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- MALDI-TOF MS (6)
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Organisationseinheit der BAM
- 6 Materialchemie (9)
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Eingeladener Vortrag
- nein (12)
Ring-expansion polymerizations (REPs) catalyzed by two cyclic tin catalysts (2-stanna-1.3-dioxa-4,5,6,7-dibenzazepine [SnBiph] and
2,2-dibutyl-2-stanna-1,3-dithiolane [DSTL]) are performed at 140 °C in bulk.
Small amounts (4 vol%) of chlorobenzene or other solvents are added to
facilitate transesterification reactions (ring–ring equilibration) in the solid poly(l-lactide)s. In the mass range up to m/z 13 000 crystalline PLAs displaying a so-called saw-tooth pattern in the MALDI-TOF mass spectra are obtained indicating the formation of extended-ring crystals. The characteristics of extended-ring crystallites and folded-ring crystallites are discussed. Furthermore, extremely high melting temperatures (Tm’s up to 201.2 °C) and melting enthalpies (𝚫Hm’s up to 106 J g−1)) are found confirming that 𝚫Hm max, the 𝚫Hm of a perfect crystal, is around or above 115 J g−1 in contrast to literature data.
Characterization of randomly branched polymers utilizing liquid chromatography and mass spectrometry
(2014)
Branching in polymers is an important way to modify the materials properties, however the characterization of random branching in polymeric materials is a challenge in polymer analysis. In this work, liquid adsorption chromatography methods are developed for a commercially available hyperbranched polyester (Boltorn™). This Chromatographie techniques was then coupled to offline MALDI-TOF MS analysis, a first in the analysis of randomly branched polymers. The coupling of these two techniques provides superior MALDI-TOF spectra, enabling the easy identification of structural subdistributons based on theoretical molecular weight. Detailed analysis of the MALDI-TOF spectra shows that these Chromatographie conditions separate cyclic Boltorn polymers (with no core molecule) from non-cyclic polymers (with core molecule), and these are the only two architectures observed. MALDI MS also confirms that the Chromatographie Separation mode is adsorption, but further analysis is needed to determine if there is a Separation by degree of branching.
The performance of a miniaturized channel for the separation of polymer and metal nanoparticles (NP) using Asymmetrical Flow Field-Flow Fractionation (AF4) was investigated and compared with a conventional AF4 system. To develop standard separation methods, experimental parameters like cross flow, gradient profile and injection time were varied and optimized.
Corresponding chromatographic parameters were calculated and compared. Our results indicate that the chromatographic resolution in the miniaturized channel is lower, whereas significantly shorter analyses time and less solvent consumption were obtained. Moreover, the limit of detection (LOD) and limit of quantification (LOQ) obtained from hyphenation with a UV-detector are obviously lower than in a conventional channel, which makes the miniaturized channel interesting for trace analysis.
We will report on a new kind of ring-expansion polymerization (REP) of cyclic esters based of three classes of catalysts.
In contrast to REP described previously these new polymerizations are characterized by a self-extrusion of the catalysts resulting in cyclic homopolyesters as the only reaction product. These REP of L-lactide were performed in bulk at temperatures between 100 and 180°C without racemization. A simplified scheme of a REP catalyzed by BuCa or SnBi is presented below. With meso-lactide temperatures down to 60°C were realized. Depending on catalyst, time and temperature with equal quantities of even and odd-numbered cycles a strong predominance of either even or odd-numbered cycles was found.
In addition to molar mass distribution (MMD) synthetic polymers often exhibit an additional chemical heterogeneity distribution, expressed by different end groups and other structural variations (e.g. tacticity, copolymer composition etc.). Ionization in MALDI MS is always strongly affected by such chemical properties. For example, the abundance of cyclics in MALDI TOF mass spectra is frequently reported to greatly exceed that of linears. Thus, the MALDI ionization behavior of various neat end-capped linear poly(L-lactide)s and one cyclic poly(L-lactide) was investigated and compared with that of blends of both structures. Moreover, the influence of the cationizing salt was investigated too.
Neat compounds and various blends of cyclic and linear species were prepared and studied using two MALDI TOF mass spectrometers under identical conditions with regard to sample preparation and instrumental conditions, except for the laser power and the salt used for cationization. Polymer samples were additionally characterized by NMR and SEC.
The steady increase of the laser intensity caused an exponential increase of the peak intensities of both linear and cyclic polylactides.The response of linear polylactides (in the investigated molecular mass range), whether as neat polymer or in blends with other linear polylactides was almost similar. This clearly supports our assumption that ionization in MALDI is probably unaffected by the end group structure.The variation of the laser power shows only little effect on the intensity ratio of linear-to linear and cyclic-to-linear polylactides in blends. Whereas neat linear polylactides at all laser intensities have a significantly higher abundance than neat cyclics, in mixtures of both an overestimation of cyclic species in MALDI TOF mass spectra of polylactides was found. However, this is far less distinct than frequently reported for other polymers.Concluding, peak suppression of linear polymers in mixtures of both architectures can be excluded, which also means, that polylactides showing only peaks of cyclic compounds in their MALDI - TOF mass spectra do not contain a significant fraction of linear analogues.
Our study is the first systematic comparison of the MALDI ionization of neat and blended cyclic and linear polylactides.
Hyphenated techniques
(2012)