Darmstadt, Germany
Darmstadt, Germany

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Hiller W.,TU Dortmund | Pasch H.,Stellenbosch University | Sinha P.,German Institute for Polymers | Wagner T.,Max Planck Institute for Polymer Research | And 3 more authors.
Macromolecules | Year: 2010

The online coupling of liquid chromatography at critical conditions (LCCC) and NMR was used for the analysis of block copolymers. Polyisoprene-b- poly(methyl methacrylate) (PI-b-PMMA) copolymers synthesized by living anionic polymerization were separated regarding chemical composition by LCCC using single solvents as mobile phases. The analysis of the chemically different LCCC fractions was conducted by on-flow 1H NMR. To separate the copolymers from the respective homopolymers, critical conditions of polyisoprene (PI) and poly(methyl methacrylate) (PMMA) were used. Critical conditions were obtained by varying the column temperature. The comprehensive chemical composition and microstructure analysis by 1H NMR revealed that quantitative information on the PI/PMMA content as well as the microstructure of PMMA (isotactic, atactic, and syndiotactic triads) and PI (1,2-PI, 1,4-PI, 3,4-PI) was obtained. For the first time the determination of the true molar masses and true chemical compositions of the block copolymers was achieved by determining the microstructure distribution. © 2010 American Chemical Society.

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.

Otte T.,Postnova Analytics GmbH | Otte T.,German Institute for Polymers | Klein T.,Postnova Analytics GmbH | Brull R.,German Institute for Polymers | And 2 more authors.
Journal of Chromatography A | Year: 2011

The elution behaviour of linear and branched polyethylene samples in SEC was studied. For the branched samples an abnormal late co-elution of large and small macromolecules manifests itself as an abnormal re-increase of the molar mass and the radius of gyration values detected with multi angle light scattering at high elution volumes in SEC. The late co-elution of small and large macromolecules cannot be explained by the SEC mechanism alone. The influence of several experimental parameters on the late co-elution was studied. It was found that the type of SEC column and the flow rate have a significant influence. The late eluting part of the sample was fractionated and separated by HT-SEC- and HT-AF4-MALS. The different results of both methods have been discussed with the aim to find possible explanations for the late elution. The experiments indicate that especially large branched structures show an increased tendency for the phenomenon. © 2011 Elsevier B.V.

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.

MacKo T.,German Institute for Polymers | Brull R.,German Institute for Polymers | Stadler F.J.,Chonbuk National University | Losio S.,CNR Institute for Macromolecular Studies
Analytical and Bioanalytical Chemistry | Year: 2011

A new separation principle was recently introduced into the analytical characterization of polyolefins by researchers from the German Institute for Polymers in Darmstadt. It was demonstrated that polyolefins can be selectively separated via high-performance liquid chromatography on the basis of their adsorption/desorption behaviours at temperatures as high as 160 °C. A Hypercarb® column packed with porous graphite gave the best results. The mobile phase consisted of a mixture of 1-decanol and 1,2,4-trichlorobenzene. In this work, the same chromatographic system is applied to the separation of ethylene/alkene and ethylene/norbornene copolymers. It was found that the elution volumes of the samples correlate linearly with the average chemical composition of samples. The elution volume is indirectly proportional to the concentration of branches in the ethylene/alkene copolymer. Branching shortens the length of continuous methylene sequences of the polymer backbone, thus decreasing the probability of orientation of a methylene sequence in a flat conformation on the graphite surface, which enables the most intensive van der Waals interactions between the methylene backbone and the carbon surface. An opposite trend in the elution order has been found for ethylene/norbornene copolymers. The elution volume of the ethylene/norbornene copolymers increased with the concentration of norbornene. It indicates pronounced attractive interactions between graphite and the cyclic comonomer. © 2010 Springer-Verlag.

Chitta R.,German Institute for Polymers | Macko T.,German Institute for Polymers | Brull R.,German Institute for Polymers | Kalies G.,University of Leipzig
Journal of Chromatography A | Year: 2010

The elution behavior of linear polyethylene and isotactic, atactic and syndiotactic polypropylene was tested using three different carbon column packings: porous graphite (Hypercarb), porous zirconium oxide covered with carbon (ZirChrom-CARB), and activated carbon TA 95. Several polar solvents with boiling points above 150 °C were selected as mobile phases: 2-ethyl-1-hexanol, n-decanol, cyclohexylacetate, hexylacetate, cyclohexanone, ethylene glycol monobutyl ether and one non-polar solvent, n-decane. Polyethylene standards were completely or partially adsorbed in all tested sorbent/solvent systems. Polypropylene standards were partially adsorbed on Hypercarb and carbon TA95, but did not adsorb on ZirChrom-CARB. ZirChrom-CARB retained polyethylene pronouncedly when 2-ethyl-1-hexanol, cyclohexylacetate or hexylacetate were used as mobile phases at temperature 150 or 160 °C, while all three basic stereoisomers of polypropylene eluted in size exclusion mode in these sorbent/solvent pairs. This is very different from the system Hypercarb/1-decanol, which separated polypropylene according to its tacticity. The opposite elution behavior of polyethylene and polypropylene in system ZirChrom-CARB/2-ethyl-1-hexanol (polypropylene eluted, polyethylene fully adsorbed) enabled to realize separation of blends of polyethylene and polypropylene. Ethylene/1-hexene copolymers were separated according to their chemical composition using system Hypercarb/2-ethyl-1-hexanol/1,2,4-trichlorobenzene. © 2010 Elsevier B.V.

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.

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.

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.

MacKo T.,German Institute for Polymers | Brull R.,German Institute for Polymers | Zhu Y.,University of Memphis | Wang Y.,University of Memphis
Journal of Separation Science | Year: 2010

Polyolefins are the most widely produced synthetic polymer commodity and are found in countless applications ranging from bottles, packaging films to bullet-proof jackets, etc. Such widely different applications rely on high variability in the physical properties of polyolefins, which is a result of variations in microstructure, chemical composition and molar mass. Though polyolefins contain only carbon (C) and hydrogen (H) atoms, the microstructures of polyolefins are extremely variable, differing in the nature of the monomers (e.g. ethylene versus propylene), the degree of branching, chemical composition in the case of copolymers and finally their molar masses. Production, research and development of polyolefins require the analysis of polyolefin samples in terms of all these parameters. Development of efficient and robust analytical techniques based on the interactive LC is reviewed. The needed computational/theoretical studies to understand the retention mechanism in the newly developed chromatography systems are discussed. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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