Abstract The regulation of topological structure of covalent adaptable networks (CANs) remains a challenge for epoxy CANs. Here, we report a strategy to develop strong and tough epoxy supramolecular ...thermosets with rapid reprocessability and room-temperature closed-loop recyclability. These thermosets were constructed from vanillin-based hyperbranched epoxy resin (VanEHBP) through the introduction of intermolecular hydrogen bonds and dual dynamic covalent bonds, as well as the formation of intramolecular and intermolecular cavities. The supramolecular structures confer remarkable energy dissipation capability of thermosets, leading to high toughness and strength. Due to the dynamic imine exchange and reversible noncovalent crosslinks, the thermosets can be rapidly and effectively reprocessed at 120 °C within 30 s. Importantly, the thermosets can be efficiently depolymerized at room temperature, and the recovered materials retain the structural integrity and mechanical properties of the original samples. This strategy may be employed to design tough, closed-loop recyclable epoxy thermosets for practical applications.
Adhesives have been widely applied in various fields. However, most industrial adhesives contain organic solvents, which are toxic and difficult to clean after use. Importantly, most adhesives are ...used in a relatively small temperature range (0-50 °C), which is due to the fragmentation of the morphology and properties of supramolecular polymer gels at low temperatures. Most of the supramolecular adhesives need to be heated during the bonding process, which cannot meet the requirements of low-temperature adhesion in daily life and industry. In this study, based on the concept of using deep eutectic solvents (DESs) as a platfonn, cyclodextrin (ß-CD) and carboxyl tenninated hyperbranched polyester (DCHP) were used to prepare solvent-free supramolecular polymer gel (CD-DCHP), which was non-toxic and easy to clean. Due to the joint action of deep eutectic solvent and supramolecular polymer structure, CD-DCHP showed excellent mechanical properties, super strong adhesion (up to 4.55 MPa on glass surface), and excellent low-temperature perfonnance (up to 1.64 MPa at -60 °C). This supramolecular polymer gel also showed excellent tolerance to acids, alkalis, and various organic solvents. It greatly expanded the application of DES and provided a new approach to the development of supramolecular adhesives.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Vanadium phosphorus oxide (VPO) was immobilized on SBA-15 via a facile impregnation process. The structure and VPO species on SBA-15 were characterized by XRD, TEM, BET, FTIR and XPS techniques. It ...was found the VPO/SBA-15 catalysts maintained the two-dimensional hexagonal structure of SBA-15, and the supported VPO species existed in a highly dispersed amorphous state. VPO/SBA-15 catalyst was tested for the ammoxidation of dichlorotoluenes (DCTs) to corresponding dichlorobenzonitriles (DCNs) in a lab-scale tube reactor. Compared with VPO/SiO
2
(large-pore silica-supported VPO), VPO/SBA-15 exhibited appreciable enhancement in the catalytic performance due to the unique channel structure of SBA-15. The yield and selectivity toward 2,4-DCN increased by 7% and 6%, while toward the sterically hindered 2,6-DCN increased by 7% and 13%, respectively.
Graphical abstract
MoV
2
O
8
micro-cuboids were environment-friendly prepared via a facile one-step solvothermal route followed by thermal treatment with vanadium pentoxide and ammonium molybdate as raw materials ...without using harmful solvents or surfactants. Characterization by XRD, FTIR, XPS, SEM and TEM showed that MoV
2
O
8
formed a layered structure by the stacking of nanosheets and assumed a micro-cuboid shape with a thickness of 150∓30 nm, a width of 350∓110 nm and a length of 680∓18 nm. For the first time, the catalytic properties of MoV
2
O
8
micro-cuboids were investigated for the gas-phase ammoxidation of
p
-chlorotoluene (PCT) to
p
-chlorobenzonitrile (PCBN). The as-prepared catalyst exhibited high activity and selectivity in the ammoxidation of PCT to PCBN, with a near 100% conversion and 83.6% yield.
Graphical abstract
Lightweighting of automotives is crucial for the decrease of fuel and energy consumption, as well as CO2 emission and environmental pollution. Polymer composites, especially the high strength glass ...fiber/polyamide (GF/PA) composites, have great potential in lightweight; however, they have not been universally accepted due to their insufficient performance. Here, a stearate‐ended hyperbranched polyester (HBP‐12‐n) is designed and high‐performance GF/PA6 composites with high GF content are prepared. The flowability of the composites can be further increased by combining carboxyl‐ended hyperbranched polymer (HyPer C181) with HBP‐12‐n. Compared with unmodified GF/PA6 composites, the melt flow index (MFI) can be increased remarkably to 587% by adding a 0.7 wt% mixture of HBP‐12‐75 and HyPer C181, and the strength and toughness remain competitive. The simultaneous improvement in MFI and impact strength of GF/PA6 composites is the first discovery of this kind, and a synergistic mechanism of amphiphilic bridging‐deformation slipping‐interfacial strengthening of hyperbranched polymers is proposed to account for this phenomenon. This work provides a simple strategy to fabricate GF/PA6 composites with the extensive application for automotive parts and has great prospects in making automotives lightweight and reduction of CO2 emissions.
A series of stearate‐ended hyperbranched polyester (HBP‐12‐n) by the esterification reaction between the hydroxyl groups of HBP‐12 and stearic acid is synthesized. The melt flow inde of the glass fiber/polyamide 6 (GF/PA6) blends can be increased approximately 5.87 times upon the mixed use of HBP‐12‐75 and carboxyl‐ended hyperbranched polymer (HyPer C181), without sacrificing the strength and toughness of the composites.
Formulation and shaping of heterogeneous catalysts are vital in the successful industrial application. Here micro-sized vanadium chromium composite oxides catalysts with the spherical shape were ...prepared via spray drying with colloidal silica as a binder material. The physicochemical properties of catalysts with different Cr/V molar ratios were characterized by XRD, XPS, FT-IR, TPR, and particle size distribution analysis. It was revealed that the addition of Cr inhibited the formation of the crystalline phase V
2
O
5
and decreased the reduction temperature of pentavalent vanadium species, and also resulted in the formation of monoclinic CrVO
4
and a highly dispersed state of vanadia species. VCrO/SiO
2
particles with various Cr/V atomic ratio were studied as catalysts for
p
-chlorotoluene ammoxidation to
p
-chlorobenzonitrile, in which the catalyst with Cr/V ratio of 1 exhibited the best catalytic performance. When the Cr/V ratio was less than 1, mixed phases of orthorhombic CrVO
4
and monoclinic Cr
2
V
4
O
13
were formed and resulted in a low catalytic activity. With the increase of Cr/V ratio, the content of monoclinic CrVO
4
in the catalysts increased, resulting in the catalytic activity of the catalysts improved. However, too large an amount of Cr led to the formation of highly oxidizing hexagonal-Cr
2
O
3
phase, which reduced the selectivity of the catalytic reaction.
Graphic abstract
P
-
Phenyl-bridged bis-salicylaldiminato binuclear titanium complexes
Ti
2
L
1
,
Ti
2
L
2
and the corresponding momonuclear counterpart
TiL
4
were synthesized and characterized by
1
H NMR,
13
C NMR, ...FT-IR, and elemental analysis. The binuclear titanium complex
Ti
2
L
1
showed good catalytic performances for ethylene polymerization and copolymerization with norbornene or 1,5-hexadiene. For ethylene polymerization, the binuclear titanium complex
Ti
2
L
1
exhibited highest activity of 8.70 × 10
5
g/mol(Ti)
.
h
.
atm at 70 °C and retained an activity of 3.00 × 10
5
g/mol(Ti)
.
h
.
atm at 90 °C, which showed much higher thermal stability compared with its bi- and mono-nuclear derivatives
Ti
2
L
3
and
TiL
4
,
due probably to the rigid phenyl-bridged structure offering more stable state of active metal centers. The binuclear complex
Ti
2
L
1
could catalyze ethylene copolymerization with norbornene (NB) or 1,5-hexadiene (1,5-HD) to produce copolymer bearing cyclic groups. Compared with mononuclear complex
TiL
4
, the binuclear
Ti
2
L
1
showed higher catalytic activity and incorporation rate of comonomer for ethylene/NB copolymerization. The mononuclear complex
TiL
4
could barely catalyze the copolymerization of ethylene and 1,5-HD, however, the binuclear analogue
Ti
2
L
1
exhibited an activity of 1.67 × 10
5
g/mol(Ti)·h·atm with 4.74% of incorporation rate of 1,5-HD for ethylene/1,5-HD copolymerization, implying that the bimetallic synergistic effect could greatly improve the catalytic performance of the bis-salicylaldiminato binuclear titanium complexes.
Dichlorobenzonitriles are important organic intermediates for the production of many fine chemicals and are produced most economically and environment-friendly in industry by ammoxidation of ...dichlorotoluenes. In this paper, 2,4-dichlorobenzonitrile were prepared by direct ammoxidation of 2,4-dichlorobenzyl chloride with higher yield at much lower reaction temperature compared with ammoxidation of 2,4-dichlorotoluene, which proved that the multi-chlorobenzyl chlorides could be successfully ammoxidized to corresponding benzonitriles. Subsequently, a novel route for efficient preparation of 2,5-dichlorobenzonitrile was developed by chloromethylation of
p
-dichlorobenzene first, followed by catalyzed ammoxidation of the 2,5-dichlorobenzyl chloride. The products were confirmed by
1
H NMR, MS, and elemental analysis with a total yield of 67%. This is the first case to prepare 2,5-dichlorobenzonitrile by catalytic gas-phase ammoxidation and also afforded a simple and economical approach for preparation of multi-chlorobenzonitriles.
Graphical Abstract
By employing a novel low-temperature synthetic pathway, highly ordered cubic mesoporous materials with hitherto the largest pores (up to 27 nm) and unit cells (up to 44 nm) have been successfully ...obtained.
A novel tandem catalysis system consisted of salicylaldiminato binuclear/mononuclear titanium and 2,6-bis(imino)pyridyl iron complexes was developed to catalyze ethylene in-situ copolymerization. ...Linear low-density polyethylene (LLDPE) with varying molecular weight and branching degree was successfully prepared with ethylene as the sole monomer feed. The polymerization conditions, including the reaction temperature, the Fi/Ti molar ratio, and the structures of bi- or mononuclear Ti complexes were found to greatly influence the catalytic performances and the properties of obtained polymers. The polymers were characterized by differential scanning calorimetry (DSC), high temperature gel permeation chromatography (GPC) and high temperature
C NMR spectroscopy, and found to contain ethyl, butyl, as well as some longer branches. The binuclear titanium complexes demonstrated excellent catalytic activity (up to 8.95 × 10
g/molTi·h·atm) and showed a strong positive comonomer effect when combined with the bisiminopyridyl Fe complex. The branching degree can be tuned from 2.53 to 22.89/1000C by changing the reaction conditions or using different copolymerization pre-catalysts. The melting points, crystallinity and molecular weights of the products can also be modified accordingly. The binuclear complex
with methylthio sidearm showed higher capability for comonomer incorporation and produced polymers with higher branching degree and much higher molecular weight compared with the mononuclear analogue.
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