We have specialized on the characterization and structure elucidation of polymeric materials of all kinds, with special focus on linear copolymers and thermosetting materials, especially melamine resins. It is not only our aim to provide analysis of well-known materials but most of our work is dedicated to the structural (and therefore reaction mechanism) elucidation of our self-designed polymers and copolymers. At the moment three central topics are core competence of our group, which are ANALYTICAL PYROLYSIS, POLYMER MASS SPECTROMETRY, and POLYMER AGING STUDIES.
Analytical pyrolysis (Pyrolysis-GC/MS)
Especially when dealing with thermosetting materials (e.g. phenolic , melamine, epoxy, or polyurethane resins) pyrolysis is a very versatile and sensitive technique which gives access to a lot of information. Also composite materials can easily be analyzed, as the degradation products allow for the identification of the individual materials used. Of special interest is a modification of the technique, where tetramethylammonium hydroxide (TMAH) is added to the sample prior to analysis. With this simple trick polar bonds are cleaved and the resulting mostly polar compounds, which in most cases show very bad chromatography behavior, are transferred into their corresponding methyl derivatives. The latter one are much less polar and can now easily be analyzed on the GC/MS system.
The equipment currently available is a CDS 5250 pyrolysis autosampler with a Thermo Trace GC/MD800 quadrupol mass spectrometer, a CDS 2000 manual pyrolyzer, and a Gerstel pyrolysis system attached to a Thermo Trace GC/Polaris ion trap mass spectrometer.
Polymer mass spectrometry
If employed correctly, some valuable information on the polymer can be gathered by mass spectrometry. Repeat units, endgroup determination, molar mass distributions and in case of copolymers even distributions can be determined. However, serval things have to be obeyed, most important: the polymer has to be ionized in order to be analyzed by mass spectrometry and the polydispersity must not be too large. So sample preparation is an essential step and we have focused on the optimization utilizing different approaches:
Dried droplet preparation is the most widely used sample preparation technique in MALDI mass spectrometry, but care must be taken in order to prevent inhomogenous sample spots. If not done correctly, mass transfer phenomena occur and one gets different results depending on where the measurement is done. We are doing a lot of work in order to overcome the problems of spot to spot reproducibility and homogeneity of the sample preparation in order to be able to do quantitative analyses. With mass spectrometry imaging (MSI) we have analyzed the influence of the individual parameters and found a way to prevent the formation of the so called coffee rings.
If the polymers have a too high polydispersity they cannot be analyzed directly by mass spectrometry. In order to overcome this problem the polymers have to be fractionated into smaller more homogenous fractions. This can either be done by sequential precipitation of a polymer solution by adding another solvent or online by coupling a GPC system to a MALDI target preparation system.
Polymer aging studies
Polymers (or as people often call them: plastics)are used in everyday life and for many different applications. In many of these applications a lifetime of tenth of years is expected, however, lifetime prediction is often based on very basic mechanical testing. We are investigating the influence of various environmental parameters and try to stress the polymers under harsh conditions in order to accelerate the natural aging processes. Then the polymers are analyzed in terms of changes to the chemical structure, e.g. decreasing chain lengths or formation of oxidation products. Several parameters such as molar mass and molar mass distribution or the stabilization of the polymers and how they influence the degradation process are investigated.
The analytical techniques applied are mostly FTIR microscopy, Raman microscopy, analytical pyrolysis, mass spectrometry and size exclusion chromatography.