Junxiao Yang

Palladium catalyzed/silver tuned selective mono-/tetra-acetoxylation of o-carboranes via B–H activation

A palladium catalyzed/silver tuned selective mono- and tetra-acetoxylation of o-carboranes has been developed, and a series of mono- and tetra-acetoxylated o-carboranes decorated with active groups have been synthesized with moderate to good yields as well as excellent selectivity. A mechanism involving electrophilic palladation and cyclopalladation of the B-H bond was proposed.

Palladium catalyzed regioselective mono-alkenylation of o-carboranes via Heck type coupling reaction of a cage B–H bond

A regioselective mono-alkenylation of o-carboranes on B(8) and B(9) via palladium catalyzed Heck type coupling of a cage B–H bond has been developed, and kinds of B(8)/B(9)-alkenyl-o-carboranes decorated with active groups have been synthesized with moderate yield as well as good regioselectivity. A PdII catalyzed electrophilic B–H activation mechanism was also proposed.

Decomposable double-walled hybrid nanorods: formation mechanism and their effect on flame retardancy of epoxy resin composites

Double-walled Al–P–Si hybrid decomposable nanorods, which have a silica coated aluminum phosphonate nanostructure, were in situ prepared by thorough but ordered reconstruction of montmorillonite. The reconstruction was facilely performed through hydrothermal reaction of montmorillonite with diphenyl phosphoric acid. The formation process of nanorods involves the decomposition of montmorillonite, the repolymerization to generate aluminum phosphonates, the assembly via π–π stacking interactions to form a 1D nanostructure, and the coating of silica on aluminum phosphonate nanorods. Interestingly, it was found that only layered silicates exhibited such reconstruction into hybrid nanorods. The decomposition of the nano-sized sandwich structure may lead to highly reactive Si–O tetrahedra and a synergistic reaction process. The nanorods showed decomposition around 400 °C, producing nanoparticles mainly composed of aluminum silicates. The fire property test showed that epoxy/Al–Si–P hybrid nanorod nanocomposites exhibited outstanding flame retardant performance. One possible explanation for this is that nano-sized particles resulting from decomposition easily migrated to the surface of epoxy resins, consequently forming protective layers.

Conjugated polymers based on modified benzo[1,2-b:4,5-b′]dithiophene and perylene diimide derivatives: Good optical properties and tunable electrochemical performance

Three original conjugated polymers were devised and synthesized via the alternating conjugated polymerization of the electron-donating monomer of the modified benzo[1,2-b:4,5-b′]dithiophene (BDT) and electronaccepting monomers of perylene diimide (PDI), dithienyl-perylene diimide (DTPDI) and dithienocoronene diimide (DTCDI), respectively. The synthesized conjugated polymers presented excellent thermal stability (Td >400 °C) as well as broad absorption in visible region and narrow gap of energy level (1.80 to 2.01 eV). Moreover, P(BDT-DTCDI) exhibited strong fluorescence properties (λemmax=736 nm with excitation at 680 nm). According to the theoretical calculations, P(BDT-PDI) and P(BDT-DTPDI) displayed significant polymer backbone torsion (41.44° and 39.64°), and P(BDT-DTCDI) had highly coplanar backbone with negligible angle between BDT and DTCDI. The results indicated that P(BDT-DTCDI) had potential applications in the fields of organic thin-film transistors (OTFTs) and fluorescence materials, and P(BDT-PDI) and P(BDT-DTPDI) could be used as a stable n-type semiconductor for polymer solar cells.

A nitrogen-rich, azaindole-based microporous organic network: synergistic effect of local dipole–π and dipole–quadrupole interactions on carbon dioxide uptake

A new type of microporous organic polymer with azaindole units (N-PEINK) has been designed. The resulting N-PEINK exhibits good chemical and thermal stability with a decomposition temperature of 550 °C. Taking advantage of the synergistic effect of local dipole–π and dipole–quadrupole interactions between azaindole and carbon dioxide (CO2), the CO2 uptake capacity of the polymer reaches 20.8 wt% (1.0 bar, 273 K) with high selectivities (CO2/N2 = 97, CO2/CH4 = 18), making the polymer a promising microporous material for application in CO2 separation and capture. Furthermore, the azaindole-based microporous organic polymer also exhibits a high hydrogen storage (2.67 wt%) at 1.0 bar and 77 K. For comparison, the microporous organic polymer with indole units (PEINK) was also prepared.

Synthesis and properties of cross-linkable polysiloxane via incorporating benzocyclobutene

Benzocyclobutene (BCB), as a reactive group, was incorporated into the side chains of polysiloxane via platinum/carbon hydrosilylation reaction. The hydrosilylation reaction showed good tunability for the incorporation ratio of BCB pendant groups. Differential scanning calorimetry results revealed that upon heating the BCB-containing polysiloxanes, great exothermic reaction occurred via [4+2] cycloaddtion reaction involving vinyl and BCB. The onset decomposition temperature (T donset) of the BCB-siloxane resins reaches 518°C. This high T d demonstrates an excellent thermal resistance. The high-temperature performance of the resulting polymers illustrates the power of benzocyclobutene pendant groups in the design and preparation of potential high-performance silicon resins.

pH and redox dual stimuli-responsive injectable hydrogels based on carboxymethyl cellulose derivatives

AbstractpH and redox dual stimuli-responsive injectable hydrogels were prepared by cross-linking oxidized carboxymethyl cellulose (oxi-CMC) with 3,3′-dithiobis (propionohydrazide) (DTP) via Schiff base reaction under physiological condition. The hydrogels showed good performance such as tunable gelling time, appropriate rheology properties, high swelling ratio and low degradation rate. In vitro release studies confirmed that bovine serum albumin (BSA) as a model drug exhibited a sustainable release at pH 7.4 and an accelerated release under a lower pH 5.0 and/or reducing environments. The results signified that oxi-CMC/DTP hydrogels could be an attractive candidate for drug delivery system, tissue engineering or cell scaffold materials.

Platinum catalyzed sequential hydroboration of decaborane: a facile approach to poly(alkenyldecaborane) with decaborane in the mainchain.

Catalytic sequential hydroboration of decaborane for the synthesis of poly(organodecaborane), with decaborane in the mainchain, is reported for the first time. Under a platinum catalytic system, poly(6-hexenyldecaborane) and poly(6-norbornenyldecaborane) are obtained with well-defined structures and a moderate yield. Thermogravimetric analysis demonstrates that the char yields are 73% and 82%, respectively.

Recent Progress in Benzocyclobutene Related Polymers

The developing history of polymer materials tells that the invention of novel polymers with excellent performance is generally originated from the synthesis of new polymerizable monomers. Among kinds of monomers, benzocyclobutene (BCB) has attracted much interest because of its unique molecular structure and polymer properties (1-2). The structure of BCB is shown as following with the numbering system, the CA name of which is bicyclo[4,2,0]octa-1,3,5-triene. In terms of the four-membered ring structure, BCBs are able to transform into the reactive o-quinodimethane, also known as o-xylylene, upon heating at around 200 oC. This very reactive specie readily undergoes interand intramolecular DielsAlder reaction with various dienophiles to produce polycyclic compounds with high stability, such as cyclooctadiene. On the other hand, the polymerization of oquinodimethane similar to that of 1,3-diene would give linear polymers. Additionally, the reaction of BCB does not require any catalyst and release any small molecules, thus hardly introducing any impurities into materials. These features undoubtedly offer BCB based materials several superiorities in several specific applications, such as microelectronic applications, optic applications, electrical applications, etc.

Synthesis and characterization of new 4-vinylsilylbenzocyclobutene/ vinylsilylbenzene random copolymers

In this work, a copolymerization of 4-(1′,1′-dimethyl-1′-vinyl) silylbenzocyclobutene (4-DMVSBCB) and CH2=CHSiMe2Ph (DMVSPh), which have similar structure, was performed by the anionic polymerization method, leading to a synthesis of a series of cross-linkable random copolymers. Attractively, the 4-DMVSBCB/DMVSPh ratio in the copolymer was almost consistent with the DMVSPh/4-DMVSBCB feed ratio, which allows the control of polymer structure. Most importantly, the replacement of partial 4-DMVSBCB by DMVSPh units provided relatively economical materials which were capable of preserving almost all the advantages of poly(4-DMVSBCB). Furthermore, the curing dynamic of copolymers can be tuned by varying 4-DMVSBCB incorporation ratio.