bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methyl rotation of pendant trimethyl moieties in polymethacrylates
Authors: Zhan Yongjian , Jin Xigao , Qian Renyuan , Cao Qijuan , Meng Qing'an 
Published: April 2003

AbstractThe methyl rotation of a series of polymethacrylates \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} [{\rm CH}_2 \hbox{---} {\rm C}({\rm CH}_3){\rm COOX}({\rm CH}_3)_3 \rlap{--}]_n $\end{document} 1 a – c where XC, Si and Sn, was studied by observing the solid‐state 1H NMR spin‐lattice relaxation. Minima of the spin‐lattice relaxation times for methyl group rotation in the OX(CH3)3 pendant groups, T1, min, were found at 165, 75 and 55 K for polymers 1a (XC), 1b (XSi) and 1c (XSn), respectively, at a resonance frequency of 30 MHz. The data indicate that methyl rotation is less restricted when it is bonded to an atom with larger covalent radius.
Determination of the number of active centers in Ziegler‐Natta polymerization of propene using sulfur‐containing terminating agents 2. Tagging of growing chains during retardation of polymerization by carbon disulfide
Authors: Vozka Pavel , Mejzlík Jiří 
Published: April 2003

AbstractThe CS2‐induced retardation of propene polymerization catalyzed by TiCl3/AiEt2Cl and TiCl3/AlEt3 systems was investigated. From the two systems, the latter was much more active in polymerization and also exceedingly more susceptible to retardation by CS2. At least for the TiCl3/AlEt2Cl‐catalyzed polymerization, there is no diffusion limitation imposed on the reaction of growing chain with CS2. It was found that the number of sulfur tags introduced by the above CS2 treatment is dominantly related to the ratio of polymerization rates before and after CS2 addition. Monomer plays a dual role during the CS2 treatment: on one hand it enhances the CS2 insertion into the growing metal‐polymer bond, on the other hand it competes with CS2 in the same reaction. CS2 reacts preferentially with centers of highest reactivity. It allows, in principle, the determination of the reactivity distribution of active centers. Several potential side reactions which might lead to an increase of the number of tags in polymer were considered. None of the side reactions play an important role except for a reaction of CS2 with chains formed via transfer with the organometal compound in AlEt3‐cocatalyzed polymerization.
Poly(ether/ester)s based on poly(butylene terephthalate) and poly(ethylene glycol), 1. Poly(ether/ester)s with various polyether: polyester ratios
Authors: Fakirov Stoyko , Gogeva Tanya 
Published: April 2003

AbstractA series of poly(ether/ester)s 1 based on poly(butylene terephthalate)Systematic IUPAC nomenclature: poly(oxytetramethyleneoxyterephthaloyl).
and poly(ethylene glycol) is synthesized. 1H and 13C nuclear magnetic resonance, infrared and differential scanning calorimetry (DSC) measurements prove a block structure of the prepared copolymers. The DSC curves suggest the existence of a three‐phase morphology — two amorphous phases for both polyether and polyester segments, and a crystalline phase for the polyester segments. Small angle X‐ray scattering (SAXS) measurements lead to the same conclusion. The degree of crystallinity assigned to the polyester fraction differs insignificantly and is similar to that of the homopolymer. SAXS data show approximately the same long spacing for all crystallizable copolymers. The tensile parameters of the studied polymers are similar to those of available commercial products based on poly(butylene terephthalate) and poly(tetrahydrofuran).
Poly(ether/ester)s based on poly(butylene terephthalate) and poly(ethylene glycol), 2. Effect of polyether segment length
Authors: Fakirov Stoyko , Gogeva Tanya 
Published: April 2003

AbstractStructure‐properties relationships of poly(ether/ester)s (PEEs) 1 based on poly(butylene terephthalate) (PBT) and poly(ethylene glycol) (PEG) are studied. By varying the length of the soft segments (PEG) of molecular weights 600, 1000 and 2000) two series of PEEs are obtained, (i) with constant mole ratio PBT:PEG (the PBT block length being approximately the same) and (ii) with constant weight ratio PBT:PEG (different PBT segment length). The block structure is proved by 1H nuclear magnetic resonance and differential scanning calorimetry studies. A three‐phase morphology is established, i.e. two amorphous phases (polyether and polyester) and a crystalline phase (PBT), each one distinguished by its own transition temperature. At low temperatures (between −60 and 20°C) a fourth phase (crystalline PEG) appears. Small angle X‐ray scattering intensity and long spacing increase abruptly for the compositions with PEG 2000. The mechanical characteristics of the studied PEEs depend on the weight ratio of the two types of blocks.
Fluorinated polyurethanes, 1. Synthesis and characterization of fluorine‐containing segmented poly(urethane‐urea)s
Authors: Takakura Teruo , Kato Masao , Yamabe Masaaki 
Published: April 2003

AbstractTo produce high performance antithrombus elastomers, a series of new fluorine‐containing segmented poly(urethane‐urea)s was synthesized from 2,2,3,3,4,4,5,5‐octafluorohexamethylene diisocyanate (1) and α‐hydro‐ω‐hydroxypoly(oxyalkylene)s (5a, b and 6) or fluorinated dioxa‐1,10‐decanediols (3 and 4) (as the soft segments) via the prepolymers (7) which subsequently were reacted with various diamines including a fluorinated aliphatic diamine (2) as chain‐extenders. High‐molecular‐weight polymers were obtained in high yields with 5a and nonfluorinated diamines. Spectroscopic analysis of the prepolymers and the chain‐extended polymers indicated their structures to be highly ordered. Stress‐strain curves of films cast from a DMF solution indicated the polymers to be typical elastomers with tensile strength as much as 600–700 kg/cm2.
Dielectric relaxation properties of linear polythioethers
Authors: Díaz‐Calleja Ricardo , Riande Evaristo , Guzmán Julio 
Published: April 2003

AbstractValues of the dielectric loss tangent were obtained as a function of temperature for poly(pentamethylene sulfide) (P5MS) and poly(1,3‐dithiocane) (PDTC). Both P5MS and PDTC exhibit a β absorption, located in the vicinity of their respective glass transition temperatures, −105°C and −73°C, which is believed to be associated with micro‐Brownian motions in the amorphous phase of the crystalline polymers. The glass‐rubber transitions of the polymers are discussed in terms of the flexibility of the chains, as expressed by their conformational partition functions and entropies.
Ion aggregation in magnesium‐neutralized polyester resins — Small angle X‐ray scattering study
Authors: Habassi Chefik , Brigodiot Maryvonne , Fradet Alain , Williams Claudine E. 
Published: April 2003

AbstractEvidence for ion aggregation was found in SAXS studies of models of unsaturated polyester resins: magnesium icosanoate, magnesium α,ω‐dicarboxylatopoly(ethylene adipate), ‐poly(1‐hexylethylene adipate), ‐poly(propylene succinate), and ‐poly(propylene maleate‐co‐fumarate), swollen by various solvents or in the dry state. The results were compared with those obtained for commercial unsaturated polyester resins after neutralization with MgO, leading to the conclusion that the formation of aggregates is the key phenomenon of the so‐called thickening reaction of polyester resins. The existence of high amounts of branched units in the polyester chain does not appear to hinder ion aggregation. The aggregates are small (Guinier radius RG = 4 to 9 Å) and their average distance increases with chain length and swelling.
Quelques avantages de la polymérisation induite par un plasma froid microonde
Authors: Poncin‐Epaillard Fabienne , Brosse Jean‐Claude 
Published: April 2003

AbstractPlasma induced polymerizations using an RF (13,56 MHz) or a microwave (433 MHz) generator were compared. The microwave plasma induced polymerization of a multifunctional acrylate (3‐ylomethylpentamethylene triacrylate) (trimethylolpropane triacrylate) (1) was studied as a function of different macroscopic parameters (chemical nature of gas, time, discharge power, distance between the surfatron and the substrate etc.). The involved mechanisms were found to be similar to those in the RF plasma. One of the advantages of the microwave apparatus is the possibility of working in the post‐discharge regime with selected reactive species. Evidence of the chemical structure of the polymer at its surface is given by ATR‐FTIR spectroscopy.
Amphiphilic block copolymers as phase transfer agents in toluene‐water two‐phase systems
Authors: Berlinova Iliyana V. 
Published: April 2003

AbstractAmphiphilic block and star‐shaped copolymers based on polystyrene and poly(ethylene oxide) were used as phase transfer catalysts in the reaction of aqueous potassium iodide with 1‐bromooctane in toluene. The effects of composition and molecular architecture on observed reaction rates were examined. At constant copolymer composition, reaction rates increased with decrease of molecular weight of the copolymer. The catalytic activity of the amphiphilic block copolymers was correlated with their ability to extract potassium picrate from water into toluene. The results are discussed on the basis of the concept of one ion, one ligand transport.
Presence of fragmentation products in the cationic oligomerization of 1‐butene
Authors: Priola Aldo , Audisio Guido 
Published: April 2003

AbstractIn the cationic oligomerization of 1‐butene in the presence of BF3‐proton donor complexes a mixture of hydrocarbons was obtained. By means of GC‐MS analysis, beside the peaks corresponding to (C4)n products, the presence of significant amounts of products with different carbon atom numbers was revealed, indicating that fragmentation processes are operative in these systems. Moreover, in the different oligomer fractions, saturated and unsaturated hydrocarbons were found. Experiments of propene oligomerization, performed under similar conditions, yield a lower amount of fragmentation products and almost exclusively unsaturated products. Possible reaction mechanisms are presented.
Copolymerization of styrene and methyl α‐cyanocinnamate, 1. Synthesis, NMR‐assignment, reactivity ratios
Authors: Bednarski Ralf , Braun Dietrich , Borbély János , Kelen Tibor 
Published: April 2003

AbstractThe free‐radical copolymerization of styrene and methyl α‐cyanocinnamate was studied. The copolymers were investigated by means of NMR spectroscopy. From the assignment of the signals both in 1H and 13C NMR spectra it follows that not only head‐to‐tail but also head‐to‐head coupling of styrene and methyl α‐cyanocinnamate monomeric units occurs in the copolymers. The composition data of the copolymers can be described by the penultimate model as seen from the linear distribution of the data points in a modified Kelen‐Tüdös representation.
Telechelic poly(thio‐1,4‐phenylene)s and poly(thio‐1,4‐phenylene)‐block‐polyamides
Authors: Freund Lothar , Heitz Walter 
Published: April 2003

AbstractPoly(thio‐1,4‐phenylene)s (PPS) 5a–d with reactive end groups like carboxyl, nitro, cyano and aldehyde groups were synthesized under high as well as atmospheric pressure. Carboxyl terminated telechelics 5a were used as starting materials for the synthesis of poly(thio‐1,4‐phenylene)‐block‐polyamides. Semicrystalline and amorphous polyamides like Nylon 6 and Trogamide® served as coblocks. The formation of block copolymers was approved by the solubility behavior, the NMR and IR spectra as well as high temperature GPC. The thermal stability increases with the fraction of PPS. By DSC, phase separation of the block copolymers was observed at certain compositions and molecular weights.
Scanning electron microscopy and ultrasonic investigations of the morphology of polypropylene (PP) films
Authors: Sadiku Emmanuel Rotimi 
Published: April 2003

AbstractUltrasound measurements (at four different frequencies) in the range 15 MHz–75 MHz corresponding to a low frequency pulse technique were made on polypropylene (PP) films of different draw ratios, λa = 1,0, 2,8, 4,9 and 5,8. Process‐dependent properties such as draw ratio (and/or thickness), quenching and annealing are functions on which attenuation depends. The logarithm of attenuation for all the samples increases almost linearly with frequency (an instrumental parameter). Such linearity is not observed when looking into the dependence of attenuation on draw ratio or thickness. This is explained in terms of the structural and morphological nature of the samples. The variation of attenuation with draw ratio indicates an exponential increase at frequencies greater than 17 MHz. The increase is very sharp at frequencies of 60,11 and 71,00 MHz. At a frequency of 16,58 MHz, a gradual linear increase in attenuation is observed with draw ratio. On the other hand, as expected, the converse situation of these observations is noted in the dependence of attenuation on film thickness.
Magnesium and calcium ions transport by synthetic analogues of teichoic acids with 1,2‐ and 1,3‐linked phosphodiester units
Authors: Wódzki Romuald , Kłosiński Paweł 
Published: April 2003

Abstract2‐Ethylhexylpoly(trimethylene 1,3‐phosphate) (3), poly(1,2‐glycerol phosphate) (1) and poly‐(1‐acetoxy‐2,3‐glycerol phosphate) (2) were synthesized and used as synthetic analogues of teichoic acids. Their properties as a carrier of magnesium and calcium ions were examined in the competitive exchange diffusion process with the countertransport of hydrogen or sodium ions. It turned out that polymers with 1,2‐glycerol phosphate units (1,2) exhibit lower ability to transport preferentially magnesium ions than poly(1,3‐alkylene phosphate)s (3). In all cases the efficiency of polyphosphates in preferential transport of magnesium ions is higher when transport is coupled with proton counterflow.
Use of constants from Mark‐Houwink‐Sakurada equation for estimating the characteristic ratio of a polymer chain
Authors: Kas̆tánek Alois 
Published: April 2003

AbstractA new procedure for the estimation of the characteristic ratio of flexible chain polymers is proposed. It is based on a combination of the parameters of the Mark‐Houwink‐Sakurada equation with a theoretical relationship of Kurata and Stockmayer. It is checked against data obtained under “theta” conditions. Good results are provided with systems where the Mark‐Houwink‐Sakurada exponent is lower than 0,65.
Kinetic investigation of photopolymerizations induced by laser beams
Authors: Decker Christian , Moussa Khalil 
Published: April 2003

AbstractReal time infrared (RTIR) spectroscopy was used to study the kinetics of the polymerization of acrylic monomers exposed to the 337,4 nm continuous emission of a Kr+ laser. Conversion versus time curves were directly recorded in the millisecond timescale, thus allowing a precise evaluation of the polymerization rate and of the induction period due to O2 inhibition. The influence of the type and concentration of photoinitiator and of the laser beam intensity on the polymerization profile was examined for a 20 μm thick polyurethane‐acrylate (Actilane 20) coating. The growth of the radical concentration and its dependence on the initiation rate was determined from the kinetics of the dark polymerization which develops just after the laser exposure. Pulsed laser irradiation proved to be very effective in initiating the polymerization, the overall quantum yield reaching values up to 2500 mol · photon−1.
Isotactic polystyrene: An unusually large lamellar thickness as an effect of a thermodynamically good solvent
Authors: Allegra Giuseppe , Ganazzoli Fabio , Meille Stefano V. , Giunchi Giovanni , Heenan Richard K. , Higgins Julia S. , Luzzati Silvia , Nyström Bo , Roots Jaan 
Published: April 2003

AbstractIsotactic polystyrene samples crystallized from concentrated solutions (> 10% by weight) in the thermodynamically good solvent toluene display a lamellar thickness L = (170 ± 15) Å at room temperature, as determined by neutron scattering investigation. This thickness is about twice the value reported for samples crystallized in poor solvents. The results may be interpreted in terms of a substantially smaller melting enthalpy of the polymer in toluene, producing a proportionally inverse increase of the thickness L̄c of the central, crystalline portion of the lamellae. In turn, we suggest that the overall thickness L of the lamellae increases more than proportionally with L̄c, due to the need of accomodating in the amorphous zone increasing amounts of polymer containing steric defects. The decrease of the melting enthalpy is also qualitatively consistent with growth rate results. The half‐peak width of the Bragg diffraction peaks suggests that the crystalline fraction of the lamellar thickness is about 50%, in approximate agreement with results obtained by Overbergh, Berghmans and Reynaers (J. Polym. Sci., Polym. Phys. Ed. 14, 1177 (1976)) from bulk‐crystallized samples showing about the same values of L and L̄c as observed by us.
Crosslinkable liquid‐crystalline main‐chain polymers
Authors: Peter Karin , Rätzsch Manfred 
Published: April 2003

AbstractCrosslinkable liquid‐crystalline main‐chain polymers were prepared by high temperature polycondensation in solution. The polymers have reactive double bonds in the flexible spacer. Orientation of chains in the liquid‐crystalline state was not changed by crosslinking. Crosslinked polymers exhibit a high increase of the mesophase range and a higher E‐modulus than the uncrosslinked ones.
Photodegradation of poly(tert‐butyl methacrylate) in air and in the presence of sulfur dioxide and nitrogen dioxide
Authors: Dulog Lothar , Huber Adalbert 
Published: April 2003

AbstractThe photodegradation of poly(tert‐butyl methacrylate) films under 100 ppm sulfur dioxide in air or 100 ppm nitrogen dioxide in air and in mixtures of the gases in air, at constant temperature (30°C) and humidity (30%), was studied. In the presence of sulfur dioxide and nitrogen dioxide under irradiation the polymer shows a rapid degradation, while the thermal degradation is very small, as well as the photodegradation in air. The measured effect of photodegradation of thin films was stronger than that of thicker films. An equation was derived to characterize the degradation by an autoacceleration and a linear part. FTIR spectroscopy shows the formation of carboxylic acids.
Side reactions during preparation and handling of oligomers and polymers from 2‐vinylpyridine
Authors: Schmitz F. P. , Hilgers H. , Gemmel B. 
Published: April 2003

AbstractSide reactions which have been proposed during the last 20 years to occur during the polymerization and oligomerization of vinylpyridine were reviewed, and some of them evidenced by experiments. The occurrence of ring substitution at the pyridine ring was demonstrated by model reactions. In addition, chain rearrangement in solution was observed. From the experimental results conclusions are drawn for the choice of the appropriate conditions for preparation and handling of polymers and oligomers of vinylpyridine.
The flocculation of kaolin suspensions with anionic polyacrylamides of varying molar mass and anionic character, 2. Polarographic study of the adsorption of anionic polyacrylamides onto clay
Authors: Petzold James C. , Herrington Thelma M. 
Published: April 2003

AbstractA selective method using polarography was developed for the determination of the degree of adsorption of anionic polyacrylamides onto Kaolinite. Four polymers of the same anionic character but different molar mass were studied. Limiting adsorption of the polyacrylamides onto the clay increased with their molar mass.
Model reactions for the synthesis of poly(1,4‐phenylenevinylene). The palladium‐catalyzed arylation of ethylene with halogenated arenes or benzoyl chlorides
Authors: Brenda Martin , Greiner Andreas , Heitz Walter 
Published: April 2003

AbstractPoly(1,4‐phenylenevinylene) was obtained by reacting dibromoarenes with ethylene in a palladium‐catalyzed reaction. Defects of the polymer structure were elucidated by model reactions. Side reactions in the reaction of halogenated arenes and ethylene or styrene, catalyzed by Pd, could be minimized by low catalyst concentrations and low reaction temperatures. The Pdcatalyzed reaction of aroyl chlorides with ethylene or styrene was probed by model reactions.
13C NMR study of the reaction of unsymmetrical diacids with 4,4′‐bis(2,3‐epoxypropoxy)biphenyl
Authors: Galiá Marina , Mantecón Ana , Cádiz Virginia , Serra Angels 
Published: April 2003

AbstractSeveral polymers were synthesized by reaction of unsymmetrical diacids with 4,4′‐bis(2,3‐epoxypropoxy)biphenyl. The reaction progress was followed, and the structure of the polyesters obtained was evaluated by means of 13C NMR spectroscopy. It appeared to be possible to achieve control in the polymer structure as a function of reactivity of the diacids. To obtain unequivocal assignments and to characterize thoroughly the NMR spectra of the polymers, several model compounds resembling the polymer backbone were synthesized.
Structure and conformation of tetrafluoroethylene‐hexafluoropropene copolymer
Authors: Villani Vincenzo , Pucciariello Rachele , Fusco Roberto , Marega Carla , Marigo Antonio , Zannetti Roberto 
Published: April 2003

AbstractA conformational analysis was performed on an isolated chain of a tetrafluoroethylene‐hexafluoropropene copolymer. The minimum of the conformational energy corresponds to a helix‐like chain containing planar zig‐zag sequences next to the CF3 group. A disordered structural model based on a hexagonal packing of the chains was tested by comparing the corresponding calculated X‐ray diffraction pattern with the experimental one.
On the behaviour of benzo‐1,3‐dioxolan‐2‐one and benzo‐1,3‐dioxan‐2‐one versus carbanionic species
Authors: Bialas Norbert J. , Kühling Steffen , Keul Helmut , Höcker Hartwig 
Published: April 2003

AbstractAttempts of anionic ring‐opening polymerization of benzo‐1,3‐dioxolan‐2‐one (1) with sec‐butyllithium or potassium dihydronaphthylide as initiators in different solvents and under a variety of reaction conditions revealed that this monomer cannot be polymerized. Possible reasons for this finding are discussed. Benzo‐1,3‐dioxan‐2‐one (2) was prepared and characterized for the first time. Anionic ring‐opening polymerization of this monomer yields a polymer with a non‐uniform constitution, viz., loss of carbon dioxide occurs during polymerization. The mechanism of formation of this polymer is discussed on the basis of product analysis and analysis of the active species formed during polymerization. Attempts to synthesize 5,6‐benzo‐1,3‐dioxepan‐2‐one (3) failed.
Glass transition temperatures of comb‐like polymers. Poly(ethylene oxide)‐polyacrylates and ‐polymethacrylates
Authors: Yan Feng , Déjardin Philippe , Frère Yves , Gramain Philippe 
Published: April 2003

AbstractA series of twelve poly(ethylene oxide) (PEO)‐polyacrylates and ‐polymethacrylates with PEO side chains, ranging in molecular weight from 164 to 1000, was studied by differential scanning calorimetry in order to analyse the behaviour of the glass transition temperature. It is shown that the glass transition temperature Tg first decreases with increasing side‐chain length to attain a constant value corresponding to the Tg of linear PEO. Contrary to the n‐alkyl homologous polymers, the influence of the side‐chain crystallization is weak and only appears for long side chains (number‐average molecular weight M̄n > 450). The proposed reason is the higher content of amorphous side‐chain units between the backbone and the crystallites in PEO as compared to alkyl chains. A relation predicting variations of Tg in comb‐like polymers with the length of the side chains is proposed. This relation, based on variation of the Tg of the side chain with its length, fits the experimental results for n‐alkyl and PEO side‐chain polyacrylates and polymethacrylates using only one parameter characterizing the nature of the side chain.