bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of the conformational transition of poly(methacrylic acid) after a pH jump, 2. Studies of nonradiative energy transfer
Authors: Horský Jiří , Morawetz Herbert 
Published: April 2003

AbstractDoubly labeled poly(methacrylic acid) (PMA) samples with two different concentrations of carbazole and anthracene labels were prepared, and one sample was divided into two fractions of different molecular weight. Emission spectra were recorded in solutions without added salt, at ionic strengths 0,05 and 0,40 and in a 2 : 1 water‐methanol mixture, as a function of pH. The nonradiative energy transfer (NET) from carbazole donor to anthracene acceptor decayed as the PMA coils expanded. On mixing solutions of the labeled PMA with buffer solutions of varying ionic strength in water or aqueous methanol in a stopped‐flow apparatus, the expansion of the PMA was monitored by the decrease in anthracene emission intensity when the solution was irradiated in the carbazole absorption band. Only part of the process could be followed, since the initial expansion occurred in a sub‐millisecond time. Some studies were also carried out on the kinetics of chain contraction when partially neutralized PMA solutions were acidified. The changing NET with the conformational transition of PMA was correlated with the change in the intrinsic viscosity of the polymer. The kinetic data obtained were generally in excellent agreement with those of an earlier study in which conformational changes of PMA were monitored by the changing emission of a dansyl label. In particular, the surprising slowness of the final approach to equilibrium was substantiated.
Quantum yields of the photochromic reactions of heterocyclic fulgides and fulgimides
Authors: Deblauwe Veerle , Smets Georges 
Published: April 2003

AbstractQuantum yields of photocyclization of a fulgide 1a and its corresponding fulgimide 1b upon irradiation with ultraviolet light, and of the back decoloration reaction of the cyclic product 3 on irradiation with visible light, were determined in different solvents and in polymer matrices. The isomerization of the (Z)‐isomers to the (E)‐isomers is very sensitive to the glass transition temperature Tg of the matrix, especially in the case of copolymers of N‐styrylfulgimides 1c with styrene where the photochrome is linked to the polymer chain.
A study of the reduction of polyacetylene by organopotassium compounds and the structure of the resulting conducting polymer
Authors: Mathis Claude , Weizenhöfer Robert , Lieser Günter , Enkelmann Volker , Wegner Gerhard 
Published: April 2003

AbstractHighly oriented trans‐polyacetylene prepared by the method of Edwards and Feast was reduced by exposure to various potassiumorganic compounds. The degree of reduction y could be adjusted to values between y = 0,01 and y = 0,15. X‐ray investigations performed with samples held under in situ conditions revealed 3 different structures. Long‐range order could not be observed up to y = 0,10. For 0,11 ≤ y ≤ 0,15 the chains pack in a square lattice. Here and for y ≤ 0,10 the chains are not in register. The distance between K+ ions which are arranged in chains of various lengths is controlled by the trans‐polyacetylene (0,48nm). Threedimensional order is only observed for y = 0,15, the chains, however, are then tilted with respect to a square basal plane, and K+ ions are only 0,40 nm apart.
The sequence length‐distribution in eutectoid copolymers as obtained from an analysis of the melting process
Authors: Rosenberger Bernd , Asbach Gerd Ingo , Kilian Hanns‐Georg , Wilke Wolfgang , Rodriguéz Mario 
Published: April 2003

AbstractThermodynamics of eutectoid copolymers is based on the assumption that the co‐units are eutectic units. At low concentration of one of these units (non‐crystallizable units, nc‐units), crystallizable sequences (c‐sequences) are formed. Segregation of the eutectic units leads to lamella‐shaped extended c‐sequence crystals, the thickness distribution of which is controlled by the c‐sequence length‐distribution (“structure‐c‐sequence length relationship”). According to thermodynamics the lamellar crystals have to melt selectively and consecutively with respect to their mean thickness. For eutectoid copolymers it is, therefore, possible to deduce the c‐sequence length‐distribution from a thermodynamic analysis of the whole melting process. A computer‐aided method of analyzing differential scanning calorimetry measurements is applied to various semicrystalline copolymers (low‐density polyethylene (LDPE), vicinal‐chlorinated polyethylene, copolymers with OCH2 units). Theoretical structure parameters (crystallinity, mean crystal thickness) and small‐angle X‐ray scattering (SAXS) ‐pattern computed from the c‐sequence length‐distribution are shown to be in good accord with the experimental data. The universal features of the crystallization behaviour of eutectoid copolymers are emphasized. The influence of topochemical reactions onto the distribution of the eutectic co‐units of copolymers containing oxymethylene units is discussed.
X‐ray investigation on highly oriented polyacetylene, 1. Crystal structure of cis‐ and trans‐polyacetylene
Authors: Perego Giovanni , Lugli Gabriele , Pedretti Ugo , Cesari Marco 
Published: April 2003

AbstractThe crystal structure of cis‐ and trans‐polyacetylene (PA) is investigated by X‐ray analysis on highly oriented polymers. cis‐ and trans‐PA are characterized by the same crystalline packing (Pnam space group) with a setting angle of 51°. A random distribution of short‐range in‐phase and out‐of‐phase bond alternation within the lattice is proposed for trans‐PA. For cis‐PA, the “cis‐transoid” model gives a better agreement between experimental and calculated intensities than the “trans‐cisoid” model. The results of the present work are compared with those reported in the literature which were obtained by investigating unoriented or partially oriented PA.
X‐ray investigation on highly oriented polyacetylene, 2. Crystal structure of cis‐ and trans‐polyacetylene
Authors: Perego Giovanni , Lugli Gabriele , Pedretti Ugo , Cesari Marco 
Published: April 2003

AbstractThe crystal structure of cis,trans‐polyacetylene (c, t‐PA) is investigated by X‐ray analysis on highly oriented samples with different contents of the two configurations. The structure is built up of mosaic‐like cis‐trans mixed crystals with the unit cell parameters perpendicular to the chain axis varying continuously between those of all‐cis‐PA and those of all‐trans‐PA. The mixed crystals contain three‐dimensionally ordered blocks of cis‐configuration and three‐dimensionally ordered blocks of trans‐configuration, arranged to each other in a nematic‐like lattice. Distorted short trans‐sequences, characterized by an appropriate slight variation of bond angles, are proposed as junctions between regular cis‐ and regular trans‐segments. The mixed crystals model gives calculated intensities for hk0 reflections in good agreement with experimental observation. Information concerning the average sequence length of cis‐ and trans‐segments in c,t‐PA are given and discussed. The formation of block‐type mixed crystals suggests that cis‐to‐trans isomerization proceeds without lattice disruption but with a mechanism not purely random.
X‐ray investigation on highly oriented polyacetylene, 3 Crystal structure of the iodine/trans‐polyacetylene complex
Authors: Perego Giovanni , Lugli Gabriele , Pedretti Ugo , Allegra Giuseppe 
Published: April 2003

AbstractThe crystal structure of iodine/trans‐polyacetylene complexes (CHIy)x (y = 0,009, 0,035, 0,17 and 0,30) was investigated by X‐ray diffraction analysis of highly oriented samples. An iodine‐containing phase (PAI) was observed in all cases, accompanied by residual crystallinity due to pristine polyacetylene (PA) for y < 0,17. A structural model is proposed for PAI, consisting of blocks of iodine‐saturated PA (PAIs) and blocks of PA, arranged in a mosaic‐like lattice, paracrystalline in character. PAIs, corresponding to (CHI0,40)x, is formed by layers of (CH)x chains alternating with layers containing polyiodide chains, the latter being characterized by ordered stacking of sequentially disordered (I3−‐I5−‐I3−) groups. I… C non‐bonded interactions are identified in the lattice, which may be responsible for the electron transfer from the polymer to the polyiodide anions. Short‐range transverse correlation occurs within the polyiodide layers with a resulting quasi‐regular two‐dimensional lattice of iodines. The iodine and the polymer lattices are incommensurate along c. The model fits the experimental data from an X‐ray fibre diagram. A mathematical expression is derived, which allows to evaluate the intensity scattered by the iodine lattice. An approximate expression of the non‐equatorial intensity along the ξ reciprocal direction was obtained, which accounts for the modulation of the streaks observed in the fibre pattern.
Copolymers of acrylates with sulfur dioxide: Synthesis and structural studies by 13C NMR spectroscopy
Authors: Florjańczyk Zbigniew , Floriańczyk Tadeusz , Zygadło Ewa 
Published: April 2003

AbstractThe copolymerization of sulfur dioxide with methyl, ethyl, butyl or 2‐ethylhexyl acrylate was studied. The influence of the composition of monomer feed and reaction temperature on the composition of the copolymers was investigated. The maximum content of sulfonyl units in the copolymers, obtained at −78°C, was found to be ca. 30 mol‐% and to decrease with increasing temperature. The sequence distribution in the copolymers was determined by 13C NMR spectroscopy. It was proved that acrylates do not undergo alternating propagation with SO2, and the minimum number of acrylate monomeric units in a homosequence is 2. The results obtained were compared with those obtained from studies on the copolymerization of SO2, with other monomers, and are discussed in terms of the alternating copolymerization theory and the penultimate model.
Preparation of block copolymers by ring‐opening polymerization of cycloalkenes initiated by a tungstencyclopentylidene complex
Authors: Greene Ruth M. E. , Ivin Kenneth J. , Rooney John J. , Kress Jacky , Osborn John A. 
Published: April 2003

AbstractThe possibility of making block copolymers at room temperature from the monomer pairs 2a,b/1, 4/1, 5/1 and 5/3 (1 = norbornene = bicyclo[2.2.1]hept‐2‐ene; 2a,b = anti‐ and syn‐7‐methylbicyclo[2.2.1]hept‐2‐ene; 4 = methyl endo‐bicyclo[2.2.1]hept‐5‐ene‐2‐carboxylate; 5 = endo‐bicyclo[2.2.1]hept‐5‐ene‐2‐carbonitrile; 3 = 1,5‐cyclooctadiene) was explored using

as initiator of metathesis polymerization in CD2Cl2. The reactions of successive small amounts of the monomers with the catalyst were first followed by 1H NMR to determine the rate of the reaction and the stability of the metal‐carbene propagating species. AB and ABA type block copolymers were prepared on this basis and analysed by GPC. An increase in molecular weight after each addition was observed in most cases. Secondary metathesis reactions of double bonds in the polymer chains appear to be significant only for blocks formed from 3.
Overtone absorption in macromolecules for polymer optical fibers
Authors: Groh Werner 
Published: April 2003

AbstractThe development of polymer optical fibers (POF) leads to the fundamental question about the lowest loss attainable with organic polymers. In the present paper, we address this question with experimental and theoretical work on vibrational overtone absorption of different molecular bonds, which is the dominant loss contribution in POF's. The investigations, the first of their kind for several bonds, show good agreement between experiment and theory for the experimentally accessible CH‐, CD‐, and OH‐vibrations. Applied to CF‐, CCl‐, and (CO)‐ vibrations, the calculations lead to the conclusion that in the most important wavelength region 600 – 900 nm fully halogenated polymers show a negligible loss contribution due to overtone absorption. In these cases, the theoretical lower loss limit should be a few dB/km.
On the additive nature of the first‐order interactions at the trifunctional branch points in copolymers of ethylene and a larger 1‐alkene
Authors: Mathur Saubhagya C. , Mattice Wayne L. 
Published: April 2003

AbstractThe characteristic ratio and its temperature coefficient were examined for alternating copolymers of ethylene and propylene. The stereochemical composition covers the entire range from racemic through meso. Two different assignments, τ = 0 and σ, were used for the statistical weight employed when a methylene group participates in simultaneous first‐order interactions with another methylene group and a methyl group. The best description of the conformational properties of the alternating copolymers is achieved with the larger value for τ. This assignment is the one that would be expected if the first‐order interactions were pair‐wise additive.
Synthesis and properties of thermotropic liquid‐crystalline polymers containing transition metals
Authors: Hanabusa Kenji , Higashi Jun‐ichi , Koyama Toshiki , Shirai Hirofusa , Hojo Nobumasa , Kurose Akio 
Published: April 2003

AbstractNew thermotropic, liquid‐crystalline polyesters (5a, b, 6a, b) with mesogenic bipyridinediyl units were synthesized. They form complexes with Fe(II) and Cu(II) salts. Homopolyesters 5a, b, containing no metal or less than a certain amount of metal, are smectic. A nematic mesophase was observed in the case of copolyester 6a, b. The structural properties of a polyester complex 5a with Cu, as crystal, liquid‐crystal and isotropic liquid, were examined by ESR.
Saturated polyesters as emulsifiers for emulsion copolymerization of unsaturated polyester resins with styrene
Authors: Baumann Harald , Joos Betina , Funke Werner 
Published: April 2003

AbstractIntramolecularly crosslinked macromolecules (ICM) from unsaturated polyesters (UP) and styrene, respectively from technical divinylbenzene (t‐DVB), were prepared by emulsion copolymerization (ECP). Saturated polyesters of different compositions and molar masses between 1200 and 2400 were used as emulsifiers (ESP). The influence of molar mass and structure at various concentrations of the ESP on yield, number and diameter of the ICM and their composition was studied. For comparison, also sodium dodecyl sulfate (SDS) was used as emulsifier.
13C NMR analysis of ethyl chain‐end groups: A method for active site investigation in Ziegler‐Natta catalysis
Authors: Sacchi Maria Carmela , Locatelli Paolo , Tritto Incoronata 
Published: April 2003

AbstractThe stereoregularity of the insertion of the first propene unit into the active titanium‐ 13CH2CH3 bond is evaluated, by 13C NMR analysis, in highly regular polypropene samples prepared in the presence of different traditional and high yield Ziegler‐Natta catalytic systems. Selectively enriched aluminiumalkyls are used as cocatalysts. The comparison of the data obtained shows that the ratio between the erythro and threo placement of the first propene unit varies from one catalyst to the other and represents a reproducible character of each system. Some suggestions about steric features of the active sites of the different catalytic systems are inferred.
Polymers with pendant carbazolyl groups, 4. Photoconductive properties of some polysiloxanes with pendant carbazolyl groups
Authors: Domes Helmut , Fischer Reiner , Haarer Dietrich , Strohriegl Peter 
Published: April 2003

AbstractThe photoconductive properties of a series of polysiloxanes with pendant carbazolyl groups (1a—c) are described. In these polymers the carbazole moieties are separated from the siloxane backbone by alkylene spacers of different length. The properties of the novel compounds are compared with the well known photoconductor poly(N‐vinylcarbazole) and the model compound N‐isopropylcarbazole. Effective charge carrier mobilities were measured by means of the time‐of‐flight technique. Polymer 1a exhibits the largest carrier mobility of the three polysiloxanes. The mobilities for polymers 1b and 1c are somewhat smaller and comparable to poly(N‐vinylcarbazole). The transport of charge carriers in an amorphous material can be described as a hopping process. The activation energy for that process was calculated from the temperature dependence of the carrier mobility. The polysiloxanes 1a—c show the same activation energy of about 0,6 eV. The activation energies in poly(N‐vinylcarbazole) and N‐isopropylcarbazole are of the same magnitude as in the polysiloxanes. Two different models were used for evaluating the mobility data. The field dependence of the carrier mobility is best described by a modified version of Gill's model whereas no distinction between the two models could be made from the temperature dependence of the mobility.
Polymere Protonenschwämme, 1. Synthese von Monomeren auf der Basis von Naphthalin und Fluoren
Authors: Hallensleben Manfred L. , Kansy Hartmut 
Published: April 2003

Abstract1,8‐Bis(dimethylamino)‐4‐(4‐vinylphenyl)naphthalene (33), 1,8‐bis(dimethylamino)‐4‐(4‐vinylbenzyl)napthalene (35), 4,5‐bis(dimethylamino)‐9‐(4‐vinylbenzyl)fluorene (37) and 4,5‐bis(dimethylamino)‐9,9‐bis(4‐vinylbenzyl)‐fluorene (38) were synthesized as potential vinyl monomers.
Can lewis acids initiate the polymerization of cyclic siloxanes via direct addition?
Authors: Jordan Elisabeth , Lestel Laurence , Boileau Sylvie , Cheradame Hervé , Gandini Alessandro 
Published: April 2003

AbstractFollowing a preliminary report stating that ethylboron sesquitriflate initiates the polymerization of hexamethylcyclotrisiloxane (D3), a more rigorous investigation was carried out to ascertain that cyclic siloxanes can indeed be polymerized by Lewis acids without the intervention (cocatalysis) of proton‐donor impurities. The evidence gathered with this strong boron Lewis acid suggested that direct initiation does occur, although its efficiency is much lower than that of an equivalent amount of a strong Brønsted acid. The use of a sterically hindered pyridine was a key factor in discriminating between monomer protonation and direct initiation.
Syntheses of thermotropic poly(azine‐ether)s derived from 2,4‐hydroxybenzaldehyde and 2,4‐dihydroxyacetophenone
Authors: Marcos Mercedes , Navarro Fernando , Oriol Luis , Serrano Jose Luis 
Published: April 2003

AbstractPoly(azine‐ether)s (1a and 1b) derived from 2,4‐dihydroxybenzaldehyde and 2,4‐dihydroxyacetophenone, respectively, were synthesized by condensation of the corresponding dicarbonyl monomer (2a or 2b) containing 10 methylene units with hydrazine hydrate. For the preparation of 1a ethanol or acetonitrile were found to be the best solvents, DMF or 1,4‐dioxane for the preparation of 1b. The liquid‐crystalline behaviour of the polymers was studied by DSC and on the hot stage of a polarizing microscope. All of them formed nematic mesophases in melts.
Synthèse et copolymérisation d'acrylamides comportant le groupement dihydroxyphosphoryloxyalkyle
Authors: Touet Joël , Pierre Chantal , Brown Eric , Boschetti Egisto 
Published: April 2003

Abstractω‐Aminoalkyl dihydrogen phosphates 5a–c, 7 and 9 were obtained in a simple and reproducible fashion by O‐phosphorylation of the corresponding aminoalcohols with ClPO3H2 generated in situ by controlled hydrolysis of POCl3. Reaction of these phosphates with acrylic or methacrylic anhydride in water/THF mixture afforded a series of new acrylic monomers (11a–h) bearing a phosphoryl group. Inverted emulsion copolymerization of the latter with the hydrophilic comonomers N‐[1,1‐bis(hydroxymethyl)‐2‐hydroxyethyl]acryl‐ or methacrylamide (12a or 12b) and with the cross‐linker N,N′‐methylenediacrylamide (13) afforded various gels in the form of spherical beads. Preliminary experiments showed that some of these copolymers could be efficiently used as stationary phases for the separation of proteins by ion‐exchange chromatography.
Acrylamide polymerization photoinitiated by HCrO4−
Authors: Fageol Patrick , Bolte Michèle 
Published: April 2003

AbstractThe photoredox process occurring between HCrO4− and acrylamide (AAm) leads to the formation of chromium(III) and polyacrylamide. The influence of pH, monomer concentration, absorbed light intensity Ia and chromium(VI) concentration on the polymerization rate Rp are reported. Two different domains are detected as a function of chromium(VI) concentration: At low concentration, where Rp increases with chromium concentration, a process of termination by mutual annihilation of the macroradicals accounts for the experimental dependence Rp ∝ [AAm]3/2 · Ia. At higher concentration, Rp decreases when the chromium concentration increases; a process of oxidative termination of the radicals by chromium(VI) is involved corresponding to a dependence Rp ∝ [AAm]2. Ia. The evolution of the polymer molecular weight as a function of the different parameters controlling the polymerization is described.
Studies on syntheses and permeabilities of special polymer membranes, 70. Permeation and separation characteristics for aqueous alcoholic solutions by evapomeation and pervaporation through polystyrene membranes
Authors: Uragami Tadashi , Morikawa Takeshi 
Published: April 2003

AbstractPermeation and separation characteristics of methanol/water and ethanol/water mixtures by evapomeation and pervaporation through unelongated and biaxially elongated polystyrene membranes were investigated under various conditions. All polystyrene membranes predominantly permeated water molecules in both methods. Permeation rates in the case of evapomeation were smaller than those of pervaporation, but the separation factors in the former case were greater than those in the latter. The separation factors through the biaxially elongated polystyrene membrane were larger than those of the unelongated polystyrene membrane, this value being ca. 1500 for an azeotropic mixture of ethanol/water. Permeation and separation mechanisms through these polystyrene membranes involved in both membrane separation techniques are discussed from the viewpoints of solution‐diffusion of permeating molecules and of the membrane structure.
Investigations of poly(vinyl alcohol)/poly(N‐vinyl‐2‐pyrrolidone) blends, 1. Compatibility
Authors: Ping Zheng‐Hua , Nguyen Quang Trong , Néel Jean 
Published: April 2003

AbstractBlends of crystallizable poly(vinyl alcohol) (PVA) with poly(N‐vinyl‐2‐pyrrolidone) (PVP) made from aqueous solutions appear to be miscible in the whole composition range according to DSC results. A large negative value of the interaction parameter between the two polymers was found from melting point depressions. IR spectroscopy evidenced compatibility of the two polymers on a molecular level. DSC, density and IR results all show a proportion of pure PVA crystallites in blends, which decreases with increasing PVP content and becomes nil at about 50 wt.‐% of PVP. However, close examination of the hydroxyl stretching region of the blends indicates the presence of organized regions of PVA beyond this limit. According to IR results, the sequence of decreasing hydrogen‐bonding power should be the following: multiple hydroxyl‐hydroxyl bonding in organized PVA regions, hydroxyl‐carbonyl bonding between the two polymers, and simple hydrogen‐hydrogen bonding in amorphous PVA regions. It appears that the PVA component can be held in the amorphous state by hydrogen bonding with the PVP component when there is a sufficient amount of the latter in the blend. The amorphous part of PVA is compatible with PVP, but the crystallizable part is not in its most stable form.