Characterization of ethylene‐propylene copolymers with high‐temperature gradient adsorption liquid chromatography and CRYSTAF

Abstract

Blends of linear polyethylene (PE) and isotactic polypropylene (iPP) with different average molar masses and a series of ethylene-propylene (EP) copolymers with different chemical composition as well as blends of PE, Ipp, and EP copolymers were separated using a carbon-column packing (HypercarbV R ) and gradients of 1-decanol or 2-ethyl-1-hexanol ! 1,2,4-trichlorobenzene (TCB). The separation is based on full adsorption of linear PE on the carbon sorbent at temperature 160 C. However, iPP is not adsorbed and elutes in size exclusion mode. The random EP copolymers have been adsorbed in the column packing and separated according to their average chemical composition after application of the gradient starting with alcohol and ending with pure TCB. The elution volumes of the copolymers depended linearly on the average concentration of ethylene in the copolymers. The HPLC elution profiles were correlated with the CRYSTAF elution profiles. In contrast to CRYSTAF, fully amorphous polyolefin samples were separated with the high-temperature adsorption liquid chromatography.

Recent Advances in High-Temperature Fractionation of Polyolefins

“…Independence of the elution volumes on the molar mass >15-20 kg/mol was also found for PE [164] and EP, EB, EO and ethylene/1-decene copolymers [161]. It is typical for adsorption phenomena that adsorption depends on the shape of a molecule, on positions and numbers of functional groups, on polarizability of the molecule, as well as on the type and nature of the sorbent and the solvents.…”

“…Macko et al demonstrated the usefulness of the approach for EPC [164] and copolymers of propylene with different tacticities [165]. Moreover, terpolymers of ethylene, propylene and a diene monomer (EPDM) were separated [166].…”

“…It was found that both comonomers, ethylene and diene, are adsorbed. On the other hand, adsorption of EP [164], ethylene-butene (EB), ethylene-hexene (EH), ethylene-octene (EO) or ethylene/1-decene copolymers depends linearly on the average content of ethylene [161]. This is very practical from the point of evaluation of chromatograms.…”

High‐Temperature Solvent Gradient Liquid Chromatography of Model Long Chain Branched Polyethylenes

“…However, the fact that all LCB elute in the same volume range as for the similarly constituted samples without LCB (PEL90 and PEL195) is a clear indication that the retention strength is driven by the presence of SCB (i.e., by the average ethylene sequence length) with an insignificant effect of the LCB junction. It was also shown [37] that linear PE with a molar mass > 14 kg/mol (14-1050 kg/mol) eluted in the 1-decanol/TCB/Hypercarb system with elution volumes which differed each from one another by about 0.2 mL. The elution volumes of the LCB PE samples also differ by about 0.2 mL each from one another ( Figure 2).…”

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

“…The separation in HT‐HPLC depends mainly on the chemical composition of the polyolefin and in EP copolymers separation is according to the ethylene content of the sample . Several studies had been done on HT‐HPLC of metallocene EP copolymers but their focus was on the bulk samples . Fractionation of metallocene EP copolymers by TREF and subsequent HT‐HPLC analysis has not been reported in the literature.…”