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Dalitz F.,Karlsruhe Institute of Technology | Cudaj M.,Karlsruhe Institute of Technology | Cudaj M.,PSS Polymer Standards Service GmbH | Maiwald M.,BAM Federal Institute of Materials Research and Testing | Guthausen G.,Karlsruhe Institute of Technology
Progress in Nuclear Magnetic Resonance Spectroscopy | Year: 2012

A study was conducted to demonstrate process and reaction monitoring by low-field nuclear magnetic resonance (NMR) spectroscopy. The study focused on the development of a robust low-field spectroscopic technique which had the potential to be widely applicable in an industrial or technical environment. The development was related to time-domain (TD-) NMR and high-field Fourier-transform (FT) NMR. Reaction monitoring by NMR had been performed inside the probe and the magnet, providing an in situ possibility for monitoring the reaction progress by diverse NMR methods. MAS-studies were also performed to observe polymerization, while heterogeneous catalytic reactions had been investigated by imaging methods. One of the most attractive features of quantitative NMR spectroscopy was that the proportionality of the peak area to the number of nuclei was essentially identical for all nuclei of the same species in a mixture.

Hiller W.,TU Dortmund | Sinha P.,Stellenbosch University | Hehn M.,TU Dortmund | Pasch H.,Stellenbosch University | Hofe T.,PSS Polymer Standards Service GmbH
Macromolecules | Year: 2011

It is shown that online coupling of liquid chromatography at critical conditions (LCCC) and 1H NMR spectroscopy can be used to separate and analyze polyisoprenes with respect to their isomeric microstructures. It was possible to separate blends of copolymers consisting predominantly of 3,4- and 1,4-isoprene units by using critical conditions of 1,4-PI. Critical conditions of 1,4-PI were established such that polymers containing predominantly 3,4-PI elute in the size exclusion mode. Furthermore, on-flow NMR detection allows for the complete eluate analysis and the detection of all three isomeric species, such as 1,2-, 1,4-, and 3,4-isoprene, in the eluting fractions. These three individual moieties were correctly quantified in the individual blend components. It was also found that the 3,4-PI samples were random terpolymers of 1,2-, 1,4-, and 3,4-isoprene, whereas the 1,4-PI samples were copolymers of 1,4- and 3,4-isoprene. In addition, SEC-NMR allowed for a fast and precise molar mass calibration and the calculation of the relevant molar mass parameters Mw and Mn. © 2011 American Chemical Society.

Maier H.,Fraunhofer Institute for Structural Durability and System Reliability | Malz F.,Fraunhofer Institute for Structural Durability and System Reliability | Reinhold G.,PSS Polymer Standards Service GmbH | Radke W.,Fraunhofer Institute for Structural Durability and System Reliability
Macromolecules | Year: 2013

The development of a chromatographic method capable to separate poly(methyl methacrylate-stat-methacrylic acid) samples with methacrylic acid contents of up to 50% by chemical composition is described. For this purpose a gradient ranging from chloroform to dimethylacetamide on a PSS PROTEEMA column was applied. The application of a conventional gradient resulted in severe breakthrough peaks. Therefore, the recently developed concept of SEC gradients was used. No breakthrough peaks were observed, and the peaks corresponding to samples of different content of methacrylic acid were well resolved. A nearly linear relationship between elution volume and methacrylic acid content was observed. The developed method allows determination of the chemical composition distribution of the above-mentioned class of polymers. © 2013 American Chemical Society.

Cudaj M.,Karlsruhe Institute of Technology | Guthausen G.,Karlsruhe Institute of Technology | Hofe T.,PSS Polymer Standards Service GmbH | Wilhelm M.,Karlsruhe Institute of Technology
Macromolecular Chemistry and Physics | Year: 2012

Current results and limitations of a novel SEC-MR-NMR (size-exclusion chromatography-medium resolution nuclear magnetic resonance) system are presented, delivering a direct correlation of chemical structure and molecular weight. A 20 MHz 1H NMR spectrometer based on permanent magnets was combined with a SEC setup. The NMR sensitivity was improved by digital filters, shims, and a self-built flow probe when compared with time-domain instruments. For optimum NMR signal-to-noise ratio (S/N) of polymer fractions and concomitantly reduced S/N of solvent signals, deuterated solvents or protonated solvents, with solvent suppression, were applied. Results are presented after optimization of both NMR and chromatographic components such as column dimension and volume flow. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Shakun M.,Fraunhofer Institute for Structural Durability and System Reliability | Maier H.,Fraunhofer Institute for Structural Durability and System Reliability | Heinze T.,Friedrich - Schiller University of Jena | Kilz P.,PSS Polymer Standards Service GmbH | Radke W.,Fraunhofer Institute for Structural Durability and System Reliability
Carbohydrate Polymers | Year: 2013

Two series of sodium carboxymethyl celluloses (NaCMCs) derived from microcrystalline cellulose (Avicel samples) and cotton linters (BWL samples) with average degrees of substitution (DS) ranging from DS = 0.45 to DS = 1.55 were characterized by size exclusion chromatography with multi-angle laser light scattering detection (SEC-MALLS) in 100 mmol/L aqueous ammonium acetate (NH4OAc) as vaporizable eluent system. The application of vaporizable NH4OAc allows future use of the eluent system in two-dimensional separations employing evaporative light scattering detection (ELSD). The losses of samples during filtration and during the chromatographic experiment were determined. The scaling exponent as of the relation s21/2~Mas was approx. 0.61, showing that NaCMCs exhibit an expanded coil conformation in solution. No systematic dependencies of a s on DS were observed. The dependences of molar mass on SEC-elution volume for samples of different DS can be well described by a common calibration curve, which is of advantage, as it allows the determination of molar masses of unknown samples by using the same calibration curve, irrespective of the DS of the NaCMC sample. Since no commercial NaCMC standards are available, correction factors were determined allowing converting a pullulan based calibration curve into a NaCMC calibration using the broad calibration approach. The weight average molar masses derived using the so established calibration curve closely agree with the ones determined by light scattering, proving the accuracy of the correction factors determined.

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