Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Dokumenttyp
Sprache
- Englisch (9)
Referierte Publikation
- ja (9) (entfernen)
Schlagworte
- MALDI-TOF MS (3)
- Polylactide (3)
- Amphiphilicity (1)
- Artificial weathering (1)
- Catalysts (1)
- Charge-to-size-ratio (1)
- Crosslinking (1)
- Crystalinity (1)
- Crystallization (1)
- Degradation (1)
Organisationseinheit der BAM
- 6 Materialchemie (9) (entfernen)
The 2-methoxyphenol units (G-units) in lignin are modified by demethylation and oxidation to provide the activated lignin as one part of an advanced biobased two-component (2K) adhesive system, which exhibits promising shear strengths in dry and underwater applications. The activation of lignin is straightforward and generates quinones via demethylation and periodate oxidation. These act as Michael acceptors and react smoothly with multi-thiol-star polymers to yield thiol-catechol connectivities (TCCs). The mussel-inspired material platform acts as a very robust and versatile adhesive, combining low-cost and readily available lignin with multi-thiols to achieve outstanding adhesion strengths of up to 15 MPa in dry application. In particular, the 2K system is compatible with the marine biological environment and shows no acute toxicity to sensitive organisms such as fish eggs. Thus, one possible application of this material could be an adhesive for setting temperature-resistant corals in damaged reefs.
The usefulness of seven different Tin catalysts, Bismuth subsalicylate and Titan tetra(ethoxide) for the polycondensation of ethyl L-lactate (ELA) was examined at 150 °C/6 d. Dibutyltin bis(phenoxides) proved to be particularly effective. Despite the low reactivity of ELA, weight average molecular masses (Mw) up to 12 500 were found along with partial crystallization. Furthermore, polylactides (PLAs) of similar molecular masses were prepared via ELA-initiated ROPs of L-lactide by means of the four most effective polycondensation catalysts. The crystalline linear PLAs were annealed at 140 or 160 °C in the presence of these catalysts. The consequences of the transesterification reactions in the solid PLAs were studied by means of matrix-assisted laser desorption/ionization (MALDI TOF) mass spectrometry, gel permeation chromatography (GPC) and small-angle X-ray scattering (SAXS). The results indicate that polycondensation and formation of cycles proceed in the solid state via formation of loops on the surface of the crystallites. In summary, five different transesterification reactions are required to explain all results.
In a laboratory test, transparent high‐density polyethylene (HDPE) jerrycans have been exposed to both UV radiation and 55 wt‐% nitric acid solution at (41 ± 2)°C, for up to 20 days. For comparison, UV radiant exposure (21 days) and nitric acid exposure (up to 6 weeks) were performed separately, at nearly equal temperatures. The damages are compared with FTIR spectroscopy in ATR and HT‐gel permeation chromatography(GPC) on a molecular level and with hydraulic internal pressure testing as a component test. For the used jerrycans, relevant oxidation can only be found after the combined exposure. This is caused by the decomposition of nitric acid into nitrous gases by UV radiation, which is also observed at lower concentrations (28 wt‐%). After 6 days of laboratory exposure, this is rated as critical, which corresponds to about 1/10 year in Central Europe, according to the UV radiant exposure. The gradual increase in oxidative damage shows the reproducibility of the test.
The polycondensations of adipic acid and 1,10-decanediol catalyzed by toluene sulfonic acid (TSA) were reinvestigated using MALDI TOF mass spectrometry and NMR spectroscopy. Unexpected reactions of TSA were detected along with incomplete conversion of the monomers. Furthermore, transesterification reactions of end-capped poly(1,10-decanediol adipate) and end-capped poly(ε-caprolactone) catalyzed by TSA were studied. Despite the quite different (ionic) reaction mechanisms, it was found that for polycondensations performed in bulk intermolecular transesterification is more efficient than the intramolecular “back-biting”; this scenario was not considered in the Jacobson–Stockmayer theory of reversible polycondensations.
These results also confirm that the Jacobson–Stockmayer explanation of reversible polycondensations solely on the basis of ring chain equilibration is not only devoid of any experimental evidence, but also in contradiction to the results elaborated in this work.
Lignosulfonates are industrial biorefinery products that are characterized by significant variability and heterogeneity in their structural composition. Typically, they exhibit high dispersities in molar mass (molar mass distribution-MMD) and in functionalities (functionality-type distribution - FTD), which crucially affect their material usage. In terms of FTD, state-of-the-art Lignin analytics still rely mainly on the determination of functional group contents, which are statistical averages with limited explanatory power. In contrast, our online hydrophobic interaction chromatography−size-exclusion chromatography 2D-LC approach combines the determination of both MMD and FTD in a single measurement to provide a comprehensive picture of the characteristic composition of industrial lignosulfonates information hitherto inaccessible by state-of-the-art lignin analytics. In this way, the complex inter - relationships between these two important structural parameters can be studied in an unprecedented manner. In this study, we reveal the considerable differences in terms of hydrophobic composition and its dispersity present in a range of different industrial lignosulfonates - data desperately needed in tailoring and refining of lignosulfonate composition for material usage.
SnOct2 (Sn(II) 2-ethylhexanoate) catalyzed ROPs of L-lactide were performed in bulk with eight different alcohols as initiators. The time was varied between 1 h and 24 h for all initiators. For two initiators the temperature was also lowered to 115 ◦C. Even-numbered chains were predominantly formed in all polymerizations at short times, but the rate of transesterification (e.g. even/odd equilibration) and the molecular weight distribution were found to depend significantly on the nature of the initiator. Observed transesterification reactions also continued in solid poly (L-lactide), and with the most active initiator, almost total equilibration was achieved even at 130 ◦C. This means that all chains including those of the crystallites were involved in transesterification reactions proceeding across the flat surfaces of the crystallites. The more or less equilibrated crystalline polylactides were characterized by DSC and SAXS measurements with regard to their melting temperature (Tm), crystallinity and crystal thickness.
The structure and composition of polycarbonate polydimethylsiloxane copolymer (PC-co-PDMS) was investigated by applying various analytical approaches including chromatographic separation methods, spectrometric, and spectroscopic detection techniques. In particular, size exclusion chromatography (SEC) and liquid adsorption chromatography operating at different conditions (e.g. using gradient solvent systems) were used to achieve separations according to molar mass and functionality distribution. The coupling of both techniques resulted in fingerprint two-dimensional plots, which could be used to easily compare different copolymer batches. Matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometry was applied for structural investigations. The different ionization behavior of both comonomers, however, strongly limited the applicability of this technique. In contrast to that, Fourier-transform Infrared (FTIR) spectroscopy could be used to quantify the amount of PDMS in the copolymer at different points in the chromatogram. The resulting methodology was capable of distinguishing PC-co-PDMS copolymer from PC homopolymer chains present in the material.
Polyether and -ester urethanes (PU) were exposed to artificial weathering at 40 °C and artificial UV radiation in a weathering chamber. In 3 parallel exposures, humidity was varied between dry, humid, and wet conditions. Material alteration was investigated by various analytical techniques like size exclusion chromatography
(SEC), liquid chromatography-infrared spectroscopy (LC-FTIR), thermal-desorption gas chromatography-mass spectrometry (TD-GC-MS), fluorescence mapping and dynamic mechanical analysis (DMA). Our results show that depending on the weathering conditions, different degradation effects can be observed. By means of SEC an initial strong decrease of the molar masses and a broadening of the mass distributions was found. After a material dependent time span this was followed by a plateau where molar mass changes were less significant. A minor moisture-dependent degradation effect was only found for polyester PU. Fluorescence measurements on two materials revealed an increase in the luminescence intensity upon weathering process reaching a saturation level after about 500 h. The changes in the optical properties observed after different exposure conditions and times were very similar. The TD-GC-MS data showed the fate of the stabilizers and antioxidant in the course of weathering. LC-FTIR measurements revealed a change in peak intensities and the ratio of urethane and carbonyl bands.
From simple homopolymers to functionalized, 3-dimensional structured copolymers, the complexity of polymeric materials has become more and more sophisticated. With new applications for instance in the semiconductor or pharmaceutical industry, the requirements for the characterization have risen with the complexity of the used polymers. For each additional distribution, an additional dimension in analysis is needed. Small, often isomeric heterogeneities in topology or microstructure can usually not be simply separated chromatographically or distinguished by any common detector, but affect the properties of materials significantly. For a drug delivery system for example, the degree of branching and branching distribution is crucial for the formation of micelles. Instead of a complicated, time consuming and/or expensive 2d-chromatography or ion mobility spectrometry (IMS) method, that also has its limitations, in this work a simple approach using size exclusion chromatography (SEC) coupled with electrospray ionization mass spectrometry (ESI) is proposed. The online coupling allows the analysis of reconstructed ion chromatograms (RIC) of each degree of polymerization. While a complete separation often cannot be achieved, the derived retention times and peak widths lead to information on the existence and dispersity of heterogeneities. Although some microstructural heterogeneities like short chain branching can for large polymers be characterized with methods such as light scattering, for oligomers where the heterogeneities just start to form and their influence is at the maximum, they are inaccessible with these methods. It is also shown, that with a proper calibration even quantitative information can be obtained. This method is suitable to detect small differences in e. g. branching, 3d-structure, monomer sequence or tacticity and could potentially be used in routine analysis to quickly determine deviations.