bluuebunny/crossref_metadata_2025_split huggingface dataset:
A UV/visible spectroscopic study of water‐soluble conjugated polyenes prepared via the ring‐opening metathesis polymerization reaction
Authors: Amir‐Ebrahimi V. , Byrne Declan , Hamilton James G. , Rooney John J. 
Published: April 2003

AbstractA series of water‐soluble conjugated polyenes, based on the poly(furanylvinylene) structure, have been prepared from readily available starting materials using ring‐opening metathesis polymerization followed by dehydrogenation of the resulting polymer. 13C NMR analysis of the precursor polymers shows that the stereochemistry of the main‐chain double bonds varies from 93% trans to 10% trans and is retained in the water‐soluble derivatives, allowing different degrees of extended conjugation. This is reflected in the UV/vis spectra of the materials. The polymers may be cast into films from aqueous solution, and the UV/vis spectra exhibit vibrational fine structure indicative of conformational rigidity; significantly this fine structure is retained on redissolving the high‐trans but not the high‐cis films. The absorption maximum of the visible spectrum shows a stronger pH dependence in the high‐cis polymers than in the high‐trans, and this is interpreted in terms of the different modes of hydrogen bonding which cis and trans units can adopt.
A stereochemical and statistical analysis of metallocene‐promoted polymerization
Authors: Farina Mario , Di Silvestro Giuseppe , Terragni Alberto 
Published: April 2003

AbstractThe metallocene catalysts active in propylene polymerization can be divided into five classes, depending on whether the catalytic sites are chirotopic or not, and on the symmetry relationship between the catalytic sites bound to the same metal atom. Under the hypothesis of a purely alternating mechanism for propagation, class III and class IV catalysts, respectively, give rise to prevailingly isotactic and syndiotactic polymers. Four probabilistic schemes have been developed for interpreting the stereosequence distribution of polypropylene in terms of pentads. They take into account the two sources of steric control, chirotopicity of the catalyst site and configuration of the chain end, and the presence, besides the alternating mechanism, of successive addition steps at the same catalytic site.
Lithium alkylnickelate and alkylpalladate bimetallic “ate” complexes as initiators for anionic polymerization of methyl methacrylate
Authors: Mardare Daniela , Matyjaszewski Krzysztof 
Published: April 2003

AbstractAnionic‐coordinative polymerization of methyl methacrylate (MMA) was carried out in the presence of new bimetallic initiators based on lithium alkylnickelates and alkylpalladates in tetrahydrofuran, at −78°C. Well‐defined poly(methyl methacrylate), PMMA, with molecular weights increasing linearly with conversion and relatively narrow polydispersities (M̄w/M̄n = 1,26 to 1,4) were prepared by initiation with some of the “ate” complexes. In the presence of lithium “ate” Ni‐based complexes, PMMA with enhanced syndiotacticity [(rr) = 73 to 75%] was formed.
Polymerization in microemulsions — a new approach to ultrafine, highly functionalized polymer dispersions
Authors: Antonietti Markus , Basten Rainer , Lohmann Sabine 
Published: April 2003

AbstractPolymerization in microemulsions is a new polymerization technique which allows the synthesis of ultrafine latex particles within the size range 5 nm < R < 50 nm and with narrow size distribution. This article presents a short review of the current literature in this field. Beside a short introduction into some kinetic aspects of polymerization in microemulsions, we mainly focus on the synthetic aspects of this technique such as the particle size control and the analysis of the diversity of surfactants which allow formation of polymerizable microemulsions. The control of the chemical functionality or nature of the particle surfaces which may be as large as 300 m2/g and its use for chemistry is a further topic of this paper. A personal analysis of the actual future trends in this rapidly developing field such as the polymerization of complex morphologies is closing the paper.
Study on the miscibility of poly(2‐hydroxyethyl methacrylate)/poly(styrene‐co‐acrylamide) blends by nonradiative energy transfer fluorescence spectroscopy
Authors: Zhu K. J. , Ji Wang 
Published: April 2003

AbstractThe miscibility of poly(2‐hydroxyethyl methacrylate)/poly(styrene‐co‐acrylamide) (PHEMA/PSAm) blends was investigated by nonradiative energy transfer fluorescence spectroscopy using anthracene‐labeled PHEMA and carbazole‐labeled PSAm. The results show that the ratio of the carbazole and anthracene emission intensity, Ic/Ia, passes through a minimum at 47 to 57 mol‐% of acrylamide in PSAm copolymers in the blends, indicating that a ‘miscible window’ exists. It also was found that the results are consistent with those obtained by differential scanning calorimetry. The driving force for the miscibility of PHEMA/PSAm may be explained with a mean‐field theory.
Synthesis of organosilicon‐containing macromonomers through an anionic polyaddition reaction
Authors: Nagasaki Yukio , Tsuruta Teiji 
Published: April 2003

AbstractLithium diisopropylamide (LDA) induces metalation reaction of 4‐(trimethylsilylmethyl)‐styrene (SMS) to form lithiated SMS (SMSLi). SMSLi initiates the anionic polymerization of SMS to form oligomers with a polymerizable vinyl end‐group. Mechanistic studies revealed that the propagation proceeds mainly by the addition reactions of SMSLi to the double bond of preformed oligomers in the early stage of the polymerization. In the later stage of the polymerization, propagations between preformed oligomers take place concurrently. The extent of polyaddition enchainments in the oligomers was found to increase when the reaction was carried out keeping the monomer concentration as low as possible. Reactivities of the organosilicon‐containing macromonomers were also estimated by UV, MO calculations, and radical homopolymerization.
Polymers from multifunctional isocyanates, 10. Thermotropic polyurethanes from triad liquid‐crystalline diesterdiisocyanates
Authors: Mormann Werner , Brahm Martin 
Published: April 2003

AbstractBinary hard‐segment type polyurethanes from para‐linked triad aromatic or cycloaliphatic diisocyanatodiesters (1,4‐phenylene dibenzoate, diphenyl terephthalate, diphenyl trans‐1,4‐cyclohexanedicarboxylate and dicyclohexyl trans‐1,4‐cyclohexanedicarboxylate) and aliphatic diols as chain extenders are described. Due to the favorable aspect ratio of the triad mesogens most of the polyurethanes have an enantiotropic (nematic) mesophase. The influence of substituents in the mesogen and of the chain extender on the thermal transitions of the polyurethanes was studied and compared with the properties of the parent isocyanates.
Polymers from multifunctional isocyanates, 11. Thermotropic copolyurethanes from triad diesterdiisocyanates
Authors: Mormann Werner , Benadda Saria , Brahm Martin 
Published: April 2003

AbstractTwo series of hard‐segment type polyurethane copolymers from para‐linked triad and diad aromatic or cycloaliphatic diisocyanatoesters using aliphatic low‐molecular‐weight diols as chain extenders are described. The first series has been made from one diisocyanate and two different chain extenders, the second from two different diisocyanates and one chain extender. The influence of the copolymer composition on the thermal transitions has been studied. Crystalline and glassy polyurethanes can be made with a wide range of isotropization temperatures. Systematic variation of the mole fraction of either the isocyanates or the chain extenders gives clearing transitions between those of the two binary polymers. An almost linear relationship between clearing temperature and the composition was found for polymers prepared from two isocyanates. With two different chain extenders, isotropization temperatures deviate slightly from a linear relationship.
X‐ray structural studies of various octyl‐substituted polythiophenes
Authors: Mårdalen Jostein , Fell Hans Jörg , Samuelsen Emil J. , Bakken Eivind , Carlsen Per H. J. , Andersson Mats R. 
Published: April 2003

AbstractThe structure of poly(octylthiophene)s and alternating octylthiophene‐thiophene‐copolymers with a varying degree of intrachain regularity was studied by means of X‐ray diffraction and optical absorption measurements. Although these polymers show a varying degree of crystallinity, evidence is found that they all tend to pack as relatively straight parallel chains. The lateral packing distance depends strongly on the regularity and the relative amount of alkyl side chains. Generally poly(thiophene)s with a larger relative amount and higher stereoregularity of the octyl side chains tend to pack more ordered. On the other hand, a large conjugation length (high degree of chain planarity), as revealed by optical absorption spectroscopy, and a crystalline packing of the polymer chains are not found to be interdependent. For the polymer with highest degree of crystallinity two surprisingly different crystalline structures were found for the two versions with different regularity, viz. poly(3‐octylthiophene) and poly(3,3′‐dioctyl‐2,2′ bithiophene). For the latter we find evidence of a polymer chain twist between adjacent head‐to‐head coupled thiophene rings, and we propose a structural model for its crystalline packing. Our new model can explain previously measured differences in spectroscopic and transport‐related properties for these two stoichiometrically identical polymers.
Crosslinking copolymerization of cyclic ketenacetals with low shrinkage in volume
Authors: Schulze Thomas , Klemm Elisabeth 
Published: April 2003

AbstractThe copolymerization of 9,9‐dimethyl‐4‐methylene‐3,5,8,10‐tetraoxabicylco[5.3.0]decane (4) with 3,9‐bismethylene‐2,4,8,10‐tetraoxaspiro[5.5]undecane (5) was investigated. While 4 polymerizes after radical attack to form highly viscous linear polyesters with a number‐average molecular weight of 5000, the addition of 5 in variable amounts leads to insoluble samples. It is shown that the material properties can be controlled by using various contents of 5 in the storable and persistable monomer 4. According to the application purpose, it is possible to produce gel‐like or rubber‐like as well as hard polymer samples.
Stability of solutions of aromatic polyamides containing carborane units in the main chain
Authors: Gladkova Elena A. , Petrus Vladimír , Horský Jiří 
Published: April 2003

AbstractThe stability of aromatic polyamide chains containing 1,7‐dicarba‐closo‐dodecaborane units was investigated in dilute solution by viscometry and sedimentation analysis at 25°C. Traces of impurities in dimethylformamide bring about degradation of the polymer and formation of polyanions, which become manifest in the viscosity by the polyelectrolyte effect. Neutral salts suppress this effect. Degradation is not hindered in an inert atmosphere. The solutions in N,N‐dimethylacetamide and N‐methyl‐2‐pyrrolidone are also unstable. No degradation occurs in solutions in tetrahydrofuran stabilized with 2,6‐di‐tert‐butyl‐4‐methylphenol. Hence, reliable measurements of the molecular characteristics of this polymer can be carried out only in stabilized peroxide‐free tetrahydrofuran.
End‐group analysis of poly(phenyl glycidyl ether), 3. Isopropoxy and chlorine groups using 1H and 13C nuclear magnetic resonance
Authors: Ronda Joan Carles , Serra Angels , Mantecón Ana , Cádiz Virginia 
Published: April 2003

AbstractNon‐hydroxylic end‐groups in the soluble fraction of poly(phenyl glycidyl ether) (PPGE) obtained with the aluminium isopropoxide (AIP)/ZnCl2 initiator system are studied using nuclear magnetic resonance (NMR) spectroscopy. To make assignments, model compounds are synthesized and several PPGEs are prepared with various initiator systems. Isopropoxy and chlorine groups are identified and quantified using NMR spectroscopy and microcoulometry, respectively. Primary and secondary carbons attached directly to OiPr and Cl are detected by NMR spectroscopy, but, as can be expected, the primary ones are more plentiful due to the fact that they come from the more probable attack in this mechanism of ring‐opening. Other unsaturated terminal groups are also investigated but their presence cannot be detected.
Cationic ring‐opening oligomerization of hexamethylcyclotrisilazane and octamethylcyclotetrasilazane
Authors: Duguet Etienne , Soum Alain 
Published: April 2003

AbstractThe study of the ring‐opening oligomerization of hexamethylcyclotrisilazane (D3NH) and octamethylcyclotetrasilazane (D4NH), initiated by methyl triflate in 1,2‐dichloroethane, was carried out. Size‐exclusion chromatography (SEC) analysis indicated the occurrence of an equilibrated reaction between macrocycles such as (SiMe2NH)n (with 3 ≤ n ≤ 13) (Me:CH3). Kinetic measurements showed that these oligomerizations are first order relative to both monomer and active center concentrations at the beginning of the reaction. The initial rate constants of propagation (kpx)0 and the ratios of propagation and back‐biting ones (kpx/kx) were estimated. Complementary experiments allowed us to propose a mechanism of the oligomerization.
Studies on the phosphorylating polycondensation catalyzed by 4‐dimethylaminopyridine
Authors: Mao Hai‐Quan , Zhuo Ren‐Xi , Fan Chang‐Lie , Jiang Xue‐Song , Liu Wu‐Ping , Yi Hong 
Published: April 2003

AbstractThe phosphorylating polycondensation in solution catalyzed by 4‐dimethylaminopyridine (DMAP) was studied for the first time. The polymerization rate and the average molecular weight of the polyphosphate are increased by using DMAP as a catalyst. The influence of reaction conditions on the catalytic activity of DMAP were preliminarily investigated.
Intermolecular nonradiative energy transfer. Effect of spacer length carrying donor and acceptor fluorophores in water‐soluble copolymers of poly[N‐(2‐hydroxypropyl)‐methacrylamide]
Authors: Vyprachtický Drahomír , Pokorná Veronika , Mikeš František 
Published: April 2003

AbstractCopolymers of monomers containing donor (carbazole) and acceptor (dansyl) fluorophores with N‐(2‐hydroxypropyl)methacrylamide (HPMA) with “low” and “high” contents of the fluorophores were prepared. At any given fluorophore concentration, the efficiency of nonradiative energy transfer (NET) is always higher for polymers with a lower content of fluorophore labels. At higher concentrations of fluorophore, the mutual interpenetration of the polymer coils reduces this difference. Copolymers of HPMA containing donor and acceptor fluorophores attached to the end of “short” and “long” side chains were synthesized. Increase in NET between copolymers carrying fluorophores at the end of the aliphatic “long” spacer was interpreted as due to hydrophobic interaction of long methylene side chains. The fluorescence quantum yield of carbazole fluorophores in the model compound and in copolymers are discussed in terms of solvent polarity and the polarity of the polymer microenvironment.
Microemulsion polymerization of butyl acrylate, 3. Effect of the monomer concentration
Authors: Capek Ignác , Potisk Pavol 
Published: April 2003

AbstractThe oil‐in‐water (o/w) microemulsion polymerizations butyl acrylate initiated with a watersoluble (ammonium peroxodisulfate, AP) and/or and oil‐soluble (dibenzoyl peroxide, DBP) radical initiator at different monomer feed compositions and monomer concentrations were investigated. The rate of polymerization shows nucleation and termination intervals. The rate of polymerization is found to increase with the BA concentration. The polymerization is faster with AP than with DBP. The average number of radicals per particle increases exponentially with both the monomer concentration and the particle size. The number of particles decreases with monomer concentration. The molecular weights parallel the rate of polymerization and are larger in the systems with DBP.
Photolysis, thermolysis, and protolytic decomposition of a triazene polymer in solution
Authors: Nuyken Oskar , Stebani Jürgen , Lippert Thomas , Wokaun Alexander , Stasko Andrej 
Published: April 2003

AbstractThe depolymerization of a triazeno‐group containing photopolymer, poly[oxy‐1,4‐phenyleneazo(methylimino)hexamethylene(methylimino)azo‐1,4‐phenylene], is investigated in a tetrahydrofuran (THF) solution. Irradiation of the material leads to a clean decomposition of the photolabile polymer, as monitored by UV spectroscopy and gel‐permeation chromatography (GPC). As compared to the photolysis in THF solution, the light‐induced decomposition rate of a polymer in a polymer film is shown to be much slower. The highly photosensitive triazeno group also decomposes thermally at temperatures above approx. 220°C. The kinetics of thermal degradation of the polymer in substance was investigated at a temperature of 256°C, and monitored by GPC measurements. During this decomposition, one first observes the development of higher molar‐mass fractions, which result from grafting reactions of primary radicals. Upon further thermolysis the triazene polymer is completely degraded to low‐molar‐mass products. The volatile decomposition products were identified by gas chromatography/mass spectrometry (GC/MS) analysis. The protolytic decomposition, which represents the retrosynthesis of the triazene polymer, was studied in a 9:1 mixture of tetrahydrofuran and an aqueous citrate buffer solution. Although the decomposition rate in this solvent mixture is slow, as compared to the depolymerization in diluted hydrochloric acid, a clean decomposition of the triazene polymer is obtained.
Thermal reaction between N‐phenylmaleimide and 2‐allylphenol as a model for the crosslinking reaction in bismaleimide polymerization with diallylbisphenol A
Authors: Reyx Danièle , Campistron Irène , Caillaud Christophe , Villatte Martine , Cavedon Annick 
Published: April 2003

AbstractThe thermal reaction between N‐phenylmaleimide and 2‐allylphenol was taken as a model reaction in order to obtain information about chain extension and crosslinking mechanisms of the thermal curing of bismaleimides with diallylbisphenol A. Isolation (preparative HPLC) and characterization (1H and 13C NMR, FT‐IR, HPLC/SM) of a monoadduct and two original triadducts (principally low molecular weight products of the reaction) and studies as a function of time (0–6h) of this thermally induced reaction (160–250°C) with equimolar quantites of N‐phenylmaleimide and 2‐allylphenol, as well as with an excess of N‐phenylmaleimide, give direct evidence of the occurrence of an ene‐reaction and further Diels‐Alder and retro Diels‐Alder reactions with rise in temperature.
Relaxation and charge transport in mixtures of zwitterionic polymers and inorganic salts
Authors: Rozanski Stanislaw A. , Kremer Friedrich , Köberle Peter , Laschewsky André 
Published: April 2003

AbstractDielectric spectroscopy is employed to analyze the molecular dynamics and the charge transport in mixtures of zwitterionic polymers of the type poly{3 [N(ω‐methacryloyloxyalkyl)] N, [N‐dimethylammonio propanesulfonate] with sodium iodide in the frequency range of 102Hz–107 Hz and in the temperature range of 110 K‐400 K. The amount of inorganic salt added varies from 0–200 mol‐% relative to the number of zwitterionic groups present in the polymer, contributing strongly to the conductivity. One relaxation process is observed whose relaxation rate depends strongly on the length of the aliphatic spacer between the polymethacrylate main chain and the zwitterionic group. Exhibiting an Arrhenius‐like temperature depence with activation energy EA = 47 KJ/mol, this relaxation process is assigned to fluctuation of the quaternary ammonium groups in the side chains. At higher temperatures, the dielectric properties and the conductivity are primarily dominated by the mobile inorganic ions: conductivity strongly depends on the salt concentration, showing a pronounced electrode polarization effect. The frequency and salt concentration, dependences of the conductivity can be quantitatively described as hopping of charge carriers being subject to spatially randomly varying energy barriers. For the low‐frequency regime and for the critical frequency marking the onset of the conductivity's dispersion, the Barton‐Nakajima‐Namikawa (BNN) relationship is fulfilled.
“Compatibilizing effect” in interpenetrating polymer networks
Authors: Du Prez Filip , Goethals Eric J. 
Published: April 2003

Abstractα,ω‐Acrylate terminated poly(1,3‐dioxolane) (polyDXL) was copolymerized with methyl acrylate and methyl methacrylate for the synthesis of block copolymer networks. It was shown by dynamic mechanical thermal analysis (DMTA) that the presence of covalent bonds between poly DXL and the polyacrylate leads to a high degree of compatibility. In contrast, the combination of the same two components in network form, leading to sequential interpenetrating polymer networks (IPN's), resulted in phase‐separated materials. When the above‐mentioned block copolymer structures, in which one of the blocks is chemically identical to the polyacrylate used in the second network, were applied in the first network of the IPN, an increase of miscibility between the two types of polymers was observed. DMTA analysis revealed that the morphology of these IPN's could be varied from phase‐separated to homogeneous materials by increasing the polyacrylate fraction in the first block copolymer network. The possibility to degrade the poly DXL segments in an acid environment allows the complete degradation and extraction of one network in the IPN's and hence provided an interesting approach to the study of domain characteristics by optical microscopy.
A novel imaging system by dye‐sensitized photooxidation of oxazole groups attached to a polymer backbone, 4. Effect of oxazole content and spacer length
Authors: Ito Hiromitsu , Ichimura Kunihiro 
Published: April 2003

AbstractOxazole derivatives attached to a polymer backbone were transformed efficiently to the corresponding triacylamide compounds in a thin film by photooxidation using various dyes as photosensitizers. This photoinduced transformation proved to be applicable to a photoresist with positive tone and a holographic grating formation by development with an aqueous solution of amines to dissolve exposed areas of the film. In this system, the length of the methylene chain connecting the oxazole ring to the polymer backbone and the content of oxazole units in the polymer influence the efficiency of the image formation as well as development conditions.
Continuous fractionation of poly[(dimethylimino)decamethylene bromide] and molecular weight dependence of the glass transition
Authors: Schultes Klaus , Wolf B. A. , Meyer Wolfgang H. , Wegner Gerhard 
Published: April 2003

Abstract30 g of the ionene poly[(dimethylimino)decamethylene bromide] were fractionated by a continuous counter‐current extraction method (CPF) using ethylene glycol monoethyl ether as the solvent and diisopropyl ether as the non‐solvent component. The efficiency of the separation was checked by viscometry and gel‐permeation chromatography (GPC) measurements. Eight fractions of different molar mass were prepared for differential scanning calorimetry (DSC) experiments. With bromide as counter‐ion, the glass transition temperature of the ionene increases from ca. 60 to 85°C as the intrinsic viscosity of this material (in 0,4 M aqueous solutions of KBr at 25°C) rises from ca. 14 to 22 mL/g. When bromide is replaced by tetrafluoroborate, the glass transition temperature remains almost constant at ca. 60°C, irrespective of the molar mass of the ionene.