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Papers by Robert Brüll
Separation of ethylene-norbornene copolymers using high performance liquid chromatography
Journal of Chromatography A, 2021
The elution behavior of ethylene-norbornene (EN) copolymers prepared with various catalysts was s... more The elution behavior of ethylene-norbornene (EN) copolymers prepared with various catalysts was studied in selected binary solvent gradients using porous graphite (HypercarbTM) as stationary phase. It was found that the elution volumes of the EN copolymers correlated with their average norbornene content. For a series with norbornene content lower than 20 mol % the correlation was positive (i.e. increasing elution volumes with increasing norbornene content), whereas for a series with norbornene contents above 20 mol % it was negative (decreasing elution volumes with increasing norbornene content). It is known that EN copolymers have complicated microstructures that depend on norbornene content and the catalyst system used for synthesis. Thus, it is supposed that the opposing trends in the elution behavior of the EN copolymers are caused by differences in their microstructure, ultimately governed by the norbornene content. Our conclusions are supported by results from NMR spectroscopy, which revealed the microstructure, and differential scanning calorimetry (DSC).
Hyphenating high temperature high performance liquid chromatography (HT-HPLC) with high temperatu... more Hyphenating high temperature high performance liquid chromatography (HT-HPLC) with high temperature size exclusion chromatography (HT-SEC) (high temperature two dimensional liquid chromatography (HTHPLC x HT-SEC or HT 2D-LC)) leads to an isocratic elution in the second dimension, which in turn enables to use IR detector (quantitative detection) for monitoring the eluting polymers. Experimental data obtained from HT 2D-LC with IR detector are usually presented as contour plots, which can be mathematically described in matrices. Quantitative data about chemical composition, molar mass and concentration of all the segments, which are present in a polymer, can be obtained, after calibrating the HPLC separation (HPLC elution volume vs chemical composition), SEC separation (SEC separation vs molar mass) and response of the IR detector (IR response vs mass of the polymer). A new procedure based on subtraction and addition of matrices is described, which enables quantitative comparison of d...
Solubility of Polyethylene in n-Hexane and Cyclohexane: Experimental Determination and Comparison with Solid–Liquid Equilibria-Based Predictions
Industrial & Engineering Chemistry Research, 2021
Chemical Engineering Journal, 2021
Though synthetic plastics are indispensable in our everyday life, the uncertainty surrounding the... more Though synthetic plastics are indispensable in our everyday life, the uncertainty surrounding the sustainability of fossil reserves has led to the development of a novel class of plastics, referred to as bio-based plastics. Poly(lactic) acid (PLA) is the most frequently used member of this family. However, due to the lack of a holistic recycling strategy, its large scale utilization can turn out to be an acute source of plastic pollution in the future. Unlike other attempts directed towards chemical recycling of PLA which violate the basic principles of green chemistry, the following research establishes an eco-friendly recycling concept aimed at the production of a valuable lactate ester through solvent assisted transesterification of PLA waste. The scope of this research is not only limited to the selection of an appropriate system (solvent, nucleophile and catalyst) but also extends to analysing the selectivity of the solvent towards the PLA fraction in a commingled stream and the effect of the concentration of nucleophile and different PLA substrates on the yield of the lactate ester. It was observed that, irrespective of the source of PLA, a high yield of ethyl lactate (approx. 80%) with complete retention of stereochemistry was obtained for a molar ratio of nucleophile per mole repeat unit of PLA (n nuc :n rpu) equivalent to 3. Thus, this work represents an attempt towards instituting circular bio-economy by overcoming the engineering and environmental challenges associated with PLA-waste management and production of ethyl lactate; while strictly adhering to the principles of green chemistry and sustainable chemical engineering.
Journal of Chromatography A, 2020
Additives are added to polymers in small concentration to achieve desired application properties ... more Additives are added to polymers in small concentration to achieve desired application properties widely used to tailor the properties. The rapid diversification of their molecular structures, with often only minute differences, necessitates the development of adequate chromatographic techniques. While modified silica so far is the workhorse as stationary phase we have probed the potential of porous graphitic carbon (Hypercarb TM) for this purpose. The results show that the multitude of physicochemical interactions between analyte molecules and the graphitic surface enables separations of polyolefin stabilizers with unprecedented selectivity. To support the chromatographic results the adsorption capability of Hypercarb TM for selected antioxidants and UV absorbers has been determined by Raman spectroscopy and argon physisorption measurements. The shift of the Graphite-band in the Raman spectra of Hypercarb TM upon infusion with additives correlates with the changes in the Adsorption Potential Distributions. The results of argon physisorption measurements go hand in hand with the chronology of desorption of the additives in liquid chromatography experiments. The elution sequence can be explained by van der Waals or London forces, ππ-interactions and electron lone pair donor-acceptor interactions between the graphite surface and analyte functional groups.
Accurate determination of the layer thickness of a multilayer polymer film by non-invasive multivariate confocal Raman microscopy
The Analyst, 2019
We present a confocal Raman depth profiling technique combined with multivariate spectral decompo... more We present a confocal Raman depth profiling technique combined with multivariate spectral decomposition. The method allows for non-invasive layer structure and chemical composition determination on polymer multilayer films with micrometer accuracy.
Chromatographia, 2019
Ethylene-vinyl acetate (EVA) copolymers are in dependence on their chemical composition, amorphou... more Ethylene-vinyl acetate (EVA) copolymers are in dependence on their chemical composition, amorphous, or semicrystalline materials. Therefore, fractionation techniques which are based on crystallization, such as temperature rising elution fractionation (TREF) and crystallization fractionation (CRYSTAF), cannot offer information about the chemical composition distribution of these polymers in the case of amorphous samples. Liquid chromatography has been shown to be a valuable alternative; yet, systems based on silica gel lacked in terms of long-term stability. Using porous graphite, this drawback may be overcome. An HPLC column packed with porous graphite Hypercarb™ and a solvent gradient 2-ethyl-1-hexanol (or cyclohexanone) → 1,2,4-trichlorobenzene can separate EVA copolymers over the full range of VA content at temperatures above 100 °C. A linear dependence between the VA content of the copolymers and their elution volume could be established. Moreover, the chromatographic resolution is larger than obtained using silica gel as stationary phase.
Porous graphite as platform for the separation and characterization of synthetic polymers – an overview
Journal of Chromatography A, 2019
Porous graphite as sorbent differs significantly from all other HPLC column packings. It stands o... more Porous graphite as sorbent differs significantly from all other HPLC column packings. It stands out due to its chemically extremely homogeneous surface, which moreover is planar on an atomic level. This sorbent, according to its non-polar but polarizable surface, is able to adsorb polar as well as non-polar small molecules as well as macromolecules. Moreover, it enables their separation induced by minute differences in their molecular architecture, which includes the aspects of planarity, branching or tacticity of macromolecules. Although graphite had already been used many years for the separation of small molecules, the application of porous graphite for separations in the domain of synthetic polymers has been rare. In 2009 it was found that porous graphite enables the separation of polyethylene and polypropylene on the basis of their full adsorption and desorption, when suitable solvents are used. This approach has led to the fast elaboration of HPLC systems for separations of various polar modified as well as non-polar polyolefins. Due to pronounced adsorptive interactions, porous graphite is applicable even at temperatures as high as 160 °C. The results presented in this paper manifest that porous graphite enables to obtain important information about the composition distribution of various synthetic polymers, the architecture of macromolecules (i.e., branching) or their tacticity, and underlines its enormous application potential.
Imaging techniques: Innovative tools for polymer characterization and failure analysis
Macromolecular Materials and Engineering, 2002
![Research paper thumbnail of [2-(Isopropylthio)benzoato-O,S]phenyl(triphenylphosphine)palladium(II) tetrahydrofuran solvate](https://attachments.academia-assets.com/97141142/thumbnails/1.jpg)
](Acta Crystallographica Section C Crystal Structure Communications, 2000
Liquid Chromatography-Infrared and Size Exclusion Chromatography-infrared Analysis for Polymer Characterization
Applications, Theory and Instrumentation, 2010
Fourier transform infrared spectroscopy (FTIR) can be used as a detector in liquid chromatography... more Fourier transform infrared spectroscopy (FTIR) can be used as a detector in liquid chromatography, giving detailed information on the molecular structure of the effluents after separation. Achieving structural details of chemical compounds after their separation makes the coupling of interactive liquid chromatography (IC) and size exclusion chromatography (SEC) with IR spectroscopy a versatile analytical tool superior to refractive index (RI), ultraviolet (UV), and evaporative light scattering detectors (ELSDs). LC/IR offers an alternative to LC/MS and LC/NMR to study the chemical composition of the eluted compounds. The hyphenation can be realized in two ways, namely, the on flow with an IR flow cell and off-line via solvent elimination. Both approaches are discussed with regard to their advantages and limitations and different solvent-elimination interfaces are compared. The coupling of LC with FTIR using the IR flow cell and the solvent-elimination interfaces is demonstrated on selected samples, including interactive and size exclusion models at ambient and high temperatures. Keywords: LC; SEC; FTIR; chemical composition analysis; molecular weight distribution; coupled methods; solvent elimination; flow cell
Macromolecular Chemistry and Physics, 2010
The quantity of absorbance of linear polarized light depends for a given wavelength on the angle ... more The quantity of absorbance of linear polarized light depends for a given wavelength on the angle between an absorbing transition moment vector and the electric vector of the polarized light. Fraser used this relationship to interpret the infrared dichroism in axially oriented polymers. This model can be extended to calculate the orientation in three dimensions by transforming the Fraser's equation into a P 2-Legendre polynomial. As a result the orientation in three directions-f x , f y , and f z-can be calculated directly from the individual absorbances measured with an electric vector along the axes of interest, the structural absorbance A 0 of the sample, and the angle of the transition moment vector in reference to the chain axis. Applying the f values into 'Hermans' Orientation function', it becomes possible to calculate the average angle of the chain axis with reference to the axes of interest.
e-Polymers, 2005
Ethylene - methyl methacrylate block copolymers are semicrystalline polymers that dissolve in org... more Ethylene - methyl methacrylate block copolymers are semicrystalline polymers that dissolve in organic solvents only at high temperatures. Accordingly, microstructure analysis by solution methods must be conducted at temperatures above 130°C. For the analysis of block copolymers of different compositions several analytical techniques were used, including high-temperature size-exclusion chromatography (SEC), hyphenated SEC-FTIR, and CRYSTAF (crystallisation analysis fractionation). While SEC with refractive index detection indicated a certain multimodality of the samples, SEC coupled with FTIR revealed that the samples were chemically inhomogeneous and may contain homo- and copolymer fractions. The presence of polyethylene and poly(methyl methacrylate) homopolymers in the copolymer samples was confirmed by CRYSTAF analysis, when the total concentration as well as the carbonyl group distribution were monitored separately. Chromatographic separation of the different sample components wa...
Analytical Methods, 2015
A new method for quantification of the comonomer content in ethylene/1-olefin copolymers has been... more A new method for quantification of the comonomer content in ethylene/1-olefin copolymers has been introduced by using Raman spectroscopy.
Die Angewandte Makromolekulare Chemie, 1999
The homo-oligomerisation of 1-pentene in the presence of various bridged and non-bridged metalloc... more The homo-oligomerisation of 1-pentene in the presence of various bridged and non-bridged metallocenes and methylaluminoxane (MAO) at room temperature and at 60 8C, respectively, has been studied. The use of the bridged catalysts rac-[C 2 H 4 (Ind) 2 ]ZrCl 2 (1) and [(CH 3) 2 Si(Ind) 2 ]ZrCl 2 (2) leads to the formation of isotactic poly(1-pentene). The use of Cp 2 ZrCl 2 (3), Cp 2 HfCl 2 (4) and [(CH 3) 5 C 5 ] 2 ZrCl 2 (5) leads to the formation of atactic poly(1-pentene). The stereoregularity of the isotactic poly(1-pentene) obtained with 1 was higher than that of the poly(1-pentene) synthesised with 2. The degree of polymerisation was highly dependent on the metallocene catalyst. Oligomers ranging from the dimer of 1-pentene to poly(1-pentene) with a number-average molar mass M n = 5100 g mol-1 were formed. The 1 H NMR spectra of the samples were analysed with regard to functional groups and these were attributed to different chain termination processes. A MALDI-TOF spectrum of low-molar-mass poly(1-pentene) could be recorded using dithranol as matrix and adding silver trifluoroacetate to promote ion formation. ZUSAMMENFASSUNG: Die Homooligomerisation von 1-Penten wurde bei Raumtemperatur bzw. bei 60 8C mit verbrückten und unverbrückten Metallocenen und Methylaluminoxan (MAO) untersucht. Die verbrückten Katalysatoren rac-[C 2 H 4 (Ind) 2 ]ZrCl 2 (1) und [(CH 3) 2 Si(Ind) 2 ]ZrCl 2 (2) führten zu isotaktischem Poly-1penten, wogegen Cp 2 ZrCl 2 (3),Cp 2 HfCl 2 (4) und [(CH 3) 5 C 5 ] 2 ZrCl 2 (5) ataktisches Poly-1-penten lieferten. Die Stereoregularität des mit 1 hergestellten isotaktischen Poly-1-pentens war größer als die des mit 2 erhaltenen Poly-1-pentens. Der Polymerisationsgrad zeigte eine starke Abhängigkeit vom verwendeten Metallocen-Katalysator. So konnte die Bildung von Pentendimeren bis hin zu Poly-1-penten mit einer zahlenmittleren Molmasse M n von 5100 g mol-1 beobachtet werden. Die 1 H NMR-Spektren wurden bezüglich funktioneller Gruppen analysiert und diese unterschiedlichen Kettenabbruchreaktionen zugeordnet. Ein MALDI-TOF-Spektrum von niedermolekularem Poly-1-penten konnte mit Dithranol als Matrix mit Zugabe von Silbertrifluoracetat erhalten werden.
Macromolecular Chemistry and Physics, 2014
A series of copolymers of ethylene with propene, 1-hexene, 1-octene, and 1-octadecene is characte... more A series of copolymers of ethylene with propene, 1-hexene, 1-octene, and 1-octadecene is characterized by size-exclusion chromatography (SEC), nuclear magnetic resonance spectroscopy (NMR), crystallization analysis fractionation (CRYSTAF), and high-temperature interactive liquid chromatography. Four different solvent pairs are used as the mobile phase, while porous graphite is used as the column packing. The elution volumes of the polymer samples do not correlate with their average molar mass (SEC); however, they correlate with the average chemical composition (NMR). High performance liquid chromatography (HPLC) enables separation of the copolymers over the full range of their composition and independent of their crystallinity. Dependence between the elution volume and the average chemical composition distribution (CCD) of the copolymer is linear and it is a function of the length of branches as well as the type of the mobile phase. The CCDs of copolymers derived from HPLC profi les are similar to, yet broader than the CCDs obtained with CRYSTAF.
Studying Binary Solvent Mixtures as Mobile Phase for Thermal Gradient Interactive Chromatography (TGIC) of Poly(ethylene-stat-1-octene)
Industrial & Engineering Chemistry Research, 2014
ABSTRACT Thermal gradient interactive chromatography (TGIC) is an emerging analytical tool to det... more ABSTRACT Thermal gradient interactive chromatography (TGIC) is an emerging analytical tool to determine the chemical composition distribution of polyolefins. TGIC separates polyolefins based on their interaction with graphitic carbon at different temperatures in an isocratic mobile phase. In the case of copolymers of ethylene and 1-olefins, TGIC offers a larger commoner range of separation than crystallization based techniques. However, currently TGIC shows approximately only half of the resolution compared to crystallization based techniques for an ethylene content higher than 92 mol % when 1,2-dichlorobenzene (ODCB) and 1,2,4-trichlorobenzene (TCB) are used as the mobile phase. We conducted a systematic study exploring the potential of using different binary solvent mixtures as the mobile phase to increase the resolution in TGIC of poly(ethylene-stat-1-octene). Apart from the well-established chlorinated aromatic solvents like ODCB and TCB, for the first time, binary solvent mixtures containing alkanes and aliphatic alcohols have been evaluated as components of the mobile phase using an evaporative light scattering detector. As an outcome, optimized binary solvent mixtures could be identified that enabled an improvement in resolution. This was exemplarily verified by separating a model blend of two poly(ethylene-stat-octene) samples with varying 1-octene content.
Materials Science, 2011
A bimodal high density polyethylene (HDPE) has been successfully fractionated by analytical size ... more A bimodal high density polyethylene (HDPE) has been successfully fractionated by analytical size exclusion chromatography into molar mass fractions with M w 's ranging from 3.6 kg/mol to 8 000 kg/mol, and subsequently deposited on germanium disks using the Lab Connections Transform method. After removal of the fractions from the disks, having masses in between 10 µg-150 µg, differential scanning calorimetry has been successful in measuring the (re)crystallization and melting behavior of these fractions. Comparing the crystallization and melting peak temperatures of the fractions with those of narrow molar mass linear polyethylenes points to the HDPE being linear below and short chain branched above 100 kg/mol respectively. This value coincides roughly with the 'split' between the molar mass distributions resulting from the first and the second polymerization reactor-confirming the addition of 1-butene in the second reactor.
Ultra high molar mass polyolefins and their characterization by high temperature-asymmetrical flow field-flow fractionation
Please help us populate SUNScholar with the post print version of this article. It can be e-maile... more Please help us populate SUNScholar with the post print version of this article. It can be e-mailed to: scholar@sun.ac.zaNatuurwetenskappeChemi
Separation of ethylene-norbornene copolymers using high performance liquid chromatography
Journal of Chromatography A, 2021
The elution behavior of ethylene-norbornene (EN) copolymers prepared with various catalysts was s... more The elution behavior of ethylene-norbornene (EN) copolymers prepared with various catalysts was studied in selected binary solvent gradients using porous graphite (HypercarbTM) as stationary phase. It was found that the elution volumes of the EN copolymers correlated with their average norbornene content. For a series with norbornene content lower than 20 mol % the correlation was positive (i.e. increasing elution volumes with increasing norbornene content), whereas for a series with norbornene contents above 20 mol % it was negative (decreasing elution volumes with increasing norbornene content). It is known that EN copolymers have complicated microstructures that depend on norbornene content and the catalyst system used for synthesis. Thus, it is supposed that the opposing trends in the elution behavior of the EN copolymers are caused by differences in their microstructure, ultimately governed by the norbornene content. Our conclusions are supported by results from NMR spectroscopy, which revealed the microstructure, and differential scanning calorimetry (DSC).
Hyphenating high temperature high performance liquid chromatography (HT-HPLC) with high temperatu... more Hyphenating high temperature high performance liquid chromatography (HT-HPLC) with high temperature size exclusion chromatography (HT-SEC) (high temperature two dimensional liquid chromatography (HTHPLC x HT-SEC or HT 2D-LC)) leads to an isocratic elution in the second dimension, which in turn enables to use IR detector (quantitative detection) for monitoring the eluting polymers. Experimental data obtained from HT 2D-LC with IR detector are usually presented as contour plots, which can be mathematically described in matrices. Quantitative data about chemical composition, molar mass and concentration of all the segments, which are present in a polymer, can be obtained, after calibrating the HPLC separation (HPLC elution volume vs chemical composition), SEC separation (SEC separation vs molar mass) and response of the IR detector (IR response vs mass of the polymer). A new procedure based on subtraction and addition of matrices is described, which enables quantitative comparison of d...
Solubility of Polyethylene in n-Hexane and Cyclohexane: Experimental Determination and Comparison with Solid–Liquid Equilibria-Based Predictions
Industrial & Engineering Chemistry Research, 2021
Chemical Engineering Journal, 2021
Though synthetic plastics are indispensable in our everyday life, the uncertainty surrounding the... more Though synthetic plastics are indispensable in our everyday life, the uncertainty surrounding the sustainability of fossil reserves has led to the development of a novel class of plastics, referred to as bio-based plastics. Poly(lactic) acid (PLA) is the most frequently used member of this family. However, due to the lack of a holistic recycling strategy, its large scale utilization can turn out to be an acute source of plastic pollution in the future. Unlike other attempts directed towards chemical recycling of PLA which violate the basic principles of green chemistry, the following research establishes an eco-friendly recycling concept aimed at the production of a valuable lactate ester through solvent assisted transesterification of PLA waste. The scope of this research is not only limited to the selection of an appropriate system (solvent, nucleophile and catalyst) but also extends to analysing the selectivity of the solvent towards the PLA fraction in a commingled stream and the effect of the concentration of nucleophile and different PLA substrates on the yield of the lactate ester. It was observed that, irrespective of the source of PLA, a high yield of ethyl lactate (approx. 80%) with complete retention of stereochemistry was obtained for a molar ratio of nucleophile per mole repeat unit of PLA (n nuc :n rpu) equivalent to 3. Thus, this work represents an attempt towards instituting circular bio-economy by overcoming the engineering and environmental challenges associated with PLA-waste management and production of ethyl lactate; while strictly adhering to the principles of green chemistry and sustainable chemical engineering.
Journal of Chromatography A, 2020
Additives are added to polymers in small concentration to achieve desired application properties ... more Additives are added to polymers in small concentration to achieve desired application properties widely used to tailor the properties. The rapid diversification of their molecular structures, with often only minute differences, necessitates the development of adequate chromatographic techniques. While modified silica so far is the workhorse as stationary phase we have probed the potential of porous graphitic carbon (Hypercarb TM) for this purpose. The results show that the multitude of physicochemical interactions between analyte molecules and the graphitic surface enables separations of polyolefin stabilizers with unprecedented selectivity. To support the chromatographic results the adsorption capability of Hypercarb TM for selected antioxidants and UV absorbers has been determined by Raman spectroscopy and argon physisorption measurements. The shift of the Graphite-band in the Raman spectra of Hypercarb TM upon infusion with additives correlates with the changes in the Adsorption Potential Distributions. The results of argon physisorption measurements go hand in hand with the chronology of desorption of the additives in liquid chromatography experiments. The elution sequence can be explained by van der Waals or London forces, ππ-interactions and electron lone pair donor-acceptor interactions between the graphite surface and analyte functional groups.
Accurate determination of the layer thickness of a multilayer polymer film by non-invasive multivariate confocal Raman microscopy
The Analyst, 2019
We present a confocal Raman depth profiling technique combined with multivariate spectral decompo... more We present a confocal Raman depth profiling technique combined with multivariate spectral decomposition. The method allows for non-invasive layer structure and chemical composition determination on polymer multilayer films with micrometer accuracy.
Chromatographia, 2019
Ethylene-vinyl acetate (EVA) copolymers are in dependence on their chemical composition, amorphou... more Ethylene-vinyl acetate (EVA) copolymers are in dependence on their chemical composition, amorphous, or semicrystalline materials. Therefore, fractionation techniques which are based on crystallization, such as temperature rising elution fractionation (TREF) and crystallization fractionation (CRYSTAF), cannot offer information about the chemical composition distribution of these polymers in the case of amorphous samples. Liquid chromatography has been shown to be a valuable alternative; yet, systems based on silica gel lacked in terms of long-term stability. Using porous graphite, this drawback may be overcome. An HPLC column packed with porous graphite Hypercarb™ and a solvent gradient 2-ethyl-1-hexanol (or cyclohexanone) → 1,2,4-trichlorobenzene can separate EVA copolymers over the full range of VA content at temperatures above 100 °C. A linear dependence between the VA content of the copolymers and their elution volume could be established. Moreover, the chromatographic resolution is larger than obtained using silica gel as stationary phase.
Porous graphite as platform for the separation and characterization of synthetic polymers – an overview
Journal of Chromatography A, 2019
Porous graphite as sorbent differs significantly from all other HPLC column packings. It stands o... more Porous graphite as sorbent differs significantly from all other HPLC column packings. It stands out due to its chemically extremely homogeneous surface, which moreover is planar on an atomic level. This sorbent, according to its non-polar but polarizable surface, is able to adsorb polar as well as non-polar small molecules as well as macromolecules. Moreover, it enables their separation induced by minute differences in their molecular architecture, which includes the aspects of planarity, branching or tacticity of macromolecules. Although graphite had already been used many years for the separation of small molecules, the application of porous graphite for separations in the domain of synthetic polymers has been rare. In 2009 it was found that porous graphite enables the separation of polyethylene and polypropylene on the basis of their full adsorption and desorption, when suitable solvents are used. This approach has led to the fast elaboration of HPLC systems for separations of various polar modified as well as non-polar polyolefins. Due to pronounced adsorptive interactions, porous graphite is applicable even at temperatures as high as 160 °C. The results presented in this paper manifest that porous graphite enables to obtain important information about the composition distribution of various synthetic polymers, the architecture of macromolecules (i.e., branching) or their tacticity, and underlines its enormous application potential.
Imaging techniques: Innovative tools for polymer characterization and failure analysis
Macromolecular Materials and Engineering, 2002
Acta Crystallographica Section C Crystal Structure Communications, 2000
Liquid Chromatography-Infrared and Size Exclusion Chromatography-infrared Analysis for Polymer Characterization
Applications, Theory and Instrumentation, 2010
Fourier transform infrared spectroscopy (FTIR) can be used as a detector in liquid chromatography... more Fourier transform infrared spectroscopy (FTIR) can be used as a detector in liquid chromatography, giving detailed information on the molecular structure of the effluents after separation. Achieving structural details of chemical compounds after their separation makes the coupling of interactive liquid chromatography (IC) and size exclusion chromatography (SEC) with IR spectroscopy a versatile analytical tool superior to refractive index (RI), ultraviolet (UV), and evaporative light scattering detectors (ELSDs). LC/IR offers an alternative to LC/MS and LC/NMR to study the chemical composition of the eluted compounds. The hyphenation can be realized in two ways, namely, the on flow with an IR flow cell and off-line via solvent elimination. Both approaches are discussed with regard to their advantages and limitations and different solvent-elimination interfaces are compared. The coupling of LC with FTIR using the IR flow cell and the solvent-elimination interfaces is demonstrated on selected samples, including interactive and size exclusion models at ambient and high temperatures. Keywords: LC; SEC; FTIR; chemical composition analysis; molecular weight distribution; coupled methods; solvent elimination; flow cell
Macromolecular Chemistry and Physics, 2010
The quantity of absorbance of linear polarized light depends for a given wavelength on the angle ... more The quantity of absorbance of linear polarized light depends for a given wavelength on the angle between an absorbing transition moment vector and the electric vector of the polarized light. Fraser used this relationship to interpret the infrared dichroism in axially oriented polymers. This model can be extended to calculate the orientation in three dimensions by transforming the Fraser's equation into a P 2-Legendre polynomial. As a result the orientation in three directions-f x , f y , and f z-can be calculated directly from the individual absorbances measured with an electric vector along the axes of interest, the structural absorbance A 0 of the sample, and the angle of the transition moment vector in reference to the chain axis. Applying the f values into 'Hermans' Orientation function', it becomes possible to calculate the average angle of the chain axis with reference to the axes of interest.
e-Polymers, 2005
Ethylene - methyl methacrylate block copolymers are semicrystalline polymers that dissolve in org... more Ethylene - methyl methacrylate block copolymers are semicrystalline polymers that dissolve in organic solvents only at high temperatures. Accordingly, microstructure analysis by solution methods must be conducted at temperatures above 130°C. For the analysis of block copolymers of different compositions several analytical techniques were used, including high-temperature size-exclusion chromatography (SEC), hyphenated SEC-FTIR, and CRYSTAF (crystallisation analysis fractionation). While SEC with refractive index detection indicated a certain multimodality of the samples, SEC coupled with FTIR revealed that the samples were chemically inhomogeneous and may contain homo- and copolymer fractions. The presence of polyethylene and poly(methyl methacrylate) homopolymers in the copolymer samples was confirmed by CRYSTAF analysis, when the total concentration as well as the carbonyl group distribution were monitored separately. Chromatographic separation of the different sample components wa...
Analytical Methods, 2015
A new method for quantification of the comonomer content in ethylene/1-olefin copolymers has been... more A new method for quantification of the comonomer content in ethylene/1-olefin copolymers has been introduced by using Raman spectroscopy.
Die Angewandte Makromolekulare Chemie, 1999
The homo-oligomerisation of 1-pentene in the presence of various bridged and non-bridged metalloc... more The homo-oligomerisation of 1-pentene in the presence of various bridged and non-bridged metallocenes and methylaluminoxane (MAO) at room temperature and at 60 8C, respectively, has been studied. The use of the bridged catalysts rac-[C 2 H 4 (Ind) 2 ]ZrCl 2 (1) and [(CH 3) 2 Si(Ind) 2 ]ZrCl 2 (2) leads to the formation of isotactic poly(1-pentene). The use of Cp 2 ZrCl 2 (3), Cp 2 HfCl 2 (4) and [(CH 3) 5 C 5 ] 2 ZrCl 2 (5) leads to the formation of atactic poly(1-pentene). The stereoregularity of the isotactic poly(1-pentene) obtained with 1 was higher than that of the poly(1-pentene) synthesised with 2. The degree of polymerisation was highly dependent on the metallocene catalyst. Oligomers ranging from the dimer of 1-pentene to poly(1-pentene) with a number-average molar mass M n = 5100 g mol-1 were formed. The 1 H NMR spectra of the samples were analysed with regard to functional groups and these were attributed to different chain termination processes. A MALDI-TOF spectrum of low-molar-mass poly(1-pentene) could be recorded using dithranol as matrix and adding silver trifluoroacetate to promote ion formation. ZUSAMMENFASSUNG: Die Homooligomerisation von 1-Penten wurde bei Raumtemperatur bzw. bei 60 8C mit verbrückten und unverbrückten Metallocenen und Methylaluminoxan (MAO) untersucht. Die verbrückten Katalysatoren rac-[C 2 H 4 (Ind) 2 ]ZrCl 2 (1) und [(CH 3) 2 Si(Ind) 2 ]ZrCl 2 (2) führten zu isotaktischem Poly-1penten, wogegen Cp 2 ZrCl 2 (3),Cp 2 HfCl 2 (4) und [(CH 3) 5 C 5 ] 2 ZrCl 2 (5) ataktisches Poly-1-penten lieferten. Die Stereoregularität des mit 1 hergestellten isotaktischen Poly-1-pentens war größer als die des mit 2 erhaltenen Poly-1-pentens. Der Polymerisationsgrad zeigte eine starke Abhängigkeit vom verwendeten Metallocen-Katalysator. So konnte die Bildung von Pentendimeren bis hin zu Poly-1-penten mit einer zahlenmittleren Molmasse M n von 5100 g mol-1 beobachtet werden. Die 1 H NMR-Spektren wurden bezüglich funktioneller Gruppen analysiert und diese unterschiedlichen Kettenabbruchreaktionen zugeordnet. Ein MALDI-TOF-Spektrum von niedermolekularem Poly-1-penten konnte mit Dithranol als Matrix mit Zugabe von Silbertrifluoracetat erhalten werden.
Macromolecular Chemistry and Physics, 2014
A series of copolymers of ethylene with propene, 1-hexene, 1-octene, and 1-octadecene is characte... more A series of copolymers of ethylene with propene, 1-hexene, 1-octene, and 1-octadecene is characterized by size-exclusion chromatography (SEC), nuclear magnetic resonance spectroscopy (NMR), crystallization analysis fractionation (CRYSTAF), and high-temperature interactive liquid chromatography. Four different solvent pairs are used as the mobile phase, while porous graphite is used as the column packing. The elution volumes of the polymer samples do not correlate with their average molar mass (SEC); however, they correlate with the average chemical composition (NMR). High performance liquid chromatography (HPLC) enables separation of the copolymers over the full range of their composition and independent of their crystallinity. Dependence between the elution volume and the average chemical composition distribution (CCD) of the copolymer is linear and it is a function of the length of branches as well as the type of the mobile phase. The CCDs of copolymers derived from HPLC profi les are similar to, yet broader than the CCDs obtained with CRYSTAF.
Studying Binary Solvent Mixtures as Mobile Phase for Thermal Gradient Interactive Chromatography (TGIC) of Poly(ethylene-stat-1-octene)
Industrial & Engineering Chemistry Research, 2014
ABSTRACT Thermal gradient interactive chromatography (TGIC) is an emerging analytical tool to det... more ABSTRACT Thermal gradient interactive chromatography (TGIC) is an emerging analytical tool to determine the chemical composition distribution of polyolefins. TGIC separates polyolefins based on their interaction with graphitic carbon at different temperatures in an isocratic mobile phase. In the case of copolymers of ethylene and 1-olefins, TGIC offers a larger commoner range of separation than crystallization based techniques. However, currently TGIC shows approximately only half of the resolution compared to crystallization based techniques for an ethylene content higher than 92 mol % when 1,2-dichlorobenzene (ODCB) and 1,2,4-trichlorobenzene (TCB) are used as the mobile phase. We conducted a systematic study exploring the potential of using different binary solvent mixtures as the mobile phase to increase the resolution in TGIC of poly(ethylene-stat-1-octene). Apart from the well-established chlorinated aromatic solvents like ODCB and TCB, for the first time, binary solvent mixtures containing alkanes and aliphatic alcohols have been evaluated as components of the mobile phase using an evaporative light scattering detector. As an outcome, optimized binary solvent mixtures could be identified that enabled an improvement in resolution. This was exemplarily verified by separating a model blend of two poly(ethylene-stat-octene) samples with varying 1-octene content.
Materials Science, 2011
A bimodal high density polyethylene (HDPE) has been successfully fractionated by analytical size ... more A bimodal high density polyethylene (HDPE) has been successfully fractionated by analytical size exclusion chromatography into molar mass fractions with M w 's ranging from 3.6 kg/mol to 8 000 kg/mol, and subsequently deposited on germanium disks using the Lab Connections Transform method. After removal of the fractions from the disks, having masses in between 10 µg-150 µg, differential scanning calorimetry has been successful in measuring the (re)crystallization and melting behavior of these fractions. Comparing the crystallization and melting peak temperatures of the fractions with those of narrow molar mass linear polyethylenes points to the HDPE being linear below and short chain branched above 100 kg/mol respectively. This value coincides roughly with the 'split' between the molar mass distributions resulting from the first and the second polymerization reactor-confirming the addition of 1-butene in the second reactor.
Ultra high molar mass polyolefins and their characterization by high temperature-asymmetrical flow field-flow fractionation
Please help us populate SUNScholar with the post print version of this article. It can be e-maile... more Please help us populate SUNScholar with the post print version of this article. It can be e-mailed to: scholar@sun.ac.zaNatuurwetenskappeChemi