Copolymer Characterization and 2D Chromatography
Video Application: 2D Polymer Analysis
2D Polymer AnalysisDr. Martina Adler, PSS Mainz, talks about 2-dimensional chromatography of polymers and explains why the combination of interaction chromatography with GPC/SEC is a powerful, high-peak-capacity technique to investigate complex (co)polymers and to determine composition and molar mass in a single experiment.
Solutions for copolymer characterization and 2D Chromatography
Copolymers can be characterized in various ways. Several methods are available that provide molar mass averages Mn, Mw, Mz, the polydispersity index PDI, the complete molar mass distribution (MMD) as well as the copolymer composition.
Schematic on-line 2D Chromatography system- conventional GPC/SEC with two concentration detectors (RI, UV, ELSD) or two different concentration signals (UV1 and UV2) making additional use of calibrated individual signal responses (further details see e.g. H. Schlaad, P. Kilz, Analytical Chemistry, Vol. 75, No. 6, March 15, page 1548 (2003))
- Polymer-HPLC with HPLC-type separations and calibration with standards of the same type and known composition.
- 2D Chromatography where the analysis power of two different chromatographic methods (HPLC, GPC/SEC, TREF, IC, CE, GC) is combined either off-line or (more convenient) on-line.
If copolymers made of unknown comonomers need to be characterized GPC/SEC (2D) on-line coupling with FTIR- or MALDI detection can be used for substance identification.
PSS products and services for copolymer characterization and 2D Chromatography
PSS offers complete turn-key systems for 2 detector GPC/SEC, Polymer-LC, and 2D copolymer analysis as well as service analysis in our analytical service department.
The PSS 2D Polymer Analyzer turn-key system is based on the modular SECcurity² GPC System including WinGPC MCDS and the software modules
The use of additional PSS products for 2D Chromatography will result in time and cost savings:
The data acquisition with automatic transfer from dimension 1 into the 2nd dimension is controlled with the WinGPC UniChrom 2D software wizard, that supports beginners and specialists alike.
PSS HighSpeed GPC/SEC columns significantly decrease the analysis time of 2D runs.
PSS specialty copolymer reference materials are available from stock, for special requests use the PSS custom polymerization service.
PSS 2D Primer: Request your free pdf-copy and/or printed copy.
Schematic LC-FTIR coupling.For substance identification PSS offers a FTIR/MALDI interface that can be connected to any LC (GPC/SEC, HPLC) instrument. While the LC fractionates the sample, the interface evaporates the solvent and sprays the sample of a Germanium disc (for FTIR detection) or a MALDI target (for MALDI-TOF analysis). By this approach all solvent interference is eliminated and the spectra
obtained are library quality and computer
searchable for rapid identification.
This solution is also available as service analysis in our analytical service department.
Theoretical background copolymer characterization and 2D Chromatography
Why are copolymers special and what does multiple distributions mean?
In addition to the molar mass distribution copolymers have a chemical composition distribution (comonomer distribution), therefore they are complex polymers with more than one molecular heterogeneity and multiple distributions. Other distributions may additionally be present, e.g functional distribution, architecture distribution, structural distribution.
For the characterization of the different types of molecular heterogeneity it is necessary to use a wide range of analytical techniques. Preferably, these techniques should be selective towards a specific type of heterogeneity, e.g. size (molecular weight - GPC/SEC) and composition (Polymer-HPLC, LAC). The combination of two or more selective analytical techniques is assumed to yield multidimensional information on the molecular heterogeneity.
For a detailed review see also P. Kilz, H. Pasch, Encyclopedia of Analytical Chemistry, R.A. Meyers (Ed.) pp. 7495–7543 (2000)
Complex (co)polymers have multiple distributions. For comprehensive analysis 1-dimensional characterization is not sufficient.
What is special about copolymers in GPC/SEC?
GPC/SEC separates according to hydrodynamic volume, independent on the chemical composition of the investigated macromolecules. Two molecules with the same hydrodynamic volume, Vh, will elute at the same elution volume, Ve. The molar mass M (obtained from the calibration curve) will then also be the same. This is why GPC/SEC works perfectly for linear homopolymers and is accurate when chemically matching molar mass calibration standards have been used.
For Copolymers it has to be taken into account that the hydrodynamic volume, Vh, depends on the degree of polymerization, Pn, as well as on the composition x. Therefore two random or sequential copolymers which differ in Pn (proportional to molar mass M) and in composition can elute at the same elution volume. If only GPC/SEC is used, it is not possible to distinguish between these copolymers. Even with advanced detection (light scattering, viscometry, and/or Triple detection) a detailed analysis is not possible. For these polymers efficient separation techniques like Polymer-HPLC/LAC and 2D Chromatography are needed. For block copolymers synthesized using controlled or living polymerization the GPC/SEC approach with 2 concentration detectors is also very useful. However, the increased peak efficiency of 2D Chromatography can also add additional information for block copolymers and residual homopolymer.
What are the main advantages of 2D Chromatography?
2D Chromatography allows to separate selective towards a specific type of heterogeneity, e.g. composition and molar mass. The peak capacity in an isocratic 1-dimensional separation is very limited. Coelution can be a serious problem. The corresponding peak capacity in an n-dimensional separation is considerably higher due to the fact that each dimension contributes to the total peak capacity.
2 peaks in GPC/SEC, 2 peaks in HPLC: only 2D hyphenation allows unambiguous peak identification and molar mass correlation