Constructing responsive and adaptive materials by dynamic covalent bonds is an attractive strategy in material design. Here, we present a kind of dynamic covalent polyureas which can be prepared from the highly efficient polyaddition reaction of pyrazoles and diisocyanates at ambient temperature in the absence of a catalyst. Owing to multiphase structural design, poly(pyrazole-ureas) (PPzUs) show excellent mechanical properties and unique crystallization behavior. Besides, the crosslinked PPzUs can be successfully recycled upon heating (~130 °C) and the molecular-level blending of polyurea and polyurethane is realized. Theoretical studies prove that the reversibility of pyrazole-urea bonds (PzUBs) arises from the unique aromatic nature of pyrazole and the N-assisting intramolecular hydrogen transfer process. The PzUBs could further broaden the scope of dynamic covalent bonds and are very promising in the fields of dynamic materials.
A highly enantioselective synthesis of indolines by asymmetric hydrogenation of 1H-indoles and 3H-indoles at ambient temperature and pressure, catalyzed by chiral phosphine-free cationic ruthenium complexes, has been developed. Excellent enantio- and diastereoselectivities (up to >99 % ee, >20:1 d.r.) were obtained for a wide range of indole derivatives, including unprotected 2-substituted and 2,3-disubstituted 1H-indoles, as well as 2-alkyl- and 2-aryl-substituted 3H-indoles.
Super
black materials
with extremely low reflectance and high absorption of incident light
are crucial in various applications with strict optical requirements.
However, the existing super black materials suffer from technical
complexity in practical use whereas the underlying physics of their
ultralow reflectance is still unclear. Herein, hierarchical porous
carbon spheres are prepared using poly(vinylidene chloride-co-vinyl chloride) as a precursor. Dehydrochlorination treatment
has proved to be very crucial for the morphology robustness of the
porous polymer spheres during carbonization process. Coatings cast
from the dispersion of these carbon spheres exhibit a hemispherical
reflectance of <0.2% in the visible region and <0.3% in the
range of 300–2000 nm, and the lowest reflectance of 0.14% can
be reached. This super black coating has great advantages in its easy
availability of starting materials, low equipment requirement, and
high adaptability onto various substrates. Besides, a theoretical
investigation suggests that a small scatterer size and low volume-filling
ratio are the two most essential factors in realizing ultralow reflectance,
which also offers an instructive guidance for the rational design
of super black materials.
The first highly effective and enantioselective hydrogenation of quinolines catalyzed by chiral cationic Ru-diamine complexes in undegassed water was developed.
The construction of a single polymer
network with extreme stretchability,
relatively high mechanical strength, and fast and facile autonomous
room-temperature self-healing capability still remains a challenge.
Herein, supramolecular polymer networks are fabricated by synergistically
incorporating metal–ligand and hydrogen bonds in poly(propylene
glycol) (PPG). The representative specimen, PPG-Im-MDA-1.5-0.25-Cu,
shows a combination of notable mechanical properties involving an
extreme stretching ratio of 346 ± 14× and a Young’s
modulus of 2.10 ± 0.14 MPa, which are superior to the previously
reported extremely stretchable polymeric materials. Notably, the destroyed
specimen can fully recover mechanical performances within 1 h. The
tunability of mechanical properties and self-healing capability has
been actualized by merely tailoring the content of a chain extender.
The application of the as-prepared supramolecular PPG network in constructing
a flexible and self-healable conductor has been demonstrated. This
strategy provides some insights for preparing extremely stretchable
and self-healable polymeric materials.
To investigate the detailed mechanisms for lignite methanolysis,
we used ReaxFF reactive force field to perform a series of molecular
dynamics simulations (MDSs) on a unimolecular model compound. The
α-O-4 and β-O-4 types
of lignite-related model compounds were selected as representatives
of linkages in lignites. The reaction products predicted by ReaxFF
MDSs are consistent with those from experimental results reported.
The initiation reaction observed in ReaxFF MDSs involving the ether
linkage cleavage and methanol participation closely matches the results
observed from previously reported experiments. The agreement of these
results with available experimental observations demonstrates that
ReaxFF MDSs can give an atomistic description of the initiation mechanism
for methanolysis and provide useful insights into the complicated
reaction processes.
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