bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and characterization of biaxial nematic side chain polymers with laterally attached mesogenic groups
Authors: Hessel Friedrich , Herr Rolf‐Peter , Finkelmann Heino 
Published: April 2003

AbstractThe synthesis and characterization of liquid crystalline side chain polymers with mesogenic groups laterally attached to the polymer main chain are described. By variation of the terminal group, mesogenic moiety or spacer length, a change in the glass transition temperature, the nematic to isotropic transformation temperature and the stability of the nematic phase can be achieved. With increasing length of terminal groups, a distinct odd‐even effect of the nematic to isotropic phase transformation temperature and also a strong decrease of the glass transition temperature is observed. Macroscopic homeotropic alignment can be achieved in an electric or magnetic field. Conoscopic investigations show optical biaxial behavior of the nematic phase. A chiral nematic copolymer is the first example of a thermotropic biaxial cholesteric phase.
Synthese und Komplexierungseigenschaften von monomeren und polymeren 5‐Methacryloylaminosalicylsäure‐Derivaten
Authors: Lange Kai , Ritter Helmut 
Published: April 2003

AbstractThe synthesis of monomeric and polymeric 5‐methacryloylaminosalicylic acid derivatives is described. The interaction of these ligands with Fe(III), Ti (IV) and Ca(II) ions was investigated by photometric, conductometric and viscosimetric measurements.
Polyethers for biomedical applications. Polymerization of propylene oxide by organozinc/organotin catalysts
Authors: Bots Jan Gert , van der Does Leen , Bantjes Adriaan , Boersma Jaap 
Published: April 2003

AbstractThe polymerization of propylene oxide to obtain a high‐molecular‐weight polymer with an atactic structure required for the application as artificial blood vessels was investigated using combinations of organozinc and organotin compounds as catalyst. The composition of the most active catalyst, resulting from the reaction of diphenyltin sulfide with bis(3‐dimethyl‐aminopropyl)zinc, was found to be R(C6H5)2Sn(SZn)2R with R = (CH2)3N(CH3)2. Using this catalyst, an anionic coordination polymerization was observed with neither stereoselectivity nor living type or cationic features. At low catalyst concentration (0,03 mol‐% Zn) a high‐molecular‐weight poly(propylene oxide) (PPOX) was obtained in 80–90% yield (Mw = 500000; 40% isotactic). Lowering of the catalyst concentration and increasing the polymerization temperature changed the kinetics and the stereochemistry of the polymerization leading to polymers of lower molecular weight and to a decrease in the isotactic PPOX fraction to 20%, probably due to an association of the catalytic species.
Polymerization of 2‐diethylamino‐1,3,2‐dioxaphosphorinane, 2. Kinetics
Authors: Kałużyński Krzysztof , Penczek Stanisław 
Published: April 2003

AbstractKinetic studies of the anionic polymerization of 2‐diethylamino‐1,3,2‐dioxaphosphorinane were performed in THF solution with (CH3)3SiO−K+ as initiator at temperatures close to r.t. Initiation involves nucleophilic attack of the anion on P atom in the monomer molecule. Breaking of the PO bond leads to an alcoholate anion as the growing species. Polymerization was shown to proceed via macroion‐pairs and to be nearly living; e.g. at r.t. for every 250 propagations there is one termination. Rate constant of propagation k = 3,4 ± 0,31·mol−1·s−1 at 25°C, ΔH = 13,3 kcal·mol−1 and ΔS = −32,2 cal·mol−1·K−1. The ratio k/k was determined by solving a kinetic scheme involving propagation and termination. It was shown that termination consists in the alcoholate anion attack on P in either polymer or monomer molecule with expulsion of (C2H5)2N− anion and formation of a PO bond. The dialkylamide anions cannot reinitiate polymerization. In solving the kinetic scheme it was assumed that termination involving both polymer and monomer proceeds with rate constants equal to each other.
Photo‐oxydation du polystyrène à grandes longueurs d'onde (λ > 300 nm) et à 60°c
Authors: Khalil Zahi , Michaille Sylvie , Lemaire Jacques 
Published: April 2003

AbstractAn analytical and kinetic study of the photo‐oxidation of polystyrene in the solid state carried out at long wavelengths (λ > 300 nm) is reported. The concentration of the primary hydroperoxides has been determined throughout photo‐oxidation using chemical titrations. IR and FTIR spectrometry were used to analyze the hydroxylated and carbonylated intermediate groups formed. Hydrogen‐bonded alcohols (3540 cm−1), aromatic ketones (1690 cm−1), and unsaturated esters (1725 cm−1) were observed. The UV‐absorbing products formed in the photo‐oxidation enter a photothermal equilibrium; this allows to select only two structures to account for the yellowing of photooxidized polystyrene.
Poly(3‐dodecyl‐2,5‐thiophenediyl), a soluble and conducting polythiophene
Authors: Sato Masa‐aki , Tanaka Susumu , Kaeriyama Kyoji 
Published: April 2003

AbstractPoly(3‐dodecyl‐2,5‐thiophenediyl)(PDDT) films were prepared by means of electrochemical polymerization of 3‐dodecylthiophene. PDDT is soluble in benzene, chloroform and tetrahydronaphthalene, and oxidized PDDT is soluble in tetrahydronaphthalene. The degree of polymerization was found to be 90 and the conductivity of an as‐grown film, containing hexafluorophosphate anion, is 67 S/cm. While the cyclic voltammograms of an as‐grown film have two anodic peaks and two cathodic peaks, those of a film cast from an oxidized polymer solution has one anodic peak and one cathodic peak. Two peaks would correspond to two conjugation length. Oxidized PDDT is partly soluble in chloroform, retaining oxidized states. UV‐near infrared spectra in solution were compared with those in a solid film. The energy of the interband transition was found to be much higher in the solution than in the film. The results indicate a rigid oxidized part and a flexible neutral part in the polymer chain. The concentration dependence of the spectra indicates that oxidized PDDT does not aggregate in solution.
Retardation of the TiCl3·1/3 AlCl3/AlEt2Cl catalyzed propylene polymerization by allene and its relevance to the determination of the number of active centers
Authors: Kratochvíla Jan , Mejzlík Jiří 
Published: April 2003

AbstractThe retardation of the TiCl3/AlEt2Cl catalyzed propylene polymerization by allene was studied. On the basis of the results, a mechanism of the competitive chemisorption on active centers was proposed. A non‐linear dependence of the polymerization rate on the amount of allene consumed can be described in terms of the existence of two types of active centers, their numbers being 2 and 20 mmol·mol, respectively, differing very substantially in the adsorption coefficients. Copolymerization of propylene with allene was investigated, using the above catalytic system. Assuming identical active centers, the following copolymerization parameters were obtained: r1 = 0,66 ± 0,66 and r2 = 40 ± 30. Based on these results, the consumption of allene by copolymerization during the retardation of propylene polymerization was described in quantitative terms.
Metathesis degradation of partially phenylated 1,4‐polybutadiene
Authors: Stelzer Franz , Hummel Klaus , Graimann Christof , Hobisch Josefine , Martl Michael G. 
Published: April 2003

Abstract1,4‐Polybutadiene was partially phenylated in allyl position by bromination with N‐bromosuccinimide and subsequent Grignard‐Wurtz reaction with phenylmagnesium bromide. Substitution was to a certain degree coupled with double bond shift. The polymer structure was investigated via metathesis degradation with (E)‐4‐octene. The degradation products were identified by means of a GC/MS system and determined by GC. Cases of isomerism of products with one phenyl group were investigated. A metathesis product with two phenyl groups in one constitutional unit was found. A distribution function, based on a statistical scission of the macromolecules, was used for evaluations at different metathesis reaction times. Proofs of the reduced reactivity of CC double bonds in the neighbourhood of substituents were received. The yields of the different constitutional units in metathesis products were determined. These were compared with the results of computer simulations in a simplified model. The validity of computer simulations was thereby confirmed.
Synthesis of high‐molecular‐weight poly(L‐lactide) initiated with tin 2‐ethylhexanoate
Authors: Leenslag Jan W. , Pennings Albert J. 
Published: April 2003

AbstractThe bulk polymerization of L,L‐dilactide was studied as a function of polymerization temperature (Tp), time and concentration of catalyst (tin 2‐ethylhexanoate). Poly(L‐lactide) (PLLA), with the highest value of intrinsic viscosity ([η] = 13 dl · g−1; M̄v ≈ 1 · 106) and heat of fusion (ΔHm = 64,7 J · g−1), was synthesized at a low catalyst concentration (0,015 wt.‐%) and at the lowest Tp studied (100°C), just above the melting point of L,L‐dilactide (98°C). The ceiling temperature of PLLA was found to be 275°C, as deduced from an M̄v max. − Tp curve. The M̄w/M̄n ratios of as‐polymerized PLLA samples ranged from 2 to 3. Fractions of PLLA with M̄v max. were already present at 50% conversion. The experimental results support a proposed nonionic insertion polymerization mechanism. Polymerization at 100–140°C resulted in early crystallization of PLLA leading to a rather untangled polymer and microporous (pores up to 100 nm) sample texture.
Effect of bound water on structural change of regenerated cellulose
Authors: Hatakeyama Tatsuko , Ikeda Yoshimitsu , Hatakeyama Hyoe 
Published: April 2003

AbstractPhase transition of water sorbed in regenerated cellulose (II), for water contents ranging from 0 to 1,0 (water/dry cellulose, g/g), was investigated by differential scanning calorimetry (DSC). It was found that the amount of water bound to each glucose unit is ca. 3 mol considering that water diffuses only into the amorphous region of cellulose. The increase of this amount by adding excess water to cellulose suggests that the amorphous region of cellulose II increases in the presence of water. The transient state, at a water content ranging from 0,4 to 0,6, where the intermolecular distance expands, is reflected in an intermediate crystallization at a temperature between the crystallization of free water and freezing bound water. Mechanical properties of cellulose II under moist conditions were related to the results obtained by DSC. Further, the strength at break of cellulose II was compared with that of natural cellulose (I). The strength of cellulose II decreases in presence of bound water, whereas that of cellulose I increases. Based on the comparison of the results of DSC and mechanical properties of cellulose I and II, the difference is attributed to the structural change of the amorphous region when water molecules are bound to the hydroxyl groups of cellulose. The defect or internal strain of the amorphous region of cellulose I decreases and the molecular chain is transformed into a more regular arrangement when water molecules break hydrogen bonds. On the other hand, the amorphous chain of cellulose II takes a more released and expanded arrangement in presence of water molecules which break hydrogen bonds in the crystalline region of cellulose II. The decrease of crystallinity was observed by x‐ray diffraction.
Synthesis and thermodynamic studies on the protonation of a new polymeric amino diacid
Authors: Fini Adamo , Casolaro Mario , Nocentini Mila , Barbucci Rolando , Laus Michele 
Published: April 2003

AbstractA linear poly(amido‐amine) carrying a malonic acid moiety in the side chain of the repeating unit was synthesized and characterized. Its behaviour in aqueous solution was investigated by potentiometric, viscometric and calorimetric techniques. The basicity constant relative to the tertiary nitrogen atom decreases linearly by increasing the overall degree of protonation, while the tendency of each carboxylate ion to accept a proton is influenced by the presence of the neighbouring negative charge. The change of the basicity constants with the degree of protonation is due to entropic terms leading to energetics of protonation independent of the degree of protonation.
Synthesis and tacticity characterization of a novel series of liquid crystalline side chain polymers with oligo(ethylene oxide) spacers
Authors: Duran Randolph , Gramain Philippe 
Published: April 2003

AbstractA novel series of liquid crystalline side chain polymers containing oligo(ethylene oxide) spacers was synthesized and characterized. These included acrylates, methacrylates, and methacrylate copolymers. Although all polymers were polymerized free radically, NMR tacticity studies showed a systematic variation of the observed tacticity of the methacrylate series, the isotactic content decreasing with increasing spacer length. The data indicate that the spacer length and mesogenic group play a role in determining microstructure during polymerization.
Structure and amounts of counter ions in polypyrrole films prepared from aqueous solutions of sodium tosylate
Authors: Shen Yueqiang , Qiu Jinjin , Qian Renyuan , Carneiro Kim 
Published: April 2003

AbstractA series of conducting polypyrrole films was prepared from aqueous TsONa solution of different concentrations, and investigated by means of elemental analyses and scanning electron microscopy. The results show that the different concentrations of the supporting electrolyte TsONa do not only cause different amounts of counter ions in the film, but also cause a different structure and morphology of the film.
The synthesis of poly(allylamine) containing covalently bound cyclodextrin and its catalytic effect in the hydrolysis of phenyl esters
Authors: Seo Toshihiro , Kajihara Taketoshi , Iijima Toshiro 
Published: April 2003

AbstractA poly(allylamine) {poly[1‐(aminomethyl)ethylene]} (2) containing covalently bound β‐cyclodextrin (CD) residues (3) was synthesized. The inclusion ability of CD was enhanced in this polymer 3. A pronounced catalytic acceleration of the hydrolysis of p‐ and m‐nitrophenyl acetate by 3 as compared with that of 2 indicates the cooperative effect of CD and amino groups on the polymer chains.
The optical‐configuration parameter for ethene‐propene copolymers
Authors: Saiz Enrique , Mark J. E. 
Published: April 2003

AbstractRotational isomeric state theory is used to predict values of the optical‐configuration parameter Δa for ethene‐propene copolymers as a function of chemical composition, chemical sequence distribution, and stereochemical structure of the propylene sequences. The calculations are based on information available for ethene and propene homopolymers, and on the model used to interpret the unperturbed dimensions of these copolymers. Values of Δa were generally found to decrease significantly with increase in the fraction of propylene units, but to be relatively insensitive to chemical sequence distribution and stereochemical structure. The extent of their agreement with experiment is consistent with comparisons previously reported for a variety of homopolymers. It is intermediate to the poor agreement generally obtained for symmetric chains (such as polyethylene) and the satisfactory agreement generally obtained for asymmetric chains (such as polypropylene).
Rheological and thermal properties of carrageenan gels. Effect of sulfate content
Authors: Watase Mineo , Nishinari Katsuyoshi 
Published: April 2003

AbstractDynamic viscoelasticity and differential scanning calorimetry (DSC) measurements were carried out in order to examine the effect of sulfate content on the gelling mechanism of concentrated kappa‐ and iota‐carrageenan solutions. Alkaline pre‐treatment was very effective to enhance the gelling ability of kappa‐carrageenan. The melting temperature of the gels and the temperature at which elastic modulus begins to decrease rapidly were shifted to higher temperatures with increasing concentration of gels. Elastic modulus increased with increasing concentration, while endothermic enthalpy showed a maximum at a certain concentration. The effect of thermal history on DSC behavior was also examined.
Molecular weight dependence of interaction parameter and demixing concentration in polymer‐polymer‐good solvent systems. comparison with theory
Authors: Kaddour Latifa Ould , Anasagasti Maria Soledad , Strazielle Claude 
Published: April 2003

AbstractThe dependence of the interaction parameter χAB between two unlike polymers A and B and of their demixing concentration cK on their molecular weight is investigated. The experiments were performed by means of light scattering (spinodal and “optical theta” conditions) on two polymer pairs: polydimethylsiloxane‐polystyrene and polydimethylsiloxane‐poly(methyl methacrylate) in various thermodynamically good solvents. The results are in agreement with the predictions of new scaling laws (χAB ∼ M−0,46 and cK ∼ M−0,63) derived from renormalization group calculations.
An unexpected mode of cationic oligomerization of 1‐vinyl‐4,5,6,7‐tetrahydroindole
Authors: Trofimov Boris Alexandrovich , Morozova Ludmila Vasil'evna , Sigalov Mark Vladimirovich , Mikhaleva Al'bina Ivanovna , Markova Marina Viktorovna 
Published: April 2003

Abstract1‐Vinyl‐4,5,6,7‐tetrahydroindole in the presence of Brønsted acids (HCl, H2SO4, HOAc) and Lewis acids (BF3 · OEt2, FeCl3, TiCl3, SnCl4, SiCl4, Et3SiCl, Me2, PhMeSiCl2) undergoes an alternative oligomerization involving both the double bond and the α‐position of the pyrrole ring to form the dimer 1‐vinyl‐2‐[1‐(4,5,6,7‐tetrahydro‐1‐indolyl)ethyl]‐4,5,6,7‐tetrahydroindole in a yield up to 68% and oligomers of the same backbone, soluble (major product) and insoluble (minor product) in hot hexane, the latter being enriched by oxidized and hydrolyzed tetrahydroindole units. The molecular weights of the former oligomers were assessed from 1H NMR spectra to range from 1000 to 2000.
Synthesis of poly(ϵ‐caprolactone) macromonomers
Authors: Gnanou Yves , Rempp Paul 
Published: April 2003

AbstractMacromonomers of poly(ϵ‐caprolactone) were synthesized according to a two‐step method. ω‐Hydroxypolycaprolactone was first obtained by protonic deactivation of the growing alkoxide site, under conditions such as to minimize the draw‐backs of anionic polymerization of ϵ‐caprolactone: slow initiation with respect to propagation, occurrence of reshuffling and backbiting reactions. In a second stage, the polymer was fitted with an endstanding unsaturation, according to methods derived from peptide chemistry. The macromonomers obtained were characterized accurately (control of MWD, functionalization).
Structural variations of DNA + Mn2+ complexes during helix‐coil transition
Authors: Sorokin Victor A. , Fedorov Vladimir F. , Leontiev Victor S. , Blagoi Yuri P. , Galkin Vladimir L. 
Published: April 2003

AbstractThe helix‐coil transition in Phage T2 DNA in the presence of 6,4 · 10−3 mol/l Mn2+ is studied using light scattering and UV spectroscopy. The transition range is about 0,5°C. Near the temperature of the end of melting Tf the molecular weight Mw and the radius of gyration Rz of the complex are observed to decrease to about one half. At a temperature 0,1–0,25°C higher than Tf, Mw and Rz pass through a minimum, which implies that aggregation is preceded by unwinding of DNA strands. Thus, rise in temperature rather than Mn2+ ‐induced aggregation causes DNA + Mn2+ melting.
Critical chain lengths in polystyrene bulk diffusion
Authors: Antonietti Markus , Fölsch Karl Josef , Sillescu Hans 
Published: April 2003

AbstractDiffusion coefficients D of singly and doubly end‐labeled polystyrenes (PS) with molecular weights in the range 6500 ≤ M ≤ 75400 were measured in a PS matrix of molecular weight M′ = 111000, and in matrices with M′ = M. At 212°C, we find no influence of the label. In a power‐law description D = D0 · M−α · M′−β we find α = 2,0 for M′ = 111000 and α + β = 2,4 for M = M′. The crossover to Rouse‐like behavior for short‐M chains is at Me ≈ 18000 for the former (high M′), and at Mc ≈ 33000 in the latter (M′ = M) case. At 185°C, we find a more complex scaling behavior and different D values for singly and doubly labeled PS.
A fourier transform infrared and nuclear magnetic resonance study of cyclized natural rubber
Authors: Patterson Dwight Juan , Koenig Jack L. 
Published: April 2003

AbstractFourier transform infrared (FTIR), 1H NMR, and 13C NMR have been used to characterize the structure of natural rubber cyclized with p‐toluenesulfonic acid. The samples studied were only partially cyclized. The cyclized portions contained both mobile and rigid domains. Crosslinking occurred during the cyclization reaction. The cyclized samples showed a distribution of functionalities including some oxidation products. All three types of olefinic segmented end groups were formed during cyclization (di‐, tri‐, and tetrasubstituted olefins). The loss of the exocyclic species leads to the formation of cross‐linked networks.
Self‐diffusion coefficient of flexible‐chain polymers in solution and in the melt
Authors: Budtov Vladilen P. 
Published: April 2003

AbstractA theory was developed for predicting the self‐diffusion coefficients Dp of macromolecules and of oligomers in solution and in the melt. For moderate‐concentration ranges account was taken of decreasing intramolecular hydrodynamic interaction with increasing concentration. In the high‐concentration range the scaling theory was used. The dependence of Dp on concentration, molecular weight, and quality of the solvent was described by a common relationship as a function of √c[η] with mass concentration c and intrinsic viscosity [η]. If the dependence is considered in the form Dp ∝ cβ, then the value of the exponent β varies between 0 and 2. If the dependence of the local viscosity is taken into account, then β is greater than 2. An analysis of the relationships of Dp for oligomers and polymers in melts was also conducted. The theoretical results obtained describe quantitatively the available experimental data. These results were used for the interpretation of the decreasing decay rate of macroradicals with increasing conversion (gel effect).
Zur theoretischen beschreibung der kinetik der radikalischen terpolymerisation von styrol mit N‐vinyl‐2‐pyrrolidon und methylmethacrylat anhand des klassischen copolymerisationsmodells
Authors: Quella Ferdinand , Czerwinski Wojciech K. , Braun Dietrich 
Published: April 2003

AbstractThe polymerization rate of the ternary monomer system, styrene, N‐vinyl‐2‐pyrrolidone, and methyl methacrylate, was investigated in bulk at 60°C with AIBN as initiator. The results were interpreted by means of the well known classical reaction model and a newly derived simplified reaction model. The classical rate equation describes the reaction rate correctly in general, however, supplementary assumptions are needed for this special monomer system. The simplified reaction model is useful to estimate the terpolymerization rate, if initiation rates for the monomer mixtures are not known.
Addition of the 1‐cyano‐1‐methylethyl radical to α‐methylstyrene
Authors: Behari Kunj , Bevington John C. , Huckerby Thomas N. 
Published: April 2003

Abstract1‐Cyano‐1‐methylethyl end‐groups in copolymers of α‐methylstyrene (MST) with methyl methacrylate (MMA) and with styrene (STY) have been examined by 13C NMR; the end‐groups have been derived from initiators suitably enriched with carbon‐13. It has been shown that at 60°C MST closely resembles STY in reactivity towards the 1‐cyano‐1‐methylethyl radical. MST is 1,89 times as reactive as MMA towards the radical at 40°C; the corresponding factors at 60 and 100°C are 1,69 and 1,55, respectively. There is no evidence for reversibility in the reaction of MST with the 1‐cyano‐1‐methylethyl radical.