159][160]. The retained polymer was desorbed from the column using a linear gradient from 1-decanol to TCB.…”