Synthesis, characterization and properties of a novel fluorinated methacrylate polymer

A fluorinated monomer of 2-(2,2,2-trifluoroethoxy)ethyl methacrylate (FEMA) was prepared by a “one pot” process and then a novel fluorinated methacrylate polymer, poly[2-(2,2,2-trifluoroethoxy)ethyl methacrylate] (PFEMA), was successfully synthesized via miniemulsion polymerization using cetyltrimethyl ammonium bromide (CTAB) as emulsifier, hexadecane (HD) as co-stabilizer and 2,2′-azobisisobutyronitrile (AIBN) as initiator. The chemical structure of PFEMA was characterized by FT-IR, ¹H NMR and ¹⁹F NMR. GPC results show that the number average molecular weight (M_n) of PFEMA was as high as 8.5 × 10⁵ g/mol and the polydispersity index (PDI) was only 1.3. SEM and DLS characterizations showed that the morphology of PFEMA latex was uniform spheres with the diameter of about 110–125 nm. It was also found that PFEMA has high thermo-stability (T_d > 200 °C), low glass transition temperature (T_g = 13.0 °C), and nice hydrophobicity (θ_water = 99.9°). Comparison studies on PFEMA and poly(2,2,2-trifluoroethyl methacrylate) show that an introduced functional group (–CH₂CH₂O–) has a significant effect on lowering T_g and improving hydrolysis resistance without impairing surface properties.     

Characterisation of hybrid xerogels synthesised in acid media using methyltriethoxysilane (MTEOS) and tetraethoxysilane (TEOS) as precursors

The mild synthetic conditions provided by the sol-gel process and the versatility of the colloidal state allow for the mixing of inorganic and organic components at the nanometre scale in virtually any ratio for the preparation of hybrid materials. Our interest in hybrid xerogels focuses on combining their porosity with other properties to prepare optic-fibre sensors. The specific aim of this paper is to synthesise hybrid xerogels in acid media using methyltriethoxysilane (MTEOS) and tetraethoxysilane (TEOS) as silica precursors and to investigate the effect of the MTEOS molar ratio on the structure and porous texture of xerogels. Gelation time exponentially increased as the MTEOS molar ratio increased. Increasing the MTEOS molar ratio yielded xerogels with lower density and lower particle size. The incorporation of MTEOS resulted in new FTIR bands at 1276 and 791 cm⁻¹, which was attributed to vibrational modes of methyl group. The band around 1092 cm⁻¹ associated with siloxane bonds shifted to lower wavenumbers and split into two bands. The ²⁹Si spectra only showed the Q ⁿ (n=2, 3, 4) signal in xerogels with 0% MTEOS and the T ⁿ (n=2, 3) signal in xerogels with 100% MTEOS; hybrid xerogels showed both Q and T signals. From XRD peaks at 2θ around 9°, we inferred that xerogels (>70% MTEOS) consisted of nanocrystalline CH₃–SiO_3/2 species. Increasing the MTEOS molar ratio produced xerogels with lower pore volumes and lower average pore size. The integration of methyl groups on the surface decreased the surface polarity and, in turn, the characteristic energy.     

Modification of epoxy-novolac resins with polysiloxane containing nitrile functional groups: synthesis and characterization

Synthesis of the statistical epoxidized polycyanopropylmethylsiloxane-co-polydimethylsiloxanes (PCPMS-co-PDMS) has been demonstrated. The modified polysiloxanes were prepared via a two-step method; (1) the ring-opening polymerization of octamethylcyclotetrasiloxane (D₄) and tetramethylcyclotetrasiloxane (D₄H), (2) hydrosilylation reaction of the polysiloxane prepolymers with allyl cyanide and allyl glycidyl ether. Molar ratios of D₄H and D₄ were varied to produce the modified polysiloxanes with differences in polarity. ¹H-NMR, ²⁹Si-NMR, ¹³C-NMR and FTIR were used to monitor the formation of the modified polysiloxanes and DSC was used to study their thermal behaviors (T_g, −118 to −68 °C). The use of the modified polysiloxanes as an elastomeric component in epoxy-novolac networks was also investigated. TEM and their transition temperatures suggested that the epoxy-novolac networks with high content of PDMS modifiers exhibited microphase separation. The fracture toughness properties of the networks with the polysiloxane modifiers were improved over the controls without polysiloxanes.     

Synthesis and properties of polysiloxane xerogels containing tetrasulfide groups

Polysiloxane xerogels with a functional group content of 1.1?C1.9 mmol/g have been obtained by the hydrolytic condensation of the alkoxysilanes Si(OC₂H₅)₄ and [(C₂H₅O)₃Si(CH₂)₃S₂]₂ in the 2 : 1, 4 : 1, and 8 : 1 ratios. It has been demonstrated by ¹³C and ²⁹Si CPMAS NMR spectroscopy that the xerogels have a polysiloxane framework with dipropyl tetrasulfide bridges, silanol groups, unhydrolyzed ethoxyl groups, and hydrogen-bonded water molecules on the surface. The xerogels have a porous structure. As the molar ratio of the reacting alkoxysilanes is increased in the above-specified range, the specific surface area of the xerogel increases (from 89 to 312 m²/kg) and the same is valid for other structure-adsorption characteristics. The synthesized polysiloxane xerogels readily sorb Hg²⁺ from acidified solutions. Their static sorption capacity can be as high as 1.5 g Hg per gram of sorbent. However, in the course of time, the 1 : 1 complexes forming on the xerogel surface undergo transformations accompanied by the release of mercury sulfide and/or Hg²⁺ reduction to mercury metal.     

Electron Paramagnetic Resonance and Differential Scanning Calorimetry Studies of Thorium and Tin Phosphate Xerogels

Different transparent phosphate xerogels were synthesized using concentrated solutions of metal chlorides and phosphoric acid with a proper mole ratio of both components. By this method we prepared bulk samples of thorium and tin(IV) phosphate xerogels by drying at room temperature or at 350 K. Some properties of these amorphous materials were studied by means of differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) techniques. Depending on mole ratio metal/phosphate, these xerogels show, near 180 K, inflection points which we interpret asT _g . Samples dried at 425 K lose their transparency and have noT _g . Thus, it seems that the “glassy” state is due to water molecules remaining in the material. The same properties were confirmed by EPR studies of the xerogels doped with Cr³⁺ and Fe³⁺ ions as probes. These results show the existence of two different phases in the xerogels: a liquid-like one, in the range from 190 K to 350 K and a solid-like one, in the range from 4 K to 190 K.     

Solid-State NMR Study of Phase Separation and Order of Water Molecules and Silanol Groups in Polysiloxane Networks

Homogeneity and structure of organically modified polysiloxane networks prepared by sol-gel co-condensation, as well as location and nature of water molecules and silanol groups were studied by 1D and 2D solid-state NMR. ¹H–²⁹Si and ¹H–¹H interatomic distances were estimated from variable contact-time CP/MAS experiments, ¹H NMR chemical shifts and off-resonance WISE NMR. A structure model of these networks is proposed and discussed. The fraction of proton-inaccessible units Q⁴ in the networks decreases with increasing amounts of dimethylsiloxane (D) and methylsiloxane (T) units. In contrast to systems prepared by co-condensation of tetraethoxysilane (TEOS) with dimethyl(diethoxy)silane (DMDEOS), proton-inaccessible units form essential fraction in networks prepared by co-condensation of TEOS with methyl(triethoxy)silane (MTEOS). The proton-accessible part of the networks with high O/Si ratios is nano-heterogeneous phase, which is composed of water containing Q ⁱ particles separated by copolymer domains. The overall homogeneity and uniformity of binding sites around silanol groups increases by co-condensation TEOS with DMDEOS or MTEOS, while the amount of physisorbed water as well as the hydrogen bond strength decreases, as compared with neat silica gel prepared by polycondensation of TEOS.     

Porous xerogels with a bifunctional surface layer of the composition ≡Si(CH<Subscript>2</Subscript>)<Subscript>3</Subscript>SH/≡Si(CH<Subscript>2</Subscript>)<Subscript>2</Subscript>H<Subscript>3</Subscript>

The sol-gel method with ethanol as a solvent and fluoride ion as a catalyst was used to prepare polysiloxane xerogels containing both 3-mercaptopropyl and n-propyl groups in the surface layer. An increase in the relative amount of n-propyltriethoxysilane in the initial reaction solution was found to result in the formation of xerogels with developed porous structures, which was accompanied by an increase in the specific surface area from 370 to 550 m²/g; simultaneously, other porous structure parameters such as sorption volume and pore size exhibited a tendency to increase. Atomic-force microscopy was used to show that the xerogels synthesized comprised aggregates of mean size 30 nm. An analysis of the IR and ¹³C cross-polarization magic angle spinning NMR data led us to conclude that the surface layer of bifunctional xerogels contained not only 3-mercaptopropyl and n-propyl groups but also silanol groups, part of nonhydrolyzed alkoxy groups, and H-bonded water molecules. The ²⁹Si cross-polarization magic angle spinning NMR spectra revealed the presence of structural units of the compositions T¹ [(≡SiO)Si(OR’)₂(CH₂CH₂CH₃) and/or (≡SiO)Si(OR’)₂(CH₂)₃SH, R’ = H, OCH₃, or OC₂H₅], T² [(≡SiO)₂Si(OR’)(CH₂CH₂CH₃) and (≡SiO)₂Si(OR’)(CH₂)₃SH], and T³ [(≡SiO)₃SiCH₂CH₂CH₃ and (≡SiO)₃Si(CH₂)₃SH] in the xerogels synthesized.     

Determination of aflatoxins in cereal flours by solid-phase microextraction coupled with liquid chromatography and post-column photochemical derivatization-fluorescence detection

A new method for the determination of aflatoxins B₁, B₂, G₁, and G₂ (AFB₁, AFB₂, AFG₁, AFG₂) in cereal flours based on solid-phase microextraction (SPME) coupled with high performance liquid chromatography with post-column photochemical derivatization and fluorescence detection (SPME–HPLC–PD–FD) has been developed. Aflatoxins were extracted from cereal flour samples by a methanol:phosphate buffer (pH 5.8, I = 0.1) (80:20, v/v) solution, followed by a SPME step. Different SPME and HPLC–PD–FD parameters (fiber polarity, temperature, pH, ionic strength, adsorption and desorption time, mobile phase) have been investigated and optimized. This method, which was assessed for the analysis of different cereal flours, showed interesting results in terms of LOD (from 0.035 to 0.2 ng g⁻¹), LOQ (from 0.1 to 0.63 ng g⁻¹, respectively), within and inter-day repeatability (2.27% and 5.38%, respectively) linear ranges (up to 20 ng g⁻¹ for AFB₁ and AFG₁ and 6 ng g⁻¹ for AFB₂ and AFG₂), and total raw extraction efficiency (in the range 55–59% at concentrations in the range 0.3–1 ng g⁻¹ and 49–52% at concentrations in the range 1–10 ng g⁻¹). The results were also compared with the purification step carried out by conventional immunoaffinity columns.     

Evaluation of high pressure oxygen microwave-assisted wet decomposition for the determination of mercury by CVAAS utilizing UV-induced reduction

The UV-induced cold vapor generation with formic acid coupled to AAS after high pressure oxygen microwave decomposition was developed for determination of total Hg in analytical samples. Certified reference materials were decomposed in 1.5 mol L^{− 1} HNO₃ and 0.6 mol L^{− 1} H₂O₂. Microwave decomposition with oxygen has allowed the use of diluted reagents. The oxygen at a pressure of ca. 15 bar was delivered during the mineralization to the closed vessel. Interference by unused residues of H₂O₂ and HNO₃ was observed. In order to overcome the negative effect of remaining oxidants pre-reduction with hydroxylammonium chloride at a concentration 0.75 mmol L^{− 1} was used. Recovery of mercury in four reference materials containing 0.20–1.99 µg g^{− 1} Hg were 99–104% of certificate values. The limits of detection and quantification in the sample solutions were determined as 0.12 and 0.38 µg L^{− 1}, which corresponds to absolute detection limits of 12 and 38 ng g^{− 1} for total mercury, respectively. The results were in good agreement with the t-test at a 95% confidence level of the certified values in the investigated reference materials. The relative standard deviation was better than 7% for most of the samples.     

Synthesis and physical–chemical properties of hydrolyzed nanosized mesoporous fluorocarbon materials and carbon–fluorocarbon composites

Hydrolysis of nanosized mesoporous superstoichiometric fluorocarbon material FS (CF_{1.20 ± 0.03}) and carbon–fluorocarbon nanocomposites NCFC (CF_{0.93 ± 0.03}) by 10% KOH in aqueous-alcohol solution was studied and yielded two new classes of the hydrolyzed fluorocarbon nanomaterials: hydroxofluorocarbon nano-material FS–OH of general formula sp³-C_1−yF_n−x(OH)_x (n = 1; x > 0.1, y ∼ 0.05–0.1) and carbon–hydroxofluorocarbon nanocomposites NCFC–OH of general formula sp²-C_m*sp³-C_1−yF_n−x(OH)_x (n = 1; x ∼ 0; y ∼ 0.1–0.2).FTIR and Raman studies of FS–OH and NCFC–OH materials have shown that hydrolysis of sp³-C–F-bonds in these materials leads a decrease of sp³-C–F amount and appearance of characteristic absorption bands for sp³-C–OHO, carboxyls and carbonyls, typical for oxidized graphites, carbon blacks and various soots. These phenomena, in combination with C,H,F-analyses for FS–OH and NCFC–OH products have allowed to state that hydrolysis of FS and NCFC in KOH solutions can be explained by the substitution reactions of surface sp³-C–F to sp³-C–OH and sp²>CO containing groups.Observed hydrolytic reactions are also accompanied with processes of the colored solutions origin (yellow – for FS and red-brown – for NCFC). These solutions have UV-VIS spectra identical to graphene oxide and graphitic acid.     

Synthesis of photocrosslinkable fluorinated polydimethylsiloxanes: Direct introduction of acrylic pendant groups via hydrosilylation

The synthesis of photocrosslinkable fluorinated polydimethylsiloxanes was achieved through direct hydrosilylation with copoly(dimethyl)(methyl‐hydrogen) siloxane. First, the hydrosilylation of a fluorinated olefin allowed the introduction of a fluorinated group onto the polysiloxane. Then, a second hydrosilylation of allyl methyl methacrylate led to the polysiloxane bearing both fluorinated and photocrosslinkable groups. This method, compared with a previous method of copolycondensation, is shown to be easier and more efficient. All the new products synthesized were characterized by IR, ¹H NMR, ¹⁹F NMR, and ²⁹Si NMR. A formulation containing the fluorosilicone was crosslinked after being coated on a mesoporous membrane and was evaluated as a vapor permeation membrane. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3722–3728, 2000     

含氟高分子/SiO_2杂化疏水材料的制备及涂层表面性质

采用自由基溶液聚合与溶胶-凝胶法相结合的方法制备了含氟高分子/SiO2杂化疏水材料.通过甲基丙烯酸十二氟庚酯(FA)与乙烯基三乙氧基硅烷(VTES)共聚合成了含氟硅共聚物(PFAS),进一步通过原硅酸乙酯(TEOS)与PFAS共聚物溶液共水解缩聚制备了具有含氟侧基的碳碳主链高分子和硅氧网络的含氟高分子/SiO2杂化疏水材料.研究结果表明,SiO2组分含量提高可以显著增加杂化材料薄膜的涂敷厚度,改善其耐久性能,而对杂化材料疏水性能的影响不大.     

Weak hydrogen bonds from Cp donors to CC acceptors

In the crystal structure of 1, pairs of molecules are connected by mutual C(Cp)–H?CC interactions which have a geometry suggestive of weak hydrogen bonding (1[(η⁵-C₅H₅)Fe(CC−C₇H₇–2,4,6)(CO)₂]). The shorter of the H?C distances is only 2.59 Å, which is a distance that is typically observed for C–H?CC hydrogen bonds of stronger donors such as chloroform or alkyne groups.     

Enantiomer-specific determination of hexabromocyclododecane in fish by supramolecular solvent-based single-step sample treatment and liquid chromatography–tandem mass spectrometry

A single-step, environmentally friendly sample treatment was developed and used in combination with liquid chromatography–tandem mass spectrometry (LC–MS/MS) for the quantitation of hexabromocyclododecane (HBCD) stereoisomers in fish. It was based on the microextraction of the stereoisomers with a supramolecular solvent (SUPRAS) made up of reverse aggregates of decanoic acid (DeA). The procedure involved the stirring of the fish sample (750 mg) with 600 μL of SUPRAS for five minutes, subsequent centrifugation for extract separation from matrix components and direct analysis of the extract after dilution 1:1 with methanol. Individual enantiomers of α-, β- and γ-HBCD were separated on a chiral stationary phase of β-cyclodextrin and quantified by monitoring of the [M−H]⁻ → Br⁻ transition at m/z 640.9→80.9. Driving forces for the microextraction of HBCD in the SUPRAS involved both dispersion and dipole–dipole interactions. Quantitation limits for the determination of individual HBCD enantiomers in hake, cod, sole, panga, whiting and sea bass were within the intervals 0.5–3.4 ng g⁻¹, 0.9–2.5 ng g⁻¹, 0.6–1.4 ng g⁻¹, 1.0–5.6 ng g⁻¹, 0.8–1.3 ng g⁻¹ and 0.5–3.5 ng g⁻¹, respectively. Recoveries for fish samples fortified at the ng g⁻¹ level ranged between 87 and 114% with relative standard deviations from 1 to 10%. The sample treatment proposed greatly simplifies current procedures for extraction of HBCD stereoisomers and is a useful tool for the development of a large scale database for their presence in fish.     

Determination of tetrabromobisphenol-A,tetrachlorobisphenol-A and bisphenol-A in soil by ultrasonic assisted extraction and gas chromatography–mass spectrometry

In this work, an isotope dilution method for the determination, in agricultural and industrial soil samples, of tetrabromobisphenol-A, tetrachlorobisphenol-A and bisphenol-A by gas chromatography–mass spectrometry was developed. The compounds were extracted from soil by sonication assisted extraction in small columns (SAESC) with a low volume of ethyl acetate as extraction solvent. For dirty soil samples, such as industrial soils, a simultaneous clean-up on an acidified Florisil–anhydrous sodium sulfate mixture was carried out to remove interferences. After extraction, solvent was evaporated and analytes were derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and determined by isotope dilution gas chromatography with electron impact mass spectrometric detection in the selected ion monitoring mode (GC–MS–SIM), using ¹³C₁₂ labeled compounds as internal standards. Recoveries from spiked samples were between 88% and 108% and the estimated limits of detection (S/N = 3) varied from 30 pg g⁻¹ to 90 pg g⁻¹. The response obtained with this method was linear over the range assayed, 5–300 ng ml⁻¹, with correlation coefficients equal or higher than 0.999. The validated method was used to investigate the levels of these phenolic compounds in soil samples collected from different locations in Spain. Bisphenol-A was detected in all samples at concentrations from 0.7 ng g⁻¹ to 4.6 ng g⁻¹ in agricultural soils and from 1.1 ng g⁻¹ to 44.5 ng g⁻¹ in industrial soils. Tetrabromobisphenol-A was found in various soil samples at levels in the range of 3.4–32.2 ng g⁻¹ in industrial soils and at 0.3 ng g⁻¹ in one agricultural soil, whereas tetrachlorobisphenol-A was not detected.     

Optimized cleanup method for the determination of short chain polychlorinated n-alkanes in sediments by high resolution gas chromatography/electron capture negative ion-low resolution mass spectrometry

The performances of three adsorbents, i.e. silica gel, neutral and basic alumina, in the separation of short chain polychlorinated n-alkanes (sPCAs) from potential interfering substances such as polychlorinated biphenyls (PCBs) and organochlorine pesticides were evaluated. To increase the cleanup efficiency, a two-step cleanup method using silica gel column and subsequent basic alumina column was developed. All the PCB and organochlorine pesticides could be removed by this cleanup method. The very satisfying cleanup efficiency of sPCAs has been achieved and the recovery in the cleanup method reached 92.7%. The method detection limit (MDL) for sPCAs in sediments was determined to be 14 ng g⁻¹. Relative standard deviation (R.S.D.) of 5.3% was obtained for the mass fraction of sPCAs by analyzing four replicates of a spiked sediment sample. High resolution gas chromatography/electron capture negative ion–low resolution mass spectrometry (HRGC/ECNI–LRMS) was used for sPCAs quantification by monitoring [M−HCl]⁻ ions. When applied to the sediment samples from the mouth of the Daliao River, the optimized cleanup method in conjunction with HRGC/ECNI–LRMS allowed for highly selective identifications for sPCAs. The sPCAs levels in sediment samples are reported to range from 53.6 ng g⁻¹ to 289.3 ng g⁻¹. C₁₀- and C₁₁-PCAs are the dominant residue in most of investigated sediment samples.     

Development of an analytical methodology for the determination of the antiparasitic drug toltrazuril and its two metabolites in surface water,soil and animal manure

This paper presents the development, optimization and validation of a LC–MS/MS methodology to determine the antiparasitic veterinary drug toltrazuril and its two main metabolites, toltrazuril sulfoxide and toltrazuril sulfone, in environmental surface water, soil and animal manure. Using solid phase extraction and selective pressurized liquid extraction with integrated clean-up, the analytical method allows for the determination of these compounds down to 0.06–0.13 ng L⁻¹ in water, 0.01–0.03 ng g⁻¹ dw in soil and 0.22–0.51 ng g⁻¹ dw in manure. The deuterated analog of toltrazuril was used as internal standard, and ensured method accuracy in the range 96–123% for water and 77–110% for soil samples. The developed method can also be applied to simultaneously determine steroid hormones in the solid samples. The antiparasitic drug and its metabolites were found in manure and soil up to 114 and 335 pg g⁻¹ dw, respectively. Little is known regarding the environmental fate and effects of these compounds; consequently more research is urgently needed.     

Photoconductivity of C60‐doping benzocarbazole‐substituted polysiloxanes on an operating wavelength of 633 nm

A novel polysiloxane having benzo[a]carbazole, benzo[a,i]carbazole, and benzo[a,g]carbazole pendant groups has been synthesized and characterized. We studied the electric‐field‐induced xerographic properties, the photogeneration efficiency, and the photoconductivity of C₆₀‐doping polymeric composites at a wavelength of 633 nm. C₆₀‐doping with benzo[a,g]carbazole‐substituted polysiloxane shows a photogeneration efficiency of 56.55 × 10^?5 and a photoconductivity of 52.2 pS/cm at E = 100 V/µm, which was found to be higher than that of the other benzocarbazole‐substituted polysiloxane composites. Copyright © 2009 John Wiley & Sons, Ltd.     

The structure of mimetite,arsenian pyromorphite and hedyphane – A Raman spectroscopic study

The minerals mimetite Pb₅(AsO₄)₃Cl, arsenian pyromorphite Pb₅(PO₄,AsO₄)₃Cl and hedyphane Pb₃Ca₂(AsO₄)₃Cl have been studied by Raman spectroscopy complimented with infrared spectroscopy. Mimetite is characterised by a band at 812–3 cm⁻¹ attributed to the A_g mode. For the arsenian pyromorphite this band is observed at 818 cm⁻¹ and for hedyphane at 819 cm⁻¹. For mimetite and hedyphane bands at 788 and 765 cm⁻¹ are attributed to A_u and E_1u vibrational modes and are both Raman and infrared active. For the arsenian pyromorphite, Raman bands at 917–1014 cm⁻¹ are attributed to phosphate stretching vibrations. Raman spectroscopy clearly identifies bands attributable to isomorphous substitution of arsenate by phosphate. The observation of low intensity bands in the 3200–3550 cm⁻¹ region are assigned to adsorbed water and OH units, thus indicating some replacement of chloride ions with hydroxyl ions.     

An investigation on structure and texture of silica-magnesia xerogels

Silica-magnesia xerogels were prepared by reacting tetraethoxysilane (TEOS) and magnesium chloride (MgCl₂) under acidic conditions. The TEOS/MgCl₂ molar ratio was varied from 1:0 to 0:1. The xerogels were characterized by a set of complementary techniques, namely, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Magnesium contents of silica-magnesia xerogels were between 1.3 and 16.0 wt%. Increasing TEOS/MgCl₂ molar ratio affords higher homogeneity and crystallinity. The presence of low Mg content (<5%) increases specific surface area compared to bare silica. A cubic grain morphology was observed for xerogels with higher Mg content.