bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural behaviour of thermotropic liquid crystals from poly(4‐vinylpyridine) fully and partially quaternized with a mesogenic group
Authors: Navarro‐Rodriguez Dámaso , Guillon Daniel , Skoulios Antoine , Frère Yves , Gramain Ph. 
Published: April 2003

AbstractLiquid crystals were obtained from poly(4‐vinylpyridine) quaternized with 1‐bromooctane and 1‐bromododecane ω‐substituted with 4′‐methoxy‐4‐biphenyloxy mesogenic groups. Their thermotropic polymorphism was studied by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction. Three types of smectic mesophase, namely A, B, and E, were identified and described from a structural point of view. Their structure was found to be very similar to that previously reported for their monomer counterparts. The mesogenic pendant groups are arranged in single layers with the polymer backbones inserted in between. As a function of decreasing degree of quaternization, the smectic period increases slowly, reflecting the expansion of the sublayers containing the polymer backbones along with the free pyridine rings.
Kinetics of step polymerization of 3,6‐dibromo‐N‐ethylcarbazole catalyzed by a Ni(0)‐based complex
Authors: Aboulkassim Aïcha , Faïd Karim , Siove Alain 
Published: April 2003

AbstractThe dehalogenative polycondensation of 3,6‐dibromo‐N‐ethylcarbazole was catalyzed by a Ni(0)‐based complex, generated in N,N‐dimethylacetamide by electroreduction of NiBr2/2,2′‐bipyridine. The process involves three different successive reaction steps: electrolysis of Ni(II) to Ni(0); insertion of the latter into a CBr bond of monomer leading to CNiBr* active species; dehalogenative coupling between active sites and monomer, yielding oligomers. From kinetics of electrogeneration of the catalytic system in the absence of monomer, a first‐order reaction was determined. Insertion and coupling reactions were found to be second order, and comparison of the values of the corresponding rate constants clearly showed that couplings is the rate‐determining step of the process.
Syndiospecific polymerization of styrene with the catalytic system [Ti2(OC2H5)8Cl]2Mg2(μ‐Cl)2/methylaluminoxane compared with MgCl2‐supported and unsupported Ti(OC2H5)4
Authors: Dall'Occo Tiziano , Sartori Franco , Vecellio Giancarlo , Zucchini Umberto , Maldotti Andrea 
Published: April 2003

AbstractAs a part of our interest in the performance of [Ti2(OC2H5)8Cl]2Mg2(μ‐Cl)2 as Ziegler‐Natta catalyst, the polymerization of styrene with a toluene solution of this compound and methyl‐aluminoxane as cocatalyst was performed. It was found that the present catalytic system promotes the syndiospecific polymerization of styrene with high stereoregularity and the results were compared with those obtained with MgCl2‐supported or unsupported Ti(OC2H5)4 catalysts. Determination of the titanium oxidation states and electron spin resonance (ESR) measurements both in the absence and in the presence of styrene were carried out for all the catalytic systems aimed at shedding some light on the nature of the active species.
Synthesis of poly(vinyl alcohol) having a thiol group at one end and new block copolymers containing poly(vinyl alchohol) as one constitent
Authors: Sato Toshiaki , Terada Kazutoshi , Yamauchi Junnosuke , Okaya Takuji 
Published: April 2003

AbstractPoly(vinyl alcohol) (PVA) and poly(vinyl acetate) having a thiol group at one end were synthesized by free‐radical polymerization of vinyl acetate in presence of thioacetic acid as a chain transfer agent followed by treating with sodium hydroxide/methanol and ammonia, respectively. It was found that block copolymers containing the PVA sequence as one constituent were obtained by the redox‐initiated polymerization of some vinyl monomers, for example, acrylic acid (AA) and acrylamide (AAm), using PVA having a thiol end group as reductant and an oxidant such as potassium bromate and potassium persulfate.
Investigation of the mechanism of chain termination and transfer by 1,2‐butadiene in the butyllithium‐initiated polymerization of 1,3‐butadiene in non‐polar solvents
Authors: Puskas Judit E. 
Published: April 2003

Abstract1,2‐Butadiene (BD‐1,2) was shown to be a chain terminating/transferring agent in the butyllithium (nBuLi)‐initiated polymerization of 1,3‐butadiene in hexane solvent by Adams et al. Based on model reactions and circumstantial evidence they proposed that BD‐1,2 terminates the polymerization by extracting Li from the living chain end. The lithiated BD‐1,2 formed may initiate new chains causing chain transfer or isomerize to lithiated ethylacetylene (system. name: 1‐butyne), a nonactive species. This paper proposes a modification of the mechanism suggested by Adams et al. Kinetic investigations of the model reaction between nBuLi and BD‐1,2 by infrared spectroscopy have shown that the first, and rate‐determining, step is the isomerization of BD‐1,2 to ethylacetylene, followed by lithiation. It is proposed that the lithiated ethylacetylene can initiate new chains, thereby causing chain transfer.
Synthesis and properties of thermotropic liquid‐crystalline polymers linked through bis(ß‐diketonato)copper(II) complex
Authors: Hanabusa Kenji , Isogai Tadashi , Koyama Toshiki , Shirai Hirofusa 
Published: April 2003

AbstractThermotropic liquid‐crystalline polymers (2a–2e, 3a–3c) linked via the bis(ß‐diketonato)‐copper(II) complex were prepared by mixing the bifunctional bidentate ligand (1a–1c) with copper(II) chloride. The homopolymers 2c–2e and the copolymers 2a–3c were ascertained to exhibit a stable mesophase by means of polarizing microscopic observation. The homopolymers show at least a smectic mesophase and the copolymer exhibit both smectic and nematic ones. Fibers were prepared by melt‐drawing of the molten polymers at the mesophase temperature into air at room temperature except for 2a and 2b. Electron spin resonance (ESR) spectra of the melt drawn fibers indicated that the plane of the square planar bis(ß‐diketonato)copper(II) complex in the fiber is oriented parallel to the fiber axis. X‐ray diffraction patterns from the melt‐drawn fibers are characterized by several sharp inner reflections at meridional position and a diffuse one at equatorial position, suggesting that the fibers possess an axial orientation with smectic A phase which is frozen in during melt‐drawn spinning.
Charge‐transfer complexation in mixtures of polysiloxanes containing carbazolyl electorn‐donor and dinitrobenzoyl electron‐acceptor moieties
Authors: Setz Stefan , Schneider Hans Adam 
Published: April 2003

AbstractThe study of the charge transfer (CT) complexation in mixtures containing carbazolyl electron donor (D) and dinitrobenzoyl electron‐acceptor (A) moieties show stronger association effects in mixtures of polysiloxanes than in mixtures of low‐molecular‐weight model compounds. The increasing CT‐association in polymer systems is explained by a “macromolecular cage effect”. Cooperativity effects are believed to cause a “zip‐like” matching of the complementary polymeric backbones. UV‐spectroscopy and viscometric data indicate the formation of both bimolecular D : A and trimolecular D:2A associates.
New copolymethacrylates with azo‐chromophores in the side chain
Authors: Czapla Sylvia , Ruhmann Ralf , Rübner Joachim , Zschuppe Veit , Wolff Dietmar 
Published: April 2003

AbstractThe synthesis and characterization of new poly({6‐[4‐(4‐cyanophenylcarbamoyl)phenoxy]hexyl methacrylate}‐co‐{6‐[4‐(4‐ cyanophenylazo)phenoxy]hexyl methacrylate}) are reported. Their liquid‐crystalline properties are investigated using differential scanning calorimetry, polarizing microscopy and X‐ray diffraction techniques. The glass transition temperatures and the clearing points can be influenced by variation of the copolymer composition. The substances offer a relatively broad temperature range of mesomorphic properties suitable for photochemical studies.
Nucleation of the ß‐modification of isotactic polypropene on the surface of different crystalline phases of linear trans‐quinacridone pigments
Authors: Filho Delson dos Santos , Oliveira Clara Marize Firemand 
Published: April 2003

AbstractDifferent crystalline phases of linear trans‐quinacridone (LTQ) pigments were prepared and added to isotactic polypropene (i‐PP). It was observed by X‐ray diffraction that the nucleation efficiency of the β‐modification of i‐PP strongly depends on the crystalline phases of LTQ. The α‐phase of LTQ does not induce the formation of the β‐modification of i‐PP but the δ‐modification of LTQ is a more effective β‐nucleator than the other crystalline phases of LTQ.
Crystallization kinetics of the ß‐modification of isotactic polypropene containing different crystalline phases of linear trans‐quinacridone pigments
Authors: Filho Delson dos Santos , Oliveira Clara Marize Firemand 
Published: April 2003

AbstractThe crystallization behavior of the ß‐modification of isotactic polypropene (i‐PP) induced by different crystalline phases of linear trans‐quinacridone (LTQ) is investigated. The crystallization of the ß‐modification depends on the crystalline phases of LTQ added to i‐PP and the cooling rates during crystallization from the melt. Non‐isothermal crystallization kinetics of i‐PP examined by differential scanning calorimetry indicated that the nucleating activity of the crystalline phases of LTQ is associated to the variation in fold surface free energy (δe) of formation of both the α‐and β‐modifications.
Electronic vs. Steric effects of substituents on the intramolecular excimer fluorescence from dilute solutions of halogen‐substituted polystyrenes
Authors: Chakraborty D. K. , Kurian J. , Trumbo D. , Harwood H. J. , Kennedy J. P. , Mattice Wayne L. 
Published: April 2003

AbstractSteady state fluorescence measurements in dilute solution have been performed for eight halogenated polystyrenes and for poly(2,5‐dimethylstyrene). The monomers for halogenated polymers are o‐X‐styrene (X = F, Cl, Br), m‐fluorostyrene, p‐X‐styrene, and p‐chloro‐α‐methylstyrene. The position of the excimer band and the ratio of the intensities of the excimer and monomer fluorescence depend on the substitution. The results for poly(p‐chloro‐α‐methylstyrene) and poly(2,5‐dimethylstyrene) can be rationalized by a conformational analysis that examines the preferred geometries for face‐to‐face complexes by rings bonded to chain atoms i and i + 2. The results for the other polymers cannot be explained by a conformational analysis. They appear to arise from a combination of factors that alter the electronic properties of the chromophore.
Sorption and permeation properties of poly(p‐phenylene sulfide) crystallized in the presence of sorbed gas molecules
Authors: Schultze Joachim Dirk , Böhning Martin , Springer Jürgen 
Published: April 2003

AbstractThe sorption behaviour of CO2 and N2 in poly(p‐phenylene sulfide), PPS, crystallized in the presence of CO2 and N2O molecules was studied at 298 K in the pressure range of 1–30 bar. The CO2 transport properties of these samples were investigated at the same temperature in the pressure range of 1–20 bar. The temperature dependence of the CO2 transport parameters was examined between 293 and 343 K at a pressure of 5 bar, for the virgin material, thermal and CO2 crystallized specimen only. All measured properties are compared with those of PPS crystallized by annealing at vacuum conditions to a similar degree of crystallinity, and with the virgin, nearly amorphous material. For the samples crystallized in the presence of sorbed gases an increased CO2‐solubility was observed. A part of unrelaxed free volume is proposed to remain in the samples after crystallization in presence of sorbed gas molecules. These voids formed under sorbed gas conditions seem to be stable even after removal of the sorbed molecules. The measured diffusion coefficients for CO2 were lower in the samples crystallized in the presence of gas molecules, compared to the virgin sample. This is expected to be due to an increased diffusive resistance by passing the interfaces of the formed voids. Permeability, which is governed by both, diffusion and sorption, undergoes non‐uniform changes. An attempt is made to explain this behaviour based on the dual‐mode‐sorption and dual‐mobility model.
Positional effects of the methacrylate group on polymerization and microstructure of micelle‐forming quaternary ammonium salts studied by NMR spectroscopy
Authors: Dais Photis , Paleos Costas M. , Nika Georgia , Malliaris Angellos 
Published: April 2003

AbstractThe microstructure of polymers obtained by γ‐irradiation of monomer surfactant molecules above the critical micelle concentration (CMC) is investigated by means of 13C NMR spectroscopy. The polymer obtained from the monomer bearing the methacrylate group at the end of the hydrocarbon chain fits the Bernoullian propagation model with Pm = 0,18 indicating a highly syndiotactic polymer, whereas that obtained from the monomer having the polymerizable group at the polar head was found to be purely syndiotactic (Pm = 0).
Irreversible activation effects in ethylene polymerization
Authors: Pasquet Véronique , Spitz Roger 
Published: April 2003

AbstractActivation and deactivation phenomena commonly observed in the case of slurry or gas phase ethylene polymerization kinetics are associated to molecular aspects of the formation and inhibition of active centers. As a preliminary study of the problem, we have to identify what step during the formation or action of the active centers is concerned by the well‐known activating agents: temperature, ethylene pressure and α‐olefins addition. They all lead to an irreversible increase in the polymerization rate, which can be attributed to the creation of new active centers. Hydrogen was also considered, since it is an activator for propene polymerization, but it deactivates ethylene polymerization. This deactivation is often partially reversible. Different explanations of this complex behaviour are presented.
Synthesis and characterization of poly[2,3,9,10,16,17,23,24‐octakis(dodecyloxycarbonyl)phthalocyaninatogermoxane]
Authors: Dulog Lothar , Gittinger Andreas , Roth Siegmar , Wagner Thomas 
Published: April 2003

AbstractIn this article we describe the preparation of poly[2,3,9,10,16,17,23,24‐octakis(dodecyloxycarbonyl)phthalocyaninatogermoxane] by thermal polycondensation of 2,3,9,10,16,17,23,24‐octakis(dodecyloxycarbonyl)phthalocyaninatogermanium dihydroxide, and its characterization. The average molar mass of the resulting polymer was determined. High molar masses are assessible, e.g., M̄w = 360000 g/mol, M̄n = 140000 g/mol, at moderate temperature for the polycondensation (200°C). The polymer shows a liquid‐crystalline phase in an extremely large temperature range. Furthermore, Langmuir‐Blodgett films (LB films) of the polymer and of the monomer were prepared and characterized. In LB films the phthalocyanine rings are preferentially oriented normal to the dipping direction.
Synthesis of polyamic acid di‐tert‐butyl esters by direct polycondensation of di‐tert‐butyl esters of tetracarboxylic acids with diamines using diphenyl (2,3‐dihydro‐2‐thioxo‐3‐benzoxazolyl)phosphonate
Authors: Ueda Mitsuru , Mori Hideharu 
Published: April 2003

AbstractThe direct polycondensation using the activating agent diphenyl (2,3‐dihydro‐2‐thioxo‐3‐benzoxazolyl)phosphonate (1) was successfully applied to the synthesis of polyamic acid tert‐butyl esters, which readily undergo AAL 1 type acid‐catalyzed deesterification. Polycondensations of di‐tert‐butyl esters of tetracarboxylic acids with diamines were conducted in N‐methyl‐2‐pyrrolidone in the presence of triethylamine at room temperature, producing poly(amide‐ester)s with inherent viscosities up to 1,1 dL · g−1. The effects of various factors, such as solvent, amount of solvent, and amount of the activating agent, were studied. The poly(amide‐ester)s are readily soluble in dipolar aprotic solvents and can be cast into uniform films from their solutions. Thermogravimetry of the polymers showed that the deesterification and imidization occur around 150–200°C, giving polyimides.
Poly(Phthalidylidenearylene)S. Transformation of poly(3,3‐phthalidylidene‐4,4′‐biphenylene) in acidic media
Authors: Zolotukhin Mikhail G. , Fattakhov Rinat K. , Kovardakov Viktor A. , Egorov Aleksander E. , Salazkin Sergei N. , Sultanova Venera S. , Muslukhov Rinat K. , Khalilov Leonard M. 
Published: April 2003

AbstractThe behaviour of poly(3,3‐phthalidylidene‐4,4′‐biphenylylene) (PPB) in acidic media was studied. In solvents with high acidity e.g. concentrated sulfuric acid, chlorosulfonic acid or PCl5, the phthalide groups of PPB were transformed into anthracen‐9‐one groups. Exposure time, solvent and temperature were found to affect the rearrangement of 3,3‐diphenylphthalide and PPB in the presence of PCl5. The resulted polymers are soluble in common organic solvents and contain either 10‐chloro‐10‐aryl‐anthracen‐9‐one, or after hydrolysis, 10‐hydroxy‐10‐arylanthracen‐9‐one units. Flexible and transparent polymer films were prepared by casting from the solution.
Kinetic and electron paramagnetic resonance studies on radical polymerization. Radical‐initiated polymerization of methyl N‐phenylitaconamate in N,N‐dimethylformamide
Authors: Sato Tsuneyuki , Okazaki Masanori , Seno Makiko , Tanaka Hitoshi 
Published: April 2003

AbstractThe polymerization of methyl N‐phenylitaconamate(methyl 2‐methylenesuccinanilate (1)) with dimethyl 2,2′‐azodiisobutyrate (2) was studied in N,N‐dimethylformamide (DMF) kinetically and by means of electron paramagnetic resonance (EPR) spectroscopy. The polymerization rate (Rp) at 55°C is given by the equation: Rp = k[2]0,58 · [1]1,6. The overall activation energy of the polymerization was calculated to be 54,2 kJ/mol. The number‐average molecular weight of poly(1) was in the range between 5000 and 17000. From an EPR study, the polymerization system was found to involve the EPR‐detectable propagating polymer radical of 1 at practical polymerization conditions. Using the concentration of polymer radicals, the rate constants of propagation (kp) and termination (kt) were determined for 55°C. The rate constant of propagation kp (between 8,4 and 12 L · mol−1 · s−1) tends to somehow increase with increasing monomer concentration. On the other hand, kt (between 1,9. 10−5 L · mol−1 · s−1) increases with decreasing monomer concentration, which results from a considerable dependence of kt on the polymer‐chain length. Such monomer‐concentration‐dependent kp and kt values are responsible for the high dependence of Rp on the monomer concentration. Thermogravimetric results showed that thermal degradation of poly(1) occurs rapidly at temperatures higher than 200°C and the residue at 500°C amounts to 26% of the initial polymer. For the copolymerization of 1 (M1) with styrene (M2) at 55°C in DMF the following copolymerization parameters were found: r1 = 0,52, r2 = 0,31, and Q, e values Q1 = 1,09 and e1 = +0,55.
Catalysis of the transesterification of poly[ethylene‐co‐(vinyl acetate)] by organometallic compounds in the melt
Authors: Hu Guo‐Hua , Sun Yi‐Jun , Lambla Morand 
Published: April 2003

AbstractThe transesterification reaction of poly[ethylene‐co‐(vinyl acetate)] (EVA) with 1‐octanol was studied in the molten state by the use of a batch mixer (Haake Rheocord) as the reactor. The conversion of the vinyl acetate group into the vinyl alcohol group was determined by Fourier transform infrared spectroscopy (FTIR). Several organometallic compounds were used as catalysts, of which tin‐based compounds, such as dibutyltin dilaurate and dibutyltin oxide, showed the highest activities. Experimental results suggested that the real catalyst is an intermediate product (dialkoxide) formed between an organotin compound and the reactive alcohol. This was confirmed by examining the interaction between a tin compound and an alcohol with the help of different techniques like infraed spectroscopy, high‐performance liquid chromatography and mass balance. Finally, a mechanism for the transesterification in the presence of an organotin compound as catalyst was proposed, suggesting that the overall reaction rate is proportional to the concentrations of the ester and the alcohol, and to the square root of the catalyst concentration. This was fully supported by kinetic studies.
One‐step synthesis of functional polymers by polycondensation: Polyesters with pendant hydroxyl side groups from potassium malate or tartrate and 1,4‐dibromobutane
Authors: Sepulchre Marie‐Odile , El Idrissi Hassan , Sepulchre Maurice , Spassky Nicolas 
Published: April 2003

AbstractPolyesters with pendant hydroxyl side groups such as (R,S)‐ and (S)‐poly(tetramethylene malate)s and (R,R)‐poly(tetramethylene tartrate)s of moderately high molecular weights were prepared by polycondensation, at 105°C in 1‐methyl‐2‐pyrrolidone for 16 to 80 h, from potassium malate or tartrate and 1,4‐dibromobutane. It was shown by a detailed analysis of the 1H and 13C NMR spectra of the prepared polyesters that no branching occurs in the course of the reaction. The nature of the end‐groups was also clearly established by NMR spectroscopy. The presence of large cycles in the final products cannot be completely excluded.
Liquid‐crystalline polyacrylates containing biphenyl and chiral terminal groups in the side chain, 1. Influence of the spacer length on the liquid‐crystal behavior
Authors: Tabrizian Maryam , Bunel Claude , Vairon Jean‐Pierre , Friedrich Claude , Noël Claudine 
Published: April 2003

AbstractThree acrylate monomers having mesogenic moieties based on 4‐(n)‐alkyloxy‐4′‐(2‐chloro‐propanoyloxy)biphenyl (n = 6, 8 or 10) have been synthesized. There is no evidence for liquid‐crystal properties in any of the three new monomers. The corresponding polymers have been prepared by free‐radical polymerization. Their liquid‐crystal behavior has been investigated by differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction. On cooling from the isotropic liquid, smectic A (SA), smectic B (SB) and crystalline phases (probably crystal‐like SE phases) have been evidenced. It should be noted that the chlorine atoms in the chiral groups do impose a local ordering of the mesogenic side groups.
Improved NMR characterization of high‐molecular‐weight polymers and polyelectrolytes through the use of preliminary ultrasonic degradation
Authors: Kulicke Werner‐Michael , Otto Matthias , Baar Andreas 
Published: April 2003

AbstractHigh‐molecular‐weight polymers, especially ionic polymers, give rise to highly viscous solutions which are likely to entrap air bubbles, even at low concentrations. The 13C NMR spectra of these solutions exhibit poor signal‐to‐noise ratios and broad bands due to the shortened T2 relaxation times. Qualitative evaluation is thus made very difficult, and quantitative evaluation becomes impossible. In 1H spectroscopic analysis of xanthan, these problems occur at concentrations as low as 0,5 wt.‐%. A method of viscosity reduction is required that reduces the molecular weight but does not affect the tacticity or comonomer distribution nor lead to the formation of monomers. From the various methods that were examined, ultrasonic degradation was found to be the best means of fulfilling these requirements. This study includes both coiled synthetic polymers, such as polyacrylamide or poly(acrylamide‐co‐sodium acrylate), and semirigid biopolymers, such as xanthan or schizophyllan, with a view to finding a generally applicable method. It was shown that the recording time could easily be reduced by a factor of up to 20 and that the resolution was enhanced. No change in the functional groups was observed in any of the polymers, and in the case of xanthan no cleavage of side chains occurred. In schizophyllan the triple helix structure also remained intact after degradation. It is postulated that degradation is attributed to elongational flow conditions produced by cavitation in ultrasonic fields.