Poly(N-ethylmethacrylamide) thermally-sensitive microgel latexes: effect of the nature of the crosslinker on the polymerization kinetics and physicochemical properties

Thermally-sensitive crosslinked submicronic particles were prepared by an emulsion/precipitation process of N-ethylmethacrylamide (NEMAM), using potassium persulphate as initiator and four different crosslinkers; ethylene glycol dimethacrylate (EGDMA), 1,3-butanediol dimethacrylate (1,3-BDDMA), 1,4-butanediol dimethacrylate (1,4-BDDMA) and tetraethylene glycol dimethacrylate (TEGDMA). At first, polymerization kinetics was studied by NMR, revealing the negligible effect of the crosslinker nature. On the contrary, the water-soluble polymer amounts, the final hydrodynamic particle size, the swelling ability, the electrokinetic properties were found to be dependent upon the nature of crosslinker. The final latexes were found to be narrowly size distributed irrespective of the crosslinker agent’s chemical nature. In this study, the water solubility of the cross-linker was reported to be an important criterion, but other factors, such as diffusion and reactivity, have to be taken into consideration. To cite this article: P. Hazot et al., C. R. Chimie 6 (2003).     

Submerged microcontact printing (SmuCP): an unconventional printing technique of thiols using high aspect ratio, elastomeric stamps

A technique for microcontact printing of thiols in liquid media is presented. Elastomeric poly(dimethyl siloxane) stamps are used to pattern gold surfaces with thiol-based self-assembled monolayers. The liquid (water in this case) has been used as an incompressible support and, advantageously, also acts as a medium in which alkylthiol ink molecules are poorly miscible. Consequently, we have been able to produce patterned thiol monolayers using stamps with aspect ratios unsuitable for conventional microcontact printing (i.e., 15:1) and present evidence to suggest that it is possible to use stamps with aspect ratios of up to 100:1.     

Preparation and characterization of carboxylic-containing poly(methyl methacrylate) nanolatexes

Poly(methyl methacrylate) (PMMA)-based latex particles bearing carboxylic groups at the surface were prepared via emulsion polymerization. The polymerization recipe and process were optimized in order to target monodisperse particles with diameters around 100 nm. The polymerizations were performed using 4,4-azobis(4-cyanopentanoic) acid (ACPA) as initiator and sodium dodecyl sulphate (SDS) as surfactant. The polymerization conversion was determined by both gas chromatography and gravimetry. The final latexes were characterized with respect to particle size, size distribution, surface charge density, electrokinetic properties (i.e. electrophoretic mobility vs pH and ionic strength) and colloidal stability (i.e. coagulation rate constants vs pH and stability factor vs ionic strength).     

catalytic activity of comgal, coal and mgal of mixed oxides derived from hydrotalcites in the selective catalytic reduction of no with ammonia

Summary Calcined CoMgAl LDHs and a Co-impregnated LDH were characterized by XRD, N₂ physisorption, TPR and ICP elemental analysis, then tested in the selective catalytic reduction (SCR) of NO with ammonia. Cobalt deposited by impregnation on LDH leads to the more active and selective catalyst. On this type of catalyst nearly 80% of conversion and selectivity to N₂ were reached at 578 K with a volume space velocity of 2200 h^-1.     

Analysis of the fusariotoxins zearalenone and vomitoxin (deoxynivalenol) in human foods and animal feeds by high-performance liquid chromatography (HPLC)

Summary HPLC procedures for analyses of the fusariotoxins zearalenone and vomitoxin in individual food- and feedstuffs as well as in mixed feed are described. Zearalenone is separated on a column with polar stationary phase (25 cm × 4.6 mm i.d., particle size 7 m), eluted with a chloroform-isooctane (75/25, v/v)+1.5% methanol mixture and detected fluorometrically. The quantitative determination was possible in all analyzed samples with a detection limit of 2g/kg with 70–80% recovery. Vomitoxin is fractionated by HPLC (C ₁₈ ¹ column, 25 cm×4 mm i.d., 5 m particle size) with water-methanol (60/40, v/v) mobile phase and determined by combining GLC or TLC with UV detection. The detection limit in mixed feed with interfering substances was 25 g/kg (recovery 25–35%). The separation by HPLC makes preparation of pure vomitoxin possible. The described methods are fast, simple and low cost and are suitable for routine analyses.     

Comparative study of the textural and structural properties of the aerogel and xerogel sulphated zirconia

Aerogel and xerogel sulphated zirconia with defined atomic ratio S/Zr = 0.5 and molar hydrolysis ratio h = nH₂O/nZrO₂ = 3 show different textural and structural properties after calcination at high temperatures. The aerogel obtained just after solvent evacuation develops only the tetragonal phase, whereas the xerogel dried in an oven is amorphous. Heating to a temperature above 833 K, leads to transition of the tetragonal phase to the monoclinic one for the two solids, due to sulphur loss but the tetragonal phase remains stable for the aerogel . Raman, Infrared and XPS spectroscopies show that the loss of the sulphur at high temperatures seems to be easier for the xerogel than for the aerogel.     

The effect of acrylic acid amount on the colloidal properties of polystyrene latex

Poly(styrene-co-acrylic acid) (St/AA) latices were prepared by using a batch soap-free emulsion copolymerisation in non-buffered medium. Polymerisation kinetics, followed by gravimetric method, revealed that increasing AA comonomer concentration was directly proportional to the copolymerisation rate, while adding AA comonomer caused a strong decrease of particle size of final St/AA latex particle without affecting the size distribution. Transmission electron microscopy indicated that the particles were monodispersed and spherical in shape irrespective of AA amount used in the investigated range. The colloidal stability of the latices was increased upon increasing the AA concentration; owing to the electrosteric stabilisation originated from AA-rich layer on the particle surface. In addition, electrophoretic mobility of formed particles versus polymerisation conversion exhibited the constancy of the surface charge density during the polymerisation process and was inferred for discussion of the polymerisation mechanism of this system.     

Synthesis and reactions of N-Aryl-C-arylsulfonylformohydrazidoyl bromides

Bromination of 1-arylsulfonyl-1,2-propanedione-1-aryl-hydrazones 7 in a mixture of acetic acid and acetic anhydride in the presence of sodium acetate gave N-aryl-C-arylsulfonylformohydrazidoyl bromides 5. Treatment of 5 with dibenzoylmethane, acetylacetone, ethyl acetoacetate and ethyl benzoylacetate in ethanol in the presence of sodium ethoxide yielded the pyrazole derivatives 8-11 , respectively. Reaction of 5 with potassium thiocyanate afforded the thiadiazoline derivative 14. The bromides 5 also react with nucleophiles such as morpholine, piperidine, phenoxide, thiophenoxide and benzenesulfinate anions to give the corresponding substitution products 19-23 , respectively. The structures of the products 8-23 were assigned and confirmed on the basis of their spectral and elemental analyses, their chemical behaviour and alternate synthesis wherever possible.     

Surface modification of polystyrene latex particles via atom transfer radical polymerization

The atom transfer radical polymerization (ATRP) technique using the copper halide/ N,N′,N′,N″,N″‐pentamethyldiethylenetriamine complex was applied to the graft polymerization of methyl methacrylate and methyl acrylate on the uniform polystyrene (PS) seed particles and formed novel core‐shell particles. The core was submicron crosslinked PS particles that were prepared via emulsifier‐free emulsion polymerization. The crosslinked PS particles obtained were transferred into the organic phase (tetrahydrofuran), and surface modification using the chloromethylation method was performed. Then, the modified seed PS particles were used to initiate ATRP to prepare a controlled poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) shell. The final core‐shell particles were characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, thermogravimetric analysis, and elementary analysis. The grafting polymerization was conducted successfully on the surface of modified crosslinked PS particles, and the shell thickness and weight ratio (PMMA and PMA) of the particles were calculated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 892–900, 2002; DOI 10.1002/pola.10160     

Characterization of hydrotreated Cu-ZSM-5 catalyst for the selective catalytic reduction of NO by n-decane

The steam treatment of Cu-ZSM-5 prepared by solid ion exchange involves an important decrease of the NO conversion. Characterization of the solids by NO-TPD, H₂-TPR, ²⁷Al MAS NMR shows that the catalyst deactivation is mainly due to change in copper species rather than the collapse of the zeolite framework.This revised version was published online in December 2005 with corrections to the Cover Date.