bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chiral liquid‐crystalline polymers. XI. Thermotropic behavior and chiroptical properties in solution of a new series of optically active poly (ester β‐sulfide)s
Authors: Chiellini E. , Galli G. , Angeloni A. S. , Laus M. 
Published: April 2003

AbstractThe synthesis and characterization are described of a series of optically active semiflexible poly(ester β‐sulfide)s 6*Sn with repeating units constituted by two p‐oxybenzoyl diads spaced in an alternating fashion by a sulfide‐containing polymethylene segment of variable length (n = 2‐10) and a chiral (R)‐3‐methylhexanediyl segment of high enantiomeric purity. The polymers were prepared with good yields and relatively high molecular weights and narrow degrees of dispersity by a Michael‐type polyaddition reaction of bis‐thiols to the same chiral mesogenic bisacrylate monomer. Data are reported on the characterization of their chiroptical properties in dilute solution and thermal‐optical properties in the bulk, with attention being devoted to the distinct odd‐even alternations of the cholesteric‐isotropic melt transition parameters. A comparison of the mesomorphic behavior and relevant thermodynamic quantities is presented between the present series of polymers and the achiral analogues of series 6Sn as well as the chiral, positional isomers of series mS6*. The dependence of the overall properties and their trends on very subtle structural changes is stressed, thus highlighting the critical interconnection between mesogenic cores and spacer segments in semiflexible liquid‐crystalline polyesters.
Salt catalyzed heterogeneous dilute acid hydrolysis of the difficultly accessible portion of cellulose: Effect of nature of metal co‐ion
Authors: Zaranyika Mark F. , Moses Peter , Mavunganidze Taimos 
Published: April 2003

AbstractThe effect of nature of metal co‐ion on the rate of hydrolysis, Vc, of the difficulty accessible portion of cellulose was investigated for Li+, Na+, K+, and Ca2+. For the univalent ions Vc decreases exponentially with an increase in ionic radius for a given concentration of co‐ion. For Ca2+, Vc is lower than would be predicted on the basis of ionic radius. This is attributed to the increased charge and/or increased degree of hydration. For the univalent ions the data presented suggest Vc increases sharply with concentration up to 0.25M, while for Ca2+, Vc increases more gradually up to 2.25M, before Vc begins to drop.
Ethylene polymerization catalysts from supported organotransition metal complexes. II. Chromium alkyls
Authors: Smith P. D. , Mcdaniel M. P. 
Published: April 2003

AbstractAnother class of organochromium compounds, beta‐stabilized chromium alkyls, has been synthesized and tested for catalytic activity in ethylene polymerization. Although not active alone, these compounds do exhibit remarkable activity when reacted with a partially dehydroxylated high surface area carrier. The best supports seem to be fluorided alumina or the aluminophosphates, depending on the particular chromium alkyl being tested. The worst was always silica. Both divalent and tetravalent chromium alkyls were tested and found to have high catalytic activity. Comparisons of activity and polymer structure were made between these compounds and previously studied organochromium compounds with pi‐bonded ligands.
Effects of coordinately unsaturated cobalt complexes on radical polymerization of vinyl monomers
Authors: Bhanu V. A. , Kishore K. 
Published: April 2003

AbstractThe tetrahedral cobalt(II) complexes A‐D are found to possess an unusual coordinately unsaturated nature. These additives significantly inhibit the thermal polymerization of acrylamide and further, they impart significant induction period during AIBN initiated polymerization of MMA and acrylamide. Some evidence has been obtained to show that the additives' effect plausibly results because of the reaction of the coordinately unsaturated cobalt complexes with radicals present in the system.
Radiation‐Induced degradation of polyethylene: Polymer structure and stability
Authors: Torikai Ayako , Geetha Ramarathnam , Nagaya Shigeo , Fueki Kenji 
Published: April 2003

AbstractThe radiation‐stability of annealed and quenched polyethylene (PE) was estimated by gel, FTIR, and mechanical property (elongation at break) measurements. Although both types of PE showed an equal probability in gel and carbonyl formation, the resistance to γ‐ray irradiation as probed by elongation at break (%) was superior in quenched PE compared to annealed PE. This difference is discussed from the viewpoint of polymer structure, especially the number of the tie molecules, of annealed and quenched PE.
Mechanism of photostabilization of polystyrene film by dihydroxyphenyl‐pirazoles
Authors: Sastre R. , Catalina F. , Mateo J. L. , Claramunt R. , Santa‐Maria M. D. , Catalán J. 
Published: April 2003

AbstractA new family of ultraviolet absorbers, the dihydroxyphenyl‐pyrazoles, has shown to be able to act as photostabilizers of polymers. In the present work the efficiency of the derivative 2,5 bis(pyrazol‐1′‐yl)‐1,4‐dihydroxybenzene (BPHB) in preventing the photooxidative degradation of polystyrene films have been measured. The effect of light screening on polymer photostabilization was examined by using external filter solutions of BPHB and it was found that it does not function simply as a light screener. Phosphorescence quenching experiments show that BPHB behaves also as an efficient triplet‐state quencher of the polymer in‐chain carbonyl impurity groups, which play an important part in the overall mechanism of light stabilization.
Preparation and radical ring‐opening polymerization of exo‐methylene substituted cyclic ketene acetals
Authors: Yokozawa Tsutomu , Hayashi Ryoji , Endo Takeshi 
Published: April 2003

AbstractPreparation and radical ring‐opening polymerization of the exo‐methylene substituted cyclic ketene acetals, 2,4‐dimethylene‐1,3‐dioxolane (I) and 2,5‐dimethylene‐1,3‐dioxane (II), were carried out. Ketene acetals I and II were prepared by dehydrohalogenation of the corresponding cyclic haloacetal with potassium tert‐butoxide in tetrahydrofuran at –78°C and ambient temperature, respectively. I underwent radical polymerization with essentially quantitative ring‐opening with di‐tert‐butyl peroxide in dimethylformamide at 120°C. On the other hand, II underwent both ring‐opening polymerization and vinyl polymerization under the same conditions of the polymerization of I. The differences of polymerization behavior between I and II were also discussed.
Epoxidation of styrene–butadiene–styrene block copolymer and use for gas permeation
Authors: Hsiue Ging‐Ho , Yang Jen‐Ming 
Published: April 2003

AbstractThe epoxidation of styrene–butadiene–styrene triblock copolymer (SBS) by an in situ generated peracid method is discussed. The presence of an acid acting as catalyst led to side reaction. The reactivities of internal double bonds (the 1, 4‐structure) were higher than those of the vinyl bonds (the 1, 2‐structure). In the 1, 4‐structure, the reactivities of cis‐structure were higher than those of trans‐structure. The oxirane weight content and total oxygen weight content were determined by titration and element analysis, respectively. The cohesive energy, solubility parameter, and the glass transition temperature of epoxidized SBS increased with increasing total oxygen weight content. But the molecular weight between crosslinking points decreased resulting in an increase of crosslinking density with increasing total oxygen weight content. The changes of properties of epoxidized SBS reduced the gas permeability of oxygen and nitrogen through epoxidized SBS membrane, but increased the gas selectivity between oxygen and nitrogen. When the operating temperature of gas permeation was increased, the permeability of oxygen and nitrogen increased but the selectivity decreased. For epoxidized SBS containing 7.35 wt % oxygen content, the activation energy was 9 and 12.2 kcal/mol for oxygen and nitrogen, respectively.
Electron spin resonance studies of plasma‐induced polystyrene radicals
Authors: Kuzuya Masayuki , Noguchi Akihiro , Ito Hideki , Kondo Shin‐Ichi , Noda Nahoko 
Published: April 2003

AbstractPlasma‐induced polystyrene radicals were first studied by electron spin resonance (ESR). The room temperature ESR spectrum was compared with those obtained by γ‐irradiation, UV‐irradiation, and mechanical fracture. It was found that even less than a few seconds of plasma‐irradiation gave rise to a large amount of polystyrene radicals and the ESR spectrum consisted of two types of spectra, a triplet and a single broad line. The spectral feature of the triplet was nearly identical with that of γ‐irradiated polystyrene. Thus, it was assigned to the structure of a cyclohexadienyl‐type radical formed by a nearly random addition of a hydrogen atom to the aromatic ring. The single broad line, thought to be an outline of multicomponent spectrum, was assigned to an immobilized dangling‐bond sites at the plasma‐induced crosslinked portion of the polystyrene surface.
Influence of allyl ethers on free radical polymerization of styrene
Authors: Johansson Mats , Hult Anders 
Published: April 2003

AbstractThe effect of allyl ethers on the free radical polymerization of styrene has been studied with respect to chain transfer, copolymerization, and conversion. The studies have been performed in an inert atmosphere or in air. Six different allyl ethers have been used as model substances in order to show the effect of structural differences of the ethers on the polymerization. Contrary to what was expected, no chain transfer through hydrogen abstraction was found. Nor did any copolymerization occur. When the polymerization was performed in air, the allyl ethers had a retarding effect on the polymerization rate, due to oxidation of the allyl ethers. The oxidation rate of the allyl ethers was found to be related to their structure, where the functionality and presence of intramolecular hydrogen bonding are the main factors.
Synthesis and characterization of aromatic polyamides from 1,1‐bis(4‐aminophenyl)‐2,2‐diphenylethylene and aromatic diacid chlorides
Authors: Xie Mei‐Li , Oishi Yoshiyuki , Kakimoto Masa‐Aki , Imai Yoshio 
Published: April 2003

AbstractNovel, soluble aromatic polyamides and copolyamides containing tetraphenylethylene units were prepared by the low temperature solution polycondensation of 1,1‐bis(4‐aminophenyl)‐2,2‐diphenylethylene and aromatic diamines with various aromatic diacid chlorides. Highmolecular‐weight polyamides having inherent viscosities of 0.6–1.5 dL/g and number‐average molecular weight above 21000 were obtained quantitatively. These polymers were readily soluble in various solvents such as N‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide (DMAc), and dimethyl sulfoxide and gave pale yellow, transparent, flexible films by casting from DMAc solution. The polymers had glass transition temperatures between 290 and 340°C, and started to lose weight around 400°C, with 10% weight loss being recorded at about 470°C in air.
Phase transfer catalyzed polymerization of 4‐bromo‐2,6‐dimethylphenol in the presence of either 2,4,6‐trimethylphenol or 4‐tert‐butyl‐2,6‐dimethylphenol
Authors: Percec Virgil , Wang James H. 
Published: April 2003

AbstractThe synthesis of poly(2,6‐dimethyl‐1,4‐phenylene oxide) with one 2,6‐dimethylphenol chain end (PPO–OH) and with well‐defined molecular weight by phase transfer catalyzed polymerization of 4‐bromo‐2,6‐dimethylphenol (20) in the presence of either 2,4,6‐trimethylphenol (1) or 4‐t‐butyl‐2,6‐dimethylphenol (1′) as chain initiators is described. The range of controllable molecular weights and the mechanism of molecular weight control are discussed based on the differences between the reactivities of 20, 1, and 1′ and of the corresponding reactive species. The PPO–OH synthesized from 20/1′ has structural units derived from 1′ attached only at the chain end. PPO–OH synthesized from 20/1 contains structural units derived from 1 both internally and at the chain ends. Structural units derived from side reactions were identified by 1H‐NMR spectroscopy. A reaction mechanism is proposed to account for their formation.
Complexing effect in the reaction of graft polymerization proceeding by the coordination‐radical mechanism with the participation of copper ions
Authors: Smirnova N. V. , Gabrielyan G. A. , Gal'braikh L. S. 
Published: April 2003

AbstractA new phenomenon in graft polymerization has been investigated: the complexing of growing radicals with copper ions. Graft polymerization of methacrylic acid to polycaproamide, initiated by the reversible K2S2O8–Na2S2O3 redox system in the presence of copper ions, is used as an illustration to show that the complexing of growing radicals with copper ions significantly enhances their activity. The concepts of the graft polymerization mechanism have been formulated.
Estimation of reactivity ratios using emulsion copolymerization data
Authors: De La Cal José C. , Leiza José R. , Asua José M. 
Published: April 2003

AbstractAn approach for the estimation of reactivity ratios using cumulative copolymer composition–overall conversion data obtained in batch emulsion copolymerization is presented. The approach is based on an algorithm for parameter estimation in ordinary differential equations and takes into account the partition of the comonomers between the different phases present in the system. Both copolymer composition and conversion were considered to be affected by experimental errors. The method was first checked by using simulated data that included random errors. The effect of the initial guess and level of errors on the values of the estimated reactivity ratios was investigated. Once the approach was checked, it was used to estimate the reactivity ratios of the styrene–acrylonitrile system based on data obtained in unseeded batch emulsion copolymerizations of these monomers.
On some regularities of grafting of vinylpyridine derivatives onto acetyle cellulose
Authors: Mateva Roza , Nikolov Krasimir 
Published: April 2003

AbstractThe radical graft copolymerization of vinylpyridine derivatives onto acetyl cellulose was investigated using Fe2+/H2O2 redox system as an initiator. It was proved that the addition of hydrazine hydrate increased the degree of grafting many times. The reaction mechanism of hydrazine hydrate was also investigated. A. correlation between nitrogen content and the total anion exchange capacity was established. The vinylpyridine derivatives were ordered according to their reactivity. The effects of reaction conditions on the total anion‐exchange capacity, the total conversion, the degree of grafting, and the grafting efficiency of the copolymers obtained were examined. The copolymers were characterized by IR and H‐NMR spectra, thermogravimetric analysis, elemental analysis, and total anion‐exchange capacity.
Synthesis and properties of polyethersulphone–polydimethyisiloxane block copolymers
Authors: Collyer A. A. , Clegg D. W. , Morris M. , Parker D. G. , Wheatley G. W. , Corfield G. C. 
Published: April 2003

AbstractHigh molecular weight alternating block copolymers of polyethesulphone (PES) and polydimethylsiloxane (PDMS) were prepared by the condensation of dimethylamino‐terminated PDMS oligomers and hydroxy‐terminated PES oligomers in 1,2‐dichlorobenzene. Microphase separation of the block copolymers at exceptionally short block lengths was observed by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The SiOC intersegment linkage in these materials appeared to display poor hydrolytic stability which is contrary to results obtained for other block copolymers.
Photochemical synthesis of nitroxyl free radicals in the presence of vinyl monomers
Authors: Van Den Broeck Hilde , Schmitz‐Smets Maria , Smets Georges 
Published: April 2003

AbstractThe photochemical formation of an inhibitor in the presence of monomers and a photoinitiator offers the possibility of producing positive two‐step photoresists. As inhibitor precursor sterically hindred amines have been used in the presence of air oxygen and Rose Bengal as oxidation photosensitizer. On irradiation with visible light (546 nm). stable nitroxyle radicals are formed, which act as strong inhibitors of free radical polymerization. Hexanediol diacrylate and 2‐acryloxy‐2′‐propionyl oxydiethylether were used as monomers. The photoinitiator required for the second step polymerization is benzoin isopropyl ether, which photolyzes on irradiation at 340 n,. The quantum yield of nitroxyl radical formation has been determined in solution and in polymeric films. Polymerization inhibition experiments were carried out with methyl methacrylate in solution and with neat monomers. Though the quantum yield ΦNO° is low, especially in the last case, the experiments confirm the possibilities of this two‐step procedure.
Reactions in aminosilane–epoxy prepolymer systems I. Kinetics of epoxy–amine reactions
Authors: Serier Aicha , Pascault Jean Pierre , My Lam Thanh 
Published: April 2003

AbstractThe reactions of an epoxy prepolymer based on bisphenol A diglycidylether (DGEBA) with γ‐aminopropyltriethoxysilane (γ‐APS) are studied. The results of different techniques are compared: size exclusion chromatography, differential scanning calorimetry, chemical titration, and Fourier Transform Infrared absorption. Epoxy amine reactions are shown to be faster than the crosslinking reactions between alkoxysilane and hydroxy groups, and thus, can be studied seprately. The reactivity of the epoxy group in DGEBA is compared with that of phenylglycidylether (PGE). And the reactivity of the amine group of γ‐APS is compared with that of hexylamine. The kinetic constants are calculated with a mechanism which takes into account both the catalytic and noncatalytic reactions. The ratior=k2/k1of the reactivity of the secondary to the primary amino‐hydrogens was also determined. The values ofrare 1.4 for hexylamine and 1.2 for γ‐APS. The reactivity of the epoxy groups are the same for both PGE and DGEBA.
Electronitiated polymerization of maleic anhydride by direct electron transfer
Authors: Akbulut Ural , Hacioǧlu Bi̇lge 
Published: April 2003

AbstractControlled potential electrolysis was employed to accomplish homopolymerization of maleic anhydride, by direct electron transfer. The solvent used in the polymerization studies was acetonitrile–dimethylformamide mixture (1 : 1) with the supporting electrolyte tetrabutylammonium tetra fluroborate, A brown paramagnetic polymer was obtained from the catholyte, upon electroreduction of monomer.
Polypyrrole/dodecylsulfate: Effects of different synthesis conditions
Authors: Peres Rosa C. D. , Pernaut J. M. , De Paoli Marco‐A. 
Published: April 2003

AbstractWe have studied in detail the effects of synthesis conditions, such as current density and sodium dodecylsulfate electrolyte concentration, on the electrical and mechanical properties of polypyrrole. Flexible and self‐supported films were electrochemically obtained using an aqueous solution containing pyrrole and sodium dodecylsulfate. The conductivity (2–20 S/cm) of the films increases with increases in either the current density or the electrolyte concentration. This behavior is caused by the structural changes induced by the different kinetics of film formation. Result indicate that the dodecylsulfate anion, incorporated as dopant in the polymer, randers it flexible with tensile strength in the order of MPa.
A facile synthesis for functional perfluoropolyether oligomers, diacids, diesters, and surfactants
Authors: Persico Daniel F. , Lagow Richard J. 
Published: April 2003

AbstractLinear polyester precursors provide a convenient low cost synthesis for flurocarbon surfactants, diacids, diesters, and intermediates. A reaction scheme starting with hydrocarbon linear polysters followed by conversion of the ester to a perfluoro ester by direct fluorination and subsequent treatment with nonstoichiometric amount of sulfur tetrafluoride produce upon hydrolysis of ester units remaining in the polymer, low molecular weight perfluropolyether diacids. Alternatively, this technique can be altered slightly to produce diesters and other functional perfluorocarbon intermediates.
Insoluble polystyrenes containing amide moieties and N‐alkylated nylon‐66 as phase transfer catalysts
Authors: Kondo Shuji , Inagaki Yasuhito , Yasui Haruhiko , Iwasaki Masaki , Tsuda Kazuichi 
Published: April 2003

AbstractInsoluble polystrenes containing formamide and acetamide moieties were prepared by free radical terpolymerization of the corresponding vinyl monomers, styrene, and divinylbenzene. These polymers served as phase transfer catalysts for the reaction of n‐octyl bromide with potassium thiocyanate in toluene–water system. The activity of these catalysts was affected by some factors such as stirring speed particle size, and degree of crosslinking. The activity also depended strongly on the structure of active site, copolymer composition, and spacer length which cause the difference in the adsorption of potassium ion and in the microenvironment around the active site. Furthermore, nylon‐66 was found to display the activity for phase transfer reactions, and the activity was remarkably increased by replacing the amide hydrogen with an alkyl group.
Synthesis and characterization of thiocarbonohydrazone‐based epoxy resins
Authors: Thangamathesvaran P. M. , Jain Sampat R. 
Published: April 2003

AbstractNovel epoxy resins of various thiocarbonohydrazones have been synthesized by reacting the aldehyde or ketone derivatives of thiocarbohydrazide with excess of epichlorohydrin. The resins have been characterized by elemental analyses, epoxy equivalents, 1H‐NMR and IR spectra, thermal analyses, and viscosity measurements. Curing of the resins has been carried out by mixing with thiocarbohydrazide or ethylenediamine and heating at 80°C for 48 h. A comparison of the thermal stability of the cured resin samples has been made.
Immobilization of catalase on membranes of poly(ethylene)‐g‐co‐acrylic acid and poly(tetrafluoroethylene)‐g‐co‐acrylic acid and their application in hydrogen peroxide electrochemical sensors
Authors: Da Silva M. Alves , Gil M. Helena , Piedade A. P. , Redinha J. S. , Brett A. M. Oliveira , Costa J. M. Caridade 
Published: April 2003

AbstractThe immobilization of catalase on grafted membranes of poly(ethylene)‐g‐co‐acrylic acid and poly(tetrafluoroethylene)‐g‐co‐acrylic acid and their application in hydrogen peroxide electrochemical sensors is described. The introduction of carboxylic acid groups onto a hydrophobic support provides a good environment for subsequent enzyme immobilization. This single membrane, hydrogen peroxide sensor showed significant improvement with respect to the double membrane versions. The response is very rapid, the linear range being from 10 μM up to 6 mM, with a detection limit of 4.7 μM, and a lifetime of more than 4 months.
Immobilization of glucose oxidase on nylon membranes and its application in a flow‐through glucose reactor
Authors: Da Silva M. Alves , Gil M. Helena , Redinha J. S. , Brett Ana M. Oliveira , Pereira J. L. Costa 
Published: April 2003

AbstractThe immobilization of glucose oxidase on hydrolyzed nylon‐6,6 was studied. Various spacers were introduced on the support before the coupling of the enzyme. Best results were obtained when the membrane was covered with denatured bovine serum albumin (BSA) before spacer coupling and immobilization of glucose oxidase (GOD). The influence of various factors (pH, ionic strength, etc.) on the activity of the free and immobilized enzyme was investigated. It was found that the behavior of the fixed glucose oxidase and the free enzyme is very similar. The covalently immobilized enzyme had a lifetime of around 2 months (50% of initial activity).