bluuebunny/crossref_metadata_2025_split huggingface dataset:
Melting behavior of poly(3‐alkylthiophene)s with long alkyl side‐chains
Authors: Zhao Yue , Keroack Daniel , Yuan Guoxion , Massicotte André , Hanna Roula , Leclerc Mario 
Published: April 2003

AbstractThe melting behavior of two non‐oriented poly(3‐alkylthiophene)s (P3ATs) containing 12 and 14 carbon atoms, respectively, in the alkyl side chain was investigated by means of differential scanning calorimetry. We show that the two P3ATs display three melting endotherms after an isothermal annealing from the melt. Two of the melting peaks arise from the ordered structures which are completed in the course of the quenching of the sample from the melt, and judging from the essentially constant melting temperatures and heats of fusion, they are not influenced by the subsequent isothermal annealing conditions. On the other hand, a much slower crystallization induced by the annealing, which occurs over a wide range of temperatures, is responsible for the appearance of a third melting endotherm which is strongly dependent on the crystallization condition. We show that this secondary crystallization is not a perfection of the existing ordered structures, rather it results in distinct crystals which melt at a temperature Tm slightly above the crystallization temperature Tc. Moreover, it is shown that the plot of Tm versus Tc parallels the line of Tm = Tc, and that the difference Tm − Tc increases linearly as the number of carbon atoms in the side chain decreases. On the basis of the calorimetric and X‐ray diffraction measurements, it is suggested that the secondary crystallization originates from the alkyl side chains.
Synthesis of a new polymer — polycyclopentylenevinylene bearing ge‐containing group
Authors: Finkelshtein Eugene Sh. , Portnykh Elena B. , Ushakov Nikolai V. , Gringolts Maria L. , Yampolsky Yury P. 
Published: April 2003

AbstractA new polymer, poly[5‐(trimethylgermylmethyl)‐1,3‐cyclopentylenevinylene], was synthesized via ROMP of 5‐(trimethylgermylmethyl)‐2‐norbornene in the presence of RuCl3 · 3H2O, RuCl3(PPh3)3 and RuCl2(PPh3)3 catalysts. The structure of the synthesized polymer was determined on the basis of IR, 1H NMR and 13C NMR spectra. The gas transport properties for this polymer have been studied.
Influence of indenyl ligand substitution pattern on metallocene‐catalyzed propene copolymerization with 1‐octene
Authors: Schneider Martin Julius , Mülhaupt Rolf 
Published: April 2003

AbstractCopolymerization of propene with 1‐octene (1 mol/1 mol) was performed in toluene at 40°C in the presence of homogeneous methylaluminoxane (MAO)‐activated ansa‐metallocenes in order to study the role of benzannelation and 2‐methyl‐substitution of the silylene‐bridged bisindenyl ligand on comonomer incoporation, molecular mass, molecular mass distribution, and end groups. While 2‐methyl‐substitution promoted higher degree of polymerization without affecting copolymerization parameters, benzannelation improved markedly 1‐octene incorporation. Only with MAO‐activated rac‐Me2Si(2‐MeBenz[e]Ind)2ZrCl2 catalysts vinylidene end groups were formed exclusively. Molecular weight distribution remains narrow in all experiments.
Aggregation states and bistable light switching effects in a side chain ferroelectric liquid crystalline polysiloxane
Authors: Hwang Jenn Chiu , Shu Ming Chin , Moritake Hiroshi , Yoshino Katsumi 
Published: April 2003

AbstractAggregation states and transient light scattering in the chiral smectic C phase of a ferroelectric liquid crystalline polymer (FLCP) were studied. The smectic phase shows an interlayer spacing of 38–39.5 Å, which is about 1.41 times the length of the side chain mesogenic group. The transient scattering mode obtained by repeated voltage polarity reversal. A reversible transparent‐opaque (light scattering) change was observed in the chiral smectic C state upon application of electric fields with low and high frequencies, respectiely. Both transparent and opaque states were maintained stably even when the electric field was turned off (bistable light swiching). A novel type of electro‐optical effect based on light scattering was obtained for the FLCP in the chiral smectic C state.
Living ring‐opening polymerization of lactones using cationic zirconocene complex catalysts
Authors: Hayakawa Michiya , Mitani Makoto , Yamada Tohru , Mukaiyama Teruaki 
Published: April 2003

AbstractLiving cationic ring‐opening polymerization of ϵ‐caprolactone (CL), δ‐valerolactone (VL) and 1,3‐dioxepane‐2‐one (6) was achieved at room temperature by using zirconocene borate complex catalysts. Respective block copolymerization of CL with VL or with cyclic carbonate 6 was also successfully performed. The mechanism of the present cationic living polymerization is discussed.
On the mechanism of olefin polymerization by titanocene/MAO catalysts: Relationships between metathesis and addition polymerization
Authors: Tritto Incoronata , Li San Xi , Boggioni Laura , Sacchi Maria Carmela , Locatelli Paolo , O'Neill Aideen 
Published: April 2003

AbstractEthylene polymerizations and norbornene oligomerizations catalysed by Cp2Ti13CH3Cl/MAO (Cp: cyclopentadienyl; MAO: methylaluminoxane) mixtures have been carried out at different temperatures (from ‐20°C to 20°C), in order to test the validity of carbene mechanisms in α‐olefin polymerizations. Depending on the temperature, different ratios of the cationic species [Cp2Ti13CH3]+[Cl · MAO]− and precursors of the alkylidene Cp2Ti = 13CH2 exist. The in situ polymerization of 13C enriched ethylene was monitored by 13C NMR spectroscopy. Moreover, catalytic activity was determined and polyethylene samples were analyzed by 13C NMR and gel permeation chromatography (GPC). The following evidence has been provided against the carbene mechanism in the α‐olefin polymerization with titanocene based catalysts: (a) in the in situ ethylene polymerization experiments the appearance of polyethylene signals is concurrent with the decrease of cationic [Cp2Ti13CH3]+[Cl · MAO]− signals and is not related to the intensity of the alkylidene Cp2Ti = 13CH2 signals; (b) from the 13C NMR analysis of polyethylene chain‐end groups the 13C enrichment of Cp2Ti13CH3Cl has only been found in the methyl chain‐end group and not in the methylene of the propyl chain‐end group, as should have been the case if the carbene mechanism had been valid; (c) from norbornene oligomerization (at 0°C) the addition product 2‐13C enriched methyl‐norbornane has been identified. Moreover, the identification of a 13C enriched methylidene‐norbornane dimer at higher temperatures has revealed the possibility of norbornene addition to titanium carbenes through the formation of titanacyclobutane without the opening of the norbornene ring. However, this process requires higher energies with respect to the Cossee type insertion.
Side chain liquid crystal polymers of 2,3‐disubstituted norbornenes via ring‐opening metathesis polymerisation, 3. Influence of backbone microstructure and grafting ratio on the thermotropic behaviour
Authors: Ungerank Markus , Winkler Berthold , Eder Elisabeth , Stelzer Franz 
Published: April 2003

AbstractThe ring opening metathesis polymerisation (ROMP) of (±)‐ and (−)‐exo, endo‐bis[(4′‐cyanobiphenyl‐4‐yl)oxyalkyl]norborn‐5‐ene‐2,3‐dicarboxylates using three different Schrock type molybdenum alkylidene complexes ([Mo(NAr)(CH‐t‐Bu)(OR)2] with RC(CH3)3, C(CH32)(CF3) or C(CH3)(CF3)2) resulted in the formation of side chain liquid crystalline polymers (SCLCP's). The different initiators caused changes in the backbone tacticity which were determined by means of NMR techniques. The influence of the type of tacticity on the thermotropic behaviour of the SCLCP's was investigated. The thermal properties were determined by differential scanning calorimetry (DSC). The transition temperatures increased with rising molecular weight up to a degree of polymerisation of about 40. Above this value the thermal properties remained constant with increasing molecular weight. The types of phases for the liquid crystalline polymers were elucidated by polarising optical microscopy (POM). In general, the highly tactic polymers showed a broader thermal range of the LC phase. The kind of initiator used caused changes of the thermal and thermotropic behaviour of the SCLCP's. A grafting ratio model is introduced to explain the findings. From the experimental data a structure/property relationship is developed which might help to predict liquid crystalline properties of unknown polymers.
Termination kinetics of free‐radical polymerization of styrene over an extended temperature and pressure range
Authors: Buback Michael , Kuchta Frank‐Dieter 
Published: April 2003

AbstractThe termination rate coefficient kt of the free radical bulk polymerization of styrene is determined between 30 and 90°C up to a maximum pressure of 2800 bar. The majority of polymerization experiments has been carried out at monomer conversions up to 20 per cent. In this range a single value of kt is sufficient to describe termination rate at constant pressure and temperature. Toward higher conversion, significant changes in kt are observed. The data are measured by a pulsed laser polymerization technique and partly by conventional chemically initiated experiments, both with 2,2′‐azoisobutyronitrile (AIBN) as the initiator. Online spectroscopy is applied toward measurement of styrene conversion. The experimental termination rate coefficients up to 20 per cent monomer conversion are adequately represented by the expression:

Activation volume and activation energy of kt are very close to the corresponding activation parameters that characterize the pressure and temperature dependence of the inverse of styrene monomer viscosity. Varying laser pulse repetition rate has been used to investigate a potential chain‐length dependence of kt at low conversion. It turns out that effects of this kind are not sufficiently pronounced to be safely established in view of the experimental precision of ±25 per cent that is reached in the kt determinations.
Soluble poly(1,4‐phenylenevinylene)s and poly(1,4‐phenyleneethynylene)s via suzuki coupling
Authors: Koch Friedrich , Heitz Walter 
Published: April 2003

AbstractPoly(1,4‐phenylenevinylene) and poly(1,4‐phenyleneethynylene) were prepared fromtrans‐1,2‐dibromoethylene and 1,4‐bis(2‐bromoethynyl)benzene respectively with aryldiboronic acids by a Suzuki cross‐coupling reaction. The polymers were synthesized in a two‐phase system at room temperature using silver oxide and a Pd catalyst. 3% of biaryl formation is observed as a defect structure in the PPV polymers resulting from coupling of arylboronic acid. Soluble polymers were obtained when the aryldiboronic acid is substituted with long‐chain alkoxy groups.
Characterization of chitosan and rare‐earth‐metal‐ion doped chitosan films
Authors: Jiang Hao , Liang Jim , Grant John T. , Su Weijie , Bunning Timothy J. , Cooper Thomas M. , Adams W. Wade 
Published: April 2003

AbstractA systematic study has been made on the influence of doped rare‐earth metal ions (Er3+ and Nd3+) on the molecular interaction present in thin films fabricated from chitosan‐acetic acid solutions (chitosan/HAc). FT‐IR spectroscopy (including NIR, MIR and FIR) coupled with X‐ray photoelectron spectroscopy (XPS) indicate a weak complexation between the metal ions and amine groups of chitosan. Specifically, the FIR spectra show broad bands near 550, 480 and 250 cm−1 for the doped films suggestive of metal ion‐ligand vibrations. XPS indicates multiple chemical states of N with an increased percentage of a higher binding energy state nitrogen caused by a weak interaction with the doped metal ions. Slight differences in microroughness between the doped and undoped films as observed by X‐ray reflectometry may also be related to the doping. The NIR and MIR spectra do not show any significant changes for all the doped and undoped films, implying that the basic molecular conformation of chitosan is not changed by the weak complexation.
Stepped‐up reactivity of a simple lanthanoid initiator. Polymerization of methyl methacrylate initiated with a lanthanoid alkoxide – ketene system
Authors: Sugimoto Hiroshi , Kato Makoto , Inoue Shohei 
Published: April 2003

AbstractPolymerization of MMA is achieved by using a novel initiator, most probably the lanthanum enolate growing species formed in the polymeritation of ketene with La(OiPr)3. The design of this simple initiator is based on the stimulation of the reactivity of La(OiPr)3, which by itself is inactive, upon the reaction with ketene.
Polymers from coumarins, 2. Design and synthesis of novel main‐ and side‐chain coumarin‐containing polymers
Authors: Fomine Sergei , Pérez Heriberto , Fomina Lioudmila , Tlenkopatchev Mikhail , Ogawa Takeshi 
Published: April 2003

AbstractTwo novel coumarin‐containing monomers, 3,3′‐bis(ethoxycarbonyl)‐6,6′‐bicoumarin (3) and 7‐[(2‐norbornenyl)methoxy]coumarin (7), were prepared and characterized. They give polymers with Mw up to 350 000 and are soluble in common organic solvents. Polymers were prepared by high temperature transesterification reaction (poly‐3) and metathesis polymerization (poly‐7). Poly‐10 was prepared by direct activated polymidation of 6‐aminocoumarin‐3‐carboxylic acid (10). All polymers are amorphous with glass transition Tg of 121 and 64°C for poly‐3 and poly‐7, respectively. High optical quality films can be prepared by solution casting, and in the case of poly‐3 fibers can be drawn from the melt. All polymers show strong photoemission in the region from violet (poly‐7) to blue‐green (poly‐10) (410–510 nm). An electroluminescent device was fabricated from poly‐3 with turn‐on voltage of 4 V.
Random coil dimensions of poly(1‐hexadecene)
Authors: Peña Begoña , Aroca Marcelo , Pérez Ernesto , Bello Antonio , Riande Evaristo , Benavente Rosario 
Published: April 2003

AbstractThe characteristic ratios of three samples of poly(1‐hexadecene) with different tacticities were evaluated from intrinsic viscosity and molecular weight data obtained with a size exclusion chromatograph with dual (concentration plus viscosity) detector. No significant differences were found for the characteristic ratio in the studied range of tacticities. Theoretical calculations for the unperturbed dimensions were also performed for these samples by using the rotational isomeric state model, and compared with the experimental results.
Monomer reactivity vs. regioregularity in polythiophene derivatives
Authors: Fréchette Martin , Belletête Michel , Bergeron Jean‐Yves , Durocher Gilles , Leclerc Mario 
Published: April 2003

AbstractIt has been recently reported that a simple chemical oxidation of 3‐alkoxy‐4‐methylthiophenes leads to highly regioregular polymers with enhanced electrical and optical properties. A joint experimental and theoretical study on different alkyl‐, alkylthio‐, and alkoxy‐substituted thiophenes and bithiophenes has revealed a strong correlation between the distribution of the unpaired electron π‐spin density in the oxidized starting compounds and the regionchemical structure of the resulting polymers. In particular, these calculations have clearly indicated that an asymmetric reactivity of the oxidized monomers or dimers at the 2‐ and 5‐positions can lead to polymers with a high head‐to‐tail content. This theoretical tool should be useful for the future design of regioregular and nonregioregular polymers from chemical or electrochemical oxidative polymerization reactions.
Chiral methacrylic polymers containing permanent dipole azobenzene chromophores. 13C NMR spectra and photochromic properties
Authors: Altomare Angelina , Ciardelli Francesco , Ghiloni Maria S. , Solaro Roberto , Tirelli Nicola 
Published: April 2003

AbstractDynamics in solution and photochromic properties of radical copolymers of (S)‐4‐[N‐(2‐methacryloyloxyethyl)‐N‐(2‐methylbutyl)]amino‐4′‐cyanoazobenzene with butyl methacrylate were investigated. 13C NMR and 2D heteronuclear correlated (HETCOR) spectroscopy allowed assignment of 13C NMR signals and evaluation of main chain tacticity. 13C relaxation times T1 evidenced a rather limited mobility of azobenzene chromophores. Mobility increases with increasing content of butyl methacrylate units, that acts as an internal plasticizer. The limited mobility of the spacer between azobenzene and methacrylate groups is attributed to an interaction between carbonyl oxygen and aminic nitrogen stabilized by the internal charge transfer from the amino to the cyano group. Trans to cis photoisomerization rates turned out to be independent of molecular weight and chemical composition of the investigated photochromic polymers, whereas cis to trans thermal isomerization rates increase with the content of aromatic units. These data suggest that photo‐ and thermal isomerization processes imply an in‐plane inversion and an out‐of‐plane rotation of one of the phenyl rings of the azobenzene chromophores, respectively. Preliminary second harmonic generation measurements indicate that the investigated polymers are endowed with significant non‐linear optical properties.
Polylactones, 37. Polymerizations of L‐lactide initiated with Zn(II) L‐lactate and other resorbable Zn salts
Authors: Kricheldorf Hans R. , Damrau Dirk‐Olaf 
Published: April 2003

AbstractZn(II) L‐lactate (ZnLac2) was prepared either from ZnO and ethyl L‐lactate or with slightly higher optical purity from ZnO and L‐lactide. Using water‐free ZnLac2 L‐lactide was polymerized in bulk at 120°C or 150°C. Higher yields and higher molecular weights were found at 150°C. The highest number average molecular weights (M̄n around 70 000) were obtained at monomer/initiator (M/I) ratios of 4000. Despite the high reaction temperature the isolated poly(L‐lactide)s were 100% optically pure. Analogous polymerizations were also conducted with Zn(II) L‐mandelate or Zn(II) stearate with inferior results. Poor yields and molecular weights were found, when zinc glycolate salt was used as catalyst. Furthermore, numerous polymerizations were conducted with ZnCl2, ZnBr2 or ZnI2 as initiators. Again poly(L‐lactide)s with 100% optical purity were isolated, but most molecular weights were lower and never higher than those obtained with ZnLac2. Therefore, ZnLac2 proved to be the most favorable and fully resorbable (biocompatible) initiator of this study. Finally, the combination of ZnLac2 with a primary alcohol, which plays the role of a coinitiator, allows a broad variation of the molecular weight and the introduction and modification of an ester endgroup. This approach also allows the incorporation of bioactive alcohols such as α‐tocopherol, stigmasterol or testosteron in the form of covalently bound ester endgroups.
Synthesis and characterization of acrylate‐terminated unsaturated copolyesters
Authors: Zlatanic Alisa , Djonlagic Jasna 
Published: April 2003

AbstractThe reaction of the potassium salt of acrylic acid with the potassium salt of a dicarboxylic acid and 1,4‐dibromobutane was applied to the synthesis of three series of acrylate‐terminated copolyesters: poly(tetramethylene maleate‐co‐tetramethylene phthalate) (BMPA), poly(tetramethylene fumarate‐co‐tetramethylenephthalate) (BFPA) and poly(tetramethylene phthalate‐co‐tetramethylene succinate) (BPSA). The monofunctional monomer, the potassium salt of acrylic acid, was used for the introduction of double bonds at the end of the chains and for the regulation of the molecular weight of the polyesters. The telechelic copolyesters were characterized by 1H and 13C NMR spectroscopy, in almost all cases providing an acrylate functionality of two.
Ion‐aggregation in poly[ethylene‐co‐(2‐(4‐carboxyphenoxy)ethyl methacrylate)] and poly[ethylene‐co‐(2‐(3‐carboxypyridin‐6‐yloxy)ethyl methacrylate)] based ionomers
Authors: Iwatsuki Yasuhito , Tsuchida Shigeo , Yano Shinichi 
Published: April 2003

AbstractTwo new ethylene ionomers were synthesized, poly[ethylene‐co‐(5.4‐mol‐% 2‐(4‐carboxyphenoxy)ethyl methacrylate)] partially neutralized with Zn(II) (EMAA‐BZnX), and poly[ethylene‐co‐(5.4 mol‐% 2‐(3‐carboxypyridin‐6‐yloxy)ethyl methacrylate)] (EMAA‐N) and its hydrochloride (EMAA‐NHCl). Differential scanning calorimetric (DSC), X‐ray diffraction, and dielectric and dynamic mechanical relaxation studies were made for the two ionomers to investigate the formation and structure of ionic aggregates. In EMAA‐BZnX, DSC, dielectric and dynamic mechanical data suggest the formation of ionic aggregates in the neutralization range above 40%; X‐ray diffraction data, however, did not show any ionic peak, while the ionic groups were not aggregated at all in EMAA‐NHCl. From these results, the ion‐aggregation in ionomers is discussed with respect to chemical structure and the nature of ionic groups.
Dynamo‐optical and conformational properties of poly(biphenylsulfoneterephthalamide) in concentrated sulfuric acid
Authors: Filippova Tatjana V. , Shtennikova Irina N. , Lavrenko Peter N. 
Published: April 2003

AbstractOptical and hydrodynamic properties of poly(biphenylsulfoneterephthalamide) (PPhSTPhA) (systematic IUPAC name: poly(iminoterephthaloylimino‐2,2′‐sulfonylbiphenyl‐4,4′‐diyl)) in sulfuric acid were investigated by means of flow birefringence and viscometry. Analysis of experimental molecular weight dependence on the shear optical coefficient made it possible to determine optical anisotropy of a monomer segment and a monomeric unit and the rigidity of the macromolecules. It was established that the molecules of this heterocyclic polyamide have the conformation of a kinetically rigid coil.
Studies on the phase separation of polyetherimide‐modified epoxy resin, 1. Effect of curing rate on the phase structure
Authors: Cui Jun , Chen Wenjie , Zhang Zhicheng , Li Shanjun 
Published: April 2003

AbstractThe effect of the curing rate on the phase structure of a new polyetherimide‐modified epoxy systems was studied. Through changing cure agents and cure temperature, selecting different molecular weights and end groups of the polyetherimide (PEI) polymers, the curing rates, the phase separation processes and the morphology of the cured blends were observed employing differential scanning calorimetry, time‐resolved light scattering and scanning electron microscopy. The highly active cure agent 4,4′‐oxydianiline leads to phase separation in the early stage of spinodal decomposition and to a co‐continuous phase structure. As to the 4,4′‐diaminodiphenyl sulfone cured systems, not only the curing rate, but the mobility of the PEI molecule also affected the final morphology of the PEI‐modified epoxy resin.
Anionic ring‐opening polymerization of cyclodisilazanes, 2. Influence of additives on the kinetics of polymerization
Authors: Bruzaud Stéphane , Mingotaud Anne‐Françoise , Soum Alain 
Published: April 2003

AbstractThe kinetics of the anionic ring‐opening polymerization of the DDNMe cyclodisilazane, initiated by benzyllithium, has been investigated in different experimental conditions. In non‐polar solvents, the active centers are aggregated ion pairs which are in equilibrium with a small amount of monomeric species. In the presence of additives such as THF, dioxane or tetramethyl‐ethylenediamine, there is only one type of active center. The aggregates are dissociated into light ion pairs externally solvated by the additive. The paper demonstrates also that the kinetics of the polymerization (i.e., rate constant of propagation kp) is a function of both the nature and the amount of additives.