Asymmetric Hydroalkoxylation of Non‐Activated Alkenes: Titanium‐Catalyzed Cycloisomerization of Allylphenols at High Temperatures

The asymmetric catalytic addition of alcohols (phenols) to non‐activated alkenes has been realized through the cycloisomerization of 2‐allylphenols to 2‐methyl‐2,3‐dihydrobenzofurans (2‐methylcoumarans). The reaction was catalyzed by a chiral titanium–carboxylate complex at uncommonly high temperatures for asymmetric catalytic reactions. The catalyst was generated by mixing titanium isopropoxide, the chiral ligand (aS)‐1‐(2‐methoxy‐1‐naphthyl)‐2‐naphthoic acid or its derivatives, and a co‐catalytic amount of water in a ratio of 1:1:1 (5 mol % each). This homogeneous thermal catalysis (HOT‐CAT) gave various (S)‐2‐methylcoumarans with yields of up to 90 % and in up to 85 % ee at 240 °C, and in 87 % ee at 220 °C.     

Parametric instability of a magnetic pendulum in the presence of a vibrating conducting plate

Nonlinear Dynamics - A pendulum with an attached permanent magnet swinging in the vicinity of a conductor is a typical experiment for the demonstration of electromagnetic braking and Lenz’...     

Quantitative Medium-Resolution NMR Spectroscopy Under Non-Equilibrium Conditions,Studied on the Example of an Esterification Reaction

Medium-resolution nuclear magnetic resonance spectroscopy is a promising tool for the monitoring of liquid reactions. For process analytical applications, the requirements of robustness and insensitivity of the spectrometer in relation to high temperatures and pressures are challenging. Within this study, a flow probe using a glass dewar is presented. Temperatures of flowing samples up to 130 °C and pressures up to 40 bar were successfully applied, and the corresponding temperature loss of the flowing sample at 2 ml min^?1 was <2.4 °C at 130 °C. Furthermore, if the process requires a measurement in a non-equilibrium state of magnetization, a comprehensive data treatment is given. For this purpose, the influences of the flow and T ₁ of the substances under investigation are studied in detail on the example of a homogeneously catalyzed esterification. In addition, data analysis schemes were designed such that the experiments directly revealed mole fractions from the spectra. Limited spectral resolutions and low signal-to-noise ratio still did not obstruct quantitative interpretation of the experiments.     

Neutron dosimetry device using PADC nuclear track detectors

A device consisting of poly allyl diglycol carbonate (PADC) foils with a polyethylene and polyvinyl chloride (PVC) radiator was calibrated in order to perform the dosimetry of an ²⁴¹Am-Be source covering a dose range from 0 to 3.1 mSv. Working conditions were established for a good visualization and counting of tracks: chemical attack was made in two steps with different solutions and etching times. A good fit was obtained for the dose as a function of the number of tracks per unit surface area. The calculated decision threshold was 0.12 mSv.     

Orthogonal Cationic and Radical RAFT Polymerizations to Prepare Bottlebrush Polymers

An orthogonal combination of cationic and radical RAFT polymerizations is used to synthesize bottlebrush polymers using two distinct RAFT agents. Selective consumption of the first RAFT agent is used to control the cationic RAFT polymerization of a vinyl ether monomer bearing a secondary dormant RAFT agent, which subsequently allows side‐chain polymers to be grafted from the pendant RAFT agent by a radical‐mediated RAFT polymerization of a different monomer, thus completing the synthesis of bottlebrush polymers. The high efficiency and selectivity of the cationic and radical RAFT polymerizations allow both polymerizations to be conducted in one‐pot tandem without intermediate purification.     

Topochemical acetylation of cellulose nanopaper structures for biocomposites: mechanisms for reduced water vapour sorption

Moisture sorption decreases dimensional stability and mechanical properties of polymer matrix biocomposites based on plant fibers. Cellulose nanofiber reinforcement may offer advantages in this respect. Here, wood-based nanofibrillated cellulose (NFC) and bacterial cellulose (BC) nanopaper structures, with different specific surface area (SSA), ranging from 0.03 to 173.3 m²/g, were topochemically acetylated and characterized by ATR-FTIR, XRD, solid-state CP/MAS ¹³C-NMR and moisture sorption studies. Polymer matrix nanocomposites based on NFC were also prepared as demonstrators. The surface degree of substitution (surface-DS) of the acetylated cellulose nanofibers is a key parameter, which increased with increasing SSA. Successful topochemical acetylation was confirmed and significantly reduced the moisture sorption in nanopaper structures, especially at RH = 53 %. BC nanopaper sorbed less moisture than the NFC counterpart, and mechanisms are discussed. Topochemical NFC nanopaper acetylation can be used to prepare moisture-stable nanocellulose biocomposites.