bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamics and high‐pressure viscosity of dilute solutions of poly(decyl methacrylate) and how the free volume influences them
Authors: Schott Nicole , Will Bernhard , Wolf B. A. 
Published: April 2003

AbstractLight scattering and viscometric measurements were performed for the system isooctane/poly(decyl methacrylate) of weight‐average molecular weight M̄w = 250 000 within the concentration regime of pair interaction between the macromolecules in the temperature range from 25°C to 100°C. In case of the intrinsic viscosities [η], the pressure was varied up to 3500 bar. Under isobaric conditions, the osmotic second virial coefficients A2, the z‐average radii of gyration rz and [η] pass through a maximum, the Huggins coefficient kH through a minimum, with variation of temperature. These extrema indicate a change in the heat of dilution from endothermal at low, to exothermal at high temperature T. The calculation of the temperature dependence of the intrinsic viscosity [η] (T) for isochoric conditions does not yield a maximum, provided the pressure at the lowest temperature is chosen close to atmospheric pressure; it can, therefore, be concluded that the change in the sign of the enthalpy is in this case only due to the free volume of the system which increases markedly with increasing T. For pressures larger than ≈700 bar, maxima are always observed, no matter whether the temperature is changed isobarically or isochorically. All parameters under investigation are closely interdependent: A one‐to‐one correspondence exists between [η] and A2 at 1 bar, and kH and [η] interrelate linearly for constant T.
An investigation of the self‐aggregation process of syndiotactic poly(methyl methacrylate) in solution by using infrared spectra
Authors: Dybal Jiří , Spěváček Jiří 
Published: April 2003

AbstractThe time dependence of self‐aggregation of syndiotactic (s) poly(methyl methacrylate) (PMMA) in dilute toluene or CCl4 solutions was investigated using infrared (IR) spectra measurements. The IR spectra were also recorded in s‐PMMA solutions where no self‐aggregation takes place (benzene, acetonitrile). It was found that the helix conformation with a large number of units per turn (near‐tt) in aggregated s‐PMMA is formed in parallel with intermolecular interactions of ester groups of s‐sequences. The connection between the fraction of s‐sequences in the helix conformation determined for unaggregated s‐PMMA in various solvents using IR spectra and the ability of s‐PMMA to form self‐aggregates (double helix) in a certain solvent is discussed. Intersegmental contacts which occur in s‐PMMA in CCl4, i.e. in a thermodynamically poor solvent, lead to a decrease in the equilibrium aggregated fraction, to the slowing‐down of the aggregation process and to the decomposition of the majority of aggregated structures during evaporation of the solvent; their effect is similar to that of chemical crosslinking.
Molecular mobility in polystyrene‐poly(methyl vinyl ether) blends as studied by fluorescence polarization
Authors: Halary Jean‐Louis , Larbi Fadhel Ben Cheikh , Oudin Pascal , Monnerie Lucien 
Published: April 2003

AbstractMolecular motions in different blends of polystyrene with poly(methyl vinyl ether) were investigated by fluorescence polarization measurements on small amounts of dimethylanthracene‐labeled polystyrene chains added to the system. The temperature dependence of the mobility parameter of the label was studied within the DSC glass transition and phase coexistence temperature range. Experimental data fit an expression of the WLF type, in which C1 and C2 values are roughly independent of blend composition and differ to a small extent from the ‘universal’ coefficients. Moreover, mobility determinations suggest the existence of composition micro‐heterogeneities in the blends below their phase coexistence temperature Tc when subjected to long annealing around Tc – 25°C or above.
Structural studies on 1,4‐cis‐poly(2‐methyl‐1,3‐pentadiene) synthesized with Nd catalysts
Authors: Cabassi Franco , Porzio William , Ricci Giovanni , Brückner Sergio , Meille Stefano V. , Porri Lido 
Published: April 2003

Abstract(E)‐2‐Methyl‐1,3‐pentadiene was polymerized with the AlEt2Cl‐Nd(OCOC7H15)3‐Al(iBu)3 system to a polymer consisting of 98–99% 1,4‐cis‐structure. The crude polymer was fractionated by successive extractions with boiling diethyl ether, heptane and toluene. Examination of the soluble fractions and of the residue to toluene extraction by NMR, X‐ray and DSC techniques indicated that the crude polymer consists of macromolecules differing in stereoregularity. Evidence is reported that the crystalline residue after the toluene extraction has a 1,4‐cis‐isotactic structure. The existence of two different crystalline phases is shown and the respective cell parameters have been determined. α‐Phase: a = 10,74, b = 13,04, c = 7,87 Å (−120°C), space group Pbca, Z = 8, Dc = 1,00 g · cm−3. β‐phase: a = 9,30, b = 7,73, c = 7,90 Å (25°C), space group P212121Z = 4, Dc = 0,96 g · cm−3.
The structure of one crystalline form of isotactic 1,4‐cis‐poly(2‐methyl‐1,3‐pentadiene). An application of the rietveld method
Authors: Brückner Sergio , Meille Stefano V. , Porzio William , Ricci Giovanni 
Published: April 2003

AbstractCrystalline polymers of (E)‐2‐methyl‐1,3‐pentadiene, consisting almost exclusively of 1,4‐cis units, obtained with the ternarycatalytic system AlEt2Cl‐Nd(OCOC7H15)3‐Al(iBu)3, exhibit two different crystalline forms. In this study, we determine the crystal structure of the form showing the highest melting point (175°C) through X‐ray diffraction data from stretched and unstretched samples. Diffraction data from an unstretched (powder) sample were used to carry out a refinement procedure based on the Rietveld method. The space group is orthorhombic Pbca, the cell constants are a = 10,74, b = 13,04, c = 7,87 Å, and the polymer is isotactic.
Nematic‐nematic immiscibility and induced smectic a phases in mixtures with liquid‐crystalline side‐chain polymers
Authors: Achard Marie‐France , Sigaud Gilles , Keller Patrick , Hardouin Francis 
Published: April 2003

AbstractTwo non‐ideal kinds of behaviour for solutions of liquid‐crystalline side‐chain polymer (LC polymer) solutes in nematic solvents of low molecular weight (LMW) are investigated, viz. immiscibility and induced smectic A phases. The former property already observed in the nematic state of some polysiloxanes is extended to polymethacrylates (or polyacrylates) leading to the conclusion that immiscibility is strongly influenced by the chemical structure of the whole macromolecule. The latter property responds in the same way as the former to molecular modifications, suggesting that they can be connected somehow.
Formation and structural characteristics of loosely crosslinked styrene‐divinylbenzene networks
Authors: Okay Oǧuz 
Published: April 2003

AbstractThe free‐radical copolymerization of styrene with small quantities of a commercial DVB (conc.: 0,35 to 0,53 mol‐% DVB) was carried out at 70°C in bulk or in concentrated toluene solution. The extent of the crosslinking reactions beyond the gel point and the structural characteristics of the resulting networks were examined using equilibrium swelling in toluene and gel fraction measurements. The copolymerization reactions yield loosely crosslinked networks together with varying amounts of soluble polymer. The experimental results concerning the formation of the networks and their properties can be explained using the kinetic mechanism of the copolymerization reaction and neglecting cyclization. At a low degree of initial dilution, two opposing effects of the diluent, namely dilution and plasticizing effects, were found to determine the properties of the networks. Calculations using the theory of rubber elasticity indicate that considerable amounts of free chain ends are present in the networks. The crosslinking efficiency was found to decrease, but the size of the primary chains and that of the network chains increase with increasing degree of initial dilution.
Effect of flexible spacers in liquid crystalline copolyesters containing a non‐linear biphenol moiety
Authors: Zhang Weisheng , Jin Jung‐Il , Lenz Robert W. 
Published: April 2003

AbstractA series of copolyesters 2 containing both linear mesogenic and non‐linear non‐mesogenic aromatic ester units was prepared and characterized for the ability of the latter to either modify or destabilize the liquid‐crystalline (LC) properties of the former. The mesogenic units were formed from the reaction of 1,4‐phenylene diacetate (3) with 4,4′‐decamethylenedioxydibenzoic acid (5), whereas the non‐mesogenic units were formed from reaction of the latter monomer with the diacetate of the non‐linear biphenol, sulfonylbis(1,4′‐phenylene) diacetate (4). The presence of the flexible spacer in each unit allows the copolyesters to form a nematic phase even at a content of non‐mesogenic units as high as approximately 80 mole‐%. Copolyester compositions with mesogenic unit contents approaching this limit for LC behavior appear to form melts which contain both nematic and isotropic phases below the isotropization transitions.
Oxidation of poly(2,2‐dimethyltrimethylene sulfide) in solution
Authors: Lazcano Silvia , Marco Carlos , Fatou José G. , Bello Antonio 
Published: April 2003

AbstractOxidation of poly(2,2‐dimethyltrimethylene sulfide) was carried out in chloroform solution at 25°C using trifluoroacetic acid and hydrogen peroxide. Six samples were obtained with weight fractions of sulfoxide comonomer ranging between 0,11 and 0,58, without any content of sulfone groups. When it is attempted to obtain samples with more than 60% of sulfoxide units, sulfone groups are formed. 1H NMR data show the reaction to take place in a random way. Copolymers exhibit only one glass transition temperature which increases with the number of sulfoxide units, The extrapolated glass transition temperature for the theoretical polysulfoxide corresponds to a value in the range of 261 to 264 K.
Studies on the adsorption of anionic dyes on chitosan
Authors: Maghami Ghobad G. , Roberts George A. F. 
Published: April 2003

AbstractEquilibrium adsorption measurements of three anionic dyes on chitosan, under acid conditions, show that there is a 1 : 1 stoichiometry for the interaction of sulfonic acid groups on the dyes with protonated amine groups of the chitosan for mono‐, di‐ and trisulfonated dyes. Comparison of the extents of N‐acetylation calculated from equilibrium dye adsorption values with those determined by IR spectroscopy, for a series of chitosan samples covering a wide range of N‐acetylation values, demonstrates that equilibrium adsorption measurements may be used for the analysis of chitin and chitosan.
Polymerization by [3 + 2]‐cycloaddition
Authors: Nuyken Oskar , Maier Gerhard , Burger Klaus 
Published: April 2003

AbstractThe reaction of hexafluoroacetone azine (1) with dienes 13a–d was used to synthesize polymers 14a–d of a new type with diazabicylooctanediyl units in the main chain. The influence of the structure of the diolefins on the solubility of these polymers was investigated. The soluble oligomers were characterized thoroughly by 1H NMR, 13C NMR, 19F NMR, IR and MS.
Synthesis and hydrolysis of esters from amylose and nicotinoyl chloride
Authors: Sánchez‐Chaves M. , Arranz F. 
Published: April 2003

AbstractThe modification reaction of amylose with nicotinoyl chloride using pyridine as catalyst was studied. The structure of the resulting polymers was determined by means of IR, 1H and 13C NMR spectroscopy. A linear dependence of the reaction rate on polymer, nicotinoyl chloride and pyridine was found. The activation energy was found to be 32,2 kJ/mol. The hydrolysis in the heterogeneous phase showed that the release of the active compound is dependent upon the hydrophilic character of the modified amylose polymers, the temperature as well as the pH value of the medium.
Influence of the chemical constitution of the polymer backbone on the phase behaviour of liquid‐crystalline side‐chain polymers with side‐on fixed mesogenic groups
Authors: Hessel Friedrich , Finkelmann Heino 
Published: April 2003

AbstractThe synthesis and phase behaviour of liquid‐crystalline acrylates and chloroacrylates with side‐on fixed mesogenic groups are described. Polymers which have similar mesogenic groups but whose polymer backbones differ in chemical constitution exhibit identical liquid‐crystalline to isotropic phase transformation temperatures (Tc). The glass transition temperature (Tg) decreases with increasing flexibility of the main chain and with increasing length of the terminal groups of the mesogenic side groups. All polymers with side‐on fixed mesogenic groups exhibit a nematic phase. The domain texture indicates biaxial nematic phase behaviour. In copolymers consisting of mesogenic and non‐mesogenic monomers, nematic phase behaviour is still observed, Tc is strongly depressed, and Tg is similar to that of the non‐mesogenic homopolymer.
Copolymers obtained by means of anionic ring‐opening polymerization. Poly(2,2‐dimethyltrimethylene carbonate‐tapered‐ϵ‐caprolactone)
Authors: Keul Helmut , Höcker Hartwig , Leitz Edgar , Ott Karl‐Heinz , Morbitzer Leo 
Published: April 2003

AbstractThe anionic ring‐opening polymerization of mixtures of 2,2‐dimethyltrimethylene carbonate and ϵ‐caprolactone in toluene as solvent, with sec‐butyllithium or potassium dihydronaphthylide as initiator, results in the formation of polymers of the (A‐X‐B)n type, where A represents a poly(2,2‐dimethyltrimethylene carbonate) block, B represents a poly(ϵ‐caprolactone) block and X stands for a block of the two monomers with a composition gradient; n represents the number of portions by which the monomer mixture is added to the initiator or the living system. From the time‐conversion curves it follows that the reactivity of the carbonate monomer is higher than that of the lactone. This difference in reactivity of the monomers is the reason for the special polymer architecture represented by (A‐X‐B)n. The properties of these polymers depend upon the ratio of the monomers and the number n of additions. The polymers are characterized by spectroscopic, thermoanalytical, and thermomechanical measurements.
A new method for monitoring ultra‐fast photopolymerizations by real‐time infra‐red (RTIR) spectroscopy
Authors: Decker Christian , Moussa Khalil 
Published: April 2003

AbstractAn original method based on IR spectroscopy has been developed in order to follow real‐time photopolymerizations that take place in less than one second. Conversion versus time curves were directly recorded for various multiacrylic monomers irradiated in condensed phase, thus allowing an immediate evaluation of both the rate of polymerization and the amount of residual unsaturation in the UV‐cured polymer. This method proved well suited to study the effect on the polymerization rate of the photoinitiator efficiency, the monomer reactivity, the light intensity, the film thickness, and the O2 inhibition. The dark polymerization that develops just after the UV exposure was investigated as a function of the degree of conversion and was shown to represent up to 60% of the total process. A comparison with other methods of kinetic analysis shows the unique advantages of real‐time infra‐red (RTIR) spectroscopy which permits to follow quantitatively and in situ ultra‐fast polymerizations.
Amphiphilic properties of synthetic glycolipids based on amide linkages, 3. Temperature and concentration dependence of the reduced viscosity of gel‐forming alkyl gluconamides
Authors: Pfannemüller Beate , Kühn Ilse 
Published: April 2003

AbstractIn order to follow the process of aggregation, viscosity measurements in dilute aqueous solution were performed with two carbohydrate amphiphiles: (i) N‐octylgluconamide (C8‐GA) and (ii) N‐decanoyl‐N‐methylglucamide (C10‐MGA). Both compounds ten to form a gel on cooling, the former at 65°C, the latter at 10°C. Electron micrographs have shown that the gels are composed of a loose network of thin, regularly twisted helical ropes. By viscosity measurements over a wide range of temperatures and concentrations, typical changes of the reduced viscosity were observed. Results are discussed with respect to the critical micelle concentration (CMC), the Krafft point, i. e. the critical temperature of crystallization (Tc), and the cloud point (Tcp). It is concluded that micellar aggregation to rod‐shaped particles, quasi‐crystalline aggregation to highly hydrated gels, and crystallization of monomers, the latter mediated by hydrogen bonding, are involved and compete with each other.
13C NMR study of the microstructure of poly(styrene oxide)s prepared with anionic initiators
Authors: Sepulchre Maurice , Kassamaly Asmina , Moreau Michel , Spassky Nicolas 
Published: April 2003

AbstractThe tacticity and the nature of irregularities and end‐groups in poly(styrene oxide) samples prepared using potassium alcoholates and anionic coordinated systems as initiators were studied by 13C NMR at 62,89 MHz. It was found that the polymerization initiated with potassium alcoholates fits a first‐order Markov propagation model. Head‐to‐head (HH) and tail‐to‐tail (T‐T) irregularities are detected in all the samples studied, but more than 95% of the opening of the oxirane ring occurs in the β‐position with potassium alcoholates as initiators while about 10% of α‐scission may be observed with coordinated systems. Secondary hydroxyl terminal groups and initiator moieties are identified in polymers prepared with potassium alcoholates. Poly(styrene oxide) was found to undergo chain‐scission by aging at 25°C. Among the various structures produced by the oxidative degradation process, benzoate and secondary hydroxyl groups are identified.
Direct method of synthesis of polyureas by N‐acylphosphoramidites
Authors: Rokicki Gabriel 
Published: April 2003

AbstractPolyureas and polythioureas were prepared under mild conditions by direct polycondensation of carbon dioxide and carbon disulfide, respectively, with diamines in the presence of diethyl N‐acetyl‐N‐methylphosphoramidite or its analogs containing an active PN bond. The influence of the substituents in the phosphoramidite, of the CO2 pressure, solvent, organic base and diamine structure on the yield and inherent viscosity of the polymer was investigated. A reaction mechanism involving the intermediate formation of a mixed anhydride of dialkylphosphorous and alkyl(aryl)carbamic acid is discussed.
Etude de la diaddition de l'acétate d'allyle sur les télogènes chlorofluorés possédant deux groupements CCl3 en extrémité de chaîne
Authors: Améduri Bruno , Boutevin Bernard , Lecrom Christophe , Pietrasanta Yves , Parsy Roland 
Published: April 2003

AbstractThe redox catalyzed addition of compounds such as Cl3CCF2CCl3 and Cl3CCF2CCl2CH2CHClCH2OCOCH3 to allyl acetate was studied with the purpose of obtaining telechelic products. RuCl2[P(C6H5)3]3 was used as catalyst, and its action was compared to that of cooper‐ or iron‐based catalysts. The products were isolated and their structures studied by means of 13C, 19F and 1H NMR spectroscopy. The reaction mechanism was studied to improve the yield of the diaddition product for its utilisation as monomer in polycondensation reactions. It was found that the low reactivity for a second addition is not due to the presence of a chlorine atom in β‐position of the acetate function. When allyl acetate was replaced by allyl bromide or chloride in the first addition, the second addition to allyl acetate occurred normally.
A λ5‐cylotriphosphazene with nitroxyl groups as model for a paramagnetic poly(organo‐λ5‐phosphazene)
Authors: Dulog Lothar , Möhler Hans 
Published: April 2003

AbstractReaction of hexachlorocyclotriphosphazene (syst. name: 2,2,4,4,6,6‐hexachloro‐1,3,5,2λ5,4λ5,6λ5‐triazatriphosphorine) (1) with 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl (2a) gave the hexa‐substituted λ5‐cyclotriphosphazene 3a. Electron paramagnetic resonance spectra at low concentrations (10−5 mol/L) showed a singlet only (no triplet) due to spin‐spin exchange in the molecule. The paramagnetic molar susceptibility amounts to 7229 · 10−6 cm3/mol at 300 K and does not depend on the magnetic field strength. 3a obeyed the Curie‐Weiss law between 36 and 296 K demonstrating that there is no antiferromagnetic spin exchange.
X‐ray diffraction study on the phase behaviour of a liquid‐crystalline side‐group polymethacrylate with biphenylyl mesogen moieties
Authors: Zugenmaier Peter , Menzel Henning 
Published: April 2003

AbstractX‐ray investigations at different temperatures of a polymethacrylate 1 with biphenylyl moieties as side‐group mesogens reveal structural changes at 100°C for a quenched sample of the polymer which cannot be detected by differential scanning calorimetry (DSC). A low‐order smectic phase exists between 136 and 157°C, and an isotropic phase above 157°C. The side groups are much shorter than the observed thickness of the smectic layers. Models are discussed which can account for these spacings. The phase sequence for normally cooled and at 120°C annealed samples is represented by crystalline or higher‐order smectic, low‐order smectic, isotropic. Different structures in the solid state are detected for the two differently prepared samples.
Interfacial synthesis of group IVB metalorganic polymers
Authors: Shen Hongkang , Wei Rongbao , Liang Ya , Lin Lin , Liu Meizhu , Xue Qifeng 
Published: April 2003

AbstractAlkyl, alkenyl, and alkoxy substituted dicyclopentadienyltitanium (or zirconium) dichlorides were condensed with diacids, hydroxyacids or diphenols to give metal containing polyesters, poly(ether‐ester)s, and polyethers, most of them being new. Experimental parameters were investigated, including stirring rate, reaction time, reaction temperature, steric hindrance, ratio of reactants, and reactivity of the reactants. Determinations of color‐change temperatures, solubilities and molecular weights were carried out as well as TG, DTG and IR spectroscopy of the resulting polymers.
Photoinitiators and photoinitiation, 9 Photoinitiators for radical polymerization which counter oxygen‐inhibition
Authors: Hageman Hendrik J. , Jansen Leonardus G. J. 
Published: April 2003

Abstract1‐Alkanesulfonic and 4‐alkylbenzenesulfonic esters of α‐hydroxymethylbenzoin were shown to photoinitiate the polymerization and crosslinking of acrylates. The overall rate of polymerization in bulk and of crosslinking in solution, respectively, proved to be constant within each series of homologues. However, in thin films in an air atmosphere, the overall rate of crosslinking (curing rate) proved to increase with increasing alkyl chain‐length within each series of homologues. Moreover, the curing rate obtained with the 1‐hexanesulfonic ester and its higher homologues substantially surpassed the curing rates obtained with a number of established photoinitiators, provided a small amount of an alkali metal salt (preferably a lithium salt) is present. The curing mechanism of the sulfonic esters of α‐hydroxymethylbenzoin and the role of the alkali metal salt are explained.
Extremely highly isospecific polymerization of olefins using solvay‐type TiCl3 and Cp2TiMe2 as catalyst
Authors: Soga Kazuo , Yanagihara Hisayoshi 
Published: April 2003

AbstractPolymerizations of various olefins (ethylene, propene, 1‐butene, 4‐methyl‐1‐pentene,1‐hexene, and 1‐octene) were carried out using the Solvay‐type TiCl3 catalyst combined with Cp2TiMe2. The polymers produced were characterized by DSC, solvent fractionation, GPC, and 13C NMR. It was found that the present catalyst gives linear polyethylene without ethyl branches and extremely highly isotactic poly(α‐olefins) containing very few steric defects. The catalyst seems to be most isospecific among the Ziegler‐Natta catalysts reported so far.