Organocatalyzed Trifluoromethylation of Ketones and Sulfonyl Fluorides by Fluoroform under a Superbase System

Fluoroform (HCF₃, HFC-23) is a side product in the manufacture of polytetrafluoroethylene (Teflon). Despite its attractive properties, taming HCF₃ for trifluoromethylation is quite problematic owing to its low acidity and the lability of the naked trifluoromethyl carbanion generated from HCF₃. Herein we report the organic-superbase-catalyzed trifluoromethylation of ketones and arylsulfonyl fluorides by HCF₃. The reactions were carried out by using a newly developed “superbase organocatalyst system” consisting of catalytic amounts of P₄-tBu and N(SiMe₃)₃. A series of aryl and alkyl ketones were converted into the corresponding α-trifluoromethyl carbinols in good yields under the organocatalysis conditions in THF. The superbase organocatalytic system can also be applied to the trifluoromethylation of arylsulfonyl fluorides for biologically important aryl triflones in THF or DMF in good yields. Protonated P₄-tBu, H[P₄-tBu]⁺, is suggested to be crucial for the catalytic process. This new catalytic methodology using HCF₃ is expected to expand the range of synthetic applications of trifluoromethylation.     

From the Principle of Areno-Analogy to Heterocyclopolyaromatic Compounds

Organometallic linkage of heteroaromatic compounds provided a means of synthesizing complicated combinations of heteroaromatic compounds; not only nucleophilic aromatic substitution, but also “Ar? Cu/Ar? Hal linkage”, “organometallic oxidative linkage”, and “metal amide linkage” have been employed. The heterocyclopolyaromatic compounds are made of one, two, or three kinds of heteroaromatic species as ring members. These syntheses illustrate the construction of heterocycles from large, performed structural units. Competition experiments showed that the reactivity typical of the individual species is enhanced in open-chain combinations (Ar_Nu)_n and (Ar_E)_n (Ar_Nu, Ar_E: nucleo- and electrophilic heteroaromatic systems, respectively); the opposite situation is mostly encountered in the case of Ar_Nu? A_E combinations.—Cycloocta[1,2-b:4,3-b′5,6-b″:8,7-b?]tetrathiophene, the only heterocyclopolyaromatic system yet to have been studied in detail, proved surprisingly inclined to undergo monosubstitution reactions.     

Thermo-responsive and antifouling PVDF nanocomposited membranes based on PNIPAAm modified TiO2 nanoparticles

A novel hydrophilic nanocomposite additive(TiO2-g-PNIPAAm) was synthesized by the surface modification of titanium dioxide(TiO2) with N-isopropylacrylamide(NIPAAm) via "graft-from" technique. And the nanocomposite membrane of poly(vinylidene fluoride)(PVDF)/TiO2-g-PNIPAAm was fabricated by wet phase inversion. The graft degree was obtained by thermo-gravimetric analysis(TGA). Fourier transform infrared attenuated reflection spectroscopy(FTIR-ATR) and X-ray photoelectronic spectroscopy(XPS) characterization results suggested that TiO2-g-PNIPAAm nanoparticles segregated on membrane surface during the phase separation process. Scanning electron microscopy(SEM) was conducted to investigate the surface and cross-section of the modified membranes. The water contact angle measurements confirmed that TiO2-g-PNIPAAm nanoparticles endowed PVDF membranes better hydrophlilicity and thermo-responsive properties compared with those of the pristine PVDF membrane. The water contact angle decreased from 92.8° of the PVDF membrane to 61.2° of the nanocompostie membrane. Bovine serum albumin(BSA) static and dynamic adsorption experiments suggested that excellent antifouling properties of membranes was acquired after adding TiO2-gPNIPAAm. The maximum BSA adsorption at 40 °C was about 3 times than that at 23 °C. The permeation experiments indicated the water flux recover ratio and BSA rejection ratio were improved at different temperatures.     

Synthesis and self-assembly of pH-responsive amphiphilic dendritic star-block terpolymer by the combination of ROP, ATRP and click chemistry

Novel pH-responsive amphiphilic dendritic star-block poly(l-lactide)-b-poly(2-(N, N-diethylamino)ethyl methacrylate)-b-poly(ethylene oxide) (DPLLA-b-PDEAEMA-b-PEO) terpolymers were synthesized by the combination of ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP), and click chemistry. DPLLAOH was synthesized by ROP of l-lactide (LLA) and then reacted with propargyl 3-carboxylic-propanoate to obtain alkynyl-DPLLA. PEO-b-PDEAEMA-Br was prepared by ATRP of DEAEMA and then reacted with NaN₃ to obtain PEO-b-PDEAEMA-N₃. DPLLA-b-PDEAEMA-b-PEO was easily prepared by click chemistry of alkynyl-DPLLA and PEO-b-PDEAEMA-N₃. DPLLA-b-PDEAEMA-b-PEO can assemble into micelles in water with PLLA segments as core and PEO segments as corona. The hydrophilicity/hydrophobicity of PDEAEMA can be adjusted with the alteration of pH values. Therefore, PDEAEMA segments form core or corona of micelles at pH ? 7 or pH < 7. Due to the pH-responsive property of PDEAEMA and unique structure of terpolymer, the size and conformation of the micelles can be changed to some extent by altering the pH values of solutions.     

Membrane formation mechanism and permeation properties of a novel porous polyimide membrane

The transport properties of a novel porous fluorinated polyimide membrane fabricated by a wet phase inversion process were studied with a stirred dead‐end filtration cell. The porous membrane‐forming solvents were tetrahydrofuran (THF), acetone, N,N‐dimethylacetamide (DMAc), N‐methylpyrrolidone (NMP), N,N‐dimethylformamide (DMF), and dimethylsulfoxide (DMSO). The phase separation phenomena in a ternary system of polyimide/solvent/water were investigated from cloud point curves by a titration method and binary interaction parameters. Solvent–water demixing in the system has been found to play very important roles in determining the structure and surface morphology of the polyimide membrane. The porous fluorinated polyimide membranes showed pore sizes from 4 to 500 nm and permeation properties from ultrafiltration to a microfiltration range. In this study, we particularly focused on fouling of the polyimide membranes, because fouling decreases the flux and increases the resistance. Interestingly, the porous polyimide membrane showed excellent water flux recovery after water cleaning compared with that of the polyethersulfone (PSf) membrane, which suggest that for a 6FDA‐6FAP membrane, the protein–membrane and protein–protein interaction was not so strong compared with those in a PSf membrane. Copyright © 2002 John Wiley & Sons, Ltd.     

Influence of mixed common solvent on the co-assembled morphology of PS-<Emphasis Type="Italic">b</Emphasis>-PEO and CdS quantum dots

The hybrid structures of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer and inorganic nanoparticles with good stability and biocompatibility have potential applications in drug delivery and bioimaging. Spherical co-assemblies of PS₁₂₀-b-PEO₃₁₈ and oleylamine-capped CdS quantum dots (QDs) are produced successfully in this work by adding water to a mixed common solvent, such as N,N-dimethylmethanamide (DMF)/chloroform, DMF/tetrahydrofuran (THF), or DMF/toluene. The energy dispersive X-ray (EDX) spectrum indicates that QDs are located at the interface between the core and shell of the spherical co-assemblies. The co-assembly process during water addition is traced by transmission electron microscopy (TEM) and turbidity measurement. Spherical co-assemblies are formed through budding from bilayers of the block copolymer and QDs. The morphology of the co-assemblies is related to the miscibility of the QD-dispersing solvents with water and the morphology changes from a spherical to a vesicle-like structure with DMF/toluene. Increasing THF content in the mixed solvent causes morphological transitions from spherical co-assemblies to multi-branched cylinders and micelles where QDs are located in the central core. Increasing chloroform content yields vesicle-like structures with protruding rods on the surface. The mechanism of the morphological transitions is also discussed in detail.     

Polycaprolactone-b-Poly(ethylene oxide) Biocompatible Micelles as Drug Delivery Nanocarriers: Dynamic Light Scattering and Fluorescence Experiments

Summary: Dynamic light scattering (DLS) and fluorescence experiments were carried out to study PCL₄₄-b-PEO₁₁₄ biocompatible micelles used as nanocarriers in drug delivery. Micelles prepared by a simple procedure (THF removal under nitrogen flow) exhibited a narrow size distribution with an average diameter of 100 nm. For micelles containing a hydrophobic model compound (pyrene) within the PCL core, a smaller average micellar size of 80 nm was observed, with a simultaneous broadening in the size distribution profile. In parallel to DLS results, fluorescence experiments showed evidence of pyrene encapsulation, and that the onset of the micellization process occurs at approximately 10/90 (v/v) THF/water mixtures in the case of PCL₄₄-b-PEO₁₁₄ polymer.     

Nanofiltration membranes based on poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)‐graft‐poly(styrene sulfonic acid)

Graft copolymers comprising poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) backbone and poly(styrene sulfonic acid) side chains, i.e. P(VDF‐co‐CTFE)‐g‐PSSA were synthesized using atom transfer radical polymerization (ATRP) for composite nanofiltration (NF) membranes. Direct initiation of the secondary chlorinated site of CTFE units facilitates grafting of PSSA, as revealed by FT‐IR spectroscopy. The successful “grafting from” method and the microphase‐separated structure of the graft copolymer were confirmed by transmission electron microscopy (TEM). Wide angle X‐ray scattering (WAXS) also showed the decrease in the crystallinity of P(VDF‐co‐CTFE) upon graft copolymerization. Composite NF membranes were prepared from P(VDF‐co‐CTFE)‐g‐PSSA as a top layer coated onto P(VDF‐co‐CTFE) ultrafiltration support membrane. Both the rejections and the flux of composite membranes increased with increasing PSSA concentration due to the increase in SO₃H groups and membrane hydrophilicity, as supported by contact angle measurement. The rejections of NF membranes containing 47 wt% of PSSA were 83% for Na₂SO₄ and 28% for NaCl, and the solution flux were 18 and 32 L/m² hr, respectively, at 0.3 MPa pressure. Copyright © 2008 John Wiley & Sons, Ltd.     

Heterogeneous polyelectrolyte gels as stimuli-responsive membranes

Stimuli-responsive membranes may act as “on–off switches” or “permeability valves”, producing patterns of pulsatile release, where the period and rate of mass transfer can be controlled by external or environmental triggers (e.g. pH, temperature, electric field). In this work, composite-heterogeneous polyelectrolyte gel (composite-HPG) membranes consisting of polymethacrylic acid (PMAA) gel particles dispersed within a polydimethylsiloxane (PDMS) network were developed and evaluated as pH-responsive membranes.The mechanism of permeability control for caffeine and vitamin B₁₂ through composite-HPG membranes was determined to be a synergistic function of membrane hydration and the percolating volume fraction of PMAA gel. Larger changes in permeation as a function of pH were achieved when both hydration and percolation effects occurred together than when either of these effects occurred on their own. Vitamin B₁₂ permeation was observed when the hydrated gel volume fraction was above approximately 0.38, but not below. Furthermore, the percolating fraction of composite-HPG membranes containing 28% (dry basis) PMAA gel particles was manipulated via pH to fall above (pH 7) or below (pH 3) this transition in permeability, resulting in membranes that delivered solutes of high molecular weight (vitamin B₁₂) with large on/off delivery ratios (160).     

Study on miscibility of poly(vinyl chloride) and polyepichlorohydrin by viscometric and thermal analysis

Viscometric analysis was carried out to study the miscibility of poly(vinyl chloride) (PVC) and polyepichlorohydrin (PECH) in various solvents, tetrahydrofuran (THF), methyl ethyl ketone (MEK) and dimethylformamide (DMF). The Krigbaum–Wall criterion is used here to evaluate the miscibility of the two components, and Δb is introduced which can be calculated from the viscosity curves. The results show that their attractive forces are predominant when dissolved in THF, while in MEK and DMF repulsive forces play a leading role. This is attributed to different solubilities of the two polymers in the three solvents and to different influences of the solvents on the conformation of the polymers. Thermal measurement was performed by differential scanning calorimetry to investigate the glass transition temperature (T_g) of the blends prepared from the three solvents. Phase separation is observed for the samples made from MEK and DMF, while for THF the sample exhibits a single phase.     

Polyimide polydimethylsiloxane triblock copolymers for thin film composite gas separation membranes

This article demonstrates the successful fabrication of thin‐film‐composite (TFC) membranes containing well‐defined soft‐hard‐soft triblock copolymers. Based on “hard” polyimide (PI) and “soft” polydimethylsiloxane (PDMS), these triblock copolymers (PDMS‐b‐PI‐b‐PDMS), were prepared via condensation polymerization, and end‐group allylic functionalization to prepare the polyimide component and subsequent “click” coupling with the soft azido functionalized PDMS component. The selective layer consisted of pure PDMS‐b‐PI‐b‐PDMS copolymers which were cast onto a precast crosslinked‐PDMS gutter layer which in turn was cast onto a porous polyacrylonitrile coated substrate. The TFC membranes' gas transport properties, primarily for the separation of carbon dioxide (CO₂) from nitrogen (N₂), were determined at 35 °C and at a feed pressure of 2 atm. The TFC membranes showed improvements in gas permselectivity with increasing PDMS weight fraction. These results demonstrate the ability for glassy, hard polymer components to be coated onto otherwise incompatible surfaces of highly permeable soft TFC substrates through covalent coupling. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3372–3382     

PEGylation of chitosan for improved solubility and fiber formation via electrospinning

PEG-N-chitosan and PEG-N,O-chitosan were synthesized via reductive amination and acylation of chitosan, respectively. The structures were confirmed by FTIR and H¹NMR. The extents of PEGylation increased with reducing chain lengths of either chitosan (M _v = 137–400 kDa) or poly(ethyelene glycol) (PEG, M _n = 500–2 kDa). Water solubility were easily achieved at degree of substitution (DS) as low as 0.2 for either derivtive whereas the PEG-N,O-chitosan at DS = 1.5 was soluble in organic solvents, including CHCl₃, DMF, DMSO and THF. None of the aqueous solutions of PEG-N-chitosan or PEG-N,O-chitosan alone could be electrospun into fibers. Electrospinning of PEG550-N,O-chitosan145 at 25% in DMF produced fibrous structure intermixed with beads. The efficiency of fiber formation and the uniformity of fibers were improved by increasing the solution viscosity using a cosolvent or reducing the solution surface tensions with a non-ionic surfactant. Ultra-fine fibers with diameters ranging from 40 nm to 360 nm and an average diameter of 162 nm were efficiently generated from electrospinning of 15% PEG550-N,O-chitosan145 in 75/25 (v/v) THF/DMF cosolvents with 0.5% Triton X-100^TM.     

Synthesis of novel tetrahydrofuran‐epichlorohydrin [poly(THF‐b‐ECH)] macromonomeric peroxy initiators by cationic copolymerization and the quantum chemically investigation of initiation system effects

Cationic polymerization of tetrahydrofuran (THF) and epichlorohydrin (ECH) was performed with peroxy initiators synthesized from bis (4,4′‐bromomethyl benzoyl peroxide (BBP) or bromomethyl benzoyl t‐butyl peroxy ester (t‐BuBP) and AgSbF₆ or ZnCl₂ system at 0 °C to obtain the poly(THF‐b‐ECH) macromonomeric peroxy initiators. Kinetic studies were accomplished for poly(THF‐b‐ECH) initiators. Poly(THF‐b‐ECH‐b‐MMA) and poly(THF‐b‐ECH‐b‐S) block copolymers were synthesized by bulk polymerization of methyl methacrylate (MMA) and styrene (S) with poly(THF‐b‐ECH) initiators. The quantum chemical calculations for the block copolymers, the initiating systems of the cationic polymerization of THF and ECH were achieved using HYPERCHEM 7.5 program. The optimized geometries of the polymers were investigated with the quantum chemical calculations. Poly(THF‐b‐ECH) initiators having peroxygen groups were used for graft copolymerization of polybutadien (PBd) to obtain poly(THF‐b‐ECH‐g‐PBd) crosslinked graft copolymers. The graft copolymers were investigated by sol‐gel analysis. Swelling ratio values of the graft copolymers in CHCl₃ were calculated. The characterizations of the polymers were achieved by FTIR, ¹H NMR, GPC, SEM, TEM, and DSC techniques. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2896–2909, 2010     

Synthesis,Characterization and Aqueous Solution Behavior of a pH-responsive Double Hydrophilic Block Copolymer

The pH-responsive double hydrophilic block copolymer poly(ethylene glycol)-b-poly(methacylic acid-co-4-vinyl benzylamine hydrochloride salt) (PEG-b-PMAA/PVBAHS) was synthesized. A series of PEG-b-PMAA/PVBAHS with different molecule weights and compositions were characterized by IR, ¹H-NMR, elemental analysis and TGA. With different MAA/VBAHS ratio, the PEG-b-PMAA/PVBAHS copolymers had the different isoelectric point (IEP). Supermolecular structures of the block copolymers could be formed by the interionic interactions at different solution pH. Experiment results showed that the structures of the pH-responsive copolymers in aqueous solution could be changed at different pH environments. The aggregation of this double hydrophilic block copolymer in aqueous solution was determined by both of solution pH and copolymer composition.     

Microfiltration performance of regenerated cellulose membrane prepared at low temperature for wastewater treatment

A series of regenerated cellulose membranes with pore diameters ranging from 21 to 52 nm have been prepared by dissolving cellulose in 5 wt% LiOH/12 wt% urea aqueous solution re-cooled to −12 °C. The influences of cellulose concentration on the structure, pore size, and the mechanical properties of the membrane were studied by using Wide angle X-ray diffraction, scanning electron micrography and tensile testing. Their pore size, water permeability, equilibrium-swelling ratio and fouling behaviors of the cellulose membranes were characterized. The water-soluble synthetic and natural polymers as organic matter were used to evaluate the microfiltration performance of the regenerated cellulose membrane for wastewater treatment in aqueous system. The results revealed that the organic matter with molecular weight more than 20 kDa effected significantly on the membrane pore density, and reducing factor a _2, whereas that having molecular weight less than 20 kDa exhibited a little influence on the membrane pore size reducing factor a ₁. Furthermore, a simple model to illustrate of microfiltration process of the RC membrane for wastewater treatment was proposed.     

Stimuli-responsive behavior of complex micelles based on double hydrophilic block copolymer and fluorescent indicator

The double hydrophilic block copolymer poly(ethylene glycol mono-methyl ether)-block-poly(4-vinylpyridine) (mPEG₄₃-b-P4VP₁₁₅) was synthesized by atom transfer radical polymerization. The structure, molecular weight and molecular weight distribution of mPEG₄₃-b-P4VP₁₁₅ were characterized by ¹H-NMR and gel permeation chromatography combined with laser light scattering technique. The complex micelles based on mPEG₄₃-b-P4VP₁₁₅ and the disodium 2-naphthol-3,6-disulfonate were obtained in acid aqueous solution. The morphologies of the complex micelles were observed by transmission electron microscopy. The revertible temperature and pH-responsive behaviors of complex micelles were studied by dynamic light scattering and fluorescence techniques.     

Morphology Driven by Molecular Structure of Thiazole-Based Polymers for Use in Field-Effect Transistors and Solar Cells

The effects of the molecular structure of thiazole-based polymers on the active layer morphologies and performances of electronic and photovoltaic devices were studied. Thus, thiazole-based conjugated polymers with a novel thiazole-vinylene-thiazole (TzVTz) structure were designed and synthesized. The TzVTz structure was introduced to extend the π conjugation and coplanarity of the polymer chains. By combining alkylthienyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT) or dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDT) electron-donating units and a TzVTz electron-accepting unit, enhanced intermolecular interactions and charge transport were obtained in the novel polymers BDT-TzVTz and DTBDT-TzVTz. With a view to using the polymers in transistor and photovoltaic applications, the molecular self-assembly in and their nanoscale morphologies of the active layers were controlled by thermal annealing to enhance the molecular packing and by introducing a diphenyl ether solvent additive to improve the miscibility between polymer donors and [6,6]phenyl-C71-butyric acid methyl ester (PC₇₁BM) acceptors, respectively. The morphological characterization of the photoactive layers showed that a higher degree of π-electron delocalization and more favorable molecular packing in DTBDT-TzVTz compared with in BDT-TzVTz leads to distinctly higher performances in transistor and photovoltaic devices. The superior performance of a photovoltaic device incorporating DTBDT-TzVTz was achieved through the superior miscibility of DTBDT-TzVTz with PC₇₁BM and the improved crystallinity of DTBDT-TzVTz in the nanofibrillar structure.     

Modification of poly(vinyl alcohol) membrane via blending with poly(<Emphasis Type="Italic">γ</Emphasis>-benzyl <Emphasis Type="SmallCaps">l</Emphasis>-glutamate)-<Emphasis Type="Italic">block</Emphasis>-poly(ethylene glycol) copolymer

A series of poly(vinyl alcohol) (PVA)/poly(γ-benzyl l-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) blend membranes with different PVA/PBLG-b-PEG mole ratios were prepared by pervaporation. Structure and morphologies of PVA/PBLG-b-PEG blend membranes were investigated using Fourier transformation infrared spectroscopy (FTIR), and atomic force microscopy (AFM). Mechanical and chemical properties of PVA/PBLG-b-PEG blend membrane were studied by tensile testing and other physical methods. It was revealed that the introduction of PBLG-b-PEG copolymer has significant effect on the properties of a PVA membrane.