bluuebunny/crossref_metadata_2025_split huggingface dataset:
Free‐radical polymerization of acrylates α‐substituted by trimethylsiloxy substituents. Dramatic influence of the size of the ester substituent on the polymerizability
Authors: Penelle Jacques , Verraver Sandrine , Raucq Philippe , Marchand‐Brynaert Jacqueline 
Published: April 2003

Abstractα‐Trimethylsiloxyacrylates H2CC(OSiMe3)COOR (R = methyl, ethyl, propyl, isopropyl, isobutyl, and trimethylsilyl) were synthesized and polymerized under free‐radical conditions. Despite the 1,1‐disubstitution by large substituents, all olefins were found to homopolymerize. Polymerizability is very dependent on the bulkiness of the ester substituent, the olefins with the largest ester groups being very reluctant to react. Polymerization of the methyl ester at 60°C was kinetically investigated. The rate dependence deviates from a first‐order kinetics with respect to monomer concentration (n = 1,81 (benzene solution) and 2,36 (DMF solution)), but follows the expected square‐root dependence with respect to the initiator (AIBN). A solvent dependence upon the rate of polymerization was also found. Copolymerization of the methyl ester (M1) with styrene (M2) was carried out at 60°C: r1 = 1,42, r2 = 0,46, Q = 0,47, and e = 0,04. Experimental results are rationalized on the basis of the steric hindrance introduced by the substituents and the high captodative stabilization of the propagating radicals.
Cholesterol‐containing non‐ionic amphiphilic polymers: synthesis and solubilization of cholesterol
Authors: Cho Iwhan , Jeong Sang Won 
Published: April 2003

AbstractSolubilization of cholesterol in water with cholesterol‐containing poly(N‐vinyl‐2‐pyrrolidone) was studied. The non‐ionic amphiphilic polymers were synthesized via copolymerization of cholesterol‐based monomers with N‐vinyl‐2‐pyrrolidone; the copolymers were dissolved isotropically in water to form hydrophobic microdomains solubilizing cholesterol efficiently. Electron micrographs revealed that the amphiphilic polymers undergo aggregational changes from random microphases to bilayers as free cholesterol is incorporated into the polymeric hydrophobic domains.
Mise au point sur l'analyse par chromatographie par exclusion stérique en milieu aqueux de télomères de l'acide acrylique
Authors: Boutevin Bernard , Rigal Gérard , El Asri Mohammed , Lakhlifi Tahar 
Published: April 2003

AbstractIn the case of water soluble polymers, the use of size exclusion chromatography (SEC) for the determination of the molecular weight involves numerous difficulties. In order to analyse and determine the molecular weight of acrylic acid telomers we have first tried to obtain a satisfactory and reproducible separation. In this particular case, low‐molecular‐weight standards are not commercially available. Therefore, we decided to prepare standards based on acrylic acid, either by telomerization with a fluorinated telogen or by polymerization with an initiator bearing a fluorinated group. A calibration curve was obtained from the standards. Telomers of acrylic acid with thioglycolic acid were analysed. This is a general method for determination of DPn by SEC when there is no standard for the polymers. It can be used in a wide range of DPn from 1 to 700.
Polysilanes réactifs, 5. Optimisation de la synthèse des α,ω‐bis(triméthylsilyl)oligo (méthylphénylsilane)s par prise en considération d'un mécanisme anionique
Authors: Reyx Danièle , Martins José Manuel Natário , Campistron Irène , Noireaux Patrick 
Published: April 2003

AbstractLow‐molecular‐weight organosilane polymers were prepared by sodium and potassium/sodium coupling of dichloromethylphenylsilane (1) with chlorotrimethylsilane (2). Size exclusion chromatography (SEC), IR, UV and NMR (1H, 13C and 29SI) analysis of the crude α,ω‐bis(trimethylsilyl) oligo(methylphenylsilane) (3) were performed and compared with those of the isolated shortest oligomers. According to an anionic mechanism, the solvent and alkali‐metal effects on the yield and the oligomer distribution (SEC‐resolved) allow an optimisation for the synthesis of the shortest oligomers (trisilane and tetrasilane).
Chain transfer by addition‐substitution mechanism, 4. Alkyl permethacrylates — a new class of polymerization regulators
Authors: Chaumont Philippe , Colombani Daniel 
Published: April 2003

Abstracttert‐Butyl permethacrylate (tBPM)Systematic names; t BPM: tert‐butyl peroxymethacrylate, CPM: α,α‐dimethylbenzyl peroxymethacrylate.
and cumyl permethacrylate (CPM)b act as chain transfer agents in the free radical polymerization of methyl methacrylate and styrene at 50°C. Thermal degradation of the peresters occurs as a side‐reaction during the polymerization process. A modified Mayo equation (including the first‐order decomposition of the chain transfer agents) is proposed to calculate the chain transfer constants. The thermolysis activation energy of CPM (Ea,th = 121 ± 5kJ/mol) was estimated from the Arrhenius plot of the homolytic decomposition rate constants, Kth' at various temperatures.
Styrene polymerization in methylene chloride by perchloric acid
Authors: Pepper David Charles 
Published: April 2003

AbstractThis paper makes a detailed reappraisal of earlier publications and much unpublished data on the polymerization by HClO4 over the temperature range 25°C to −97°C. The chief conclusions are: (i) The characteristic bimodal molar‐mass distributions found in polymers at temperatures down to about −30°C are not the result of intrinsic independence between propagating species, but of the intervention of irreversible transfer processes. (ii) The ‘common‐anion’ effect of added Bu4NClO4, on both the transient ionic concentration detectable at low temperatures, and on the yields and rates of polymerization, can be analysed to show the links between the rapid non‐equilibrium precursor phase and the subsequent steady phase. In that phase, the reactions are shown, by the number‐average molar mass (M̄n) of the polymer, to have the kinetic character of a ‘dormant‐living’ polymerization, near‐ideal at ca. −70°C, but deviating increasingly as transfer increases and finally dominates over the reversible termination process. (iii) That termination process is envisaged as ‘ion‐pair collapse’, the anion of the pair being ‘homoconjugated’ with a molecule of the acid, which is released on collapse. This mechanism, proposed by Szwarc, offers a satisfactory resolution of the ‘pseudo’ cationic controversy, interpreting the polymer ester molecules, not as propagating species, but as the reservoir from which propagating ion‐pairs are generated by acid‐activation.
Structure and reactivity of propagating species in anionic polymerization of 2‐vinylpyridine initiated by lithium derivatives in toluene
Authors: Hubert Philippe , Soum Alain , Fontanille Michel 
Published: April 2003

AbstractA comprehensive kinetic study of the 2‐vinylpyridine living polymerization initiated by lithium derivatives in hydrocarbon solvents was carried out. Rate constants of propagation and thermo‐dynamic parameters were determined and discussed in relation to the structure of the propagating species. 13C NMR spectrometric measurements performed on a model of the living ends corroborate the conclusions derived from the values of kinetic and thermodynamic parameters.
A combined NMR and electron spin resonance investigation of the (C5(CH3)5)Ti(CH2C6H5)3/B(C6F5)3 catalytic system active in the syndiospecific styrene polymerization
Authors: Grassi Alfonso , Pellecchia Claudio , Oliva Leone , Laschi Franco 
Published: April 2003

AbstractThe reaction of (C5(CH3)5)Ti(CH2C6H5)3 with B(C6F5)3 in chlorobenzene at 25°C produces a mixture of [(C5(CH3)5)Ti(CH2C6H5)2]+ [B(CH2C6H5)(C6F5)3]− (1) and Ti(III) complexes which have been characterized by NMR and electron spin resonance (ESR) spectroscopy, respectively. Spectroscopic data combined with polymerisation activity measurements suggest that a Ti(III) complex is the active species in the styrene syndiospecific polymerisation.
A systematic approach to the study of multicomponent polymerization kinetics: the butyl acrylate/methyl methacrylate/vinyl acetate example, 2. Bulk (and solution) terpolymerization
Authors: Dubé Marc A. , Penlidis Alexander 
Published: April 2003

AbstractA systematic study of the terpolymerization of butyl acrylate/methyl methacrylate/vinyl acetate (BA/MMA/VAc) is being conducted. In the second stage of this study, bulk (and solution) terpolymerizations of BA/MMA/VAc were performed. The polymers produced were characterized for conversion, composition and molecular weight. The terpolymerizations exhibited behaviour similar to vinyl acetate‐containing copolymerizations, that is, a “double gel effect” was observed. During the first period of the reaction the acrylic monomers virtually “copolymerized” and thus the reaction exhibited the characteristics of a “solution” copolymerization of the acrylic monomers with the vinyl acetate acting as the “solvent”. Typical “solution” polymerization behaviour, i. e., a dampened autoacceleration or gel effect, was in evidence for this first period of the reaction. After the virtual deplection of the acrylic monomers, the remaining vinyl acetate polymerized and exhibited its own characteristic gel effect. Estimates of the copolymerization reactivity ratios obtained previously were found to accurately predict terpolymer composition up to high conversion levels. Molecular weight results indicated that branched polymers were being produced at high conversions in the bulk experiments.
Well defined block copolymers of ε‐caprolactone and L‐lactide using Y5(μ‐O)(OiPr)13 as an initiator
Authors: Stevels Willem M. , Ankoné Marc J. K. , Dijkstra Pieter J. , Feijen Jan 
Published: April 2003

AbstractDiblock copolymers composed of poly(ε‐caprolactone) and poly(L‐lactide) were synthesized via sequential living ring‐opening polymerization of ε‐caprolactone and L‐lactide in dichloromethane initiated by Y5(μ‐O)(OiPr)13 (yttrium isopropoxide). A series of diblock copolymers was synthesized with ε‐caprolactone blocks of constant length (DP = 70) and lactide blocks of varying length (DP = 5–80), with polydispersities of 1,18–1,27. Molecular weights were close to theoretical values. 13C NMR spectroscopy shows the absence of transesterification reactions and racemization. The thermal properties of the block copolymers were studied using differential scanning calorimetry. The block copolymers show a certain degree of phase mixing depending on the length of the poly(L‐lactide) blocks. Crystallization of L‐lactide sequences did not occur when the block length consisted of less than 40 L‐lactic acid residues.
Crystalline and disordered state of poly(dihexylsilylene) copolymers
Authors: Frey Holger , Möller Martin , Matyjaszewski Krzysztof , Oelfin Dieter 
Published: April 2003

AbstractA systematic comparison of random copolymers, derived from poly(dihexylsilylene) (PDHS) by incorporation of monomeric units with shorter unbranched alkyl side chains, has been carried out based on calorimetry, variable temperature UV spectroscopy, and 29Si MAS (magic angle spinning) solid state NMR investigations. Also, hexylmethylsilylene units and branched monomers have been copolymerized. Up to 10% comonomer with shorter linear side chains (i. e., pentyl to propyl) could be incorporated into PDHS without impeding the all‐trans order of the crystalline phase. In this case, the UV absorption maximum of the crystalline low‐temperature phase was affected only slightly according to the length and fraction of the comonomer side chains. A less ordered crystal structure (λmax = 345–355 nm) was observed when the content of comonomers with shorter side chains was about 20%. Yet, all these materials form conformationally disordered mesophases. A clear disordering transition and corresponding thermochromism was not observed any more when 50% of propyl side chains were incorporated. The order of the crystalline and the mesophase is also strongly perturbed if only a small fraction (4%) of the side chains are branched at C2.
Hypochromism of poly(N‐vinylcarbazole)
Authors: Kowal Joanna 
Published: April 2003

AbstractThe hypochromy of poly(N‐vinylcarbazole) in relation to N‐ethylcarbazole was estimated for samples of different origin (cationic and radical polymerization). The effect of solvent polarizability and the influence of temperature as well as of the addition of nonsolvent were studied. An increase in hypochromy of the 1Lb transition and a decrease in that of the 1La transition with increasing polarizability of the solvent were observed. No change in hypochromy connected with increasing temperature and addition of nonsolvent was found.
Influence of the crown ether concentration and the addition of tert‐butyl alcohol on anionic polymerization of (butoxymethyl)oxirane initiated by potassium tert‐butoxide
Authors: Stolarzewicz Andrzej , Neugebauer Dorota , Grobelny Zbigniew 
Published: April 2003

AbstractThe influence of the crown ether concentration on the reaction rate constants and the equilibrium constant in anionic (butoxymethyl)oxirane polymerization was studied. Polymerizations of (phenoxymethyl)oxirane and (2‐(9‐carbazoyl)ethoxymethyl)oxirane were carried out for the sake of comparison. The observed changes caused by the addition of the crown ether can be related to both the structure of its complex with the counter‐ion and the structure of the monomer molecule. It was also revealed the tert‐butyl alcohol reduces the concentration of active centers and the molecular weight of the polymers.
Influence of the kind of crown ether on the anionic polymerization of (phenoxymethyl)oxirane initiated by potassium tert‐butoxide
Authors: Stolarzewicz Andrzej , Neugebauer Dorota , Grobelny Zbigniew 
Published: April 2003

AbstractThe propagation rate constant, kp, was determined for the polymerization of (phenoxymethyl)oxirane (2,3‐epoxypropyl phenyl ether) initiated by potassium tert‐butoxide in the presence of various crown ethers: 12‐crown‐4, 15‐crown‐5, 18‐crown‐6, dicyclothexano‐18‐crown‐6, dicyclohexano‐24‐crown‐8, dibenzo‐18‐crown‐6 and dibenzo‐24‐crown‐8. The equation correlating kp with complexation constants, Kc, of the crown ethers was derived.
Study of the microgelation of unsaturated polyester resins by dynamic light scattering
Authors: Liu S. B. , Yu T. L. 
Published: April 2003

AbstractA series of unsaturated polyesters were synthesized with various chemical structures and molecular weights. The effects of molecular weight and degree of unsaturation on the curing reaction of these polyesters with styrene were studied by means of dynamic light scattering and differential scanning calorimetry. Two modes of size distribution of the microgel particles formed during the curing reaction were found from dynamic light scattering data. The small particles consist of primary unsaturated polyester molecules. The large ones consists of microgel particles formed by linking adjacent polyester molecules. The size and structure of the microgel particles depend strongly on the polymer chain length and the number of vinyl groups in each unsaturated polyester chain. The experimental results of this study revealed that microgel formation has a great effect on the curing reaction of unsaturated polyester resins.
Advances in polyelectrolyte research: counterion binding phenomena, dynamic processes, and the helix‐coil transition of DNA
Authors: Nordmeier Eckhard 
Published: April 2003

AbstractThe article gives a review about the actual stand on three fields of polyelectrolyte research. They are: counterion binding phenomena, dynamic processes, and the helix‐coil transition of DNA. The most important theories on each field are presented and their predictions are compared with the results of measurements. Various effects are handled in detail. They are: counterion condensation, counterion association, counterion binding in mixed solvents, polyion diffusion, and pressure effects on the melting temperature of DNA. The main purpose of the article is to show which effects are understood theoretically and which are not. Polyelectrolyte properties are sensitive to polyelectrolyte structure and environment. Therefore, a large number of parameters are varied over a wide range. They are: salt concentration, polyion charge, counterion valence, temperature, hydrostatic pressure, and solvent composition. Another intention is to bridge the gap between biological material research such as DNA and the physics and chemistry of synthetic polyelectrolytes and to plead for a closer cooperation between the two fascinating worlds.
Synthesis and liquid‐crystalline properties of thermotropic homopolycarbonates
Authors: De Backer Christel , Van Beylen Marcel , Ottenburgs Raoul , Samyn Celest 
Published: April 2003

AbstractSix series of polycarbonates with flexible spacers have been prepared by melt condensation of aromatic diols such as 4,4′‐bis[(2‐hydroxyethyl)oxy]biphenyl, 4,4′‐bis [(6‐hydroxyhexyl)oxy]biphenyl, 1,5‐bis[(2‐hydroxyethyl)oxy]naphthalene, 1,5‐bis[(6‐hydroxyhexyl)oxy]naphthalene, 2,6‐bis[(2‐hydroxyethyl)oxy]naphthalene, 2,6‐bis[(6‐hydroxyhexyl)oxy]naphthalene, 4,4′‐bis[(6‐hydroxyhexyl)oxy]stilbene, 3,3′‐dimethyl‐4,4′‐bis[(2‐hydroxyethyl)oxy]stilbene, 3,3′‐dimethyl‐4,4′‐bis[(6‐hydroxyhexyl)oxy]stilbene, 4,4′‐bis[(2‐hydroxyethyl)oxy]‐α‐methylstilbene and 4,4′‐bis[(6‐hydroxyhexyl)oxy]‐α‐methylstilbeneFor systematic IUPAC nomenclature see Experimental part.
with several alkylene diphenyl dicarbonates. Polycarbonates with biphenyl and stilbene mesogenic groups show liquid‐crystalline behavior with the formation of a nematic phase over a temperature range of 46°C and 21°C, respectively. Amorphous polycarbonates were obtained when 1,5‐naphthalene or α‐methylstilbene groups are incorporated. Polymers with 2,6‐naphthalene and 3,3′‐dimethylstilbene groups show mesophase formation up to a certain spacer length, a transition range of 15°C and 28°C, respectively, being observed.
Influence of lateral substituents in the mesogens on the properties of liquid‐crystalline side group copolymethacrylates: dielectric relaxation spectroscopy on homopolymers
Authors: Schönhals Andreas , Geßner Uwe , Rübner Joachim 
Published: April 2003

AbstractBroad‐band dielectric spectroscopy in the frequency range from 10‐2 Hz to 106 Hz and in a temperature range from 170 K to 430 K was employed to study the molecular dynamics in polymethacrylates with novel calamitic side groups. As mesogenic units, derivatives of p‐methoxyphenyl benzoate were used where the hydrogen in the meta position of the benzoate ring is substituted by a methoxy group or by bromine. The substituted samples do not show any mesophases. The following results were obtained: (i) The β‐relaxation which corresponds to a rotational fluctuation of the mesogen around its long axis is drastically suppressed by the lateral substitution. Moreover the activation parameter of this process depends strongly on the actual mesophase structure of the material under study. (ii) The β‐relaxation is related to the dynamic glass transition of the system. It is shown that the value of the glass transition temperature of the liquid‐crystalline polymethacrylate can be understood as competition of internal plasticization and molecular ordering. (iii) The α‐relaxation corresponds to a rotational fluctuation of the side group around its short axis. From comparison of the relaxation rates of the α‐ and δ‐relaxation, the temperature dependence of the order parameter of the liquid‐crystalline polymethacrylate is estimated by dielectric spectroscopy.
Synthesis of end‐functionalized polymers by means of living anionic polymerization, 3. Synthesis of polystyrene and polyisoprene with 1,3‐butadienyl termini by reaction of their anionic living polymers with 6‐bromo‐3‐methylene‐1‐hexene
Authors: Takenaka Katsuhiko , Hirao Akira , Nakahama Seiichi 
Published: April 2003

AbstractBoth polystyrenes and polyisoprenes with 1,3‐butadienyl end‐groups were synthesized by the reactions of polystyryl and polyisoprenyl anions with 6‐bromo‐3‐methylene‐1‐hexene (3). The 1,3‐butadienyl end‐group was further transformed to an anhydride function by Diels‐Alder reaction with maleic anhydride. These end‐functionalized polymers were characterized by size exclusion chromatography (SEC), infrared spectroscopy, elemental analysis, 1H and 13C NMR, and thin layer chromatography coupled with a flame ionization detector. All analytical deta indicate that the polymers are quantitatively end‐functionalized with 3 and then with maleic anhydride. Polymers with one or two end‐functions are obtainable.
Effects of ortho‐substituents on the living polymerization of phenylacetylenes by MoOCl4‐based catalysts
Authors: Mizumoto Tomohiro , Masuda Toshio , Higashimura Toshinobu 
Published: April 2003

AbstractPolymerization of phenylacetylenes (PAs) having various ortho‐substituents were examined by using MoOCl4—n‐Bu4Sn—EtOH (mole ratio 1:1:1) as catalyst. Phenylacetylenes with no or sterically small ortho‐substituents did not polymerize in a living fashion. On the other hand, in the polymerization of phenylacetylenes having medium‐sized substituents (e.g., CH3, Cl, Br, and iPr), the number‐average molecular weights Mn of polymers increased in direct proportion to monomer consumption, while the polydispersity ratios were 1,2– 1,3, which is in favor of living polymerization. Further, monomers having bulky ortho‐groups (CF3 and Me3Ge) exhibited excellent living nature with small polydispersity ratios of ≈ 1,1. Thus, it is concluded that not the electronic but the steric effect of the ortho‐substituent is important to achieve living polymerization.
A collagen‐polypyrrole hybrid: influence of 3‐butanesulfonate substitution
Authors: Li Hwee Chze , Khor Eugene 
Published: April 2003

AbstractHybrid biomaterials derived from a water‐soluble derivative of polypyrrole, poly(sodium 4‐(3‐pyrrolyl)butanesulfonate), and soluble collagen have been synthesized by chemical polymerization of the 4‐(3‐pyrrolyl)butanesulfonate monomer in a collagen solution. Interaction between the two polymers was evident in the formation of a precipitated black polymer‐collagen gel obtained for a monomer concentration of 0,01 mol/L. The collagen content in the gel was determined to be around 38 wt.‐%. When the monomer concentration was increased five‐fold, the product was a dispersed precipitate that was polymer rich with a corresponding decrease in collagen (11 wt.‐%) content. Fourier transform infrared spectroscopy and thermal analysis of the hybrids provide signs of interaction between the sulfonic acid group on the substituted pyrrole and side groups of amino acids in collagen. The electrical conductivities of these hybrid biomaterials were found to be in the 10−2 S. cm −1 range.
Interaction of slightly crosslinked gels of poly(diallyldimethylammonium bromide) with sodium dodecyl sulfate and cetylpyridinium bromide
Authors: Starodoubtzev Sergey G. , Minh Le Thi , Makhaeva Elena E. , Philippova Olga E. , Pieper Thomas G. 
Published: April 2003

AbstractThe interaction of slightly crosslinked gels of poly(diallyldimethylammonium bromide) (PDADMAB) with both the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant cetylpyridinium bromide (CPB; system. name: N‐hexadecylpyridinium bromide) in aqueous medium has been investigated. The absorption of the anionic surfactant by the oppositely charged gel leads to contraction or collapse of the network. The absorption of the cationic surfactant by the gel‐SDS complexes results in a reswelling of the network. By means of IR and UV spectroscopy it has been shown that in the presence of the anionic detergent the cationic network absorbs the cationic surfactant. It has been shown that both reversible and irreversible complex formation in the gel phase is possible depending on the initial ratio between the components. Small‐angle‐X‐ray scattering experiments demonstrated that the complexes may have a regular microstructure.