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State-of-the-art liquid interaction chromatography (IC) allows separation of macromolecules according to chemical composition (CC), functionality or molecular topology in contrast to size-based approaches such as size exclusion chromatography (SEC), which has its limitations in distinguishing chemical structures. Yet, for macromolecules with multivariate molecular distributions, online identification and characterization of distinct components in bulk samples is a considerable challenge. A useful approach to narrow down the complexity of a given sample is preparative molar mass fractionation (pMMF) that provides fractions in mg or g scale, which can be subjected to further advanced analysis to elucidate the physical and structural properties of the sample. In this study, novel chain-walking polyethylenes (CWPE), which differ substantially in macromolecular architecture, are fractionated using pMMF. Using IC in temperature and solvent gradient modes (TGIC, SGIC), the pMMF fractions are separated according to branching topology. Quadruple-detector high temperature SEC is carried out to determine the physical properties and study the MM-dependent structural transformation of CWPE. A detailed branching analysis was carried out by means of nuclear magnetic resonance. Two-dimensional liquid chromatography (LC) hyphenating IC and SEC provides comprehensive bivariate correlations between MM and molecular topology. [ABSTRACT FROM AUTHOR]

Linear low density polyethylene (LLDPE) exhibits a complex molecular structure that is characterized by molar mass and chemical composition distributions. Both molecular parameters complementarily influence the final application properties. Typically, the molecular structure of commercial polyolefins is characterized by a set of technical parameters including the melt flow index, the crystallization and melting temperatures and the comonomer content as obtained using Fourier transform infrared or NMR spectroscopy. LLDPEs with high comonomer contents are typically regarded as plastomers or elastomers. Due to their low crystallinities, characterization of these materials using crystallization‐based analytical techniques is of limited use since the majority of the material is rather amorphous. Such materials need specific alternative analytical methods that may be based on molar mass and/or chemical composition fractionation. Here it is shown that for a comprehensive analysis of LLDPEs with similar bulk properties, preparative molar mass fractionation (pMMF) and advanced analysis of the fractions are required. The pMMF fractions are comprehensively analyzed using size exclusion chromatography, differential scanning calorimetry and high‐temperature high‐performance liquid chromatography to provide detailed information on molar mass and copolymer composition. Correlated information of these molecular parameters is obtained by comprehensive two‐dimensional liquid chromatography. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) differ significantly in their branching types and branching distributions. For a comprehensive analysis, preparative temperature rising elution fractionation and/or preparative molar mass fractionation are used to fractionate typical LLDPE and LDPE bulk resins into narrowly distributed fractions. The chain structures of the bulk resins and their fractions are further analysed using SEC, crystallization analysis fractionation, DSC and high‐temperature HPLC to provide detailed information on short chain branching in LLDPE and long chain branching in LDPE. For LDPE it is shown that the multiple fractionation approach is a powerful source of sample libraries that may have similar molar masses and different branching structures or alternatively similar branching but different molar masses. The analysis of these library samples by thermal analysis provides a much deeper insight into the molecular heterogeneity of the samples compared to bulk sample analysis. © 2018 Society of Chemical Industry Linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) differ significantly in their branching distributions. For comprehensive analysis, a multidimensional analytical approach is used that is based on the combination of preparative fractionation and advanced analytical methods. [ABSTRACT FROM AUTHOR]

ABSTRACT Classical linear low density polyethylenes (LLDPEs) are copolymers of ethylene and 1-octene or 1-hexene, respectively. In the past, other 1-olefins have been tested as comonomers but the resulting LLDPEs were never commercialized as large scale products. The present study focuses on the use of 1-heptene as an interesting comonomer for the synthesis of LLDPE. For a comparison of the molecular structure and the physical properties of 1-heptene- and 1-octene-based LLDPEs, five Ziegler-Natta LLDPEs of varying comonomer contents based on 1-heptene and 1-octene, respectively, were acquired and analysed using advanced methods. The comonomer contents of the resins were between 0.35 and 6.4 mol %. Crystallization-based techniques revealed similar bimodal distributions that are due to the formation of copolymer and polyethylene homopolymer fractions. The compositional distribution of the copolymers was studied by high-temperature (HT) HPLC and HT-2D-LC. The analytical results indicate similar chemical heterogeneities and molar mass distributions of the two sets of LLDPE up to a comonomer content of 3 mol %. Similar to the molecular structure, the physical properties of the materials are quite similar. At comonomer contents of ≥3 mol % differences between the two sets of samples are seen that are attributed to differences in the abilities of 1-heptene and 1-octene in disrupting the crystal arrangements of the polymer chains in solid state. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 962-975 [ABSTRACT FROM AUTHOR]