Bonding mechanisms and conformation of poly(ethylene oxide)-based surfactants in interlayer of smectite

A better understanding of the interactions between poly(ethylene oxide) (PEO)-based nonionic surfactants and smectite is important to fully comprehend the transport and the fate of nonionic surfactants in the environment and to design novel organo-clay composites. We studied the bonding between the surfactants and smectite and the molecular conformations of the surfactants in the interlayer of smectite. A reference polymer PEG and three nonionic surfactants—Brij 56, Brij 700, and PE-PEG—were intercalated into a smectite. The polymers and the composites were characterized with X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The XRD and FT-IR results indicate that the bulk surfactants existed as crystalline materials at room temperature, and surfactant molecules had both helical/extended diblock and planar zigzag conformations. The surfactants intercalated smectite and expanded the d(001) spacing of smectite to nearly 1.8 nm. The shapes and positions of the IR bands of interlayer surfactants were similar to those of the melted (amorphous) bulk polymers: the wagging vibrations of the CH₂ merged to a single band at 1,350 cm⁻¹, the twisting bands of CH₂ had 9 cm⁻¹ or more blue shifts. These changes imply that the PEO segments of the surfactants existed with a distorted and extended conformation in the interlayer of smectite, and this extended conformation was an intermediate form of the helical and planar zigzag conformations. The molecular conformation of the interlayer surfactant was not affected by the seven types of exchangeable cations (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cu²⁺, Ni²⁺, and H⁺) tested. There were 20 cm⁻¹ or more red shifts from the C–O–C stretching bands when the surfactants were adsorbed. The red shifts suggest that surfactants were bonded to smectite mainly through (1) H-bonding between oxygen atoms of the PEO segments and water molecules in hydration shells of the exchangeable cations, and (2) direct coordination or ion–dipole interaction between the oxygen atoms of the PEO segments and the exchangeable cations. With the extended conformation, the oxygen atoms of the PEO segments have maximum exposure to the bonding water molecules and exchangeable cations.     

Defect‐Rich Graphene Nanomesh Produced by Thermal Exfoliation of Metal–Organic Frameworks for the Oxygen Reduction Reaction

Although graphene nanomesh is an attractive 2D carbon material, general synthetic routes to produce functional graphene nanomesh in large‐scale are complex and tedious. Herein, we elaborately design a simple two‐step dimensional reduction strategy for exploring nitrogen‐doped graphene nanomesh by thermal exfoliation of crystal‐ and shape‐modified metal‐organic frameworks (MOFs). MOF nanoleaves with 2D rather than 3D crystal structure are used as the precursor, which are further thermally unraveled into nitrogen‐doped graphene nanomesh by using metal chlorides as the exfoliators and etching agent. The nitrogen‐doped graphene nanomesh has a unique ultrathin two‐dimensional morphology, high porosity, rich and accessible nitrogen‐doped active sites, and defective graphene edges, contributing to an unprecedented catalytic activity for the oxygen reduction reaction (ORR) in acid electrolytes. This approach is suitable for scalable production.     

Effect of the intercalated cation on the properties of poly(o-methylaniline)/maghnite clay nanocomposites

A detailed study about the synthesis, characterization and properties of poly(o-methylaniline)(PoMea)/maghnite nanocomposites has been performed. Changes in the characteristics of the nanocomposites, depending on the intercalated cation between the clay layers before the synthesis, have been observed. Intercalated morphology has been detected by TEM in nanocomposites containing copper-treated maghnite (Magh-Cu), while when maghnite treated with strong acids was used (Magh-H); an exfoliated material has been obtained. Also, remarkable differences in the properties of the polymers have been observed by TG-MS and FTIR, suggesting that the polymer produced with Magh-H has a higher degree of branching. The electrochemical behavior of the polymers extracted from the nanocomposites has been studied by cyclic voltammetry. Good electrochemical response has been observed for PoMea grown into Magh-Cu but not for the one polymerized into Magh-H.     

Synthesis and properties of multiblock copolymers consisting of poly(L‐lactic acid) and poly(oxypropylene‐ co‐oxyethylene) prepared by direct polycondensation

A multiblock copoly(ester–ether) consisting of poly(l ‐lactic acid) (PLLA) and poly(oxypropylene‐co‐oxyethylene) (PN) was prepared and characterized. Preparation was done via the solution polycondensation of a thermal oligocondensate of l ‐lactic acid, a commercially available telechelic polyether (PN: Pluronic‐F68), and dodecanedioic acid as a carboxyl/hydroxyl adjusting agent. When stannous oxide was used as the catalyst, the molecular weight of the resultant PLLA/PN block copolymers became very high (even with a high PN content) under optimized reaction conditions. The refluxing of diphenyl ether (solvent) at reduced pressure allowed the efficient removal of the condensed water from the reaction system and the feed‐back of the intermediately formed l ‐lactide at the same time in order to successfully bring about a high degree of condensation. The copolymer films obtained by solution casting became more flexible with the increasing PN content as soft segments. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1513–1521, 1999     

Preparation of poly(vinyl pivalate) microspheres by dispersion polymerization in an ionic liquid and saponification for the preparation of poly(vinyl alcohol) with high syndiotacticity

We report here a successful free-radical dispersion polymerization of vinyl pivalate (VPi) in an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][TFSI]) using poly(vinyl pyrrolidone) (PVP) as a stabilizer. Morphological analysis by FE-SEM revealed that poly(vinyl pivalate) (PVPi) obtained from dispersion polymerizations were in the form of spherical particles. Micron-sized, PVPi particles with a number-average molecular weight (M_n) of 166,400 g/mol could be obtained using 5% stabilizer (w/w to monomer) at 65 °C for 20 h. The effects of varying concentration of stabilizer, initiator and monomer upon polymer yield, molecular weight, and morphology of PVPi were also investigated. Analogous polymerizations in dimethyl sulfoxide (DMSO) and bulk served as references. In addition, the preparation of poly(vinyl alcohol) (PVA) by saponification of the resultant PVPi was described.     

不同链长的聚醚铵阳离子协同插层对蒙脱土性能的影响

为了制备高性能的聚合物/蒙脱土纳米复合材料, 必须对蒙脱土(MMT)进行有机改性来改善蒙脱土表面的疏水性、提高蒙脱土与聚合物之间的相容性, 同时也需要尽可能地增大蒙脱土的层间距. 为此, 提出了一种采用不同链长的聚醚铵阳离子协同插层MMT 的新方法, 即采用D2000(或T5000)聚醚铵盐与D400 聚醚铵盐协同插层MMT, 并采用X射线衍射分析(XRD)和热重分析(TGA)研究了协同插层对改性MMT 的层间距、有机含量以及耐热性的影响. 另外, 也研究了插层过程中的搅拌方式和D400 聚醚铵盐多次插层对改性MMT 的层间距、有机含量等的影响. 研究结果表明,采用长链聚醚铵阳离子协同插层更有利于提高D400 聚醚铵盐改性MMT 的层间距和有机含量; T5000 协同插层MMT中总的有机含量(64.06%)进一步增加, 这可能是因为T5000 的支链在MMT 层间形成的笼型结构既提供了更大的空隙,又起到了屏蔽作用, 同时也得到了较大的层间距(6.86 nm).     

Electrorheological characteristics of polyaniline and its copolymer suspensions with ionic and nonionic substituents

Electrorheological (ER) characteristics of ER fluids, composed of suspensions of semiconducting polyaniline and two different copolyaniline particles in silicone oil, were determined experimentally. Ionic sodium diphenylamine sulfonate and nonionic o-ethoxyaniline were used to synthesize copolyanilines, i.e. N-substituted copolyaniline and poly(aniline-co-o-ethoxyaniline), respectively. ER fluids composed of these three different polymers were compared with respect to their rheological properties under an applied electric field. It was found that ER fluids containing a copolymer with an ionic group exhibited the highest ER performance among polyaniline and its copolymer systems in a shear-rate region above 1 s⁻¹. Received: 22 February 1999 /Accepted in revised form: 25 August 1999     

Fluidic communication between multiple vertically segregated microfluidic channels connected by nanocapillary array membranes

Hybrid microfluidic/nanofluidic devices offer unique capabilities for manipulating and analyzing minute volumes of expensive or hard-to-obtain samples. Here, multilayer poly-(methyl methacrylate) microchips, with multiple spatially isolated microfluidic channels interconnected by nanocapillary array membranes (NCAMs), are fabricated using an adhesive contact printing process. The NCAMs, positioned between the microfluidic channel layers, add functionality to the inter-microchannel fluid transfer unit operation. They do so because the transport of specific analytes through the NCAM can be controlled by adjusting the ionic strength, the polarity of the applied bias, the surface charge density, and the pore size. A simplified, floating injection technique for NCAM-coupled nanofluidic devices is described and compared with conventional biased injection. In the floating injection approach, a voltage is applied across the injection channel and the slight electric field extension at the cross-section is used to transfer analytes through the nanopores to the separation channel. Floating injection excels in plug reproducibility, separation resolution, and operation simplicity, although it decreases assay throughput relative to biased injection. Floating injection can avoid the uneven distribution of analytes in the microfluidic channel that sometimes results from biased injection because of the volume mismatch between NCAM nanopore transport capacity and the supply of fluid. Moreover, the pressure-driven flow caused by the mismatch of the EOFs in the microfluidic channels connected by an NCAM must be considered when using NCAMs with pore diameters below 50 nm.     

Qualitative assessment of nanofiller dispersion in poly(ε-caprolactone) nanocomposites by mechanical testing, dynamic rheometry and advanced thermal analysis

A comprehensive overview of available methods for assessing nanofiller dispersion is presented for a wide range of layered silicate-based poly(ε-caprolactone) (PCL) nanocomposites. Focusing on their respective strengths and weaknesses, rheological, mechanical and thermal characterization approaches are evaluated in direct relation to morphological information. Pronounced changes in the rheological and mechanical properties of the materials are only observed for nanocomposites displaying the highest nanofiller dispersion levels, as confirmed by an innovative and highly reliable thermal analysis approach based on quasi-isothermal crystallization. As such, the data obtained from the different methods also allow a detailed investigation of the crucial factors affecting nanofiller dispersion, evidencing the importance of specific matrix/filler interactions and the need for proper melt processing conditions when targeting significant property enhancements. Finally, the wide potential of the developed methodologies for the characterization of polymeric nanocomposites in general is illustrated by an extension to carbon nanotube-based PCL composites, unambiguously demonstrating their complementarity and broad applicability.     

Glycolysis of poly(ethylene terephthalate) catalyzed by ionic liquids

Poly(ethylene terephthalate) (PET) from an industrial manufacturer was depolymerized by ethylene glycol in the presence of a novel catalyst: ionic liquids. It was found that the purification process of the products in the glycolysis catalyzed by ionic liquids was simpler than that catalyzed by traditional compounds, such as metal acetate. Qualitative analysis showed that the main product in the glycolysis process was the bis(hydroxyethyl) terephthalate (BHET) monomer. Thermal analysis of the glycolysis products was carried out by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The influences of experimental parameters, such as the amount of catalyst, glycolysis time, reaction temperature, and water content in the catalyst on the conversion of PET, selectivity of BHET, and distribution of the products were investigated. Results show that reaction temperature is a critical factor in this process. In addition, a detailed reaction mechanism of the glycolysis of PET was proposed.     

Effect of the direction of ester linkage on molecular shape selectivity through multiple carbonyl–π interaction with octadecyl chain branched polymers as organic phases in reversed-phase high-performance liquid chromatography

Poly(vinyl octadecanoate)-grafted porous silica (Sil-VOD_n, n = 23) was newly prepared to investigate the efficiencies of the carbonyl groups in the polymer chain for recognition of polycyclic aromatic hydrocarbons (PAHs) in RP-HPLC. In Sil-VOD₂₃, the octadecyl side chains were connected to the polymer main chain through ester linkage in opposite direction to that in poly(octadecylacrylate)-grafted silica (Sil-ODA_n, n = 25) which has been reported by us. Sil-ODA_n performs enhanced molecular shape selectivity of PAHs in RP-HPLC through multiple carbonyl–π interaction of aligned carbonyl groups which are induced by the formation of highly oriented structure of side chains. Differential scanning calorimetry of VOD₂₃ demonstrated that octadecyl alkyl chains showed crystalline to isotropic phase transition with endothermic peak at 48.7 °C which was similar to ODA₂₅ (at 47.8 °C). After grafting of both polymers, phase transition phenomenon was completely disappeared in Sil-VOD₂₃ whereas Sil-ODA₂₅ still exhibits phase transition although at lower endothermic peak top temperature (38.5 °C). This indicates that the slight structural change in Sil-VOD_n and Sil-ODA_n influence the ordered structure of side alkyl chains. Moreover, solid-state ¹³C NMR revealed that the long alkyl chain in Sil-VOD₂₃ is highly disordered as compared with that of Sil-ODA₂₅. Sil-VOD₂₃ was applied to RP-HPLC stationary phase using PAHs as π-electron containing elutes, and compared with Sil-ODA₂₅ and conventional monomeric octadecylated silica (ODS). Results confirmed that Sil-VOD₂₃ showed much higher selectivity for PAH isomers than ODS, but lower than Sil-ODA₂₅. For example, the separation factors for trans-/cis-stilbene were 1.47 (Sil-VOD₂₃), 1.70 (Sil-ODA₂₅) and 1.07 (ODS), respectively. These results indicate that carbonyl groups in Sil-VOD₂₃ are effective for molecular shape recognition of PAHs through carbonyl–π interactions even in the disordered state.     

Anti-biofouling by degradation of polymers

Copolymers of methyl methacrylate(MMA) and acrylate terminated poly(ethylene oxide-co-ethylene carbonate) (PEOC) macromonomer(PEOCA) were synthesized,and the degradation of the polymers was investigated by use of quartz crystal microbalance with dissipation(QCM-D).It is shown that the polymeric surface exhibits degradation in seawater depending on the content of the side chains.Field tests in seawater show that the surface constructed by the copolymer can effectively inhibit marine biofouling because it can be self-renewed due to degradation of the copolymer.     

Determination of polyamines by high-performance liquid chromatography with chemiluminescence detection

A method was developed for the determination of polyamines (PA) by high-performance liquid chromatography with chemiluminescence detection. It is based on the unsaturated complex of PA with Cu(II) which had a strong catalytic effect on the luminol-H₂O₂ chemiluminescence reaction. The separation of PA was carried out on a reveres phase C18 column using methanol/water (25/75, v/v) as a mobile phase. The method was applied to the analysis of putrescine and the total amount of spermine and spermidine in apple leaves and strawberry fruit. The results indicated that the method is practical and useful.     

A novel macroinimer of polyethylene oxide: synthesis of hyper branched networks by photoinduced H-abstraction process

A novel poly(ethylene oxide) macroinimer (PEO-macronimer) possesing methacryloyl and tertiary amino end groups was prepared by ring-opening polymerization of ethylene oxide initiated by potassium 2-methylaminoethoxide and termination of living ends of PEO with methacryloyl chloride. NMR analysis showed that the macronimer contains equal amount of amino and methacrolyl groups indicating efficient initiation and termination processes. The dimethylamine end group in conjunction with benzophenone under UV irradiation produced ternary amine methylene radicals via H-abstraction mechanism which initiates the polymerization. Photopolymerization in solutions at high macroinimer concentration or in films resulted in the formation of insoluble networks. The crosslinked polymers exhibit high swelling capacity in organic solvents and water due to the hyperbranched nature.     

Methanolysis of poly(lactic acid) (PLA) catalyzed by ionic liquids

Poly(lactic acid) (PLA) was depolymerized by methanol in the presence of a novel catalyst: ionic liquids. It was found that the purification method of the main products in the methanolysis catalyzed by ionic liquids was simpler than that of traditional compounds, such as sulfuric acid. Qualitative analysis indicated that the main product in the methanolysis process was methyl lactate. The influences of experimental parameters, such as the amount of ionic liquids, methanolysis time, reaction temperature, and dosages of methanol on the conversion of PLA, yield of methyl lactate were investigated. Under the optimum conditions, using ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]) as catalyst, results showed that the ionic liquid could be reused up to 6 times without apparent decrease in the conversion of PLA and yield of methyl lactate. The kinetics of the reaction was also investigated. The results indicated that the methanolysis of PLA was a first-order kinetic reaction with activation energy of 38.29 kJ/mol. In addition, a possible catalysis mechanism of the methanolysis of PLA was proposed.     

Polyethylene/Clay Nanocomposite by In‐Situ Exfoliation of Montmorillonite During Ziegler‐Natta Polymerization of Ethylene

Complete exfoliation of montmorillonite during Ti‐based Ziegler‐Natta polymerization of ethylene has been successfully carried out by using montmorillonite (MMT‐OH) modified with intercalation agents containing hydroxyl groups. Hydroxyl groups in intercalation agents offer facile reactive sites for anchoring catalysts in between silicate layers. Comparison of exfoliation characteristics between MMT‐OH and non‐intercalated montmorillonite showed that the feasibility of exfoliation during ethylene polymerization was highly dependent on the catalyst fixation method.     

The Determination of Thermodynamic Properties of Polymer Solutions by Finite-Concentration Gas Chromatography

Although the technique of gas chromatography has been widely used to study polymer properties and to obtain information on polymer solution thermodynamics, few workers have extended their results beyond infinite dilution of solvent, Finite-concentration gas chromatography has been used to study several poly(dimethylsiloxane)-solvent systems at 25°C. The results are in good agreement with those obtained by traditional vapor sorption methods. A comparison of the various available techniques has been made, and the advantages and disadvantages of each are discussed.     

Melting Point and Composition Distribution of Polyolefins by Fractionation

The fractionation technique described in this paper was used to characterize the melting-point, monomer, and blocking distributions for polymers and copolymers. It is different from the molecular-weight fractionation technique in that the fractions are obtained by using a single solvent to extract the solid polymer below its melting point at stepwise-increasing temperatures. The reproducibility of this technique is excellent, and the technique is sufficient to distinguish pellet-to-pellet variation in a commercially available polypropylene. It was used to show the influence of preparation variables on the melting-point distributions of polyethylene and polypropylene and on the monomer and blocking distribution of copolymers, and to distinguish copolymers from blends.     

Fabrication of Superoxide Dismutase (SOD) Imprinted Poly(ionic liquid)s via eATRP and its Application in Electrochemical Sensor

Superoxide dismutase (SOD) plays an important role in nearly all living cells. In this study, SOD imprinted poly(ionic liquid)s (SIPILs) were prepared on the surface of the bare Au electrode modified with nano‐palladium and nano‐gold (Au/nPd/nAu/SIPILs). SIPILs was synthesized with 1‐vinyl‐3‐propyl imidazole sulfonate ionic liquids as functional monomers via electrochemically mediated atom transfer radical polymerization (eATRP) catalyzed by SOD. The Au/nPd/nAu/SIPILs was examined by cyclic voltammetry (CV), scanning electron microscope (SEM), energy‐dispersive spectrometer (EDS) and X‐ray photoelectron spectroscopy (XPS). The Au/nPd/nAu/SIPILs was also used as an electrochemical sensor to determine SOD by differential pulse voltammetry (DPV). Under the optimal conditions, the detection range of SOD was from 1.0×10^?8 to 1.0×10² mg L^?1 with a limit of detection of 8.90×10^?9 mg L^?1 (S/N=3). Compared with other methods, the sensor based on SIPILs had the broader linear range and lower detection limit.     

Purification and partial characterization by matrix-assisted laser desorption ionization time-of-flight mass spectrometry of the recombinant transposase,TniA

This work deals with zone electrophoresis (ZE) separations of proteins on a poly(methyl methacrylate) chip with integrated conductivity detection. Experiments were performed in the cationic mode of the separation (pH 2.9) with a hydrodynamically closed separation compartment and suppressed electroosmotic flow. The test proteins reached the detector in less than 10 min under these working conditions and their migration times characterized excellent repeatabilities (0.1–0.6% RSD values). The chip-to-chip agreements of the migration times, evaluated from the ZE runs performed on three chips, were within 1.5%. The conductivity detection provided for protein, loaded on the chip at 10–1000 μg/ml concentrations, detection responses were characterized by 1–5% RSD values of their peak areas. Such migration and detection performances made a frame for reproducible baseline separations of a five-constituent mixture (cytochrome c, avidin, conalbumin, human hemoglobin and trypsin inhibitor). On the other hand, a high sample injection channel/separation compartment volume ratio of the chip (500 nl/8500 nl) restricted the resolution of proteins of very close effective mobilities in spite of the fact that in the initial phase of the separation an electric field stacking was applied. A maximum macroconstituent/trace constituent ratio attainable for proteins on the chip was assessed for cytochrome c (quantifiable when its concentration in the loaded sample was 10 μg/ml) and apo-transferrin (containing a trace constituent migrating in the position of cytochrome c detectable when the load of apo-transferrin was 2000 μg/ml). This assessment indicated that a ratio of 1000:1 is attainable with the aid of conductivity detection on the present chip.