bluuebunny/crossref_metadata_2025_split huggingface dataset:
1H‐13C NMR inverse detection of poly(3‐hexylthiophene): Characterization of the structural defects
Authors: Mucci Adele , Schenetti Luisa 
Published: April 2003

AbstractNMR inverse detection was applied to the study of regiochemistry of a highly head to tail (HT)‐regioregular poly(3‐hexylthiophene) (PHT). It proved to be a valuable tool in the characterization of polymerization defects not directly revealable or assignable by inspection of the one‐dimensional 13C spectrum. Almost all the 13C chemical shifts of the four configurational triads of PHT were derived by utilizing the aromatic protons, whereas through the α‐protons of the aliphatic chain only carbons belonging to HT‐HT connections were detected, owing to the high regiospecificity of the PHT under study and to the high multiplicity of aliphatic proton signals. The correctness of the model of the interpretation of PHT structure based on the four trimers of 3‐hexylthiophene was confirmed.
Cationic polymerization of isobutylene proceeding by redox initiation
Authors: Marek Miroslav , Pecka Jan , Halaška Vlastimil 
Published: April 2003

AbstractThe cationic polymerization of isobutylene with weak Lewis acids, such as BBr3 and FeBr3, has been studied. These halides are unable to induce individually the polymerization in nonpolar solvents, such as heptane or toluene, or they only initiate the polymerization to low conversions in polar media, such as dichloromethane. The complex compounds, formed by interaction of both Lewis acids, initiate a fast polymerization of isobutylene, which proceeds up to high conversions. The coinitiation effect of HBr in the mixture with BBr3 and FeBr3 was also investigated. The hypothetic formation of efficient initiators and the initiation mechanism of olefin polymerization are discussed on the basis of the ionogenic action of both Lewis acids.
Effects of an interfacial agent on the physico‐chemical characteristics of poly(propylene)/polyamide 6 blends
Authors: Beltrame Piez Luigi , Castelli Antonella , Canauz Michele , Canetti Maurizio , Seves Alberto 
Published: April 2003

AbstractThe present work reports investigations about the structure and the thermal behavior of blends prepared by mixing, at different weight ratios, poly(propylene) (more precisely, a propylene/ethylene random copolymer containing 6% ethylene) with polyamide 6, in the presence of poly(propylene) grafted with 1% of maleic anhydride used as a compatibilizer agent. Blends without the compatibilizer were also prepared and analyzed. The poly(propylene) structural changes in the blends were determined by wide angle X‐ray diffraction (WAXD) measurements. Differential scanning calorimetry, microscopic observations, and mechanical tests supported the occurrence of interfacial reactivity. The compatibilizing effect was confirmed by measuring the decrease of the interfacial tension between poly(propylene) and polyamide 6 due to the presence of the compatibilizer. Such a decrease resulted in improved dispersion and adhesion between the phases. A new material with interesting thermal, structural and mechanical properties was obtained.
Direct evidence of star structure from nuclear magnetic resonance spectroscopy
Authors: Pitsikalis Marinos , Hadjichristidis Nikos , Di Silvestro Giuseppe , Sozzani Piero 
Published: April 2003

AbstractUntil now the characterization of a star‐like structure has been based on an indirect method, i.e. the comparison of the molecular weight of the star polymer and its linear precursor. By preparing well‐defined and narrow‐molecular‐weight‐distribution polybutadiene and polyisoprene stars with up to four arms — using anionic polymerization techniques and the appropriate chlorosilane — and by characterising them by means of 1H and 13C NMR spectroscopy, the key point of the star, which is the core next to the silicon atom, was observed.
Photoinduced electron transfer in porphyrin‐naphthyl pairs covalently and randomly bound to α‐helical poly(L‐lysine)
Authors: Pispisa Basilio , Venanzi Mariano , Palleschi Antonio , D'Alagni Maria 
Published: April 2003

AbstractThe photophysics of protoporphyrin‐naphthyl (P‐N) pairs covalently and randomly bound to the ε‐amino groups of the side‐chains of poly(L‐lysine) (PL) were investigated by steady‐state and time‐resolved fluorescence measurements. The results indicate that quenching of excited naphthalene (λex = 280 nm) chiefly occurs by interconversion to the triplet state when the polymeric matrix is in random coil (pH ≈ 7) and by intramolecular electron transfer from ground‐state porphyrin, P → 1N*, when the polypeptide is in α‐helical conformation (pH ≈ 11), the specific rate constant of the electron transfer being 3,1 · 107 s−1 (25°C). PNPL exhibits very little exciplex fluorescence, whatever the pH, suggesting both a reduced internal Brownian motion of the chromophores, owing to the amide bond in the substituted side‐chains, and a relatively large average interprobe separation distance. This agrees with polarized fluorescence data and with the results of a conformational statistics analysis on the fully ordered PNPL, indicating that the average interchromophoric distance for which the electron transfer has the highest probability to occur is around 12 Å. The computational results allowed us to reproduce the experimental fluorescence decay curves and estimate the parameters governing the electron transfer process. Implications of these findings on the relaxation time of the heli‐xcoil transition in PNPL are briefly discussed.
Thermovolumetric properties versus glass transition temperature of diolic perfluoropoly(oxyethylene‐ran‐oxymethylene) oligomers
Authors: Danusso Ferdinando , Levi Marinella , Gianotti Giuseppe , Turri Stefano 
Published: April 2003

AbstractThe specific volume v from – 20 to 60°C and the glass transition temperature Tg was measured of a homologous series of linear diolic oligomer fractions constituted by a random perfluoro‐poly(oxyethylene‐ran‐oxymethylene) chain of fairly uniform composition and two CH2OH end units, with a degree of polymerization x̄n from 5,4 to 165,9 (M̄n from 400 to 14900). An empirical parabolic v = v(T, wE) equation of state is found as satisfactory, wE being the end copolymeric composition expressed as weight fraction of end units, inversely proportional to M̄n. A predictive bridge is then established between thermovolumetric parameters and Tg, through a highly reliable linear relation vg – Tg between experimental Tg and calculated specific volume at Tg, which leads with measurable parameters to a Tg – wE relation, in very good agreement with experimental results. For the range of M̄n above 1500–2000, simpler relations can also be used to a good approximation, which are discussed in their physical meaning and validity.
Physico‐chemical properties of hyaluronan and its hydrophobic derivatives: a calorimetric and viscometric study
Authors: Geciova Renata , Flaibani Antonella , Delben Franco , Liut Gianfranco , Urbani Ranieri , Cesáro Attilio 
Published: April 2003

AbstractThe physico‐chemical properties of a series of hyaluronan derivatives were studied with the aim of exploring some aspects of the role of electrostatic interactions on the aggregation of these chains in aqueous solution. Experimental data were obtained from calorimetric measurements of the dilution process in water. The data were analysed in terms of the structural charge parameter, ζ, with the polyelectrolyte counterion condensation theory. In addition, intrinsic viscosity data of the hyaluronan derivatives were obtained at several different values of the ionic strength and discussed on the basis of the effect of charge density change upon the elongation properties of the polyelectrolyte chains.
Effect of polyfunctional chain transfer agents on the molecular weight distribution in free‐radical polymerization, 3 Polymerization of methyl methacrylate in the presence of polyfunctional chain transfer agents
Authors: Yuan Cui Ming , Di Silvestro Giuseppe 
Published: April 2003

AbstractPolymerization of methyl methacrylate was carried out in the presence of polyfunctional chain transfer agents: 1,6‐hexanedithiol, trimethylolpropaneb tris(mercaptoglycolate) and pentaerythritol tetrakis(3‐mercaptopropionate). The theoretical results reported in the preceding papers are completely confirmed: the experimental values of the dispersion index (D = M̄w/M̄n) are 1.62 for f = 2, 1.39 for f = 3 and 1.28 for f = 4. In the case of bifunctional transfer agents the molecular weights calculated are in very good agreement with those obtained by size exclusion chromatography. The formation of star‐shaped macromolecules was confirmed by cleavage of the CSC bonds. The number‐average molecular weight decreases and the dispersion index is approximately equal to 2 after exposure to UV rays. The phenomenon of “pseudo‐living” polymerization in the presence of polyfunctional chain transfer agents is also discussed.
Synthesis of low molecular weight poly(N‐acryloylmorpholine) end‐functionalized with primary amino groups, and its use as macromonomer for the preparation of poly(amidoamines)
Authors: Ushakova Vera , Panarin Evgenji , Ranucci Elisabetta , Bignotti Fabio , Ferruti Paolo 
Published: April 2003

AbstractAmphiphilic oligomers of poly(N‐acryloylmorpholine) terminated at one end by primary amino groups have been prepared by free radical polymerization of the corresponding monomer, N‐acryloylmorpholine, in the presence of cysteamine (2‐mercaptoethylamine) as chain‐transfer agent. The polymerization reaction was performed in aqueous media at acidic pH, in order to avoid any hydrogen‐transfer addition reaction the the acrylic double bonds by the SH or NH2 groups present in cysteamine. The chain‐transfer constant of cysteamine towards N‐acryloylmorpholine, under the conditions we used, was found to be very close to 1. The aminated poly(N‐acryloylmorpholine) oligomers were found to behave as true macromonomers in polyaddition reactions with a diacrylamide, leading to new poly(amidoamines) carrying poly(N‐acryloylmorpholine) chains as side substituents.
Synthesis, thermal and phase‐conjugate properties of semirigid copolyesters with cyanoazobenzene side‐chains and azoxybenzene units in the main chains
Authors: Sato Moriyuki , Nakagawa Kazuo , Hayakawa Makoto , Mukaida Ken‐ichi , Fujiwara Hirofumi , Tada Yuji 
Published: April 2003

AbstractMelt polycondensation of a mixture of diethyl 5‐{6‐[4‐(4‐cyanophenylazo)phenoxy]‐hexyloxy}isophthalate and 4,4′‐bis(ethoxycarbonyl)azoxybenzene at various mole ratios with dihydroxyhexamethyleneoxy derivatives of diphenyls in the presence of zinc acetate afforded new combined‐type semi‐rigid copolyesters containing cyanoazobenzene side chains and an azoxybenzene unit in the main chain, which were characterized by FTIR, 1H and 13C NMR spectroscopy and elemental analyses. Differential scanning calorimetry (DSC) measurements and observations in the polarizing microscope demonstrated that some cyanoazobenzene‐rich copolyesters composed of diphenyl ether and benzophenone units form liquid crystalline (LC) phases, but the others have no LC phases in spite of introduction of an azoxybenzene mesogen into the polymer backbone. Most of the copolymers consisting of diphenyl ether and benzophenone units generated simultaneously two types of phase‐conjugate (PC) signals based on photo‐induced anisotropy (PA) and holographic components at high reflectivities by degenerate four‐wave mixing (DFWM) at low pump‐beam powers, which are one of the third‐order non‐linear optical (NLO) properties. This means that these copolyesters can be used not only a phase conjugator, but also as erasable hologram‐recording materials. It is suggested that the presence of the cyanoazobenzene side chains is of importance for the PC signal‐generating process.
New poly(amide‐imide)s syntheses, 14. Preparation and properties of poly(amide‐imide)s based on 3, 3‐bis[4‐(4‐trimellitimidophenoxy)phenyl]‐1‐oxoisoindoline
Authors: Yang Chin‐Ping , Lin Jiun‐Hung 
Published: April 2003

AbstractAn imide ring‐containing dicarboxylic acid, 3,3‐bis[4‐(4‐trimellitimidophenoxy)phenyl]‐1‐oxoisoindoline, was prepared via condensation of 3,3‐bis[4‐(4‐aminophenoxy)phenyl]‐1‐oxoisoindoline and trimellitic anhydride. A series of new aromatic bis(phenoxy)‐1‐oxo‐isoindoline‐containing poly(amide‐imide)s were prepared via direct polycondensation of this diimide‐diacid with various aromatic diamines using triphenyl phosphite and pyridine as condensing agents in N‐methyl‐2‐pyrrolidone (NMP) in the presence of calcium chloride. Most of the resulting polymers are of amorphous nature and readily soluble in polar solvents such as NMP and N,N‐dimethylacetamide. All soluble poly(amide‐imide)s afford transparent, flexible, and tough films. The glass transition temperatures of the polymers are in the range of 267–305°C and show almost no weight loss up to 450°C in nitrogen atmosphere. The properties of 1‐oxoisoindoline containing poly(amide‐imide)s are compared with those of the corresponding analogous poly(amide‐imide)s derived from 3,3‐bis[4‐(4‐trimellitimidophenoxy)phenyl]phthalide.
Characterization of dehydrochlorinated poly(vinylidene chloride) and the shock‐compressed material
Authors: Komatsu Tamikuni , Nomura Masayuki , Kakudate Youzou , Fujiwara Syuzou , Heimann R. B. 
Published: April 2003

AbstractDehydrochlorinated poly(vinylidene chloride) proved to be a conjugated polyene‐polyene polymer. Shock compression of the polymer formed a large portion of graphite and trace amounts of diamond and of an unknown carbon. The unknown carbon belongs to the hexagonal crystal system and possesses the cell dimension α0 = 0.338 nm. A comparison with known carbynes was made in terms of the crystalline parameters.
Poly(amide‐imide)s prepared from 4,4′‐[1,4(or 1,3)‐ phenylenebis(isopropylidene‐1,4‐phenyleneoxy)]dianiline, trimellitic anhydride, and various aromatic diamines
Authors: Hsiao Sheng‐Huei , Yang Chin‐Ping , Fan Jr‐Chen 
Published: April 2003

AbstractTwo imide ring‐bearing dicarboxylic acids, N,N′‐[1,4(or 1,3)‐phenylenebis(isopropylidene‐1,4‐phenyleneoxy‐1,4‐phenylene)]diphthalimide‐4‐carboxylic acid (p‐4 and m‐4), were prepared via condensation of 4,4′‐[1,4(or 1,3)‐phenylenebis(isopropylidene‐1,4‐phenyleneoxy)]dianiline (p‐3 and m‐3) with trimellitic anhydride. Two series of novel poly(amideimide)s were synthesized by the direct polycondensation of the diimide‐diacids p‐4 and m‐4, respectively, with various aromatic diamines using triphenyl phosphite and pyridine as condensing agents. The inherent viscosities of the resultant poly(amide‐imide)s were in the range of 0,43–1,68 dL/g, and most of these polymers were amorphous, as revealed by wideangle X‐ray diffractograms. Almost all the poly(amide‐imide)s were readily soluble in polar aprotic solvents such as N‐methyl‐2‐pyrrolidone (NMP), N,N‐dimethylacetamide (DMAc), and N,N‐dimethylformamide (DMF), and could be solution‐cast into transparent, flexible, and tough films. These polymers had glass transition temperatures in the range of 200‐267°C and showed no significant decomposition below 450°C, with 10% weight loss being recorded above 485°C in nitrogen or air.
Synthesis of dihydroxy terminated poly(chloroethyl vinyl ether)s by “living” cationic polymerization: evidences for side reactions and their control
Authors: Bennevault Véronique , Larrue Frédéric , Deffieux Alain 
Published: April 2003

AbstractThis paper reports on the synthesis of dihydroxy terminated poly(chloroethyl vinyl ether)s (PCEVE) via bifunctional living cationic polymerization. The bifunctional chain initiator is obtained by reacting malonaldehyde bis(diethyl acetal) with trimethylsilyl iodide (TMSI) to form the corresponding di‐α‐iodo ether derivative. The polymerization of chloroethylvinyl ether is then triggered by ZnCl2. The direct transformation of active ends into aldehyde terminals, as well as their derivatization into hydroxy groups, is described. The synthesis of high molar mass ditelechelics by bifunctional polymerization provides evidence for the occurrence of a monofunctional side initiation. The latter has been attributed to the hydrolysis of TMSI by adventitious water, which leads to the in situ formation of hydrogen iodide. In order to trap hydrogen iodide, the influence of different additives, bulky amines, metals and alkylaluminiums, was investigated. Therefore, in the presence of alkylaluminiums, it is possible to obtain a clean bifunctional polymerization up to relatively high molar mass ditelechelic PCEVE (M̄n = 33000 g/mol, M̄w/M̄n = 1.11).
Investigation of the aggregation phenomenon of polyaniline in dilute solutions
Authors: Liao Yun‐Hsin , Kwei Ti Kang , Levon Kalle 
Published: April 2003

AbstractAggregation of polyaniline chains in dilute solutions was observed in N‐methyl‐2‐pyrrolidone by light scattering, gel permeation chromatography, and viscosity measurements. The aggregation resulted in a negative second virial coefficient in light scattering measurements and concave reduced viscosity curves. The driving force for aggregation is assumed to be a combination of hydrogen bounding between the imine and amine groups and the rigidity of backbone, and the aggregation was modeled to occur via side‐on packing of wormlike chains. Polyelectrolyte‐like viscosity behavior was also observed when a small amount of salt was added and the electrostatic interaction in polyelectrolyte polymer based on the Odijk theory was used to explain the role of the salt.
Study of the propagation centre in the anionic polymerization of (meth)acrylic monomers, 4 NMR and quantum chemical study of the initiation systems containing tert‐butyl 2‐lithioisobutyrate and lithium tert‐butoxide or lithium 3‐methylpentan‐3‐olate
Authors: Kříž Jaroslav , Dybal Jiří , Janata Miroslav , Vlček Petr 
Published: April 2003

AbstractIn contrast to methyl 2‐lithioisobutyrate (I), tert‐butyl 2‐lithioisobutyrate (A) in tetrahydrofuran (THF) appears to have one form only, irrespective of concentration (0,1‐0,8 mol/L) or temperature (203–273 K). According to its relaxation characteristics, this form probably is a tetramer. The results indicate, however, that about 20% of A do not provide well‐developed NMR signals and may be present as a partly organized pseudophase. A is shown to form 2:2 and 1:3 complexes with lithium tert‐butoxide (B) and lithium 3‐methylpentan‐3‐olate (C) in THF in dependence on their mole ratio and partly on storage time. The 7Li, 1H and 13C NMR relaxation behaviour of these complexes support their essentially tetrameric nature. Although intramolecular exchange of Li atoms in a complex appears to be rapid, intermolecular exchange of any of the components is vanishingly slow on the NMR time scale. The complexes of A with either B or C exhibit remarkable stability above 273 K, in contrast to that of A itself. The quantum chemical analysis of the complexes shows that they are held together by a cooperative system of polycentric bonds and electrostatic interactions. Thus they are not easily destroyed by thermal activation but they react readily with monomer. Implications of the results for anionic polymerization of (meth)acrylates are discussed.
Novel blood compatible polyurethanes containing long‐chain alkyl groups and phosphatidylcholine analogues
Authors: Li Yu‐Jun , Matthews Kerr H. , Kodama Makoto , Nakaya Tadao 
Published: April 2003

AbstractA series of new amphiphilic polyurethanes containing long‐chain alkyl groups as hydrophobic part and phosphatidylcholine analogues as hydrophilic part in the side chains was synthesized and characterized by their IR and 1H NMR spectral data and elemental analyses. The detailed studies for polyurethane 7b show that no evidence of any blood platelet attachment was apparent from the platelet rich plasma (PRP) contact studies and by scanning electron microscopy (SEM) evaluation for the synthesized polyurethane. Moreover, it quickly forms a gel in chloroform, N,N‐dimethylformamide, dimethyl sulfoxide and even to some extent in water. Preliminary studies suggest that these new polyurethanes are very interesting due to their excellent blood compatibilities and prospective importance for biomedical applications.
Saccharide polymers, 1, Synthesis and polymerization of methyl 5‐deoxy‐2,3‐O‐iso‐propylidene‐ß‐D‐erythro‐pent‐4‐enofuranoside
Authors: Yaacoub Emile‐Joseph , Wick Stefan , Buchholz Klaus 
Published: April 2003

AbstractNew “saccharide polymers” were synthesized. For this purpose the synthesis and the polymerization of an unsaturated sugar monomer, methyl 5‐deoxy‐2,3‐O‐isopropylidene‐ß‐D‐erythro‐pent‐4‐enofuranoside, briefly called “exo‐ribene”, is described. All polymers, homo‐and co‐polymers, were synthesized under free radical conditions. The structures and compositions of the soluble “saccharide polymers” were established by elemental analysis, 1H and 13C NMR, and FT‐IR spectroscopy. Some characteristics e. g. molecular weights and optical rotations are reported. Depending on the comonomer reactivity and under optimized chain reaction conditions, saccharide polymers with various sugar content and high molecular weights have been obtained.
Mechanical field orientation of chiral smectic C polymer networks
Authors: Semmler Klaus , Finkelmann Heino 
Published: April 2003

AbstractDeformation experiments on chiral smectic C elastomers show a significant influence of the layer structure. In contrast to nematic systems a deformation of the smectic polydomain does not lead to a uniform director orientation. Obviously, the smectic layers lock in the polydomain structure in a transient network. Therefore, on experimental time scale, no equilibrium conditions can be achieved during the deformation process in the smectic state. Reducing the influence of the smectic layers by swelling the sample with toluene offers the possibility to prepare samples with uniform director orientation. In these samples the smectic layers are distributed on a cone around the director, preventing ferroelectric properties. Further deformation experiments on these aligned samples show a strong interaction of the layer orientation with the mechanical field in the smectic state. Layers which enclose large angles with the mechanical field realign to layer orientations with small angles to the deformation direction. This orientation behaviour leads to an anisotropic distribution of the layer on the cone causing a non‐centrosymmetric phase structure. This anisotropic alignment can be locked in by chemical crosslinking, leading to a highly transparent non‐centrosymmetric bulk material.
Polymers containing formamidine groups, 5 Formation of a cyclic formamidine trimer by the condensation reaction of 2,6‐diaminopyridine with triethyl orthoformate
Authors: Böhme Frank , Rillich Maik , Komber Hartmut 
Published: April 2003

AbstractThe condensation reactions of the structurally similar monomers 1,3‐phenylenediamine (1a) and 2,6‐diaminopyridine (1b) with triethyl orthoformate have been compared. Whereas the reaction of 1a resulted in an oligomeric polyformamide, a cyclic trimer was obtained almost quantitatively when monomer 1b was used. The structure of the trimer has been discussed with respect to results obtained by NMR and MALDI spectroscopy.