Polymere Materialien (Institut für Technische Chemie und Polymerchemie)

Entwicklung kombinierter Methoden

Combined characterisation, e.g. hyphenated and correlated methods often allows information not available via separated methods. Examples are the molecular weight dependence of chemical composition in an NMR-SEC (size exclusion chromatographie) combination or shear induced crystallisation in Rheo-NMR. This already represent the two main fields of this research strand: Combination with rheology and new detectors for chromatograpy, eg. size exclusion chromatography (SEC).

Rheology addresses macroscopic mechanical properties of polymers. However, additional information on the molecular scale is often necessary for a full interpretation of rheological results. Therefore, the simultaneous use of rheology with other methods is highly beneficial. So far, we have coupled small-angle X-ray scattering (SAXS), dielectric spectroscopy and low-field 1H-NMR relaxation spectroscopy with rheology [Ratzsch et al., 2017]. As an actual project, we work on the combination of rheology and IR spectroscopy.

Another focus in this topic is the development of coupled methods based on size exclusion chromatography (SEC) to achieve a simultaneous characterisation of size and chemical information. The main idea is represented in a project of the ongoing SFB1176 and it is an excellent illustration of the strong interaction of our different research strands. As we intend to synthesise precisely defined model polymers, we also need methods allowing to characterise all molecular parameters of a polymer (fig. 1). The first axis, the average size and the size distribution can be exanimated with SEC, the chemical identification and average monomer composition can be clarified either with IR-Spectroscopy or NMR-Spectroscopy. The last dimension, special functional groups or end groups, is measured via the assistance of IR-QCL-Lasers (quantum cascade laser).  

fig.1: 3-dimensional spectroscopy is needed for full characterisation of polymers. Molecular weight distribution, chemical composition and functionalisation (endgroups) are spanning up a 3-dimensional parameter space containing the full information about a polymer.

This offers the possibility to identify and quantify also rare groups, e.g. end groups or branching points. Only the combination of these three methods in one combined technique offers the possibility of correlated information, e.g. the change in composition or branching degree as a function of molecular weight. FT-IR-SEC is developed to a final state, the combinations with an IR-Laser (QCL) is already working [Morlock et al., 2018], SEC-NMR is nearly finished with the use of a 60 MHz permanent magnet, but both latter methods are still a matter of further enhancements. Actual, we can detect one Carbonyl-Group in a polymer of 500.000 g/mol, but further improvements in sensitivity and especially for accessible functional groups are still necessary.

 

Overview of combined methods developed in our group
Combinations with rheology New detectors for Chromatography
Already developed methods  
Rheo-SAXS
(Shear Rheology - Small angle X-ray scattering)
SEC - FTIR
(fourier transform infrared spectroscopy)
Developed methods in ongoing improvement  
Rheo-NMR
(Shear Rheology - Low field NMR relaxometry)
SEC - NMR
(Low Field NMR, spectrocopically resolved)
Rheo-Dielec
(Shear Rheology - Dielectric spectroscopy)
SEC - IR-QCL
(Quantum-Cascade-Laser IR spectroscopy)
DMTA-Dielec
(Dynamic mechanical analyis - Dielectric spectroscopy)
 
Planned ideas  
Rheo-IR
(Shear Rheology - IR-Spectroscopy)
HPLC - NMR
(High pressure liquid chromatographie)

 

Selected related articles connected to research strand 4: Combined methods
Please see also the full list of publications  
Polymer Crystallization Studied by Hyphenated Rheology Techniques. Rheo‐NMR, Rheo‐SAXS, and Rheo‐Microscopy
Medium resolution 1H-NMR at 62 MHz as a new chemically sensitive online detector for size exclusion chromatography (SEC-NMR)
Online Detection of Functional groups in SEC via Quantum Cascade Laser IR Spectroscopy
Low-field rheo-NMR: A novel combination of NMR relaxometry with high end shear rheology
Linear and nonlinear rheology combined with dielectric spectroscopy of hybrid polymer nanocomposites for semiconductive applications
Hyphenated low-field NMR techniques: combining NMR with NIR, GPC/SEC and rheometry
Combined Dielectric (DEA) and Dynamic Mechanical Thermal Analysis (DMTA) in compression mode
Development of a chemically sensitive online SEC detector based on FTIR spectroscopy
Online Coupling of Size Exclusion Chromatography and Low Field NMR-Spectroscopy
Online Coupling of Size Exclusion Chromatography and FT-IR-Spektroscopy
In-situ Rheo-Dielectric, ex-situ 2D-SAXS and FT-Rheology investigations of the shear induced alignment of Poly(styrene-b-1,4-isoprene) diblock copolymer melts
Observation of new states of liquid crystal 8CB under non-linear shear conditions as observed via a novel and unique Rheo/Small Angle X-ray scattering combination