bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electric field‐induced instabilities in nematic and cholesteric polyesters
Authors: Corazza Paola , Sartirana Maria Luisa , Valenti Barbara 
Published: April 2003

AbstractElectric field‐induced instabilities are investigated in the thermotropic mesophases of polyesters synthesized from 4,4′‐isopropenylenediphenol and adipic acid (polyester 1) or adipic acid and (+)‐3‐methyladipic acid (50:50) (copolyester 2). D. C. and low frequency A. C. voltages are applied. Polyester 1 behaves like a conductive nematogen with negative dielectric anisotropy. The Williams domain pattern and the dynamic scattering mode are observed; at about 5 kHz the existence of a cut‐off frequency is foreseen. According to the behavior of low molecular weight cholesterics, copolyester 2 goes from a predominantly planar texture to a focal conic one when the electric field is applied parallel to the helical axis of the planar texture. Periodic perturbations arise in polyester 1 doped with cholesteric copolyester 2 when the field is applied perpendicular to a cholesteric planar texture with oily streaks. The frequency dependence of the threshold voltage Vt for square grid is reported. As in nematic polyester 1 at about 5–10 kHz Vt appears to diverge. The behavior above Vt is in line with the results reported for low molecular weight nematic‐cholesteric mixtures with εa < 0. The square grid pattern is replaced by the tilted polygonal texture which relaxes when the field is turned‐off. Due to the higher viscosity of the polymer the recovery of the planar texture is slower than in the case of conventional mesogens.
Dependence of the long period of nylon 6 on annealing time
Authors: Hirami Matsuo 
Published: April 2003

AbstractChanges in the thickness L of lamellar crystals with annealing time on heat treatment at 200–215°C for an unoriented film (I) and a drawn yarn (II) of nylon 6 are studied by small angle X‐ray diffraction (SAXD). For sample I, both the spacing (i.e. the thickness L) and the intensity of the diffraction peak in a SAXD diagram increase abruptly within ca. 1 min, and then remain constant, while for sample II, they continue to increase slowly over a wide range of annealing time (≈ 100 h). The features found for sample I are discussed in terms of chain translational mechanisms in comparison with other polymers such as polyethylene and poly(ethylene terephthalate). From the features found for sample II, the effect of the initial orientation of the polymer on the thickening behavior of lamellar crystals is estimated. It is concluded that the restriction of molecular chain movement results in the retarded thickening behavior during the annealing process.
The molecular structure of diphenylmethyl methacrylate
Authors: Kageyama Hiroyuki , Miki Kunio , Tanaka Nobuo , Kasai Nobutami , Okamoto Yoshio , Hatada Koichi , Yuki Heimei 
Published: April 2003

AbstractThe molecular structure of diphenylmethyl methacrylate has been determined by means of X‐ray diffraction. Crystals are monoclinic, space group C2/c, a = 29, 177 (2), b = 6,017(1), c = 16,110(1) Å, β = 96,840(5)°, and Z = 8. The structure was solved by the direct method and refined by the block‐diagonal least‐squares procedure to R = 0,071 (Rw = 0,091) for 1768 measured reflections. The molecule has an antiperiplanar conformation as to the CC and CO double bonds about the C(1)C(2) bond and a synperiplanar conformation as to the CO and CO bonds about C(1)O(1).
Télomères monofonctionnels du chlorure de vinyle, 3. Cinétique par catalyse rédox
Authors: Boutevin Bernard , Piétrasanta Yves , Taha Mohamed 
Published: April 2003

AbstractA kinetic study of the redox telomerization of vinyl chloride with carbon tetrachloride was carried out. Transfer constants of PVC to the metallic ion (CFen), initiation rate (ki), and functionnality of the resulting telomers were measured. Instantaneous and cumulated polymerization degrees, (DPn)i and (DPn)cum were determined with the help of a theoretical study. These constants provide a rigorous control of the telomerization of vinyl chloride with RCCl3, (R containing an alcohol or ester group).
Correlation of data on preferential sorption using the modified flory‐huggins equation
Authors: Pouchlý Julius , Živný Antonín 
Published: April 2003

AbstractAn equation derived from the Flory‐Huggins relation with the concentration‐dependent interaction parameters gij and the ternary parameter gT was used in the correlation of reported data on the preferential sorption in macromolecular coils. A linear plot was suggested, assuming that the dependence of gT on the composition of the mixed solvent resembles that of g12, i.e. gT(u1) = ag g12(u1). Linear correlation could be carried out in 19 ternary systems out of 22, and the correlation constants were used to calculate the difference of interaction parameters g13 − (V1/V2)g23 and the proportionality constant ag. For most systems, ag is positive and smaller than unity; for systems containing chloroform it approaches zero. The difference between the interaction parameters gij and the interaction parameters χij is discussed. A comparison between the difference g13−(V1/V2)g23 obtained by a linear correlation of data on preferential sorption with the values calculated using data on the respective binary systems was possible only for the system benzene/cyclohexane/polystyrene; the fit was very good. It is shown how the individual parameters of the Flory‐Huggins equation affect the occurrence, position and type of inversion in preferential sorption.
On the principle of equal reactivity in solution polycondensation
Authors: Kuchanov S. I. , Keshtov M. L. , Halatur P. G. , Vasnev V. A. , Vinogradova S. V. , Korshak V. V. 
Published: April 2003

AbstractThe influence of the degree of polymerization of oligomers (1 ≤ l ≤ 50) on the reactivity of the OH endgroups is exemplified by the reaction of oligoterephthalates of phenolphthalein with benzoyl chloride under ϑ‐conditions. It is found that with increasing chain length l the hydroxyl group activity increases according to an S‐form law. It is suggested that the ester groups of the macromolecule influence the activity of the OH endgroups due to solvation effects. This suggestion is confirmed theoretically and experimentally.
Zur polymerisation von methylmethacrylat bis zu hohen umsätzen: Experimentelle untersuchungen zur theorie des trommsdorff‐effektes nach cardenas und o'driscoll
Authors: Panke Dietrich , Stickler Manfred , Wunderlich Winfried 
Published: April 2003

AbstractThe kinetic model given by Cardenas and O'Driscoll, which describes the bulk polymerization of methyl methacrylate (MMA) in the region of the gel effect by the concept of chain entanglements, is extended to the region of the glass effect in accordance with a proposition made by Marten and Hamielec based on the free volume theory. Equations for the calculation of the instantaneous and cumulative molecular weight distributions are derived, too. Dilatometric measurements over the entire conversion range were performed at various temperatures and with three different initiators. For each series of measurements the three adjustable parameters of the extended model were fitted to the time‐conversion data. Contrary to the assumptions, it was then found that at least one of the parameters of the model of Cardenas and O'Driscoll (α0) depends both on the concentration and the type of the initiator. The calculated molecular weight distributions are much broader than the experimental ones. Thus the model of Cardenas and O'Driscoll at its present state does not seem to describe adequately the real polymerization behavior of MMA.
Synthèse de polysiloxanes organofonctionnels, 1. Chloration des poly(diméthylsiloxane)s par le chlorure de sulfuryle
Authors: Reyx Danièle , Guillaume Pierre 
Published: April 2003

AbstractSulfuryl chloride was used as chlorination agent of poly(dimethylsiloxane)s (1) in order to obtain poly(dimethylsiloxane‐co‐chloromethylmethylsiloxane) and it was found to be more specific than molecular chlorine. Identification of chlorinated and chlorosulfonated units was shown to be possible by comparison of the results of 1H NMR spectroscopy with those obtained by GLC analysis of the mixtures obtained from octamethylcyclotetrasiloxane (2). After having shown that the distribution of the various types of methyl groups in 1 and 2, modified in this way, fits correctly a binomial law and that chlorosulfonated units can be hydrolysed, copolymers containing 20 to 25% of chloromethylated units and less than 2% of unwanted dichloromethylated units are accessible by use of this chlorination agent.
Fixation sur cellulose de médicaments libérables par voie enzymatique
Authors: Lapicque Françoise , Dellacherie Edith 
Published: April 2003

AbstractAs an approach to the programmed release of drugs a polymeric carrier (1) from which the drug would be liberated by the degradation of definite covalent chemical bonds by means of specific enzymes, was synthesized by coupling pholcodine (2), an antitussive drug, with an insoluble, physiologically inert polymer, cellulose, using L‐phenylalanine as a spacer arm. As chemical bond between drug and amino acid an ester function was chosen linking the hydroxyl group of 2 and the carboxylic end of L‐phenylalanine. This linkage is not hydrolyzed in simulated digestive fluids containing pepsin or trypsin; it is only broken in the presence of α‐chymotrypsin to release slowly the parent drug.
New polymer syntheses, 7. Synthesis and characterization of oligomeric and high molecular weight poly(4‐hydroxybenzoate)
Authors: Kricheldorf Hans R. , Schwarz Gert 
Published: April 2003

AbstractPoly(4‐hydroxybenzoate) was prepared under a variety of reaction conditions. In addition to using the well‐known monomers 4‐acetoxybenzoic acid and phenyl 4‐hydroxybenzoate, p‐tolyl 4‐hydroxybenzoate, 4‐pivaloyloxybenzoic acid, and 4‐trimethylsiloxybenzoyl chloride were also condensed. A new routine method for the determination of number average molecular weights (M̄n) was developed, namely 1H NMR spectroscopic end‐groups analysis of hydrolyzed poly‐(4‐hydroxybenzoate). By means of this technique, the relationships between monomer structure or reaction conditions, on the one hand, and the polymerization mechanism and polymer properties (e.g. M̄n), on the other hand, were investigated. Whereas bulk condensations yield molecular weights of less than 10 000, polycondensations in solution may lead to values in the range of 20000 – 50000. The best results with respect to both yield and M̄n were obtained with 4‐acetoxybenzoic acid and 4‐trimethylsiloxybenzoyl chloride. Regardless of the nature of the monomer, condensations in solution lead at first to precipitation of oligomer crystals with D̄P̄'s in the range of 6–8. Due to intra‐ and intercrystalline transesterifications, chain growth continues in these oligomer crystals even in the absence of monomer or solvent. New reaction mechanisms are discussed. Depending on the nature of the monomer and the reaction conditions, poly(4‐hydroxybenzoate) can adopt various crystal modifications. The thermal stability depends on both the degree of polymerization and crystal modifications.
Synthèse de cotélomères photoréticulables, 6. Utilisation de cotélomères biséquencés
Authors: Boutevin Bernard , Maliszewicz Marc 
Published: April 2003

AbstractPhotocrosslinkable block cotelomers were synthesized in three steps. In the first step a monomer M1 was telomerized with carbon tetrachloride or chloroform, in the second step a monomer M2 with the resulting macrotelogen, and in the third step the hydroxyl groups were esterified by cinnamic acid or acrylic acid. These reactions were carried out with ethyl acrylate (M1)/CCl4 by redox catalysis and subsequently with vinyl acetate (M2) by free radical initiation, or with vinyl acetate (M1)/CHCl3 by free radical initiation and subsequently with isoprene (M2) by redox catalysis, or with 2‐hydroxyethyl acrylate (M1)/CCl4 by redox catalysis, and subsequently with isoprene (M2) by redox catalysis.
Determination of absolute rate constants for radical polymerization and copolymerization of ethyl α‐cyanoacrylate in the presence of effective inhibitors against anionic polymerization
Authors: Yamada Bunichiro , Yoshioka Minoru , Otsu Takayuki 
Published: April 2003

AbstractThe absolute rate constants of propagation kp and of termination kt of ethyl α‐cyanoacrylate (ECNA) were determined in bulk at 30°C by means of the rotating sector method under conditions to suppress anionic polymerization; kp = 1 622 1 · mol−1 · s−1 and kt = 4,11 · 108 1 · mol−1 · s−1 for the polymerization in the presence of acetic acid, and kp = 1610 1 · mol−1 · s−1 and kt = 4,04 · 108 l · mol−1 · s−1 for the polymerization in the presence of 1,3‐propanesultone. The magnitude of k/kt determined was 6,39 · 10−3 l · mol−1 · s−1. The absolute rate constants for cross‐propagation in ECNA copolymerizations were also evaluated. Quantitative comparison of the rate constants with those of common monomers and polymer radicals shows that the strong electron‐withdrawing power of the ethoxycarbonyl and cyano groups enable the poly(ECNA) radical to add to monomers as fast as the other polymer radicals. The relatively high reactivity of ECNA, regardless of the type of attacking polymer radical, is interpreted by a transition state greatly stabilized by both the ethoxycarbonyl and the cyano groups.
On the trifluoracetylation reaction of polyamides and polyurethanes
Authors: Biagini Emilio , Gattiglia Ercole , Pedemonte Enrico , Russo Saverio 
Published: April 2003

AbstractThe kinetics and yields of N‐trifluoracetylation of polyamides, polyesteramides, polyurethanes were studied by direct titration of trifluoracetic acid formed during the conversion. For polycaprolactam a limiting yield, corresponding to a complete substitution, was always achieved, independently of polymer molecular mass. The functionalization was equally effective on ultra high molecular masses or “gels”, as well as on low molecular mass compounds (monomer and higher oligomers), making possible their fast detection in any polycaprolactam sample. As the reaction starts and proceeds for most of its time in the heterogeneous phase, the substitution rate was found to be strongly dependent on the size of polymer particles. Extension of the above reaction to polyurethanes revealed that they react much slower than aliphatic polyamides, showing relevant differences in the behaviour of aromatic and aliphatic moieties.
On the thermal mobility of the amino end groups of polyamides 6 and 6,6
Authors: Schmitz Franz P. , Mroszewski Klaus‐Dieter , Rossbach Volker 
Published: April 2003

AbstractSamples of polyamides 6 and 6,6 were reacted with the bifunctional reagent 1,5‐difluoro2,4‐dinitrobenzene at different temperatures in heterogeneous phase (swelling agents: 1,4‐dioxane/water and acetone/water). From the yields determined experimentally for the mono‐and bifunctional reaction of the reagent with the amino end groups of the polyamides the activation energies for the motion of the amino end groups were determined. The values are 30 to 67 kj/mol for the system acetone/water and 15 to 22 kj/mol for the system 1,4‐dioxane/water. Additionally, for both reaction media calculations were made to determine relative values of the temperatures at which the amino end groups are beginning to move.
Conformational analysis of polyoxyethylene using empirical force field methods
Authors: Miyasaka Taira , Yoshida Takaichi , Imamura Yoshio 
Published: April 2003

AbstractConformanational energies of various oligo (oxyethylene) isomers were calculated by the empirical force field method, and statistical mechanics calculations of the chain dimensions and the dipole moments were carried out. The results are seriously different from those obtained for poly (oxymethylene). Although the first‐order steric interactions in POE are of the same order of magnitude as those in n‐alkane chains, the second‐order interactions are significantly different. The second‐order interactions arising from rotations around two consecutive bonds of OCH2CH2OCH2 in g± g∓ conformation have greatly reduced steric repulsions. It was found that the reduced second‐order interaction plays an important role in the configurationdependent properties of POE. The agreement of the calculated values for the unperturbed dimensions and the temperature coefficients obtained from the force field method with experimentally observed ones is fairly good.
Interpenetration of spherulites in polymer blends
Authors: Gałȩski Andrzej , Grȩbowicz Janusz , Kryszewski Marian 
Published: April 2003

AbstractWhen poly(oxymethylene) is doped with increasing amounts of low molecular weight poly(oxyethylene), a stepwise disappearance of the boundaries between the spherulites is observed. At a poly(oxyethylene) content of 5 wt.‐%, the replica of a bulk sample viewed in an electron microscope seems to have only centers of spherulites and slightly marked boundaries between them. A more careful examination of the replica shows that this effect is due to strong interpenetration of the lamellae of the adjacent spherulities of poly(oxymethylene). It is well known that the mechanical properties of many two‐component systems are improved by adding small amounts of a second component. On the basis of our observations it is possible to correlate the interpenetration of spherulites with the improvement of some mechanical properties of bulk samples. Interpenetration is possible when two “hollow” dendritic spherulites are brought into contact. Such a change of the spherulite structure by an additive is due to a rejection of the additive into interlamellar regions.
Structure and hydrodynamic properties of poly[styrene‐b‐(ethene‐co‐butene)‐b‐styrene] micelles in 1,4‐dioxane
Authors: Tuzar Zdeněk , Pleštil Josef , Koňák Čestmír , Hlavatá Drahomíra , Sikora A. 
Published: April 2003

AbstractThree‐block copolymers poly[styrene‐b‐(ethene‐co‐butene)‐b‐styrene], where the middle aliphatic block amounts to about 70 wt.‐%, form micelles in 1,4‐dioxane with an aliphatic core and a polystyrene shell. The basic characteristics concerning the ratio unimer/micelles, the micellar molar mass, the radius of gyration, and the hydrodynamic radius were determined by combining the results of light scattering, small‐angle X‐ray scattering, photon correlation spectroscopy, osmometry, and viscometry. The characteristics of the micelles, approximated by the model of concentric spheres, were calculated from the data of light scattering and small‐angle X‐ray scattering. From a comparison of the geometric and hydrodynamic dimensions of the micelles it follows that in dilute solutions they behave like rigid spheres.
Kinetics of ϵ‐caprolactone polymerization and formation of cyclic oligomers
Authors: Sosnowski Stanisław , Słomkowski Stanisław , Penczek Stanisław , Reibel Leonard 
Published: April 2003

AbstractThe kinetics of the anionic polymerization of ϵ‐caprolactone, including the kinetics of macrocyclization and the kinetics of macrocycles propagation in THF solution, initiated with (CH3)3SiONa, were investigated. Rate constants of propagation (kp(n)) and of back‐biting (kd(n)) involving monomer and cyclic oligomers (macrocycles) with n = 2, 3, … monomeric units were determined for n ≤ 7. It was found that starting from the tetramer kd(n) ∼ n−1,4±0,1 and kp(n) ∼ n0,7±0,15 (in Jacobson‐Stockmayer's theory kp(n) ∼ n). This discrepancy is explained in terms of “conformational hindrance”, increasing for small cycles with the increase of the ring size until a certain ring size is reached. This hindrance decreases the availability of some of the ester groups in the macrocyclics for attack of the growing species, lowering in this way the exponent in the dependence of kp(n) on n from one to a lower value.
Elementary reactions in the cationic polymerization of oxepane. Comparison with the polymerization of tetrahydromfuran
Authors: Baran Teresa , Brzezińska Krystyna , Matyjaszewski Krzysztof , Penczek Stanisław 
Published: April 2003

AbstractIn the polymerization of oxepane (OXP), initiated with derivatives of trifluoromethanesulfonic acid, covalent and ionic active centers were simultaneously observed by 1H and 19F NMR spectroscopy. A higher proportion of secondary oxonium ions (these species detected by 19F NMR were independently observed by proton trapping with R3P in the 31P NMR spectrum). The proportion of ionic species decreases with monomer conversion, indicating a substantial contribution of bimolecular ionization of the monomer. The effective molarity in oxepane polymerization [OXP]eff ⋍ 1 mol ·I‐1 was found to be lower by a factor of 102 than [THF]eff in the polymerization of THF. The rate constant of the covalent propagation in the polymerization of OXP is similar to that measured for THF, however, due to the reduced reactivity of the oxepanium cation, the relative reactivity of the covalent active centers becomes higher than that of the ions. Thus, for OXP, in CH3NO2 at 25°C, Kpc = 3 · 10−4 mol−1 · 1 · s−1, kpi = 2 · 10−4 mol−1 · 1 · s−1 whereas for THF kpc = 5 · 10−4 mol−1 · 1 · s−1 and kpi = 2 · 10−2 mol−1 · 1 · s−1 under similar conditions. The rates of ionization and temporary termination, measured by the “temperature jump” technique, allow to determine the contributions of inter‐and intramolecular ionizations. These rates becomes equal at [OXP] = 1 mol · 1‐1 (= [OXP]eff).
Robust matrix 𝒟U‐stability analysis
Authors: Bachelier O. , Mehdi D. 
Published: April 2003

AbstractIn this paper, the problem of robust matrix root‐clustering is addressed. The studied matrices are subject to both polytopic and unstructured uncertainties. An original point is the large choice of clustering regions enabled by the proposed approach since these regions can be unions of possibly disjoint and non‐symmetric subregions of the complex plane. The precise purpose is, considering a specified polytope, to determine the greatest robustness bound on the unstructured uncertainty such that robust matrix root‐clustering is ensured. To reduce conservatism in the derivation of the bound, the reasoning relies on a framework based upon parameter‐dependent Lyapunov functions. The bound value is computed by solving an ℒ︁ ℳ︁ ℐ problem. Copyright © 2003 John Wiley & Sons, Ltd.
Is vaginal dermoid cyst a rare occurrence or a misnomer? A case report and review of the literature
Authors: Siu S.‐S. N. , Tam W.‐H. , To K.‐F. , Yuen P.‐M. 
Published: April 2003

AbstractVaginal dermoid cyst is a rare finding. Preoperative diagnosis of this lesion is difficult as the sonographic features are similar to those of an epidermal inclusion cyst. We report a case of vaginal dermoid cyst and present its sonographic characteristics. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.