bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic fourier transform infrared spectroscopy of liquid‐crystalline elastomers
Authors: Bräuchler Martin , Boeffel Christine , Spiess Hans Wolfgang 
Published: April 2003

AbstractThe influence of mechanical deformation on the orientation behaviour of the phenyl benzoate mesogenic groups in polyacrylate‐ and polymethacrylate‐based liquid‐crystalline (l. c.) elastomers with spacers of six methylene units is investigated as a function of temperature and time by means of linear‐dichroism infrared spectroscopy. The mesogens in the polymethacrylate elastomers preferably align perpendicular to the stretching direction and show a biaxial phase with homeotropic orientation. The changes in sample geometry, especially the film‐thickness variation during deformation, are studied. The orientation behaviour of the mesogens in the polyacrylate elastomers is different in the nematic and smectic phase. On stretching, the mesogens align parallel in the nematic and perpendicular to the stretching direction in the smectic phase. The orientation of a film stretched in the smectic phase, however, changes to be parallel to the stretching direction if its temperature is raised once above the smectic‐to‐nematic transition temperature. The dynamics of reorientation of the mesogens strongly depends on temperature. With high mobility of the mesogens no phase lag between deformation and orientation can be detected on a timescale of 100 ms. The orientation behaviour of l. c. elastomers is very complex and depends on many parameters, each of which is important.
Synthesis of poly(2‐ethyl‐2‐hydroxymethyltrimethylene carbonate)
Authors: Kühling Steffen , Keul Helmut , Höcker Hartwig , Buysch Hans‐Josef , Schön Norbert 
Published: April 2003

Abstract2‐Ethyl‐2‐hydroxymethyltrimethylene carbonate (5‐ethyl‐5‐hydroxymethyl‐1,3‐dioxan‐2‐one) (1) was treated with trimethylsilyl chloride, benzyl chloroformate and phenyl isocyanate to give the corresponding 5,5‐disubstituted 1,3‐dioxan‐2‐ones 2, 3 and 4. These monomers were subjected to anionic ring‐opening polymerization reactions with lithium alcoholates as initiators. The polymers obtained usually exhibit linear structure; under special conditions slightly branched polymers were obtained. Poly(2) and poly(3) were subjected to polymer‐analogous reactions—hydrolysis and hydrogenation—by which the protective groups are removed and poly(1) was obtained. The hydroxyl groups in poly(1) are susceptible to a polymer‐analogous reaction. Poly(4) obtained by reaction of poly(1) with phenyl isocyanate was identical with poly(4) obtained by ring‐opening polymerization of the corresponding monomer 4. All these new monomers were characterized by means of 1H and 13C NMR spectroscopy as well as elemental analysis. The polymers were analyzed with respect to their primary structure, their molecular weight and molecular weight distribution. The thermal properties of some of the polymers are discussed.
Cationic polymerization of methoxyallene with Lewis acids
Authors: Takahashi Tatsuya , Yokozawa Tsutomu , Endo Takeshi 
Published: April 2003

AbstractThe cationic polymerization of methoxyallene (1) was carried out with some Lewis acids at −50°C in dichloromethane. BF3OEt2 was found to be an effective catalyst for the cationic polymerization of 1. From analyses of 1H and 13C NMR spectra, the obtained polymers consist of units with the 1,2‐double bond of 1 being opened, although the 2,3‐double bond is consumed also to an amount of 24 to 43 mol‐%. This decrease in 2,3‐double bond content in the polymer may be attributed to intramolecular cyclization of the propagating cation and/or the intermolecular reaction of the propagating cation with polymer to produce a graft polymer. Moderately polar solvents such as dichloromethane proved to be best suited for obtaining polymers with high double bond content.
Polymérisation induite sous irradiation laser visible, 5. Le système éosine/amine/sel de iodonium
Authors: Fouassier Jean P. , Chesneau Eliane 
Published: April 2003

AbstractA study was conducted of the excited states of the combination eosine/amine/iodonium salt through time‐resolved laser spectroscopy, of the photolysis products formed under light exposure, and of the rates of polymerization. It allows the process to be precised and discussed. It is apparent that the iodonium salt has no effect on the initiation step of the polymerization reaction but sharply decreases the termination reactions. The formation of a complex between eosine and the iodonium salt is suggested; this complex is destroyed in the presence of amine.
Optical investigations on a liquid‐crystalline side‐chain polymer with biaxial nematic and biaxial smectic A phase
Authors: Leube Hartmann Friedrich , Finkelmann Heino 
Published: April 2003

AbstractA liquid‐crystalline side‐chain polymer with laterally incorporated naphthalene groups in the mesogenic moiety is investigated in binary mixtures with an optical uniaxial low‐molar‐mass liquid crystal. Mixtures with up to 50 mol‐% content of the monomeric liquid crystal show a biaxial nematic phase. At lower temperatures a new biaxial smectic phase is observed, which corresponds to the smectic A phase. The angles between the optical axes are measured in dependence of temperature and mixture composition. Starting from the neat polymer, the angles decrease in the nematic as well as in the smectic phase with increasing mole fraction of the uniaxial liquid crystal. From the results a phase transformation uniaxial nematic to biaxial nematic can be inferred.
Transitional properties of liquid‐crystalline side‐chain polymers derived from poly(p‐hydroxystyrene)
Authors: Attard George S. , Dave Jayrang S. , Wallington Andrea , Imrie Corrie T. , Karasz Frank E. 
Published: April 2003

AbstractA series of liquid‐crystalline polystyrene derivatives with ω‐(4‐(4‐fluorophenylazo)phenoxy)‐alkoxy pendant groups have been synthesized and characterized. Homologues with four or more methylene units in the spacer chain exhibit smectic liquid‐crystalline phases, while the homologue with three methylene units forms an amorphous glass. The smectic A‐isotropic (SA‐I) transition temperatures show a marked odd‐even effect as a function of the parity of the spacer chain. This odd‐even behaviour is also found in the variation of ΔS/R at the SA‐I transition across the series. A marked hysteresis between the transition temperatures determined on heating and the transition temperatures determined on cooling is observed. A molecular interpretation of these phenomena is proposed.
A study of interface reaction during composite formation between polybutadiene epoxide and highly dispersed silica or alumina
Authors: Hortschansky Peter , Heublein Günther 
Published: April 2003

AbstractThis paper reports on interface reactions between polybutadiene epoxide (PBDE) and highly dispersed oxides (SiO2, Al2O3) during composite formation. Mechanisms of these reactions are discussed in dependence on the nature and concentration of active surface species (Brönsted‐ and Lewis‐acid sites). Conclusions regarding the macroconformations of chemisorbed PBDE in the system PBDE/SiO2 can be drawn by determination of interface conversion between epoxide and silanol groups.
Polymers with sulfinyl and oxyethylene constitutional units as catalysts of nucleophilic substitution reactions
Authors: Valter Bohumír , Masař Bohumil , Janout Václav , Hrudková Hana , Čefelín Pavel , Tur Dzidra R. , Vinogradova Svetlana V. 
Published: April 2003

AbstractThe catalytic activity of polystyrene‐ and polyphosphazene‐supported monosulfoxides and oligo(oxyethylene)s was investigated in the Williamson alkylation of sodium phenoxide with 1‐bromooctane in 1,4‐dioxane at 75°C. Polymer‐supported monosulfoxides are less efficient than low‐molecular‐weight species. Polymer‐supported oligo(oxyethylene)s with pseudo‐crown‐ether structures show a polymer effect, which may even be stressed by the presence of onium units in the side chains.
Redox‐chemical investigations of soluble oligo(p‐phenylene)s
Authors: Bohnen Angelika , Heitz Walter , Müllen Klaus , Räder Hans‐Joachim , Schenk Rainer 
Published: April 2003

AbstractThe chemical and electrochemical reductions of two series of oligo(p‐phenylene)s with different substitution patterns are investigated. The resulting anionic species are characterized on the one hand using NMR spectroscopy and quenching experiments obtaining dianions in the case of terphenyls and quaterphenyls. On the other hand, cyclic voltammetric experiments were carried out with the results that compounds with substitution only in the terminal rings behave as typical conjugated oligomers, and substituents in the middle rings disturb the conjugation and alter the mechanism of electron transfer. Further, the charge distribution, the stereodynamic behaviour and the redox potentials are examined as a function of chain length and substitution. The reduction of the title compounds shows that only the substitution of terminal phenyl rings leads to suitable model compounds for the doping of poly(p‐phenylene).
Modification of silicone surface by graft polymerization of acrylamide with corona discharge
Authors: Okada Toshiyuki , Ikada Yoshito 
Published: April 2003

AbstractIn order to render the surface of silicone hydrophilic without changing its bulk properties, acrylamide was grafted onto its surface. A silicone sheet was first treated with a corona discharge in air to introduce peroxides onto the surface. The concentration of peroxide introduced to the surface was determined using 2,2‐diphenyl‐1‐picrylhydrazyl and the maximum concentration was about 1,80 · 10−8 mol/cm2 when the corona discharge treatment was performed with 9 or 15 kV. Graft polymerization was allowed to proceed by heating the aqueous solution of the monomer together with the immersed silicone pretreated with the corona discharge. It was critical to throughly deaerate the silicone before and after the corona discharge treatment. Unless deaeration was sufficient, graft polymerization did not occur, irrespective of heating. The friction coefficient of the poly(acrylamide)‐grafted silicone decreased drastically, even if only a small amount of poly(acrylamide) was grafted onto the surface of the silicone. Collagen could be immobilized covalently using a water‐soluble carbodiimide, 3‐dimethylaminopropyl(ethyl)‐carbodiimide hydrochloride, when the grafted poly(acrylamide) chains were converted to poly(acrylic acid) by alkaline hydroysis, in order to introduce carboxyl groups. The maximum concentration of collagen immobilized was 4,0 μg/cm2.
The measurement of concentration and stability of weak acids and a study of the ionisation of polysaccharides using buffer capacity curves
Authors: Petzold James C. , Herrington Thelma M. 
Published: April 2003

AbstractA technique using buffer capacity has been developed for evaluating the approximate pK values of the stability constant K, of polyelectrolytes. The technique has been applied to hemicellulose extracted from woodpulp (pK ≈ 3,9 (0,1 M NaCl)) and dextran (pK = 13,55 ± 0,2 (2 M NaCl)). Verification of the method has been obtained by applying it to acetic acid (pK = 4,55 ± 0,02 (0,1 M NaCl), pK = 4,70 ± 0,02 (0,001 M NaCl)) and glucose (pK = 12,00 ± 0,05 (2 M NaCl)). Glucose was found to turn peppermint green in NaOH solutions. At least 50% of the surface charge of woodpulp was found to originate from its hemicellulose coating.
Living cationic polymerization of vinyl monomers by organoaluminium halides, 7. Effect of basicity and steric hindrance of added esters on the living polymerization of isobutyl vinyl ether with C2H5AlCl2
Authors: Aoshima Sadahito , Shachi Kenji , Kobayashi Eiichi , Higashimura Toshinobu 
Published: April 2003

AbstractThe living cationic polymerization of isobutyl vinyl ether (IBVE) with 1‐(isobutoxy)ethyl acetate (1)/C2H5AlCl2 as initiating system in hexane at +40°C in the presence of carboxylates was investigated in regard to the effect of the basicity and the steric hindrance of the added esters on the rate and living nature of the polymerization. The effect of the basicity was evaluated by use of four p‐substituted ethyl benzoates (XC6H4COOC2H5; X: CH3O, CH3, H, Cl). Despite of the difference in basicity, all the benzoates gave living polymers with narrow molecular‐weight distributions (ratios of weight‐ to number‐average molecular weights Mw/Mn ≤ 1,1), whereas the polymerization rate depends on the p‐substituents as follows: CH3O < CH3 < H < Cl. Another series of experiments showed that the steric environment around the carbonyl group also affects the polymerization rate. Namely, using carboxylates with various carbonyl substituents (RCOOCH3; R: CH3, C2H5, (CH3)2CH, (CH3)3C), the polymerization rate increases with increasing bulkiness of the substituent R in the order: (CH3)3C > (CH3)2CH > C2H5 > CH3. These electronic and steric effects are consistent with the stabilization of the carbocation by the nucleophilic interaction of added bases. Fast living polymerization of IBVE can be obtained using the initiating system 1/C2H5AlCl2 in the presence of methyl chloroacetate, an ester with a strongly electron‐withdrawing group.
Conformation of phenyl rings in the helical chain polymer poly(triphenylmethyl methacrylate)
Authors: Wang Yuechuan , Ding Mengxian , Wang Fosong 
Published: April 2003

AbstractThe conformation of phenyl rings in the side groups of the helical chain polymer poly(triphenylmethyl methacrylate) (1) in solution was studied by spectroscopic methods. According to the Raman spectrum the phenyl rings of 1 and triphenylmethyl methacrylate in solution have the same depolarization ratio at 1 002 cm−1. The electronic spectra (ultraviolet and fluorescence) of 1 are similar to those of model substances, except for the “red shift” of the spectra of about 5 nm. It was concluded that the phenyl rings can rotate around the phenylC bond.
Coordination polymerization of lactides, 2. Microstructure determination of poly[(L,L‐lactide)‐co‐(ε‐caprolactone)] with 13C nuclear magnetic resonance spectroscopy
Authors: Kasperczyk Janusz , Bero Maciej 
Published: April 2003

AbstractA detailed analysis of the structure of poly[(L,L‐lactide)‐co‐(ε‐caprolactone)] IUPAC‐preferred name is dilactide:
was performed by means of high resolution 13C NMR (75 MHz) spectroscopy. The polyesters were obtained using various comonomer ratios and initiators aluminium tris(acetylacetonate) or the system Al(C2H5)3 + Zn(C2H5)2 + H2O. Signals in spectra were assigned to appropriate structural sequences. Two types of chain structure containing different sequences and depending on the initiator used in copolymerization were found.
Fabrication biocompatible de microcapsules par polymérisation ensemencée autour de microsphères d'agarose
Authors: Dupuy Bernard , Cadic Christine , Rouais François , Baquey Charles , Ducassou Dominique 
Published: April 2003

AbstractA new process for microencapsulating cells is described. Cells in solution in agarose were extruded from a syringe into a paraffin‐oil containing medium. Solid microspheres were produced when the agarose gelled. A rigid interface around each bead was produced by polymerization of a latex‐seeded aqueous solution of a mixture of 5 wt.‐% acrylamide and 0,25 wt.‐% N,N‐methylenediacrylamide. Cell viability was demonstrated by radioimmunoassay of prolactin liberated from encapsulated pituitary cells.
Effects of chain length and size of alkyl group in radical polymerization of dialkyl fumarates as studied by electron paramagnetic resonance spectroscopy
Authors: Yamada Bunichiro , Fujita Mitsuo , Otsu Takayuki 
Published: April 2003

AbstractPropagating radicals of diethyl and diisopropyl fumarates are detectable by electron paramagnetic resonance (ESR) spectroscopy in homogeneous systems at room temperature or above. Resolution of the spectra was found to be much improved by raising the temperature to 120°C, and the spectra are shown to correspond to three components according to chain length. Composition of the spectra was dependent on the polymerization conditions. The hyperfine splitting constants were determined by computer simulation of the spectra. The coupling constant for the α‐hydrogen is noted to be as small as 3 to 4 G, and those for the β‐hydrogen are ca. 4, 14 and 30 G.
Copolymerization of propene with 1‐alkenes using a MgCl2/TiCl4 catalyst
Authors: Xu Zhikang , Feng Lingxiang , Wang Dongli , Yang Shiling 
Published: April 2003

AbstractCopolymerization of propyleneSystem name: propene.
and 1‐alkenes (1‐octene, 1‐decene, 1‐dodecene, 1‐tetradecene, 1‐hexadecene) were studied with the catalyst system MgCl2/TiCl4‐Al(i‐Bu)3. It was found that the polymerization productivity and the consumption rate of propylene are improved significantly in the presence of the comonomer. The total productivity of propylene/1‐alkene copolymerizations decreases as follows: 1‐octene > 1‐decene > 1‐dodecene > 1‐hexadecene > 1‐tetradecene. The reactivity ratios were estimated from the copolymerization results.
Synthesis and structural studies of new copolyimides 2. Influence of pyromellitimide rings on copolymer structure
Authors: Orzeszko Andrzej , Mirowski Krzysztof 
Published: April 2003

AbstractThe reaction of pyromellitic dianhydride (1,2 : 4,5‐benzenetetracarboxylic dianhydride) (1) with L‐ and D‐alanine (2L) and (2D) leads to new monomers which were used to synthesize new copolymers. These copolymers were obtained as a product of the condensation of optical isomers of bis[N‐(1‐chloroformylethyl)]pyromellitimides (CFEP) with poly(ethylene glycol) PEG‐2000 (5). The effect of monomer structure on the structure and thermal properties of the polymers was studied using X‐ray diffraction, differential scanning calorimetry and thermogravimetry. The copolymers were compared with similar copolyimides obtained previously from bis(N‐chloroformylmethyl)pyromellitimide and poly(ethylene glycol), PEG 2000. The dominating effect of poly(ethylene glycol) comonomer on the crystallinity, structure and thermal stability of these new copolymers is proven.
Liquid crystal polymers containing macroheterocyclic ligands, 7. Synthesis and characterization of 4‐[(4‐methacryloyloxy)‐undecyloxy‐2‐methylphenylethynyl]phenyl (benzo‐15‐crown‐5)‐4′‐carboxylate
Authors: Rodenhouse Randall , Percec Virgil 
Published: April 2003

AbstractThe synthesis and thermal characterization of 4‐[(4‐methacryloyloxy)undecyloxy‐2‐methyl‐phenylethynyl]phenyl (benzo‐15‐crown‐5)‐4′‐carboxylate (8) and of poly(8) are described. 8 exhibits monotropic nematic and smectic mesophases, while poly(8) shows enantiotropic nematic and smectic mesophases. In spite of its very long flexible spacer, poly(8) does not display sidechain crystallization.
Synthesis of polymer latex containing SH groups on the surface, 2. Emulsion polymerization of styrene in the presence of a polymerizable isothiuronium salt as a comonomer and the subsequent hydrolysis
Authors: Watanabe Shinji , Nakahama Seiichi , Yamaguchi Kazuo 
Published: April 2003

AbstractEmulsion polymerization of styrene using various isothiuronium salts as comonomers and the subsequent alkaline hydrolysis of the product gave latices containing mercapto (SH) groups. Four styrene derivatives of isothiuronium salts and a methacrylate counterpart were employed as comonomers. The yield, size distribution, and sulfur content of the latices are affected by initiators and isothiuronium salts employed. With a cationic initiator (2,2′‐azobis[(2‐imidazolin‐2‐yl)propane] dihydrochloride) and any isothiuronium salt, latices of narrow size distributions were obtained in high yield. The sulfur content of the latices is comparable to that calculated from the feed ratio of the salt to styrene monomer. In case of an anionic initiator (K2S2O8), only 2‐[4‐vinylphenylmethyl]‐and 2‐[3‐(methacryloyloxy)propyl]‐isothiuronium chloride gave latices with narrow size distribution in high yield, whereas the sulfur content was lower than the calculated one. The isothiuronium salts on the latices were converted into mercapto groups by hydrolysis in aqueous alkaline solution. Thus, we obtained latices containing mercapto groups on the surface with narrow size distributions.
Effects of large ring‐substituents on radical polymerization behaviour of 2,6‐diisopropylphenyl methacrylate
Authors: Yamada Bunichiro , Matsumoto Akikazu , Otsu Takayuki 
Published: April 2003

Abstract2,6‐Diisopropylphenyl methacrylate (DIPPMA) noted as a monomer bearing the largest ring substituents among polymerizable o‐substituted phenyl methacrylates was homo‐ and copolymerized. Steric hindrance caused by the substituents significantly reduced the overall rate of polymerization and reactivities in copolymerization. Suppression of termination by the steric effect seems to be of minor importance. The ceiling temperature was determined to be 49°C at a concentration of 1 mol · dm−3 in benzene. The overall rate and the degree of polymerization were confirmed to decrease with increasing temperature under the influence of the ceiling temperature. Triad tacticity of poly(methyl methacrylate) derived from poly(DIPPMA) was determined to be rr = 29%, rm = 53%, and mm = 18% at 40°C, indicating that the steric effect of the large substituents on propagation rendered almost random addition.
Determination of the molecular mobility and the free volume of thin polymeric films with fluorescence probes
Authors: Anwand Dirk , Müller F. Werner , Strehmel Bernd , Schiller Kurt 
Published: April 2003

AbstractTriphenylmethane (TPM) dyes were used as fluorescence probes for the characterization of thin polymeric layers. Glass transition temperature, mobility and free volume can be determined by this method. A correlation was found between the dye fluorescence and the free volume of the polymer. Above the glass transition temperature of the polymer the activation energies for the rotation of the dye phenyl groups were found at ca. 25–35 kJ/mol, at temperatures below the glass point these energies are in the range of 5–12 kJ/mol. Nearly all probes describe the free volume equally well. A relation was found between the dye mobility and gas diffusion constants (ammonia and oxygen).
Polymerization of lactones, 12. Polymerization of L‐dilactide and L,D‐dilactide in the presence of potassium methoxide
Authors: Jedliński Zbigniew , Wałach Wojciech , Kurcok Piotr , Adamus Graz̀yna 
Published: April 2003

AbstractThe anionic polymerization of L‐ and L,D‐dilactide initiated with potassium methoxide in solution of tetrahydrofuran at a temperature of 20°C is investigated. It is found that this process leads with high yield to the corresponding polyesters. The optical rotation measurements and the microstructure of the polymers obtained indicate that side reactions, i. e. racemization and transesterification, are strongly limited.
Physical ageing of amorphous polymers. Theoretical analysis and experiments on poly(methyl methacrylate)
Authors: Pérez Joseph , Cavaille Jean Yves , Calleja Ricardo Díaz , Ribelles José Luis Gómez , Pradas Manuel Monleón , Greus Amparo Ribes 
Published: April 2003

AbstractStructural relaxation of glassy poly(methyl methacrylate) (PMMA) was studied with several techniques: differential scanning calorimetry (DSC), volumetry by thermomechanical analysis (TMA) and mechanical spectroscopy. A theory is proposed in order to interpret the data in a unique theoretical framework. This theory is developed on the basis of two main physical assumptions: (i) the existence in amorphous polymers of quasipunctual defects whose concentration decreases during structural relaxation, and (ii) the occurrence of hierarchical correlation effects conditioning molecular mobility. As a first approximation a self‐consistent semiquantitative description of the results is obtained, i. e., the experimental results obtained for the different quantities on PMMA can be accounted for employing always the same set of model parameters. However, it seems that a significant difference exists between the relaxation times associated with the different experimental techniques.