Yanbing Lu

Photo-responsive reversible micelles based on azobenzene-modified poly(carbonate)s via azide–alkyne click chemistry

Photo-induced reversible amphipathic copolymer PMPC-azo was click conjugated by connecting amphiphilic poly(ethylene glycol)-modified poly(carbonate)s (PEG-b-poly(MPC)) and azide-functional trifluoromethoxy-azobenzene (azo-N3). The resulting copolymer self-assembled into spherical micelles with a hydrophobic azo core stabilized by a hydrophilic PEG corona in aqueous solution. As characterized by time-resolved UV-vis spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM), these micelles showed reversible self-assembly and disassembly in aqueous solution under alternating UV and visible light irradiation. The model drug Nile Red (NR) was then successfully encapsulated into the micelles. Light-controlled release and re-encapsulation behaviors were demonstrated by fluorescence spectroscopy. The cell cytotoxicity of PMPC-azo micelles was also evidenced by MTT assay. This study provides a convenient method to construct smart nanocarriers for controlled release and re-encapsulation of hydrophobic drugs.

Redox-responsive, core-crosslinked degradable micelles for controlled drug release

We developed novel redox-responsive, core-crosslinked micelles (CCLMs) via a simple, one-step click chemistry reaction. CCLMs were prepared by the click reaction between poly(ethylene glycol)-b-poly(5-methyl-5-propargylxycarbonyl-1,3-dioxane-2-one) [PEG-b-poly(MPC)] amphiphilic block copolymer and bis-(azidoethyl) disulfide. The CCLMs not only presented excellent stability under physiological conditions but also achieved the controlled release of DOX in reducing environment (such as DTT, GSH). Furthermore, DOX-loaded CCLMs showed low cytotoxicity in HeLa cells and 4T1 cells by MTT assay as well as enhanced cytotoxicity against drug-resistant ADR/MCF-7 cells in vitro. Confocal laser scanning microscope (CLSM) images show that the DOX-loaded materials were easily taken up by HeLa cells, compared to free DOX as control. With its facile preparation, superior stability, and controlled release, the redox-responsive CCLMs can provide a versatile platform for drug delivery and have great potential for antitumor therapy.

Green synthesis of bisphenol F over 12-phosphotungstic acid supported on acid-activated palygorskite

In this study, acid-activated palygorskite (Pa) with tunable surface acidity was obtained by simple acidic treatment of raw clay. The new catalysts with 5–30 wt% 12-phosphotungstic acid (H3O40PW12·xH2O, PTA) were then readily prepared by the wet impregnation method. Their characteristic features were systematically investigated by various means including energy-dispersive X-ray (EDX), X-ray diffraction (XRD), N2 adsorption/desorption isotherms, Fourier-transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TGA), as well by comparison with Pa, PTA and H-Beta zeolite. The high activities of these catalysts promoted phenol to undergo hydroxyalkylation, resulting in an interesting bisphenol F (BPF) product. Among these solid acid catalysts, 10% PTA/Pa was chosen as the most suitable catalyst giving an 87% yield and 96% selectivity under mild conditions (phenol/formaldehyde mole ratio of 15 : 1; T = 343 K; catalyst concentration of 0.006 g g−1; 40 min). The surface acid strength and acidic type were characterized by ammonia temperature programmed desorption of NH3 (NH3-TPD), and FT-IR of pyridine adsorption (Py-IR). It was found that the catalytic activity could be further enhanced by impregnating PTA onto Pa due to the enhanced acid strength and the redistribution of Bronsted and Lewis acid sites. Besides, a more appropriate combination of Bronsted and Lewis acid sites was essential to achieve the highest BPF yield. Recycle experiments were conducted and a plausible mechanistic pathway was proposed according to our observations and findings.

Flame Retardancy and Mechanical Properties of Ethylene-vinyl Acetate Rubber with Expandable Graphite/Ammonium Polyphosphate/Dipentaerythritol System

Ethylene-vinyl acetate thermoset rubber (EVM) with high vinyl acetate content has been widely used in wires and cables for many years. However, the problem of melting drip and efficient flame retardance has not been effectively solved. The combination of expandable graphite (EG), ammonium polyphosphate (APP), and dipentaerythritol (DPER) as a flame retardant system for EVM rubber has been proven to be effective in preventing melting drip and improving flame retardance in this study. This is shown by limiting oxygen index (LOI) and vertical flammability (UL-94) tests. The thermal behavior of EVM treated with this instumescent-flame retardant (IFR) system was investigated by thermogravimetric analysis (TGA) experiments. The results indicated that the char residue of treated samples could reach up to 27.1% at 600°C, which is much higher than that of the untreated EVM. Scanning electron microscopy (SEM) micrographs of residue of treated and untreated EVM showed that the IFR system could promote formation of residual char which imparts the antidripping property to EVM. However, the mechanical properties, such as tensile strength (TS) and elongation at break (EB), decreased gradually with the increase of EG content. Compared to the EVM/APP/DPER system without EG, the TS decreased from 6.55 MPa to 6.13 MPa, while the EB decreased slightly from 570% to 558% when the EG content was 15 wt%.

Facile synthesis of a reduction-responsive amphiphilic triblock polymer via a selective thiol–disulfide exchange reaction

A reduction-responsive amphiphilic triblock copolymer mPEG-b-PDS-b-mPEG was synthesized via polycondensation between a dithiol and dipyridyl disulfide, followed by a selective thiol–disulfide exchange reaction. The reduction-triggered release of Nile Red by DTT was further demonstrated using fluorescence spectroscopy.

ROMP of acetoxy-substituted dicyclopentadiene to a linear polymer with a high Tg

A polydicyclopentadiene derivative was obtained via ring-opening metathesis polymerization (ROMP) of acetoxy-substituted dicyclopentadiene (AcO-DCPD) using the Grubbs 1st generation catalyst. Analyses of the polymer microstructures indicate that polymers are linear. The glass transition temperatures (Tg) of the linear polymers range from 136 °C to 159 °C, which are much higher than that of linear polydicyclopentadiene.

An Hg2+-selective chemosensor based on the self-assembly of a novel amphiphilic block copolymer bearing rhodamine 6G derivative moieties in purely aqueous media

We report on the fabrication of an amphiphilic block copolymer-based colorimetric and fluorescent chemosensor for Hg2+ ions that was prepared by sequential RAFT polymerization of N-isopropylacrylamide (NIPAM) and a novel rhodamine-based Hg2+-recognizing monomer, R6GDM. Because of its amphiphilic properties, the block copolymer P[NIPAM]-b-P[R6GDM] can self-assemble into micelles, which allows it to be used as a chemosensor in aqueous solution. Upon addition of Hg2+ ions to the micelle solution, visual color change and fluorescence enhancement were observed. Moreover, it exhibits high sensitivity and selectivity for Hg2+ ions, relatively. Besides, it can serve as a potential multifunctional sensor to pH and temperature (in a specific temperature range: 25–40 °C or 40–52 °C). The water dispersibility and biocompatibility of these polymer micelles could provide a new strategy for detecting analytes in environmental and biological systems.

Recycled LiCoO2 in spent lithium-ion battery as an oxygen evolution electrocatalyst

Lithium cobalt oxide (LCO) is a common cathode material in lithium ion batteries (LIBs). On the other hand, the recycling of electrode materials in LIBs has attracted serious attention due to environmental, resourcing and energy issues. In order to reduce the cost of the recycling and make full use of the transition metal in the cathode materials in LIBs, herein, we developed a simple method to convert the recycled LCO from spent LIBs into an efficient electrocatalyst for oxygen evolution reaction (OER). The long-time cycling of LCO in a LIB would lead to several structural changes in terms of chemical composition, particle size and metal valence etc. The altered structural properties of the recycled LCO with a relatively smaller particle size and activated surface may contribute to enhanced electrocatalytic activity for OER. The electrocatalytic activity improves with the increase of the cycle number of LIBs. As an electrocatalysts for OER, the recycled LCO from spent LIBs after cycling for 500 cycles can deliver a current density of 9.68 mA cm−2 at 1.65 V, which is about 3.8 times that of pristine LCO (2.50 mA cm−2).

Preparation and Characteration of UV-cured EA/MMT Nanocomposites Via In-Situ Polymerization

A long-chain surfactant, enzoylbenzyl-N,N-dimethyl-N-octadecylammonium bromide (BDOB) with a benzophenone group, was synthesized to modify the montmorillonites (MMT) for the preparation of nanocomposites via photo-induced polymerization. The BDOB-modified MMT was characterized by the fourier transform infrared spectrometer (FTIR), thermal gravimetric analyzer (TGA) and X-ray diffraction (XRD), and the results of XRD indicated that the intercalated structures of BDOB-modified MMT was obtained. The conversion of the bisphenol A epoxy diacrylate (EA) was quantified by the FTIR, and the results indicated that conversion increased with an increase in the amount of BDOB-modified MMT. The morphologies of the UV-cured EA/MMT nanocomposites prepared from this organically modified MMT were studied by means of XRD and TEM, and the results showed that all the samples contained an intercalated structure with partial exfoliated structure. The results of TGA and mechanical properties also indicated that the thermal and mechanical properties of UV-cured nanocomposites were significantly enhanced due to the presence of the long chain surfactant organically modified MMT.

Polycarbonate-based core-crosslinked redox-responsive nanoparticles for targeted delivery of anticancer drug

We reported a facile and efficient strategy for the construction of polycarbonate-based core-crosslinked redox-responsive nanoparticles (CC-RRNs), which can efficiently regulate the drug loading content and redox-responsive drug release. A series of CC-RRNs for delivery of doxorubicin (DOX) were synthesized by the click reaction between alkyne-bearing amphiphilic block copolymer PEG-b-poly(MPC)n (PMPC) and azide-terminated α-lipoic acid derivative (LA) and 6-bromohexanoic acid derivative (AHE) at different ratios, followed by introduction of crosslinked networks under a catalytic amount of dithiothreitol (DTT). Dynamic light scattering (DLS) experiments showed that the CC-RRNs presented more excellent stability over non-crosslinked unresponsive nanoparticles (NC-URNs) under physiological conditions. Interestingly, the DOX loading content of nanoparticles (NPs) increased as the proportion of LA moieties increased, and the maximum value was up to 20.0 ± 0.6%, close to the theoretical value of 23.1%. The in vitro redox-responsive release of DOX and MTT assays confirmed that the ratio of LA-to-AHE of PMPC-based polymers not only determined the ultimate drug release of DOX-loaded CC-RRNs in a reductive environment, but also dominated the cytotoxicity towards HepG2 cells. Confocal laser scanning microscopy (CLMS) and flow cytometry further proved the enhancement of cellular uptake and tumor accumulation. This facile strategy overcomes tedious fabrication procedures for drug nanocarriers, offers an opportunity for regulating the functionality of NPs, and thus paves the pathway for scale-up production of biodegradable drug carriers with biocompatibility, stability and targetability.