Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Dokumenttyp
- Vortrag (5)
- Zeitschriftenartikel (1)
Sprache
- Englisch (6)
Schlagworte
- Liquid chromatography (6) (entfernen)
Organisationseinheit der BAM
- 6 Materialchemie (3)
- 6.3 Strukturanalytik (3)
The structure and composition of polycarbonate polydimethylsiloxane copolymer (PC-co-PDMS) was investigated by applying various analytical approaches including chromatographic separation methods, spectrometric, and spectroscopic detection techniques. In particular, size exclusion chromatography (SEC) and liquid adsorption chromatography operating at different conditions (e.g. using gradient solvent systems) were used to achieve separations according to molar mass and functionality distribution. The coupling of both techniques resulted in fingerprint two-dimensional plots, which could be used to easily compare different copolymer batches. Matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometry was applied for structural investigations. The different ionization behavior of both comonomers, however, strongly limited the applicability of this technique. In contrast to that, Fourier-transform Infrared (FTIR) spectroscopy could be used to quantify the amount of PDMS in the copolymer at different points in the chromatogram. The resulting methodology was capable of distinguishing PC-co-PDMS copolymer from PC homopolymer chains present in the material.
Copolymer structure elucidation by multidimensional techniques with focus on UPLC x ESI-TOF-MS
(2017)
Structure elucidation of complex synthetic copolymers still represents a challenge. An one-dimensional separation technique cannot give the answer to the question: What are the molar mass distribution (MMD), the functionality distribution (FTD), the chemical composition distribution (CCD), the monomer sequence distribution (MSD), the topology differences within a single broad distributed polymer sample?
Since the first LC/ ESI-MS experiment of the Nobel prize winner John B. Fenn in 1984, the coupling of liquid chromatographic to mass spectrometric techniques gained a continuous rapid development.
Often the deficiencies of stand-alone methods can be bridged. LC, blind to structural information needs mass spectrometry as one of the most powerful detectors able to give detailed information on e.g. the repeat units, functionalization or copolymer composition of the chromatographic separated constituents. A separation prior to MS reduces radical the dispersity which is one of the reasons for failing of MS. Also problems with different ionization probabilities in complex mixtures can partly be overcame.
Different LC separation techniques as size exclusion chromatography (SEC), liquid adsorption chromatography (LAC), liquid chromatography at critical conditions (LCCC) and gradient elution liquid chromatography (GELC) combined with Matrix assisted Laser Desorption Ionization (MALDI) respectively Electrospray Ionization (ESI) Time of Flight (TOF) mass spectrometry are able to give information which otherwise are completely inaccessible. In some cases CID tandem mass spectrometry is applied. Fragmentation of suitable precursor ions resulted in typical fragment ion patterns. This technique enables an additional information on e.g. sequences, structural defects and topology of complex polymer mixtures.
Herein a new approach is demonstrated to provide evidence of different functionalities and short block sequences in statistical EO-PO copolymers. Furthermore silsesquioxane mixtures and Polyglycerols are investigated concerning occurring topology effects.
Copolymers made of polycarbonate (PC) and polydimethylsiloxane (PDMS) are broadly applied in material science. High impact-stability and transparency are the marks of bisphenol-A polycarbonate. PDMS on the other hand excels in thermal stability, flame resistance and weatherability. Combining those favourable characteristics in a copolymer yields in a ductile but impact-resistant and flame retardant material. In order to understand the synthesis process and to improve the quality and characteristics of a copolymer, knowing its structure is essential. The challenge lies in the variety of heterogeneities like molecular mass-, block-size- and block-distribution.
This study addresses the structural characterization of PC-PDMS-copolymers using different liquid chromatographic techniques, including two dimensional combinations, hyphenated to MALDI-mass spectrometry and FTIR. The large difference in polarities of PC and PDMS is a challenge for liquid chromatography as well as ionization in MALDI. Nevertheless, we were able to differentiate between homopolymer and actual copolymer, clarify the presence of cyclic structures and gain information about the PDMS blocks
Since the first LC/ ESI-MS experiment of the Nobel prize winner John B. Fenn in 1984, the coupling of liquid chromatographic to mass spectrometric techniques gained a continuous rapid development.
The lecture will give a general survey of different LC separation techniques as size exclusion chromatography (SEC), liquid adsorption chromatography (LAC), liquid chromatography at critical conditions (LCCC) and gradient elution liquid chromatography (GELC) combined with Matrix assisted Laser Desorption Ionization (MALDI) respectively Electrospray Ionization (ESI) Time of Flight (TOF) mass spectrometry.
Often the deficiencies of stand-alone methods can be bridged. LC, blind to structural information needs mass spectrometry as one of the most powerful detectors able to give detailed information on e.g. the repeat units, functionalization or copolymer composition of the chromatographic separated constituents. A separation prior to MS reduces the polydispersity which is one of the reasons for failing of MS. Also problems with different ionization probabilities in complex mixtures can partly be overcame.
On the basis of different examples on- and offline coupling principles will be compared and the pros and cons of both mass spectrometric techniques will be discussed.
Recently, MALDI imaging techniques in coupling with chromatography have become interesting e.g. for visualization of copolymer composition.