Residual Silanol Groups Research Articles

High-Performance Polyurea Improved by Reactive Nanocluster for Antibiofouling.

Polyurea has found applications in protective coatings. Yet, the too fast polymerization and lack of functions limit its application. Herein, we report a high-performance polyurea via the stepwise polymerization of an isocyanate (NCO)-terminated prepolymer consisting of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) (PPG-b-PEG-b-PPG) with a nanocluster synthesized via the hydrolysis of N-phenylaminomethyltriethoxysilane. Such a nanocluster contains low-reactivity secondary amines, so the polymerization of polyurea can be slowed down (over 1 h), which improves its wetting and adhesion to a substrate. The residual silanol groups on the nanocluster further increase the adhesion. Such polyurea exhibits high adhesion on various substrates, including glass, ceramic, steel, copper, titanium, wood, and natural rubber (∼2.35-14.64 MPa). Besides, the nanoclusters can cross-link the prepolymer into a tough network, endowing the polyurea with a high mechanical strength of ∼25 MPa, much higher than the traditional polyaspartic ester polyurea. On the other hand, the PEG segments enable the polyurea to have good fouling resistance against proteins (fibrinogen absorption was reduced by over 90%), bacteria (RBA of S. aureusE. coli and Pseudomonas sp. was less than 10%), as well as diatom (diatom density was less than 100 cells/mm2). The polyurea is expected to find applications in biomedical engineering and marine antifouling.

A mixed-mode reversed-phase/strong-anion-exchange stationary phase: Analyte-retention stability and application in the analysis of nonsteroidal anti-inflammatory drugs

Mixed-mode reversed-phase/anion-exchange chromatography (RP/AEX) is an effective method for the chromatographic analysis of acidic drugs because it combines reversed-phase chromatography (RP) with anion-exchange chromatography (AEX). However, the result repeatability for the RP/AEX analysis of acidic drugs is frequently compromised by the detrimental effects of residual silanol groups in an RP/AEX stationary phase on peak separation and analyte retention. In this study, an RP/weak-AEX stationary phase with amino anion-exchange groups, Sil-AA, was prepared. Subsequently, an RP/strong-AEX stationary phase, Sil-PBQA, was prepared by replacing the amino groups in Sil-AA with a benzene ring and a benzyl-containing quaternary ammonium salt. The chromatographic behaviors of Sil-PBQA and Sil-AA were compared, and the effect of residual silanol groups on the chromatographic behavior of an RP/AEX stationary phase was evaluated. Residual silanol groups not only caused additional electrostatic interactions for acidic analytes, but also competed with the analytes for the anion-exchange sites in an RP/AEX stationary phase. The effects of different salt-containing mobile-phase systems on the analyte-retention behavior of Sil-PBQA were investigated to develop a method that enhanced the repeatability of the RP/AEX acidic-analyte-analysis results obtained using Sil-PBQA and facilitated the separation of nonsteroidal anti-inflammatory drugs on Sil-PBQA. The ideas presented in this paper can improve the separation of peaks and repeatability of results in the RP/AEX analysis of acidic drugs.

High-pH mobile phase in reversed-phase liquid chromatography-tandem mass spectrometry to improve the separation efficiency of aminoglycoside isomers.

In chromatography, the use of extreme conditions can often lead to unique separation selectivity. In this study, a highly basic mobile phase (pH > 11), which is not typically employed for reversed-phase liquid chromatography (RPLC), was utilized in RPLC-tandem mass spectrometry (MS/MS) to achieve effective separation between electrically neutral bases of aminoglycosides (AGs). A mixture of AGs was simultaneously analyzed using 500mmol L-1 ammonia aqueous solution (pH 11.8) as the mobile phase. A total of 11 AGs, including 2 stereoisomers of neomycin (B and C) and 5 structurally similar components of gentamicin (C1, C1a, C2, C2a, and C2b), were completely separated for the first time. The high separation performance for AGs was mainly due to two factors: First, slight differences in hydrophobicity among the AGs were significantly enhanced at a high pH by the complete acid dissociation of amines. Second, the high pH of the mobile phase minimized any electrostatic interactions between the AGs and residual silanol groups in the stationary phase, resulting in extremely sharp peaks for the AGs. The sensitivity of spectinomycin decreased by more than 20% when using the highly basic mobile phase (pH 11.8) due to its degradation, therefore, a mixture of 10 AGs was analyzed with 250mmol L-1 ammonia aqueous solution (pH 11.5) with less degradation as the optimum condition. The developed analytical method could be used to determine the concentrations of trace AGs in milk with high accuracy and precision. Thus, RPLC-MS/MS using a high-pH mobile phase has great potential for the efficient separation of basic compounds containing amino sugars such as AGs.

Effect of Hydrophobic Moieties on the Assembly of Silica Particles into Colloidal Crystals

To boost the implementation of colloidal crystals (CCs) in separation science, the effects of the most common chromatographic reversed phases, that is, butyl and octadecyl, on the assembly of silica particles into CCs and on the optical properties of CCs are investigated. Interestingly, particle surface modification can cause phase separation during sedimentation because the assembly is highly sensitive to minute changes in surface characteristics. Solvent-induced surface charge generation through acid-base interactions of acidic residual silanol groups with the solvent is enough to promote colloidal crystallization of modified silica particles. In addition, solvation forces at small interparticle distances are also involved in colloidal assembly. The characterization of CCs formed during sedimentation or via evaporative assembly revealed that C4 particles can form CCs more easily than C18 particles because of their low hydrophobicity; the latter can only form CCs in tetrahydrofuran when C18 chains with a high bonding density have extra hydroxyl side groups. These groups can only be hydrolyzed from trifunctional octadecyl silane but not from a monofunctional one. Moreover, after evaporative assembly, CCs formed from particles with different surface moieties exhibit different lattice spacings because their surface hydrophobicity and chemical heterogeneity can modulate interparticle interactions during the two main stages of assembly: the wet stage of crystal growth and the late stage of nano dewetting (evaporation of interparticle solvent bridges). Finally, short, alkyl-modified CCs were effectively assembled inside silica capillaries with a 100 μm inner diameter, laying the foundation for future chromatographic separation using capillary columns.

An Evaluation of Immobilized Poly-(S)-N-(1-phenylethyl)acrylamide Chiral Stationary Phases

In this study, brush type and polymer type stationary phases were prepared based on (S)-N-(1-phenylethyl) acrylamide, and the polymeric stationary phase demonstrated superior chiral recognition ability. The two polymeric stationary phases were synthesized by two strategies, one was the “grafting from” method, which obtained polymer CSP by initiating monomer polymerization on the surface of 3-methacrylatepropyl silica gel, and the other was “grafting to”, which fixed the copolymer of (S)-N-(1-phenylethyl) acrylamide and trimethoxysilylpropyl methacrylate on silica gel. A comparison of these two bonding modes revealed that the stationary phase produced by “grafting to” had higher chiral recognition ability. Further improvement can be achieved by the end-capping of silanol groups with trimethylchlorosilane to reduce non-enantioselective retention caused by residual silanol groups and improve the peak shape of enantiomers. Chiral separation in subcritical fluid chromatography was also studied. Similar enantioselectivity results with higher resolution were observed due to the improvement of peak shape.

Organic dyes (acid red, fluorescein, methylene blue) and copper(II) adsorption on amino silica spherical particles with tailored surface hydrophobicity and porosity

Organic dyes are common constituents in wastewater and contribute to accumulation of persistent organic pollutants in the environment. Common dyes are aromatic compounds, bearing a variety of hydrophilic functional groups. Their interaction with solid surfaces can thus involve both van-der-Waals and hydrophobic interactions and electrostatic and/or hydrogen bonding. Aiming to tailor adsorbents with specific capacity for removal of dyes, silica microspheres were synthesized, combining aminopropyl functions as moderators of hydrophilic interaction and bridging aliphatic and aromatic functions as potential moderators of hydrophobic and π-stacking interactions. Two groups of samples were produced: non-porous silica spheres with amino or combined amino and hydrophobic residues; and porous polysilsesquioxane spheres incorporating aminopropyl components and organic bridges in the silica network. The hydrophilicity/hydrophobicity of the samples was studied by the absorption of water and benzene vapors. Bridged fragments, expected to promote the porosity of the samples, as well as hydrophobicity, did not contribute to the latter, because polysilsesquioxanes were bearing large numbers of residual silanol groups. Particles synthesized using tetraethoxysilane were up to 130 nm in size and held 1.6–1.8 mmol/g of amino groups, while, materials prepared from bridged silanes featured particle agglomerates up to 300 nm, 2.2–2.7 mmol/g amino groups content, and specific surface area of 540–620 m2/g. Interaction with Cu2+ was used to probe concentration and surface location of the amino functions, reaching 76–203 mg/g. Adsorption of anionic (acid red 88), neutral (fluorescein) and cationic (methylene blue) dyes was investigated revealing multiple interactions between the sorbent and sorbate. The dye sorption capacity values were 81–262 mg/g for acid red 88, 26–132 mg/g for fluorescein, and 55–146 mg/g for methylene blue. Produced silica microspheres have potential as high performance sorbents for the extraction of copper(II) ions and the dyes, and can act as fluorescent carriers after the dye adsorption.

Fabrication and Characterization of a Reversed-Phase/Strong Cation Exchange Stationary Phase Gradient

Continuous stationary phase gradients for liquid chromatography (LC) have been recently shown to be a promising method of altering selectivity. In this work, we present the first multicomponent continuous stationary phase gradient for separations involving both reversed-phase (RP) and strong cation exchange (SCX) mechanisms. These columns are fabricated using a two-step methodology based on controlled rate infusion (CRI). First, destructive CRI creates a gradient of excess silanol groups along a uniform C18 column. Next, these columns are infused with 3-mercaptopropyltrimethoxysilane (MPTMOS), which bonds to the excess silanol groups. The terminal thiols of the MPTMOS ligands are oxidized with H2O2 to create the sulfonate functionality (SO3−) needed for SCX separations. The success of the modification procedure is characterized by thermogravimetric analysis and X-ray photoelectron spectroscopy. The stability of the C18-SO3− gradients were found to have less than 5 % retention loss and the column-to-column reproducibility had a relative standard deviation under 9 %. The peak asymmetry factors for seven biogenic amines were found to be between 1.03 ± 0.04 to 1.30 ± 0.02, which illustrates minimal peak tailing due to poor packing and residual silanol groups. Characterization of the gradient columns using an isocratic mobile phase showed a unique elution order compared to a uniform C18 and SO3− columns. At lower counterion concentrations, more than 48 % of the overall retention on the gradient stationary phase is due to a SCX mechanism. Meanwhile, the RP mechanism was shown to predominate at higher counterion concentrations on the gradient columns (SCX retention contribution less than 40 %). Coupling the stationary phase gradient to a salt gradient in the mobile phase showed that the gradient phase provides a unique, intermediate selectivity to the uniform C18 and SO3− columns. Under an ACN mobile phase gradient, a significant increase (p < 0.003) in the retention times of three biogenic amines (15 – 16 %) was observed when the multicomponent gradient was oriented to have a high SO3− ligand density near the detector. This work serves as a proof-of-concept design for a multicomponent stationary phase gradient to continue fundamental studies into retention and encourage novel applications.

Modified Organosilane Monolayers With Enhanced Radiation Stability.

Organosilane monolayers containing long carbon chains are susceptible to damage when exposed to X-rays and other radiation during characterization or processing. The origin of the damage has been attributed to both energetic photons and photoelectrons. These particles can break bonds in the molecules comprising the layer altering its composition and structure and can create silanol groups at the interface between the monolayer and the silicon dioxide surface. A common practice to minimize damage is to keep the X-ray beam time as short as possible. In this study, we report a method to deposit an organosilane monolayer on silicon dioxide that withstands X-ray beam damage to the interface. Adding the small monofunctional trimethylchlorosilane to a layer composed of the long-chain trifunctional octadecyltrichlorosilane prevented X-ray beam damage for at least 4 h. Interfacial damage was monitored by titrating silanol groups with TiCl4 and water atomic layer deposition and measuring the TiO2 deposited by X-ray photoelectron spectroscopy (XPS). The small monofunctional silane reacted with residual silanol groups capping the siloxane (-Si-O-Si-O-) chains at the interface. The low silanol group concentration minimized X-ray beam damage and prevented TiO2 from depositing to the detection limit of XPS. Using a small molecule to terminate reactive groups could improve the stability of monolayers not only during characterization and processing, but also when the monolayer is a component in an electrical device by reducing sources of interfacial charge traps.

Synthesis of a poly(sulfobetaine-co-polyhedral oligomeric silsesquioxane) hybrid monolith via an in-situ ring opening quaternization for use in hydrophilic interaction capillary liquid chromatography.

An in-situ approach is described for synthesis of poly(sulfobetaine-co-polyhedral oligomeric silsesquioxane) [poly(sulfobetaine-co-POSS)] that can be used in a hybrid monolithic column as a hydrophilic liquid chromatography (HILIC) stationary phase. Synthesis involves (a) radical polymerization of octa(propyl methacrylate)-polyhedral oligomeric silsesquioxane (MA-POSS) and organic monomers such as dimethylaminopropyl methacrylate or vinyl imidazole, and (b) in-situ ring-opening quaternization between 1,4-butane sultone and the organic monomers. The sulfobetaine groups are generated in-situ monolith. This obviates the need for synthesis of sulfobetaine monomer previously. The pore size and permeability of the material can be tuned by using a binary porogenic system (polyethyleneglycol 600 and acetonitrile) and via the composition of the polymerization mixture. The optimized hybrid monolith owns its merits to the presence of POSS and sulfobetaine groups with good mechanical stability, the lack of residual silanol groups, and adequate hydrophilicity. The column filled with the monoliths was evaluated as a stationary phase for HILIC. Several kinds of polar compounds (including nucleosides, bases, phenols, aromatic acids and amides) were separated by using mobile phases with high organic solvent fractions in capillary liquid chromatography. Graphical abstractAn in-situ approach is described for synthesis of poly(sulfobetaine-co-polyhedral oligomeric silsesquioxane) hybrid monolithic column for use in hydrophilic liquid chromatography. The optimized monolith owns good mechanical stability, the lack of residual silanol groups and adequate hydrophilicity. Baseline separation of several kinds of polar compounds is achieved on the column. MA-POSS: octa(propyl-methacrylate) polyhedral oligomeric silsesquioxane; DMAEMA: dimethylaminoethyl methacrylate; AIBN: azodiisobutyronitrile. Poly(DMABS-co-POSS): poly(N-(4-sulfobutyl)-N-methacryloxypropyl- N,N-dimethylammonium-betaine-co-polyhedral oligomeric silsesquioxane).

Selectivity of the Separation of Isomeric Chlorogenic Acids under the Conditions of Reversed-Phase HPLC

The selectivity of the separation of isomeric chlorogenic acids often found in natural samples (3, 4, and 5-caffeoylquinic acids, 3CQA, 4CQA, and 5CQA, respectively) under the conditions of reversed-phase chromatography on stationary phases of different brands, Kromasil (C18, C8, and C4), Symmetry C18, Reprosil-Pur C18-AQ, Nucleosil RPC18, and Diasfer C18, is studied. The results obtained favor the retention mechanism with predominant surface adsorption. The change in the selectivity of separation of a pair of 5CQA and 4CQA correlates with a change in the activity of residual silanol groups. At their low activity, the order of elution 3CQA < 5CQA < 4CQA does not depend on the mode (isocratic or gradient), the type of organic modifier, and the addition of an acid (formic, orthophosphoric) to the mobile phase. With an increase in the activity of silanol groups, the separation of the pair of 5CQA and 4CQA deteriorates up to the inversion of retention times. A Kromasil 100-5C18 column (250 × 4.6 mm) was chosen for a reliable separation of three acids in plant samples (instant coffee, juice, and “Mate” tea).

Preparation of novel hydrophilic microporous material PML-1 membrane by topotactic transformation of layered silicate SSA-1 and applicability to the dehydration of aqueous acetic acid

Abstract Novel hydrophilic PML-1 (PML: porous material transformed from a layered silicate) membranes were prepared on a porous tubular α-alumina support by a calcination-driven topotactic transformation of a hydrothermally pre-coated layered silicate SSA-1 (SSA: silicate synthesized with a quaternary amine) layer. The effects of seed crystal, synthesis time, and repetitive synthesis on the formation and morphologies of the supported layered silicate layers and corresponding membranes were investigated in detail to reveal that repetitive synthesis allowed the preparation of a dense and continuous layered silicate layer. The performance of the PML-1 membrane with an approximately 6-μm-thick separation layer for the pervaporation dehydration of aqueous acetic acid was examined, and the observed water-selective permeability was ascribed to the presence of numerous residual silanol groups in the membrane framework. These results indicate that the prepared PML-1 membrane is applicable to the separation of water/acetic acid mixtures and hence, provide a new approach to the further development and application of layered silicates as novel membrane materials.

Optimizing support properties of heterogeneous catalysts for the coupling of carbon dioxide with epoxides

The study deals with the catalytic cyclocarbonation of epoxides to produce monomers used in the synthesis of polyurethane. A benchmark study of the textural properties of silica-based, doped or not, supports enabling the identification and optimization of the key parameters affecting the catalytic activity is reported. The results reveal that ammonium catalysts immobilized onto mesostructured supports with high surface area and low aggregation show better catalytic performances than analogue catalysts grafted onto microstuctured ones. While a high external surface area favours the grafting of ammonium salt, pore size must be large enough to enhance the accessibility of both carbon dioxide and epoxides to the catalytic sites. The activity of heterogeneous catalysts was evaluated for a model coupling reaction between carbon dioxide and propylene glycol diglycidylether. Using appropriated supports, cyclocarbonation yields are found to be higher in the presence of the heterogeneous catalyst in comparison with the homogeneous one. These results allow to confirm the beneficial effect of the presence of residual OH silanol groups at the surface of the support, which activate epoxide through forming of hydrogen bonds.

Characterization of Novel Polymer-Based Pyridine Stationary Phases for Supercritical Fluid Chromatography

2-Ethylpyridine-bonded silica is one of the most famous stationary phases employed in supercritical fluid chromatography, especially for the analysis of basic compounds and even without an additive in the mobile phase. In the present paper, we present the synthesis and characterization of three original stationary phases based on poly(vinylpyridine) polymers supported on silica. The position of nitrogen atom relative to the polymer chain was varied to be in the 2, 3, or 4 position. All these phases were prototypes, while the poly(4-vinylpyridine) phase was subsequently commercialized (DCPak P4VP from Daicel Corporation). The stationary phases obtained are characterized in supercritical fluid chromatography with carbon dioxide—methanol mobile phase, with a modified version of the solvation parameter model, to take account of ionic interactions. The three phases are also compared to a 2-ethylpyridine-bonded silica phase and a 2-picolylamine-bonded silica phase. It appears that the polymer-based pyridine phases are significantly more retentive than brush-type pyridine phases and adequately shield residual silanol groups to prevent unwanted interactions with basic compounds. The different selectivities and chromatographic performances are also evidenced with sample applications on pharmaceutical compounds, notably with a selection of 140 drug candidates.

Poly(4-vinylpyridine) based novel stationary phase investigated under supercritical fluid chromatography conditions

A novel poly(4-vinylpyridine) based stationary phase was investigated for its performance under supercritical fluid chromatography (SFC) mode. Due to its unique structure, this stationary phase has high molecular planarity recognition ability for aromatic samples possessing the same number of aromatic rings and π-electrons. Taking advantage of the planarity recognition ability observed, separations of structurally similar polycyclic aromatic hydrocarbons and steroids were achieved. This novel stationary phase afforded good peak symmetry for both acidic and basic active pharmaceutical ingredients even when excluding the use of additives such as acids, bases, and salts. These findings may be attributed to the polymeric pyridyl groups covalently-attached on silica gel, which will effectively shield the undesirable interaction between residual silanol groups on the surface and the analytes. Moreover, the properties of pyridyl group on the selector can be reversibly tuned to cationic pyridinium form by eluting trifluoroacetic acid containing modifier. Column robustness toward cycle durability testing was also confirmed.

Isocratic Resolution of Fluoroquinolone-Based Antibiotics on the Phenylethyl-Bonded Phase under Nonaqueous Elution: A Consideration of the Separation Mechanism.

This paper reports the isocratic resolution of 10 fluoroquinolone-based antibiotics and their precursors on the phenylethyl-bonded phase under the elution of the nonaqueous mobile phase composed of acetonitrile, methanol, acetic acid, and triethylamine. Most of the analytes were baseline resolved within 10 minutes. The interaction simulation and Fourier-transform infrared spectroscopy (FTIR) data indicated that the carbonyl-containing group, a secondary or tertiary amine of an analyte, was heavily involved in the retention, resulting in retention with residual silanol groups on the stationary phase. In some cases, the elution reversal or resolution enhancement of analytes was observed when the volume of acidic or basic additive in the mobile phase was dominant. However, the π-π complexation interaction between the fluorine-attached phenyl group of the analyte and the phenylethyl moiety on the stationary phase was not observed. Consequently, the resolution could not be reproduced either on the other stationary phase modified with C18, phenyl, or phenylhexyl moiety under the same chromatographic conditions or under the aqueous elution.

Properties of Sol–Gel Derived Thin Organoalkylenesiloxane Films

We have prepared film-forming solutions for the growth of dense and porous thin organoalkylenesiloxane (OAS) films based on copolymers of methyltrimethoxysilane and 1,2-bis(trimethoxysilyl)ethane (BTMSE) by a sol–gel process. The chemical composition and microstructure of the OAS films have been studied by IR spectroscopy and spectral ellipsometry in relation to the mole fraction of BTMSE and the water: methoxy groups ratio in solution. The results demonstrate that partial substitution of ethylene bridges for silicon–oxygen bonds in OAS leads to distortion of the regular ladder-like structure characteristic of polymethylsilsesquioxane films and the presence of residual silanol groups, which causes an increase in the dielectric permittivity k of the matrix material. The relative porosity in porous OAS films produced via evaporationinduced self-assembly has been shown to be determined by not only the amount of surfactant added but also the presence of a sufficient amount of silanol groups, participating in the attachment of surfactant molecules, in the matrix copolymer solution. In this connection, an important factor determining the structure of the OAS matrix and its pore structure is control over the amount of water involved in the cohydrolysis process. It has been shown that the samples with a relative porosity of 38% prepared from a film-forming solution containing 47 mol % BTMSE (m = 0.7) and 30 wt % surfactant have k ≈ 2.3 and are potentially attractive materials for use as insulators in integrated circuits.

Design and Fabrication of Polymer Layered Silicate Nanocomposites for Water Purification

ABSTRACTZeolite and cellulose-acetate nanocomposites were fabricated in this study using a combination of melt blending and solution mixing. The nanocomposites were optimized for heavy metal adsorption using spiked lead and cadmium solutions. Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy and Powder X-Ray diffraction crystallography were used for physical characterization. Fourier Transform Infrared spectra showed a reduction of the hydroxyl peak for cellulose acetate and that of the residual silanol group for zeolites symbolizing bonding during nanocomposite formation. Scanning Electron Microscope results showed an increase in voids with zeolite loading in the nanocomposites, a useful characteristic of good adsorbents. Powder X-ray diffraction crystallography results showed a reduction in 2 theta values for the nanocomposites due to penetration of the polymer into the silicate lattice e.g. zeolite 2 theta peak at 7.44°reduced to 7.09°in the nanocomposites signifying an increase in crystal lattice d- spacing from 1.188 nm to 1.247 nm. The nanocomposites adsorbed a maximum of 97.20% lead ions and 85.06% cadmium ions from solution.

イオンクロマトグラフィーによる海水中の無機陰イオンの定量─逆相系C18シリカカラムにおける残存シラノール基の効果─

イオンクロマトグラフィー（IC）による，海水中に存在する6種無機陰イオン［ヨウ素酸イオン（IO3−），臭素酸イオン（BrO3−），臭化物イオン（Br−），亜硝酸イオン（NO2−），硝酸イオン（NO3−），ヨウ化物イオン（I−）］の一斉定量を検討した．分離カラムとして残存シラノール基を持つ逆相系C18シリカカラムを用いた．溶離液に0.3 M塩化ナトリウム＋0.5 mM塩化ドデシルアンモニウム（DAC）＋5 mMリン酸緩衝液（pH 4.5）（流量1 mL min−1），検出器にUV検出器（225 nm）を用いたところ，19分以内で目的イオンの測定が可能であった．残存シラノール基を持つ逆相系C18シリカカラム（エンドキャップ未処理カラム）はエンドキャップ処理カラムと比べてBr−とNO2−間の分離が良好であった．繰り返し精度は保持時間，ピーク面積，ピーク高さの相対標準偏差（RSD（％））が1.55％ 以内（n＝5）であり，24時間の連続測定では2.97％ 以内（n＝48）であった．検量線は良好な直線性（r2>0.999）を示した．検出限界値（S/N＝3）は，IO3−（8.3 μg L−1），BrO3−（24 μg L−1），Br−（92 μg L−1），NO2−（0.8 μg L−1），NO3−（3.2 μg L−1），I−（1.0 μg L−1）であった．瀬戸内海水の標準添加による回収率は93～108％ であった．本法を瀬戸内海（広島湾）5地点で夏季の海水中陰イオン濃度の深度依存性に適用した．溶離液の流量1.5 mL min−1では対象イオンの分離・検出に問題はなく1サンプルの測定時間は13分であった．

High-resolution 29Si CP/MAS solid state NMR spectroscopy and DFT investigation on the role of geminal and single silanols in grafting chromium species over Phillips Cr/silica catalyst

Phillips Cr/silica catalyst is industrially important in ethylene polymerization. The high-resolution solid state 1H MAS NMR and 29Si CP/MAS NMR allowed the identification of the type and amount of silanols: geminal vs. single (isolated and vicinal) silanols on Phillips catalysts calcined at different temperatures, which were compared with those of the bare silica gel counterparts. The residual silanols on the catalyst and silica gel samples were all decreased with increasing calcination temperatures from 120 to 800°C. For the catalysts treated at temperatures lower than 300°C, the amount of residual silanol groups were much lower than those of the silica gel counterparts. It suggested that the chromium species were mainly grafted on the silica gel through esterification reaction with surface silanols below 300°C. The geminal silanols almost disappeared on the catalysts at 120°C, while that for the silica gel occurred at 300°C. Further increasing the calcination temperatures from 300 to 800°C, the amount of single silanols were slower decreased for the catalysts than that for the silica gel samples. It indicated that the presence of the grafted chromate species obstructed further removal of the residual single silanols. The role of silanols on the formation of surface chromate species on the well-defined polyoligomericsilsesquioxane (POSS) models containing various types of silanols was theoretically studied by density functional theory (DFT) method. It was shown that one silanol of the geminal pair and another adjacent single silanol was the most thermodynamically favored for grafting chromium species. The priority of the reaction between chromium species and different types of surface silanol groups during calcination for Phillips catalysts were experimentally and theoretically elucidated for the first time.

Synthesis and characterization of polyphenylsilsesquioxane terminated with methyl and vinyl groups low-melting glass

Polyphenylsilsesquioxane terminated with methyl and vinyl groups, a novel organic–inorganic hybrid low-melting glass (PhLMG), was synthesized via hydrolysis-condensation of phenyltriethoxysilane and termination of silanol groups with hexamethyldisiloxane (MM) and divinyltetramethyldisiloxane (ViMMVi). Fourier transform infrared spectrometry (FT-IR) and 1H nuclear magnetic resonance spectrometry (1H NMR) confirmed the chemical structure of PhLMG, and with the terminating agents increasing, the residual silanol groups accordingly reduced and even disappeared. XRD and FT-IR results demonstrated that PhLMG possessed amorphous ladder-like structure. The mean molecular weight and thermal stability of PhLMG were largely determined by the amount of the terminating agents. The glass transition temperature (Tg) of PhLMG without the terminating agents was 125 °C, while Tg of PhLMG markedly decreased after adding the terminating agents. Furthermore, the structural regularity of PhLMG was lowered with the addition of terminating agents. When the molar ratio of the composite of MM and ViMMVi to phenyltriethoxysilane was 0.05, the mean molecular weight and thermal stability maintained at higher level and silanol groups disappeared completely.