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Darmstadt, Germany

Zhu Y.,University of Memphis | Ziebarth J.,University of Memphis | Macko T.,German Institute for Polymers | Wang Y.,University of Memphis
Macromolecules | Year: 2010

Partitioning of statistical AB type copolymer chains into a slit pore was studied with Monte Carlo simulations on a simple cubic lattice with self-avoiding walk models. Only one of the monomer types, B monomers, has attractive interaction with the surface, while the A monomers have no interaction with the surface. The critical adsorption point (CAP) of the copolymer at a given chemical composition fB and sequence order parameter λ, which characterizes the degree of blockiness in the copolymer, was determined. The CAP's obtained in the simulations were compared with theoretical predictions proposed by Brun [J. Liq. Chromatogr. Relat. Technol. 1999, 22, 3027-3065]. Most simulation data agree well with Brun's theoretical equation except for sequences at the two extreme of sequence types (i.e., extremely blocky or nearly perfectly alternating). The potential separation of copolymers according to chemical composition in interactive chromatography was examined by examining the partition of copolymers at chosen surface interaction energies. Simulation results show that one can separate the copolymers according to the chemical composition only when the sequence order parameter λ is fixed or has a narrow distribution. The separation will be impaired if there is also a distribution in λ. Separation of copolymer samples according to sequence order parameter at a given chemical position is of limited resolution. © 2010 American Chemical Society. Source

Franssen N.M.G.,University of Amsterdam | Franssen N.M.G.,Dutch Polymer Institute | Remerie K.,SABIC | MacKo T.,Dutch Polymer Institute | And 3 more authors.
Macromolecules | Year: 2012

We present our results obtained in the Rh-catalyzed carbene copolymerization of diazomethane and diazoesters as a new approach to functional polymer synthesis. Copolymerization reactions were successful, and high-M w ethylene-acrylate type copolymers were obtained with a large variation in functional group content, which proved to be tunable by varying the monomer feed ratio and the way of addition. Polymer yields decrease strongly with increasing incorporation of diazomethane due to rapid I-hydride elimination. Sequential insertions of polar monomers were observed to a large extent, giving rise to copolymers with a blocky microstructure, which is a unique feature of this polymerization technique. The copolymer properties are demonstrated to be highly dependent on the functional group content and can therefore easily be varied in the window between the properties of both homopolymers. © 2012 American Chemical Society. Source

Pasch H.,Stellenbosch University | Malik M.I.,University of Karachi | Macko T.,German Institute for Polymers
Advances in Polymer Science | Year: 2013

The synthesis and characterization of polyolefins continues to be one of the most important areas for academic and industrial research. One consequence of the development of new "tailor-made" polyolefins is the need for new and improved analytical techniques for the analysis of polyolefins with respect to molar mass, molecular topology and chemical composition distribution. This review presents different new and relevant techniques for polyolefin analysis. The analysis of copolymers by combining high-temperature SEC and FTIR spectroscopy yields information on chemical composition and molecular topology as a function of molar mass. Crystallization based fractionation techniques are powerful methods for the analysis of short-chain branching in LLDPE and the analysis of polyolefin blends. Thesemethods include temperature-rising elution fractionation, crystallization analysis fractionation and the recently developed crystallization-elution fractionation. The latest development in the field of polyolefin fractionation is high-temperature interaction chromatography. Based on the principles of gradient HPLC and liquid chromatography at critical conditions this method is used for fast analysis of the chemical composition distribution of complex olefin copolymers. The efficiency of HPLC based systems for the separation of various olefin copolymers will be discussed. The ultimate development in high-temperature fractionation of polyolefins is comprehensive high-temperature two-dimensional liquid chromatography. The review will discuss some of the pioneering work that has been done since 2008. Finally, the correlation between molar mass and chemical composition can be accessed by on-line coupling of high-temperature SEC and 1H-NMR spectroscopy. It is shown that the on-line NMR analysis of chromatographic fractions from hightemperature fractionations is possible and yields information on microstructure and tacticity in addition to molar mass and copolymer composition. © Springer-Verlag Berlin Heidelberg 2012. Source

Hiller W.,TU Dortmund | Hehn M.,TU Dortmund | Sinha P.,Stellenbosch University | Raust J.-A.,German Institute for Polymers | And 2 more authors.
Macromolecules | Year: 2012

For the first time, comprehensive two-dimensional liquid chromatography (2D-LC) of complex polymers is coupled online to 1H NMR. 2D-LC is used to separate mixtures of poly(ethylene oxide)s with regard to chemical composition and molar mass. The present samples contain polymers with different end groups and chain distributions. In the first LC dimension, liquid chromatography at critical conditions (LCCC) is used for the selective separation according to the end groups. Fractions that are then uniform regarding their end groups are automatically transferred into the second LC dimension which separates the fractions regarding their chain length distributions using liquid adsorption chromatography. The eluate from 2D-LC is directly introduced into the 1H NMR for on-flow analysis. The online coupling of one- and two-dimensional chromatography with 1H NMR detection is demonstrated. The NMR is coupled to both individual separations as well as to the entire two-dimensional separation. As a result of this multidimensional analysis quantitative information is obtained on the types and topology of end groups and the chain length distributions within each functionality fraction. © 2012 American Chemical Society. Source

Otte T.,German Institute for Polymers | Brull R.,German Institute for Polymers | Macko T.,German Institute for Polymers | Pasch H.,German Institute for Polymers | Klein T.,Postnova Analytics GmbH
Journal of Chromatography A | Year: 2010

Asymmetric flow field-flow fractionation (AF4) enables to analyse polymers with very high molar masses under mild conditions in comparison to size exclusion chromatography (SEC). Conventionally, membranes for AF4 are made from cellulose. Recently, a novel ceramic membrane has been developed which can withstand high temperatures above 130 °C and chlorinated organic solvents, thus making it possible to characterise semicrystalline polyolefins by HT-AF4. Two ceramic membranes and one cellulose membrane were compared with regard to their quality of molar mass separation and the loss of the polymer material through the pores. Separating polystyrene standards as model compounds at different cross-flow gradients the complex relationship between cross-flow velocity, separation efficiency, the molar mass and peak broadening could be elucidated in detail. Moreover, the dependence of signal quality and reproducibility on sample concentration and mass loading was investigated because the evaluation of the obtained fractograms substantially depends on the signal intensities. Finally, the performance of the whole system was tested at high temperature by separating PE reference materials of high molar mass. © 2009. Source

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