On the multimodality of preparative TREF fractionation as detected by advanced analytical methods

Study of Heterogeneity of Ethylene/1-Octene Copolymers Synthesized with Zirconium and Titanium Complexes Bearing Diamine-bis(phenolate) Ligands

A series of ethylene/1-octene copolymers synthesized with diamine-bis(phenolate) complexes activated with Al(iBu)3/[Ph3C][B(C6F5)4] were subjected to preparative temperature rising elution fractionation (TREF). The complexes used differed in the type of metallic center (Zr or Ti) or the amine donor in the pendant arm of the ligand (NMe2 or NiPr2). The obtained fractions were then characterized via FTIR, DSC and GPC methods. It was found that all the copolymers had very broad chemical composition distributions, and the most heterogeneous was the copolymer produced by the titanium complex bearing a ligand with the NiPr2 donor group. The difference in the comonomer incorporation into the macromolecules of the fractions was as high as 8.3 mol%. The melting temperature and molecular weight of the fractions changed nearly linearly with the increased elution temperature. Copolymers produced by zirconium catalysts were also fractionated by molecular weight using the solvent/non-solvent technique with subsequent analysis of the fractions. It was shown that the fractions have a similar composition, low molecular weight distribution and very broad comonomer distribution. Therefore, the comonomer content in the fractions was not a function of the molecular weight as was observed for the copolymers synthesized with the Ziegler-Natta catalysts.

Multidimensional chromatographic analysis of carboxylic acid-functionalized polyethylene

Carboxy-functionalized polyethylene is comprehensively analysed using a multidimensional fractionation approach based on high-temperature HPLC, two-dimensional liquid chromatography and selective infrared detection.

A multidimensional fractionation protocol for the oligomer analysis of oxidized waxes

Oxidized waxes possess far superior properties as compared to the alkanes they are derived from. The separation of alkane oligomers via gas chromatography (GC) becomes a challenge when polar oxygen-containing functional groups are introduced or when higher molar masses are targeted. In the present study, the separation and analysis of oligomers in oxidized and non-oxidized waxes using different liquid chromatographic techniques are investigated. Oligomers in two oxidized waxes and a non-oxidized wax from which they are derived, are separated using high-temperature solvent gradient interaction chromatography (HT-SGIC) and high-temperature two-dimensional liquid chromatography (HT-2D-LC). Evaporative light scattering detector conditions are tailored to provide the best detection with the solvent system at use. It is shown that oligomers in oxidized and non-oxidized waxes can be separated and identified using the mentioned techniques. It has been found that the ELSD detector response systematically decreases as the oxidation levels of the waxes increase. Coupling of HT-HPLC and high-temperature size exclusion chromatography (HT-SEC) in a comprehensive 2D-LC setup shows a broadening of the molar mass distributions of the lower oligomer fractions as a consequence of the modification indicating changes in the oligomer chain microstructures. A preparative fractionation technique is utilized to collect specific oligomer fractions from the bulk waxes followed by hyphenation to HT-HPLC and other techniques. HPLC is shown to provide more detailed information on the oligomer composition of waxes when coupled to a pre-fractionation technique.

Branching and molar mass analysis of low density polyethylene using the multiple preparative fractionation concept

The multiple preparative fractionation concept provides sample libraries with different degrees of branching and different molar masses that are analyzed regarding the LDPE microstructure.

Combination of preparative and two-dimensional chromatographic fractionation with thermal analysis for the branching analysis of polyethylene

Multiple preparative fractionation of LDPE provides molar mass and branching fractions that are analyzed regarding their thermal properties.

Comprehensive analysis of novel grafted polyethylenes using multidimensional fractionation methods

Noval graft copolymers HDPE-g-LDPE were prepared using a dual reactor setup and characterized regarding molar mass, branching and grafting efficiency using a multidimensional analytical approach.

Comprehensive analysis of branched polyethylene: the multiple preparative fractionation concept

A concept for the comprehensive analysis of branched polyethylene is developed where a multiple fractionation protocol is used.