Preparation and characterization of poly (N-isopropylacrylamide-co-dimethylaminoethyl methacrylate) microgel latexes

Monodisperse cationic thermosensitive latex microgels have been prepared by radical-initiated precipitation polymerization of N-isopropylacrylamide, methylene bisacrylamide using 2,2′-azobis(2-amidinopropane hydrochloride) as an initiator and dimethylaminoethyl methacrylate (DMAEMA) as a cationic monomer. The final microgel latexes were characterized with respect to water-soluble polymer formation, particle size and size distribution. Adding cationic monomer (DMAEMA) was found to drastically affect the particle size, but not the size distribution as observed both by transmission electron microscopy and quasielastic light scattering (QELS). However, too high a DMAEMA concentration in the feed composition led to enhanced formation of water-soluble polymer. The volume phase-transition temperature of cleaned microgels examined by QELS (particle size versus temperature) was found to be around 32 °C and was slightly dependent on the concentration of the cationic monomer. The volume phase-transition temperature range becomes broader with increasing cationic monomer concentration. In addition, the pH of the polymerization medium was found to affect the final particle size and amount of water-soluble polymer formed. Received: 29 March 2001 Accepted: 2 July 2001     

Crystal structure of tris (phenylammonium) chloride pentachloroantimonate (III) monohydrate

The tris (phenylammonium) chloride pentachloroantimonate (III) monohydrate salt is triclinic with the following cell parameters: a = 9.4283(3), b = 11.4482(3), c = 13.1748(3)Å, = 113.493(2), = 90.381(2), = 97.331(1)°, V = 1290.86(6)ų, with Z = 2 formula units. The structure consists of [C₆H₅NH₃]⁺ cations, water molecules, Cl^– anions, and SbCl₅ square pyramids. Hydrogen bonds, established through water molecule, link the anions [SbCl₅]^2– and Cl^– and make an infinite chain in the [011] direction. Chains are linked together via another hydrogen bond network originating from the ammonium groups. A distortion of the SbCl₅ square pyramid can be attributed to the stereo activity of the Sb(III) lone electron pair.     

Crystal structure of di(N-benzyl piperidinium) pentachloroantimonate(III) dihydrate

The salt di(N-benzyl piperidinium) pentachloroantimonate(III) dihydrate crystallizes in the orthorhombic system with space group Cmc2₁, the unit cell dimensions are: a = 29.383(1), b = 10.509(2), c = 9.941(1) Å, with Z = 8. The structure shows a layer arrangement perpendicular to the a axis: planes of SbCl₆ octahedra alternate with planes of [C₁₂H₁₇N]⁺ cations. The SbCl₆ octahedra are connected through a O(W)–HCl hydrogen bonds and a chlorine bridge, so that infinite unidimensional chains of composition [SbCl₅(H₂O)₂]^2n– _n are formed in the structure along the c direction. These chains are connected to [C₁₂H₁₇N]⁺ entities by N–HCl and N–HO(W) hydrogen bonds, forming a three-dimensional network. It was found that lengths of Sb–Cl bonds may differ from each other. The differences shown as a distortion of the SbCl₆ octahedra were attributed to the Sb(III) lone electron pair stereoactivity.     

Infinitesimal bendings of high orders for homogeneous surfaces with positive curvature and a flat point

For any given n∈Z⁺ and k∈Z⁺, infinitesimal bendings of order n and of class Ck are constructed for a class of surfaces in R³. These surfaces are given as graphs of homogeneous polynomials P(x,y) and they have positive curvature except at the origin.     

A Random Multivalued Uniform Boundedness Principle

We present a generalization of the Uniform Boundedness Principle valid for random multivalued linear operators, i.e., multivalued linear operators taking values in the space L₀(,Y) of random variables defined on a probability space with values in the Banach space Y. Namely, for a family of such operators that are continuous with positive probability, if the family is pointwise bounded with probability at least >0, then the operators are uniformly bounded with a probability that in each case can be estimated in terms of and the index of continuity of the operator. To achieve this result, we develop the fundamental theory of multivalued linear operators on general topological vector spaces. In particular, we exhibit versions of the Closed Graph Theorem, the Open Mapping Theorem, and the Uniform Boundedness Principle for multivalued operators between F-spaces.Mathematics Subject Classifications (2000) 46A16, 46A30, 47A06, 47B80, 60H25.     

pH‐Sensitive methacrylic acid–methyl methacrylate copolymer Eudragit L100 and dimethylaminoethyl methacrylate,butyl methacrylate,and methyl methacrylate tri‐copolymer Eudragit E100

Poly (methyl methacrylate) derivatives such as Eudragit are largely used for drug encapsulation and in controlled oral drug delivery. With special focusing on those applications, solubilization and precipitation conditions of two pH‐sensitive Eudragit polymers, namely, L100 and E100, were investigated via systematic studies. Effects of various physicochemical parameters such as pH, polymer concentration, salinity, buffer concentration, and incubation time on the solubilization and precipitation of these polymers were investigated. In addition, pH titration of both polymers was reported. Considering both macroscopic and quantitative aspects such as the final mean particle size, size distribution, morphology, and the zeta potential, it was established that the different precited parameters could not be dissociated and exert a synergic action on the solubilization and precipitation of both polymers. Titration curves revealed two equivalences that helped estimating carboxylic content of Eudragit L100 (6 mmol/g) and ammonium content of Eudragit E100 (4 mmol/g). In this study, the solubilization and the precipitation domains were for the first time clearly established by considering the above‐mentioned parameters. Moreover, it was found that Eudragit L100 and E100 cannot be considered as classic polyelectrolytes; in fact, solubilization and precipitation domains were not affected by ionic strength.     

Experimental and theoretical study on the regioselective bis- and polyalkylation of 2-mercaptonicotinonitrile and 2-mercaptopyrimidine-5-carbonitrile derivatives

The synthetic utility of 2-mercaptonicotinonitriles 3 and 4, as well as 2-mercapto-4-oxo-6-phenyl-1,4-dihydropyrimidine-5-carbonitrile 20 as building blocks for novel bis- and poly(pyridines), along with poly(pyrimidines) via alkylation with the corresponding bis- and poy(halo) compounds was investigated. Spectroscopic and theoretical studies confirmed the S-alkylation rather than the N-alkylation.     

Reassignment of the structures of condensation products of α-keto α′-formylarylhydrazones with ethyl cyanoacetate: a novel route to ethyl 5-arylazo-2-hydroxynicotinates

The condensation of α-keto α′-formylarylhydrazones with ethyl cyanoacetate afforded ethyl 5-arylazo-2-hydroxy-6-aryl (or alkyl) nicotinates. The structures of the reaction products could be established based on X-ray crystal structure determination.     

Textural,structural and catalytic properties of zirconia doped by heteropolytungstic acid: a comparative study between aerogel and xerogel catalysts

Zirconia doped by heteropolytungstic acid HPW have been synthesized by sol–gel method using two drying techniques of the solvent evacuation. Samples were analyzed with adsorption–desorption of N₂ at 77 K, and the aerogel catalyst was found to exhibit a higher surface area and a higher average pore diameter compared to xerogel. XRD results show that aerogel develops ZrO₂ tetragonal phase, whereas xerogel is amorphous. The thermal analysis studies show that the aerogel’s thermal stability is better than the xerogel one. The catalytic behavior of the aerogel and xerogel toward the nature of the isomerization products probably depends on the acidity and the presence of carbide species. This has been explained by XPS and isopropanol dehydration reaction. In fact, the deconvolution aerogel’s Cls bands reveals the presence of four carbon species assigned to C–C, C=O, C–O and carbide species.