Abstract:Oligomerization
reactions of aliphatic diisocyanates, exclusively involving NCO groups
are discussed. The reactivity and selectivity of these reactions are
dependent on chain length, reaction conditions, and the catalyst employed.
The resulting oligomers (“dimers” and “trimers”)
sometimes deviate considerably from expectation with respect to the
structure and properties. The synthesis and characterization of well-known
derivatives such as uretdiones and isocyanurates are discussed, and
special attention is dev… Show more
“…Although in the academic literature a wide variety of organometallic compounds, − bases, − and even anion radicals are used as catalysts, patents mostly claim the production of HDI-based isocyanurate cross-linkers via the use of carboxylate catalysts. − The latter are industrially favored because of their easy synthesis and handling as well as the low color obtained for the products, which is of utmost importance for clear-coat applications. A mechanistic investigation of the cyclotrimerization of aliphatic isocyanates using carboxylate catalysts is not reported yet, which is surprising, as this could enable a better control of the reaction in terms of reactivity and selectivity (uretdione, carbodiimide, or iminooxadiazinedione are well-known side-products). Motivated by the promising benefits as well as the scale of application, we performed quantum chemical calculations on the bulk cyclization of an aliphatic isocyanate using acetate as a catalyst and supported the results with state-of-the-art analytical methods.…”
The acetate-initiated aliphatic isocyanate trimerization to isocyanurate was investigated by state-of-the-art analytical and computational methods. Although the common cyclotrimerization mechanism assumes the consecutive addition of three equivalents of isocyanate to acetate prior to product formation, we found that the underlying mechanism is more complex. In this work, we demonstrate that the product, in fact, is formed via the connection of two unexpected catalytic cycles, with acetate being only the precatalyst. The initial discovery of a precatalyst activation by quantum chemical computations and the resulting first catalysis cycle were corroborated by mass spectrometric and NMR experiments, thereby additionally revealing a catalyst migration to the second catalytic cycle. These results were further confirmed by computations, completing the full mechanistic understanding of this catalytic system. Identification of a side product with undesired properties for final coating applications allows for process optimization in the chemical industry.
“…Although in the academic literature a wide variety of organometallic compounds, − bases, − and even anion radicals are used as catalysts, patents mostly claim the production of HDI-based isocyanurate cross-linkers via the use of carboxylate catalysts. − The latter are industrially favored because of their easy synthesis and handling as well as the low color obtained for the products, which is of utmost importance for clear-coat applications. A mechanistic investigation of the cyclotrimerization of aliphatic isocyanates using carboxylate catalysts is not reported yet, which is surprising, as this could enable a better control of the reaction in terms of reactivity and selectivity (uretdione, carbodiimide, or iminooxadiazinedione are well-known side-products). Motivated by the promising benefits as well as the scale of application, we performed quantum chemical calculations on the bulk cyclization of an aliphatic isocyanate using acetate as a catalyst and supported the results with state-of-the-art analytical methods.…”
The acetate-initiated aliphatic isocyanate trimerization to isocyanurate was investigated by state-of-the-art analytical and computational methods. Although the common cyclotrimerization mechanism assumes the consecutive addition of three equivalents of isocyanate to acetate prior to product formation, we found that the underlying mechanism is more complex. In this work, we demonstrate that the product, in fact, is formed via the connection of two unexpected catalytic cycles, with acetate being only the precatalyst. The initial discovery of a precatalyst activation by quantum chemical computations and the resulting first catalysis cycle were corroborated by mass spectrometric and NMR experiments, thereby additionally revealing a catalyst migration to the second catalytic cycle. These results were further confirmed by computations, completing the full mechanistic understanding of this catalytic system. Identification of a side product with undesired properties for final coating applications allows for process optimization in the chemical industry.
“…Thus, bio-based cadaverine can be used as raw material for synthesizing diisocyanates. Compared to HDI-derived polyurethane, PDI-derived product reveals similar or even improved properties in terms of flexibility and impact resistance [ 35 , 36 ]. Scheme 1 Reactions involved in the synthesis of PDU and PDI.…”
Cadaverine is an important C5 platform chemical with a wide range of industrial applications. However, the cadaverine inhibition on the fermenting strain limited its industrial efficiency of the strain. In this study, we report an engineered
Escherichia coli
strain with high cadaverine productivity that was generated by developing a robust host coupled with metabolic engineering to mitigate cadaverine inhibition. First, a lysine producing
E. coli
was treated with a combination of radiation (ultraviolet and visible spectrum) and ARTP (atmospheric and room temperature plasma) mutagenesis to obtain a robust host with high cadaverine tolerance. Three mutant targets including HokD, PhnI and PuuR are identified for improved cadaverine tolerance. Further transcriptome analysis suggested that cadaverine suppressed the synthesis of ATP and lysine precursor. Accordingly, the related genes involved in glycolysis and lysine precursor, as well as cadaverine exporter was engineered to release the cadaverine inhibition. The final engineered strain was fed-batch cultured and a titer of 58.7 g/L cadaverine was achieved with a yield of 0.396 g/g, both of which were the highest level reported to date in
E. coli
. The bio-based cadaverine was purified to >99.6% purity, and successfully used for the synthesis of polyurethane precursor 1,5-pentamethylene diisocyanate (PDI) through the approach of carbamate decomposition.
“…Our previous experiments resulted in PU films with limited stability and scratch resistance. To improve this we report here the synthesis and properties of PU films based on Desmodur N3300, an aliphatic, low‐viscosity, solvent‐free triisocyanate based on hexamethylene diisocyanate (trimer) see Scheme . Desmodur N 3300 was used as the isocyanate component in solvent casting experiments.…”
The polyurethane industry is strongly dependent on fossil‐based polyols and polyisocyanates. Developing novel sustainable polyols from valuable biobased building blocks is a first step toward strong and durable development. The synthesis and properties of PU films based on pristine and acylated white dextrins (AVEDEX W80) as polyol and an aliphatic, low‐viscosity, solvent‐free triisocyanate based on hexamethylene diisocyanate (trimer—Desmodur N3300) as crosslinker is reported. After optimizing several conditions, such as the reaction time, reaction temperature, amount of solvent, isocyanate index, and amount per surface area, it is possible to obtain smooth PU films with good thermal properties.
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