scholarly journals Molecular design of polymer coatings capable of photo‐triggered stress relaxation via dynamic covalent bond exchange

2021 ◽  
Author(s):  
Autumn M. Mineo ◽  
Maren E. Buck ◽  
Reika Katsumata
Keyword(s):  
Stress Relaxation ◽  
Molecular Design ◽  
Covalent Bond ◽  
Polymer Coatings

scholarly journals Epoxy-Anhydride Vitrimers from Aminoglycidyl Resins with High Glass Transition Temperature and Efficient Stress Relaxation

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1148 ◽  
Author(s):  
Michael Giebler ◽  
Clemens Sperling ◽  
Simon Kaiser ◽  
Ivica Duretek ◽  
Sandra Schlögl
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Elevated Temperature ◽  
Glass Transition Temperature ◽  
Stress Relaxation ◽  
Covalent Bond ◽  
Service Temperature ◽  
Exchange Reactions ◽  
Structural Applications ◽  
Relaxation Measurements

Epoxy-anhydride vitrimers are covalent adaptable networks, which undergo associative bond exchange reactions at elevated temperature. Their service temperature is influenced by the glass transition temperature (Tg) as well as the topology freezing transition temperature (Tv), at which the covalent bond exchange reactions become significantly fast. The present work highlights the design of high-Tg epoxy-anhydride vitrimers that comprise an efficient stress relaxation at elevated temperature. Networks are prepared by thermally curing aminoglycidyl monomers with glutaric anhydride in different stoichiometric ratios. The tertiary amine groups present in the structure of the aminoglycidyl derivatives not only accelerate the curing reaction but also catalyse the transesterification reaction above Tv, as shown in stress relaxation measurements. The topology rearrangements render the networks recyclable, which is demonstrated by reprocessing a grinded powder of the cured materials in a hot press. The epoxy-anhydride vitrimers are characterised by a high Tg (up to 140 °C) and an adequate storage modulus at 25 °C (~2.5 GPa), which makes them interesting candidates for structural applications operating at high service temperature.

Recent Advances in Halogen Bond-assisted Organic Synthesis

2020 ◽  
Vol 24 (18) ◽  
pp. 2118-2152
Author(s):  
Shigeyuki Yamada ◽  
Tsutomu Konno
Keyword(s):  
Organic Synthesis ◽  
Crystal Engineering ◽  
Electron Pair ◽  
Molecular Design ◽  
Halogen Bond ◽  
Covalent Bond ◽  
Lewis Base ◽  
Organic Transformations ◽  
Hydrogen Bond Interaction ◽  
Significant Attention

Halogen bond interactions, which take place between an electrophilic halogen and the electron-pair of a Lewis base and exhibit high directionality (approximately 180°), are non-covalent bond interactions similar to the hydrogen bond interaction. Many reports on halogen bond interactions have been published thus far, but many of them discuss halogen bond in the context of crystal engineering of supramolecular architecture. Since a seminal report by Bolm in 2008, halogen bond-assisted or -promoted organic synthesis has received significant attention. This review aims to introduce the molecular design of suitable halogen bond donors and organic transformations involving halogen bond interactions to afford a variety of organic compounds.

scholarly journals Changing the Nature of the Chelating Ligand of Tetracoordinate Boron-Containing PAH Multi-resonant Thermally Activated Delayed Fluorescence Emitters Tunes the Emission from Green to Deep Red

2021 ◽  
Author(s):  
Guoyun Meng ◽  
Lijie Liu ◽  
Zhechang He ◽  
David Hall ◽  
Xiang Wang ◽  
...  
Keyword(s):  
High Performance ◽  
Molecular Design ◽  
Emission Spectra ◽  
Covalent Bond ◽  
Delayed Fluorescence ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Thermally Activated ◽  
Chelating Ligand ◽  
Chelating Compounds

Multi-resonant thermally activated delayed fluorescence (MR-TADF) materials have attracted considerable attention recently. The molecular design frequently incorporates cycloboration. However, to the best of our knowledge MR-TADF compounds containing nitrogen chelation to boron is still unknown. Reported herein is a new class of tetracoordinate boron-containing MR-TADF emitters bearing a C^N^C- and N^N^N-chelating ligands. We demonstrate that the replacement of B−C covalent bond in C^N^C-chelating ligand by B−N covalent bond affords a regioisomer, which dramatically influences the optoelectronic properties of the molecule. The resulting N^N^N-chelating compounds show bathochromically shifted absorption and emission spectra relative to C^N^C-chelating compounds. The incorporation of tert-butylcarbazole group to the 4-position of the pyridine significantly enhances both the thermal stability and the reverse intersystem crossing rate, yet has a negligible effect on the emission properties. Consequently, high-performance hyperfluorescence organic light-emitting diodes (HF-OLEDs) that utilize these molecules as green and yellow-green emitters show maximum external quantum efficiency (ηext) of 11.5% and 25.1%, and a suppressed efficiency roll-off with ηext of 10.2% and 18.7% at a luminance of 1000 cd m−2, respectively.

Stress Relaxation and the Formation of Silicides in the Process of the Crystallization of NI-NB Films on SI

1991 ◽  
Vol 49 ◽  
pp. 898-899
Author(s):  
N. Rozhanski ◽  
V. Lifshitz
Keyword(s):  
Thin Films ◽  
Stress Relaxation ◽  
Integrated Circuits ◽  
Direct Evidence ◽  
Alloy Film ◽  
Diffusion Barriers ◽  
Effective Barrier

Thin films of amorphous Ni-Nb alloys are of interest since they can be used as diffusion barriers for integrated circuits on Si. A native SiO2 layer is an effective barrier for Ni diffusion but it deformation during the crystallization of the alloy film lead to the appearence of diffusion fluxes through it and the following formation of silicides. This study concerns the direct evidence of the action of stresses in the process of the crystallization of Ni-Nb films on Si and the structure of forming NiSi2 islands.

Aldehyde gold clusters for molecular labeling

1995 ◽  
Vol 53 ◽  
pp. 858-859
Author(s):  
James F. Hainfeld ◽  
Frederic R. Furuya
Keyword(s):  
Covalent Bond ◽  
Aldehyde Group ◽  
Gold Clusters ◽  
Side Reactions ◽  
Amino Groups ◽  
Sodium Cyanoborohydride ◽  
Schiff’S Base ◽  
Protein Molecules ◽  
Hydroxysuccinimide Esters ◽  
Primary Amino

Glutaraldehyde is a useful tissue and molecular fixing reagents. The aldehyde moiety reacts mainly with primary amino groups to form a Schiff's base, which is reversible but reasonably stable at pH 7; a stable covalent bond may be formed by reduction with, e.g., sodium cyanoborohydride (Fig. 1). The bifunctional glutaraldehyde, (CHO-(CH2)3-CHO), successfully stabilizes protein molecules due to generally plentiful amines on their surface; bovine serum albumin has 60; 59 lysines + 1 α-amino. With some enzymes, catalytic activity after fixing is preserved; with respect to antigens, glutaraldehyde treatment can compromise their recognition by antibodies in some cases. Complicating the chemistry somewhat are the reported side reactions, where glutaraldehyde reacts with other amino acid side chains, cysteine, histidine, and tyrosine. It has also been reported that glutaraldehyde can polymerize in aqueous solution. Newer crosslinkers have been found that are more specific for the amino group, such as the N-hydroxysuccinimide esters, and are commonly preferred for forming conjugates. However, most of these linkers hydrolyze in solution, so that the activity is lost over several hours, whereas the aldehyde group is stable in solution, and may have an advantage of overall efficiency.

Structure of stacking faults in pyrite using TEM techniques

1992 ◽  
Vol 50 (1) ◽  
pp. 358-359
Author(s):  
Raja Subramanian ◽  
Kenneth S. Vecchio
Keyword(s):  
Lattice Structure ◽  
Stacking Faults ◽  
Covalent Bond ◽  
Group Symmetry ◽  
Iron Pyrite ◽  
Dislocation Glide ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
Contrast Analysis ◽  
Chlorine Ions

The structure of stacking faults and partial dislocations in iron pyrite (FeS2) have been studied using transmission electron microscopy. Pyrite has the NaCl structure in which the sodium ions are replaced by iron and chlorine ions by covalently-bonded pairs of sulfur ions. These sulfur pairs are oriented along the <111> direction. This covalent bond between sulfur atoms is the strongest bond in pyrite with Pa3 space group symmetry. These sulfur pairs are believed to move as a whole during dislocation glide. The lattice structure across these stacking faults is of interest as the presence of these stacking faults has been preliminarily linked to a higher sulfur reactivity in pyrite. Conventional TEM contrast analysis and high resolution lattice imaging of the faulted area in the TEM specimen has been carried out.

Effect of Integral Proteins on Frozen Membrane Fracture

1980 ◽  
Vol 38 ◽  
pp. 756-759 ◽  
Author(s):  
S. Kirchanski ◽  
D. Branton
Keyword(s):  
Lipid Bilayers ◽  
Freeze Fracture ◽  
Covalent Bond ◽  
Erythrocyte Membranes ◽  
Glycophorin A ◽  
Experimental Protocol ◽  
Transmembrane Glycoprotein ◽  
Bond Breakage ◽  
Human Erythrocyte Membranes ◽  
Integral Proteins

We have investigated the effect of integral membrane proteins upon the fracturing of frozen lipid bilayers. This investigation has been part of an effort to develop freeze fracture labeling techniques and to assess the possible breakage of covalent protein bonds during the freeze fracture process. We have developed an experimental protocol utilizing lectin affinity columns which should detect small amounts of covalent bond breakage during the fracture of liposomes containing purified (1) glycophorin (a transmembrane glycoprotein of human erythrocyte membranes). To fracture liposomes in bulk, frozen liposomes are ground repeatedly under liquid nitrogen. Failure to detect any significant covalent bond breakage (contrary to (2)) led us to question the effectiveness of our grinding procedure in fracturing and splitting lipid bilayers.

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