Helmut Much

Determination of Functionality and Molar Mass Distribution of Aliphatic Polyesters by Orthogonal Liquid Chromatography. I. Off-Line Investigation of Poly(1,6-Hexanediol Adipates)

Abstract During polycondensation of polyesters products are formed distributed in molar mass and functionality (end groups). Especially in polyurethane chemistry the knowledge of the distribution of terminal groups is necessary for correlating material properties containing different species in raw materials. The characterization of polyesters by “Liquid Adsorption Chromatography at Critical Conditions” (LACCC) is a new powerful tool for kinetics and modelling. Separation of polyesters according to their terminal groups independently of their molar mass is feasible at the critical conditions determined by the chromatographic system silica/acetone/hexane. Owing to side reactions, the number of combinations of COOH- and OH terminal groups identified was higher than expected. Cyclic species, hexanediol ether structures and alkyl-terminated homologues were identified. Model substances for all structures were synthesized. For orthogonal separation LACCC was combined off-line with SEC. With the help of preparat...

Determination of Functionality and Molecular Weight Distribution by Orthogonal Chromatography

Abstract During polymerization oligomers, telechelics and macromers with different endgroups are formed as a result of various mechanisms (starting, termination, cyclization. transfer reactions). The characterization of the resulting products is possible by using orthogonal chromatography. In order to characterize 1,3,6-trioxocane polymers, synthesized in presence of benzyl alcohol, Liquid Adsorption Chromatography (LAC) under “critical conditions” is combined with Size-Exclusion Chromatography (SEC). This method includes a preparative chromatographic separation of the product which is followed by SEC and LAC under “critical conditions” and vice versa. Results advantages and problems of this type of orthogonal chromatography are discussed.

Determination of Polymer Heterogeneity by Two-Dimensional Orthogonal Liquid Chromatography

Abstract Liquid adsorption chromatography at critical conditions (LACCC) is a versatile method for the determination of different types of chemical heterogeneity in polymers. Coupling of LACCC in the first and size exclusion chromatography (SEC) in the second dimension is a useful tool to characterize polymers. Experimental problems of this orthogonal two-dimensional chromatographic method and applications are presented. Polyesters, polyethers and macromers are characterized according to their functionality and molar mass. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is an excellent method for identification of LACCC fractions and SEC calibration. The results of two-dimensional liquid chromatography are presented by a contour map (fingerprint of polymer).

Liquid Adsorption Chromatography near Critical Conditions of Adsorption Coupled with Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

Abstract Chemical heterogeneities and molecular weight distributions of poly(ethylene oxide) (PEO)-co-polymethylene (PM) model oligomers, which are relevant to the synthesis of commonly used tensides, were investigated. For analytical characterization, the well-known principle of liquid adsorption chromatography at ‘critical conditions’ (LACCC) was modified. Near the critical conditions of adsorption of the PEO unit, e.g., at slight adsorption conditions of PM, the copolymers could be separated according to their PM chain length. The eluates were separated and single fractions of each peak were continuously transferred onto the MALDI target by means of a commercially available device. Simultaneously, the MALDI matrix solution was continuously added with a second pump. This procedure offers the possibility of the formation of homogeneous matrix-polymer textures. By MALDI-MS a complete characterization of the chemical composition (PEO and PM chain length) of each peak could be achieved. The obtained MALDI mass spectra of the eluates at different retention times could be used for the molecular weight calibration of the LAC system. In this way, an additional application of SEC, as in conventional 2D-chromatography, was avoided by using the MALDI method as quasi chromatographic separation.

Simultaneous determination of functionality type and molar mass distribution of oligo (1,3,6-trioxocane)s by supercritical fluid chromatography

Abstract Benzyloxy terminated oligo (1,3,6-trioxocane)s are separated into components of single molar mass and functionality by supercritical fluid chromatography. The assignment and quantification of the components is described. It is shown that molar mass and functionality type distribution may be determined simultaneously from one chromatogram.

Zur Charakterisierung von Si-Polymeren durch flüssigchromatographische Verfahren in Kopplung mit MALDI-TOF-MS

Summary. The coupling of the three liquid chromatographic modes with MALDI-TOF mass spectrometry is suitable for the determination of the molecular, functional, and chemical heterogeneities of Si polymers. Silsesquioxanes and siloxanes serve as examples for this method of structure identification. The substance specific construction of the SEC calibration curve by means of MALDI-MS is shown.Zusammenfassung. Die Kopplung der drei flüssigchromatographischen Modi mit MALDI-TOF-Massenspektrometrie ist zur Bestimmung der molekularen, funktionalen und chemischen Verteilungen von Si-Polymeren geeignet. Silsesquioxane und Siloxane dienen als Beispiele für diese Art der Strukturerkennung. Die substanzspezifische Konstruktion einer SEC-Eichkurve mit Hilfe der MALDI-MS wird gezeigt.

Characterization of Polymers Using Supercritical Fluid Chromatography: Application of adsorption chromatography, size exclusion chromatography and adsorption chromatography at critical conditions

Abstract Supercritical fluid chromatography (SFC) utilizes fluids or mixtures of fluids above their critical temperature and critical pressure which exhibit greater solvating properties with simultaneously reduced viscosities and higher diffusion coefficients compared with their liquid state; supercritical fluids, thus, offer new possibilities for characterizing polymers. The three modes of liquid chromatography are applied in the analysis of polystyrenes, using supercritical fluids (mixtures of dichloromethane with carbon dioxide) in each mode: adsorption chromatography for the separation of oligomers, size exclusion chromatography for the determination of molar mass distribution, and adsorption chromatography at critical conditions for the characterization of functionality type distribution. Advantages and disadvantages of size exclusion chromatography with fluids in their supercritical, subcritical and liquid phase are discussed with the system polystyrene in dichloromethane.