Chunjie Yan

Functionalized graphene oxide modified polysebacic anhydride as drug carrier for levofloxacin controlled release

Functionalized graphene oxide modified polysebacic anhydride composites were synthesized by Steglich esterification and characterized by various techniques such as Fourier transform-infrared spectrometry, differential scanning calorimetry, gel permeation chromatography, X-ray powder diffraction, dynamic light scattering, and scanning electron microscopy. In the release study using these composites, the release kinetics of drug loaded composites were studied in phosphate buffer saline, when the pH value was 7.4, at 37 °C using levofloxacin as a model antibacterial drug. In contrast to the pure polysebacic anhydride, different feeding ratio of graphene oxide modified polysebacic anhydride provides much longer drug release duration, and the drug release duration could be controlled by the molecular weight of the composites. In addition, the 2% graphene oxide modified polysebacic anhydride (Mw = 5000 D) exhibits a nearly perfect linear release behavior with an extended release time as long as 80 days, and the effective drug release amount exceeding 95%. The results of XRD indicated that the prepared graphene oxide contains adsorbing water, and it led to an obvious decrease in the molecular weight of polysebacic anhydride grafted on graphene oxide. This has affected the release behaviors to a certain extent. High molecular weight polysebacic anhydride grafted on dried graphene oxide and their release behaviors will be provided in our future work.

Preparation and Characterization of a Graphene Oxide Film Modified by the Covalent Attachment of Polysiloxane

Hybrid materials consisting of polydimethylsiloxane (PDMS) and polycyclohexyl-methylsiloxane (PCHMS) grafted graphene oxide (GO) were obtained by condensation polymerization in toluene. Fourier transform infrared spectroscopy indicates that the composites were synthesized through the formation of Si-O bond. The X-ray diffraction, scanning electron microscopy and thermogravimetric indicate that the hydrolysis polycondensation can accelerate the graft reaction. The hybrid films were prepared by simple filtration of the dispersed system of PDMS/GO/water, PCHMS/GO and PCHMS/GO/water in dimethylformamide. Tensile tests indicate the mechanical properties of the films varied with their structure. The rigid PCHMS/GO/water films have a tensile strength of 17.83 MPa, and the pliant PDMS/GO/water films have an elongation at break of 3.14%. UV-Vis spectra of GO and the hybrids indicate that the addition of polysiloxane caused a red-shift (10–20 nm) of the absorption peak.

Understanding the effects of carboxylated groups of functionalized graphene oxide on the curing behavior and intermolecular interactions of benzoxazine nanocomposites

Novel benzoxazine (BOZ)/carboxylated graphene oxide (GO-COOH) composites were prepared via in situ intercalative polymerization. The curing behaviour, morphology and intermolecular interactions of GO-COOH based nanocomposites were investigated and compared with those of a graphene oxide (GO) blend system to clarify the influence of carboxylic groups. Compared to GO, GO-COOH with a large amount of carboxylic groups, relatively higher thermal stability, and exfoliated sheet morphology might be more easily dispersed and reacted in the BOZ matrix. The GO-COOH nanoplatelet based composites possessed a different polymerization path from that of the GO based system, implying that carboxylic groups not only provided catalytic effects but also participated in the grafting polymerization reactions between carboxyl groups of GO-COOH and phenolic hydroxyl groups of BOZ. A significant improvement of both the glass transition temperature (Tg) and crosslinking network density of the GO-COOH blend system further confirmed that covalent bonding occurred between filler and polymer chains, indicating that the GO-COOH nanoplatelets had a stronger influence on the thermal property improvement of the nanocomposites than that of the GO blend system. Surprisingly, a very low amount (1 wt%) of GO-COOH can affect the thermal properties of the composite remarkably, leading to a more than 30 °C increase of Tg in comparison with pure benzoxazine.

Synthesis of Low-Density Heat-Resisting Polystyrene/Graphite Composite Microspheres Used as Water Carrying Fracturing Proppants

Low-density heat resistamt, low-cost polystyrene (PS)/graphite microspheres were successfully synthesized via in situ suspension polymerization. Scanning electron microscopy (SEM) indicated that PS/graphite composite microspheres had good sphericity, and graphite particles were evenly dispersed in microspheres. Furthermore, density analysis illustrated that the density of composites was about 1.025–1.185 g/cm3 with good suitability for carrying water. Thermodynamic testing revealed that the thermostability of the composite was dramatically improved by the introduction of graphite, which is used deep underground. In addition, the percentage of damage decreased to 1.3% with graphite ratio of 2.5% at 68 MPa. Therefore, PS/Graphite composite microspheres possess entirely feasible applications in oil exploitation as pure water carrying petroleum proppants.

Synthesis and characterization of micro/nano-structured BaHPO4/Ba3(PO4)2/Ba5(PO4)3OH phases and their luminescence

Microspheres covered with microcuboids/nanorods and nanoparticles of BaHPO4/Ba3(PO4)2/Ba5(PO4)3OH phases have been successfully synthesized by a facile hydrothermal (HT) method using the citric acid as a surfactant at different pH values. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and fluorescence spectrometry were used to characterize the samples. It was found that the pH value was a crucial factor for the phase formation and shape determination of the final products, which were discussed in detail. Attractively, the as-prepared BaHPO4/Ba3(PO4)2/Ba5(PO4)3OH samples emitted an intense blue light in a broad band from 380 to 625 nm, for which the mechanism was complex ions luminescence originating from the transition of 3T1 → 1A1 in PO43−. Meanwhile, an obvious red shift for the emission band was observed between nano- and bulk-Ba3(PO4)2 synthesized by HT and conventional solid-state (CSS) reactions, respectively, which was due to the effect of the product being nanosized. The same effect was also revealed by the fact that the decay time of the latter was about 2.5 times that of the former. Moreover, the decay mode of Ba5(PO4)3OH was different from those of BaHPO4 and Ba3(PO4)2, which was ascribed to the effect of the substitution of three OH− for one PO43− on their electronic structures.

New cobalt-mediated radical polymerization (CMRP) of methyl methacrylate initiated by two single-component dinuclear β-diketone cobalt (II) catalysts.

Two dinuclear cobalt complexes based on bis-diketonate ligands (ligand 1: 3,3′-(1,3-phenylene)bis(1-phenylpropane-1,3-dione); ligand 2: 3,3′-(1,4-phenylene)bis(1-phenylpropane-1,3-dione)) were successfully synthesized. The two neutral catalysts all showed satisfactory activities in the cobalt-mediated radical polymerization (CMRP) of methyl methacrylate (MMA) with the common initiator of azodiisobutyronitrile (AIBN). The resulting polymerizations have all of the characteristics of a living polymerization and displayed linear semilogarithmic kinetic plots, a linear correlation between the number-average molecular weight and the monomer conversion, and low polydispersities. Mono- or dicomponent low polydispersity polymers could be obtained by using the two dinuclear catalysts under proper reaction conditions. All these improvements facilitate the implementation of the acrylate CMRP and open the door to the scale-up of the syntheses and applications of the multicomponent low polydispersity polymers.

Palygorskite as Efficient Catalyst for Ring-Opening Polymerization of ϵ-Caprolactone

Fiber-like high-surface-area and natural nanostructure clay mineral palygorskite (or attapulgite, ATP) containing lots of hydroxyl groups is found to efficiently catalyze the ring-opening polymerization (ROP) of ϵ-caprolactone (ϵ-CL). The products are subsequently characterized by FTIR, 1H NMR, GPC, DSC, SEM and XPS analysis. The results show that porous PCL with relatively high molecular weight is obtained. A mechanism is proposed to illustrate that ϵ-CL is initiated by the constituent water in ATP and catalyzed by three active centers relate to hydroxyl groups on the surface of ATP. The ATP acts as a proton shuttle via its acidic hydrogen atoms and basic oxygen atoms. Moreover, there exists synergetic catalytic effect between the metal centers and Si centers.

Facile green ring-opening polymerization of L-lactide catalyzed by natural kaoline

This work demonstrates a facile and green route for the solvent-free ring-opening polymerization (ROP) of L-lactide, which is catalyzed by natural kaoline for the first time. poly(L-lactide) (PLA) in 68.5% yield was obtained under the conditions of catalysis with a mass ratio of m(kaoline)/m(LA) = 1/1500, at 140 °C for 24 h, resulting in a high molecular weight (Mn = 4.55 × 104 g mol−1) and a low polydispersity index (PDI = 1.34). The results from DSC and XRD revealed that the interactions between PLA chains weakened by the plasticizing effect of kaoline. The rigid structure of kaoline can prevent PLA chains from crystallizing, thus causing a decrease in the glass transition temperature of the obtained PLA product. O, Si and Al were shown to be the main components of kaoline, with the existence of less than 2% of Ti, Fe, K, Ca, Mg by XPS and XRF. The layered structure of kaoline was examined by SEM and TEM, which determined the polymer chain growth model and catalytic mechanism. XRF showed that the content of heavy metals in the product was lower than 5 ppm without removing the catalyst, which meets the requirement for medical devices. The catalytic behavior of kaoline lays the foundation for natural mineral catalysts in the field of medical aliphatic ester polymerizations.