Multiple Impact-Resistant 2D Covalent Organic Framework

Abstract

Exploring and designing two-dimensional (2D) nanomaterials for armor-piercing protection has become a research focus. Here, by molecular dynamics simulation, we revealed that the ultralight monolayer covalent organic framework (COF), one kind of novel 2D crystalline polymer, possesses superior impactresistant capability under high-velocity impact. The calculated specific penetration energy is much higher than that of other traditional impact-resistant materials, such as steel, poly(methyl methacrylate), Kevlar, etc. It was found that the hexagonal nanopores integrated by polymer chains have large deformation compatibility resulting from flexible torsion and stretching, which can remarkably contribute to the energy dissipation. In addition, the deformable nanopores can effectively restrain the crack propagation, enable COF to resist multiple impacts. This work uncovers the extreme dynamic responses of COF under highvelocity impact and provides theoretical guidance for designing superstrong 2D polymer-based crystalline nanomaterials.

2H‐Azirines: Recent Progress in Synthesis and Applications

“…The reaction was catalyzed by Cu(II)‐2‐ethylhexanoate under internal temperature control, providing the products with the yield up to 73 %. Moreover, Zhao et al [49] . recently developed two distinct palladium/silver catalyzed regiospecific dimerizations of 2H ‐azirines (Scheme 28b and c).…”

Palladium Catalysis: Dependence of the Efficiency of C−C Bond Formation on Carboxylate Ligand and Alkali Metal Carboxylate or Carboxylic Acid Additive. Part A: the C(sp2)−C(sp2), C(sp2)−C(sp3) and C(sp3)−C(sp3) Bonds

“…The Pd(OAc) 2 ‐catalyzed DHR of pyridine (py) with n ‐butyl acrylate in DMF in the presence of AgOAc and RCO 2 H under oxygen at 140 °C mainly led to C2 substitution in optimum yield and selectivity using t ‐BuCO 2 H and the 8:1:6:5 pyridine/olefin/AgOAc/pivalic acid ratio (Scheme 18 a) [102] . Use of Ag 2 CO 3 instead of AgOAc seems to be prejudicial to the selectivity but the reagents ratio was different [103] . The selectivity towards the C2 substitution contrasts with a previous report from Yu's team which reported the C3 alkenylation as the main pathway using Pd(OAc) 2 and Ag 2 CO 3 in DMF at 140 °C under air atmosphere and RCO 2 H‐free conditions [104a] .…”

The thermoelastic properties of monolayer covalent organic frameworks studied by machine-learning molecular dynamics

“…Li and Brédas 25 reported the elastic properties of COFs using OPLS all-atom force field potentials 26 and pointed out that the existence of structural defects will significantly reduce the stiffness of 2D COFs. Very recently, Hao et al 27 revealed that 2D COFs possess a superior impact-resistant capability under high-velocity impacts. Although these initial results reveal some fundamental mechanical characters of 2D COFs, there still exist some limitations in these MD studies.…”