Guanjun Chang

Rational design of a novel indole-based microporous organic polymer: enhanced carbon dioxide uptake via local dipole–π interactions

An indole-based microporous organic polymer (PINK) has been obtained by the condensation polymerization of 1,3,5-tris-(4-fluorobenzoyl)benzene with 3,3′-diindolylmethane via a catalyst-free nucleophilic substitution reaction. Due to the local dipole–π interactions between indole and carbon dioxide (CO2), the uptake capacity for CO2 reaches up to 16.0 wt% (1.0 bar, 273 K), and the high (CO2/N2 = 15, CO2/CH4 = 32) selectivities of the polymer make it a promising material for potential application in gas separation. Furthermore, the hydrogen storage is up to 2.48 wt% (1.0 bar, 77 K). In comparison to the reported porous organic polymers, the preparative strategy exhibits cost-effective advantages, which are essential for scale-up preparation. Its good performance for H2 storage and CO2 separation suggests that PINK with a large specific surface area shows potential use in clean energy applications and the environmental field.

Rational design of a fluorescent poly(N-aryleneindole ether sulfone) switch by cation–π interactions

Semirigid poly(N-aryleneindole ether sulfone) (PESIN) as a fluorescence emission on–off switch has been successfully achieved via the cation–π interactions. The adjustment of the protonation/deprotonation status of pyridine that regulates the formation of cation–π interactions is definitely the determinant.

Synthesis of indole-based functional polymers with well-defined structures via a catalyst-free C-N coupling reaction†

Poly(N-arylene diindolylmethane)s (PMDINs) with precise structures and high molecular weights (Mw up to 389 200) in high yields (up to 95%) were synthesized by the catalyst-free nucleophilic substitution polycondensation of 3,3′-diindolylmethane with different activated difluoro monomers via a C–N coupling reaction process. A model reaction was carried out to assist in determining the optimal reaction conditions for the polymerization and to elucidate the chemical structures of the polymers. The resulting polymers exhibited good thermal stability with high decomposition temperature (T5% ≥ 377 °C). Fluorescent spectral studies indicated that all these PMDINs had strong solid-state fluorescence. Especially, the polymer PMDIN-3 carrying sulfonyl units was a good blue-light emitter with high quantum yields (21.6%, determined against quinine sulfate). The results obtained by cyclic voltammetry suggested that PMDINs possessed good electroactivity. In addition, owing to the electrochemical activity of the indole rings at the 2-position, PMDIN-3 was readily cross-linked by electrochemical oxidation and the cross-linking film was characterized by scanning electron microscopy. High molecular weights and good comprehensive performance of the indole-based polymers suggested that the catalyst-free C–N coupling reaction of indole derivatives with difluoro monomers could be considered as an effective polymerization route for the synthesis of new functional polymers with well-defined structures.

High-Performance pH-Switchable Supramolecular Thermosets via Cation–π Interactions

Supramolecular chemistry has provided versatile and affordable solutions for the design of intelligent soft materials, but it cannot be applied in stiff materials. This paper describes a new concept for the design of high-performance supramolecular thermosets by using the noncovalent cation-π interaction as cross-linking. These supramolecular thermosets are a class of infusible and insoluble stiff polymers having excellent mechanical properties even at temperatures exceeding 300 °C. The cation-π interaction can be locally and reversibly installed and removed by aqueous treatments at high or low pH, respectively. Local manipulation of cross-linking confers these thermosets with multiple stimuli-responsive functions, such as recyclability, healability, adhesion, and nondestructive detection of cross-linking and mechanical properties.

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.

High and Selective Carbon Dioxide Capture in Nitrogen-Containing Aerogels via Synergistic Effects of Electrostatic In-Plane and Dispersive π–π-Stacking Interactions

A new strategy for CO2 capture is reported based on the synergistic effect of electrostatic in-plane and dispersive π-π-stacking interactions of amide and indole with CO2. Density functional theory illustrated that the amide group can have an increased ability to capture CO2 molecules that were just desorbed from an adjacent indole unit. We used this strategy to fabricate a microporous aerogel that exhibited a superior CO2 capture performance in both dry and wet conditions. The proposed synergistic effect is expected to be a new rationale for the design of CO2 capture materials.