bluuebunny/crossref_metadata_2025_split huggingface dataset:
New initiators for group transfer polymerization. Triphenylphosphonium‐containing ketene silyl acetals
Authors: Shen Wei‐ping , Zhu Wei‐de , Yang Ming‐fa , Wang Lan 
Published: April 2003

AbstractNew initiators for group transfer polymerization (GTP), triphenylphosphonium‐containing ketene silyl acetals, were synthesized by addition of triphenylphosphine and chlorotrimethylsilane to methyl acrylate or methyl methacrylate, respectively, giving 3‐methyoxy‐3‐trimethylsiloxy‐2‐propenyltriphenylphosphonium chloride (4a) and its 2‐methyl substituted derivative (4b), together with their corresponding oligomers (8). These phosphonium salts initiate GTP of ethyl acrylate using zinc halides as catalysts. The resulting polymers, containing a terminal triphenylphosphonium group, show a small polydispersity. In the presence of zinc halides, triphenylphosphine and chlorotrimethylsilane can be used directly to initiate GTP of acrylates and methacrylates. In this case triphenylphosphonium terminated polymers with a larger polydispersity are obtained.
Liquid‐crystalline polyurethanes, 6. Amphiphilic polyurethanes containing long alkyl chains in the side chains and amino or quaternary ammonium groups in the main chains
Authors: Tanaka Mamoru , Nakaya Tadao 
Published: April 2003

AbstractAmphiphilic polyurethanes5a–c,6a–c,10a–cand11a–ccontaining hydrophilic amino or quaternary ammonium groups in the main chain, and hydrophobic ocatadecyl or docosyl groups in the side chain, were synthesized by polycondensation of 2,2′‐octadecyliminodiethanol (3a), 2,2′‐docosyliminodiethanol (3b), bis(2‐hydroxyethyl)methyloctadecylammonium bromide (8) and bis(2‐hydroxyethyl)docosylmethylammonium bromide (9) with a diisocyanate such a hexamethylene diisocyanate (4a), 2,4‐toluylene diisocyanate (4b) and 4,4′‐methylenediphenyl isocyanate (4c). Some of them show a thermotropic liquid‐crystalline state, as determined by DSC and polarizing microscopy.
Excimer laser‐induced free‐radical copolymerization of ethylene and acrylonitrile
Authors: Brackemann Holger , Buback Michael 
Published: April 2003

AbstractThe free‐radical copolymerization of ethylene (E) and acrylonitrile (A) was studied up to 275°C and 2900 bar in continuously and in discontinuously operated devices. Polymerization is induced by KrF excimer laser light at 248 nm. In addition, results for copolymerizations with thermal and with chemical (oxygen) initiation are presented. The ethylene reactivity ratio, rE, is derived as a function of temperature. At 2450 bar, rE increases from 0,016 ± 0,003 at 150°C up to 0,055 ± 0,009 at 275°C. rE measured as a function of pressure, yields an activation volume of ΔV# (rE) = (−5,2 ± 3,5) cm3·mol−1. The kinetic information from the laser‐induced experiments is used to describe the measured overall quantum yield, ϕ0, which is found to be a few thousand monomer molecules polymerized by one absorbed laser photon. ϕ0 decreases toward higher acrylonitrile content. The kinetic parameters are also used to predict overall and acrylonitrile conversion in continuous free‐radical E/A copolymerizations with various chemical initiators.
On the relationship between room‐temperature conductivity and morphology of polyacetylene
Authors: Gläser Daniel , Schimmel Thomas , Schwoerer Markus , Naarmann Herbert 
Published: April 2003

AbstractSeveral sets of samples of elongated Naarmann‐type polyacetylene were investigated by conductivity measurements and scanning electron microscopy. For the latter investigations, a special kind of sample preparation was developed to ensure authentic information about the internal morphology of polyacetylene. We found two different types of fibrillar morphologies, one exhibiting thick bundels or strings along the elongation direction and an intermediate tissue of nonaligned fibrils, the other showing only individual, well aligned fibrils. The first type of structure has low conductivities after oxidation with iodine, whereas the second one tends to have significantly higher values. A comparison of the geometrical and electrical anisotropy shows that charge transport takes place mainly in highly aligned regions, the conductivity being a weighted average over all possible conducting paths.
Electron‐ion recombination luminescence from UV irradiation of glassy epoxy resins
Authors: Billingham Norman C. , Burdon Jeremy W. , Kozielski Karen A. , George Graeme A. 
Published: April 2003

AbstractBrief irradiation of an epoxy resin is shown to induce a chemiluminescence emission which decays over a period of minutes. At cure temperatures, the intensity of this emission passes through a minimum with cure time, correlating with the vitrification of the resin. Photo‐induced chemiluminescence can also be observed at room temperature in glassy resins. Studies of emission and excitation wavelengths, atmosphere dependence, electric field effects and thermoluminescence from irradiated resin suggest that two phenomena are responsible. For fluid resins curing in air, the emission is due to the recombination of radicals participating in the oxidation of the resin. As the resin vitrifies, the luminescence is increasingly due to recombination of photo‐induced electron‐cation pairs and is sensitive to the vitrification. This phenomenon could provide a new method for monitoring cure in thermosetting resins.
Graft copolymers of polytetrahydrofuran and butyl rubber, 1. Cationic copolymerisation of tetrahydrofuran with bromobutyl rubber
Authors: Cameron G. Gordon , Sarmouk Khiredine 
Published: April 2003

AbstractGraft copolymers of butyl rubber (BR) with polytetrahydrofuran (PTHF) were prepared from bromobutyl rubber by a cationic “grafting‐from” reaction initiated by silver perchlorate at allylic bromine sites on the rubber. By studying the influence of variables, such as temperature etc., it was shown that initiation at −20°C for 30 min, followed by polymerisation at 0°C with a [AgClO4]/[Br] ratio of ca. unity, produced near optimum reaction conditions with grafting efficiencies >90%. Copolymers containing upto 40% of grafted PTHF were obtained by this means. The BR‐g‐PTHF copolymers have a two‐phase morphology comprising amorphous BR with crystalline domains of PTHF which function as points of reinforcement in the rubber upto ca. 300 K.
Liquid‐crystalline polyethers and copolyethers based on conformational isomerism, 4. Thermotropic polyethers and copolyethers based on 1‐(4‐hydroxyphenyl)‐2‐(2‐methyl‐4‐hydroxyphenyl)ethane and flexible spacers containing an even number of methylene units
Authors: Percec Virgil , Yourd Raymond 
Published: April 2003

AbstractThe synthesis and characterization of thermotropic main‐chain liquid‐crystalline polyethers MBPE‐X and copolyethers MBPE‐X/Y based on 3‐methyl‐4,4′‐ethylenediphenol [1‐(4‐hydroxyphenyl)‐2‐(2‐methyl‐4‐hydroxyphenyl)ethane (MBPE)], which is flexible rod‐like mesogenic unit or a rod‐like mesogenic unit based on conformational isomerism, and flexible spacers containing an even number of methylene units, X, Y, are described. The particular examples presented in this paper refer to polyethers MBPE‐4, MBPE‐6, MBPE‐8, MBPE‐10, and MBPE‐12, and copolyethers MBPE‐X/Y; where X,Y = 4, 6, 8, 10, 12. MBPE‐4, MBPE‐6, MBPE‐10 and MBPE‐12 are crystalline. MBPE‐8 displays an enantiotropic nematic mesophase. Copolymerization of MBPE with different pairs of spacers containing even numbers of methylene units leads to MBPE‐X/Y copolymers displaying monotropic or enantiotropic nematic mesophases. Both liquid‐crystalline transition temperatures and the corresponding enthalpy changes of the copolymers represent weight‐averaged values of the similar parameters of the parent homopolymers. Extrapolation of the isotropic‐nematic and nematic‐isotropic transition temperatures and their corresponding enthalpy changes demonstrated that all homopolymers containing an even number of methylene units in the flexible spacer exhibit virtual nematic mesophases. The virtual isotropic‐nematic transition temperatures and the corresponding enthalpy changes were determined for MBPE‐4, MBPE‐6, MBPE‐10 and MBPE‐12. The virtual nematic‐isotropic transition and the corresponding enthalpy changes could be determined only for MBPE‐10 and MBPE‐12.
Synthese und Reduktion des Tetra‐tert‐butyltetraoxocalix[4]arens
Authors: Görmar Gerhard , Seiffarth Klaus , Schulz Manfred , Zimmermann Jochen , Flämig Gesina 
Published: April 2003

Abstract5,11,17,23‐Tetra‐tert‐butyl‐25,26,27,28‐tetrahydroxy‐2,8,14,20‐tetraoxocalix[4]arene (4) was synthesized by oxidation of the tetraacetate of 5,11,17,23‐tetra‐tert‐butyl‐25,26,27,28‐tetrahydroxycalix[4]arene (1). Compound 4 was characterized by chemical and spectroscopic methods. Reduction of 4 with hydrazine forms the starting material 1. 4 reacts with sodium borohydride to give 5,11,17,23‐tetra‐tert‐butyl‐2,8,14,20,25,26,27,28‐octahydroxycalix[4]arene (6).
Preparation of poly(amide‐imide)s by direct polycondensation with triphenyl phosphite, 3. Poly(amide‐imide)s based on bis(trimellitimide)s
Authors: Hsiao Sheng‐Huei , Yang Chin‐Ping 
Published: April 2003

AbstractSix dicarboxylic acids (1a–f) were prepared from trimellitic anhydride and 4,4′‐oxydianiline, 4,4′‐methylenedianiline, 4,4′‐sulfonyldianiline, benzidine, 1,6‐hexamethylenediamine, and 4,4′‐methylenedicyclohexylamine. These diacids were condensed directly with various aromatic diamines using triphenyl phosphite in 1‐methyl‐2‐pyrrolidone/pyridine solution in the presence of calcium chloride. The inherent viscosity of the polymers is affected by the nature of the diamine and the solubility of the resulting polymers in the reaction media. The highest ηinh‐value of a poly(amide‐imide) obtained was 1,41 dl/g (in N,N‐dimethylacetamide/5% LiCl at 30°C). Among the polymers, the wholly aromatic ones show better solubility, higher glass transition temperatures, and higher thermostability than the aliphatic‐aromatic ones. Well‐defined melting points (Tm) of most wholly aromatic poly(amide‐imide)s were not obtained by differential scanning calorimetry (DSC); however, some poly(amide‐imide)s containing aliphatic chains showed clear Tm in the first DSC heating traces. Measurements of wide‐angle X‐ray diffraction revealed that those polymers containing biphenyl or linear hexamethylene groups are partially crystalline. Flexible films with excellent tensile properties were cast from N,N‐dimethylacetamide solutions of most of the wholly aromatic poly(amide‐imide)s.
Investigations of poly(vinyl alcohol)/poly(N‐vinyl‐2‐pyrrolidone) blends, 2. Influence of the molecular weights of the polymer components on crystallization
Authors: Ping Zheng‐Hua , Nguyen Quang Trong , Néel Jean 
Published: April 2003

AbstractBlends of crystallizable poly(vinyl alcohol) (PVA) and poly‐(N‐vinyl‐2‐pyrrolidone) (PVP) of different molecular weights were prepared from aqueous solutions by evaporation and studied by Fourier‐transform IR spectroscopy. When the molecular weight of one of the polymer components increases, the PVP content at which crystallinity in PVA is no longer observed decreases. The wide band representing hydroxyl stretching splits into four components at welldefined frequencies which are assigned to (1) multiple hydroxyl‐hydroxyl bonding in organized PVA regions, (2) hydroxyls which are simply bonded to carboxyl, (3) hydroxyls doubly bonded to two carbonyls or to one carbonyl and one hydroxyl, and (4) simple hydrogen‐hydrogen bonding in amorphous PVA regions. When the PVP content increases, the relative intensity of the bond of di‐hydrogen‐bonded hydroxyls remains quasi‐invariant, while that of multiple hydrogen bonds in PVA decreases, and that of simple hydroxyl‐carbonyl bonds increases correspondingly. It appears that the higher the molecular weight, the more effective the hindrance of PVP crystallization. An explanation of the mechanism leading to the formation of different structures in the blends is proposed on the basis of these results. It stresses the importance of the role of chain dynamics in an entangled chain network, which greatly affects the kinetics of crystallization of PVA during the drying step.
Polyesters prepared by polycondensation in the presence of carbodiimides, 2. On the reaction of methyl α‐(S)‐malate with N,N′‐dicyclohexylcarbodiimide under mild conditions
Authors: Belcheva Nadya , Tsvetanov Christo , Panayotov Ivan M. , Lazarova Stoyanka 
Published: April 2003

AbstractThe reaction of methyl α‐(S)‐malate with N,N′‐dicyclohexylcarbodiimide in the presence of amines under mild conditions was studied. It was established that in solvents with weak donor properties, N‐acyl derivatives are preferentially formed instead of ester condensation products. An optically active polymer fraction was separated by precipitation in diethyl ether (yield up to 30%) with M̄n,GPC 1 000 to 4 000 and of low polydispersity M̄w/M̄n = 1,1–1,4. The method permits the preparation of optically active biodegradable condensation products with controlled molecular structure.
Influence des traitements thermiques à l'état fondu sur les cinétiques de cristallisation du poly(oxyméthylène)
Authors: Franbourg Alain , Rietsch François 
Published: April 2003

AbstractThe influence of the temperature of the melt T1 on the kinetics and the morphology of a semicrystalline polymer (poly(oxymethylene)) was investigated using thermal analysis and optical microscopy. The thermodynamic melting point T and the enthalpy of melting at thermodynamical equilibrium ΔH were determined by extrapolation of the graphs Tf = f(Tc) and ΔHf = f(Tc); (T = 198°C, ΔH = 251 J/g). For different temperatures of the melt (T1 = 185°C, 195°C, 205°C), isothermal and non‐isothermal crystallizations were analysed using the Avrami and Ozawa equations. Nucleation and spherulitic growth in this polymer were studied by using optical microscopy at elevated temperatures. Using different analyses, we observed initial nucleation followed by spherulite growth with the following influence of the temperature of the melt on the distribution and the number of spherulites: T1 < T produces many small spherulites; T1 > T gives rise to few large spherulites.
Theoretical approach to cationic polymerization of alkenylfuranes
Authors: Alvarez J. Raul , Montero Luis , Martinez Ricardo 
Published: April 2003

AbstractThe molecular species proposed for the initial steps in the cationic polymerization of alkenylfurans were modeled by MNDO theoretically fully optimized structures. It was confirmed that the anomalous reactivity of ring C‐5 of the monomers is determined by HOMO electron densitites, whereas calculated proton affinities from the semiempirical heats of formation fail to explain the low temperature experimental behavior of 2‐vinylfuran (1c) from the point of view of stability of intermediate species. However, ab initio 4‐31G calculations of proton affinities agree with the experimental facts and allow further explanations of the reactivity of furan derivatives in electrophilic media.
Observations on the swelling behaviour of copolymeric hydrogels containing N‐vinyl‐2‐pyrrolidone
Authors: Al‐Issa Mahmoud A. , Davis Thomas P. , Huglin Malcolm B. , Rego Jose M. , Rehab Mahmoud M. A.‐M. , Yip Daniel C. F. , Zakaria Mat B. 
Published: April 2003

AbstractPolymer‐water interaction parameters, sequence length distributions and contents of total, freezing and non‐freezing water have been discussed for a family of hydrogels. The xerogel precursors contained N‐vinyl‐2‐pyrrolidone (VP) with several co‐monomers of different levels of hydrophobicity present in the xerogel over a wide range of composition. Common trends in the behaviour of these systems have been noted and rationalised. In particular the findings indicate that (i) in the poly‐VP hydrogel ther are ca. 8–10 molecules of non‐freezing water per VP unit and (ii) in the copolymeric hydrogels the maximum occurring in the variation of mole fraction of VP versus mole fraction of water is due substantially to the sharp increase in uptake of freezing (or bulk) water by copolymers rich in VP.
Energy calculations on chain conformation and mode of packing of crystalline isotactic cis‐1,4‐poly(1,3‐pentadiene)
Authors: Napolitano Roberto 
Published: April 2003

AbstractConformational and packing energy calculations were performed on crystalline isotactic cis‐1,4‐poly(1,3‐pentadiene). Internal parameters corresponding to a chain conformation similar to that of other polydienes were found by conformational energy calculations. The packing energy calculations indicate that the most stable mode of packing is obtained in the P212121 space group. A possible structure of the polymer is also suggested.
Small‐angle X‐ray scattering studies on poly(vinyl alcohol)/poly(N‐vinyl‐2‐pyrrolidone) blends
Authors: Zhang Hongfang , Yin Jinghua 
Published: April 2003

AbstractThe structures of unannealed and annealed poly(vinyl alcohol) (PVAl)/poly(N‐vinyl‐2‐pyrro‐lidone) (PVP) blends were investigated by means of small‐angle X‐ray scattering (SAXS). The results indicate that the structural parameters are strongly dependent upon both composition and crystallization conditions. The amorphous region, the long period and the thickness of the lamellae increase with increasing content of PVP in the blends. Annealing increases the crystallinity significantly. The degree of crystallinity and the specific inner surface are reduced with decreasing content of PVAl. A crystal‐amorphous interface exists within the lamellae; the size of the interface is of the order of 20–25 Å.
Synthesis of polystyrene‐polycarbonate block copolymers: A reappraisal of the reaction between polystyryllithium and bisphenol‐A polycarbonate
Authors: Berti Corrado , Bonora Virna , Pilati Francesco , Chiantore Oscar 
Published: April 2003

AbstractPolystyrene (PS)/bisphenol‐A polycarbonate block copolymers were prepared by direct reaction of polystyryllithium with bisphenol‐A polycarbonate. Contrary to what was previously reported by Polowinski et al., the yields of block copolymers were low owing to side reactions. These are due to consecutive attacks of the polystyryl anions and lead to a dimeric ketone (dipolystyryl ketone, PSCOPS) and a trimeric tertiary alcohol (tripolystyryl carbinol, (PS)3COH). The block copolymers were separated from the reaction mixture and characterized.
Synthesis and properties of polymeric iron(II)‐complexes containing terpyridinyl groups
Authors: Hanabusa Kenji , Nakano Kunihiro , Koyama Toshiki , Shirai Hirofusa , Hojo Nobumasa , Kurose Akio 
Published: April 2003

AbstractA new vinyl monomer (4) containing a terpyridinyl group was prepared and radically copolymerized with styrene or methyl methacrylate. The terpyridinyl groups in the resulting copolymers (5 and 6) coordinate almost quantitatively to the Fe(II) ion and form a complex. The decrease of ηinh, accompained by the coordination to the Fe(II) ion, suggests that the formation of the Fe(II)‐complex occurs in each polymer chain with shrinking. A cyclic voltammogram of the Fe(II)‐complex of polymer 6 showed characteristic Fe2+/Fe3+ redox couples at +1,12 V vs. SCE, which was followed by a color change from purple to colorless.
Alkylumlagerungen und acidolyse der ethylidenbrücken bei der synthese von ethylidendiphenolen
Authors: Kämmerer Hermann , Kiegel Einhart 
Published: April 2003

AbstractFor the synthesis of symmetrical and unsymmetrical ethylidenediphenols the corresponding hydroxyphenylethanols (1a–c) were prepared by hydrogenation of hydroxyphenyl methyl ketones with hydrogen/Raney nickle or with lithium aluminium hydride. Condensations of the hydroxyphenylethanols with different phenols under the usual acidic conditions gave products formally resulting form transalkylations. Only the reaction of 1‐(3‐bromo‐2‐hydroxy‐5‐methylphenyl)ethanol (1c) with p‐cresol gave the expected product 2d with 82% yield. Experiments with ethylidenediphenols showed that with acids in presence or absence of phenols cleavage and recondensations take place leading to products of formal transalkylation. Based on these results a method of synthesis was developed (the so‐called “gaseous HCl‐method”) leading to the desired ethylidenediphenols, as shown in the case of 4,4′,6‐trimethyl‐2,2′‐ethylidenediphenol (2b).
A novel, facile technique for deacetylating chitin
Authors: Batista Irineu , Roberts George A. F. 
Published: April 2003

AbstractThe use of water‐miscible organic solvents such as 2‐propanol, 2‐methyl‐2‐propanol and acetone in the alkaline deacetylation of chitin was examined. Using such diluents enables adequate deacetylation to be obtained with much smaller volumes of alkali, typically 1,5 cm3 50 wt.‐% aq. NaOH per 1 g of chitin, although in general the extent of deacetylation is less than that obtained using alkali alone under the same conditions of time and temperature. Sufficient deacetylation to render the product acid‐soluble may be obtained at temperatures as low as 56°C, but temperatures of 75–80°C are preferred. The extent of chain cleavage may be reduced by addition of thiophenol or sodium borohydride to the reaction mixture, or by carrying out the deacetylation in an inert atmosphere, and chitosan having M̄v > 1 · 106 and ca. 70% deacetylated sugar units was obtained using the latter technique.
Synthèses de diols téléchéliques isomoléculaires par télomérisation
Authors: Boutevin Bernard , El Idrissi A. , Parisi J. P. 
Published: April 2003

AbstractTelechelic diols(10–13 and 15–18) were synthesized by addition of 2‐mercaptoethanol(2) and dithiols (3 and 4) to 9‐undecen‐1‐ol (9), ω‐hydroxyalkyl esters of 10‐undenoic acids (8a–c) or N‐(2‐hydroxyethyl)‐10‐undecenamide (5) in the presence of benzoyl peroxide in quantitative yields. The resulting diols have a length in the range of 15 to 50 carbon atoms. They show, however, properties of isomolecular substances.
Polystyrènes à motifs bifonctionnels: synthèses, caractérisations et modifications chimiques
Authors: Monthéard Jean‐Pierre , Boinon Bernard , Benayad Belabbas , Brigui Jamal , Camps Marcel 
Published: April 2003

AbstractFour enol esters with a styrene skeleton (3a–d) were synthesized in two steps from commercial products and polymerized or copolymerized with styrene as a comonomer. The polymers and copolymers (7 and 8) were characterized. They are stable up to 140°C and lose acetic acid upon heating. Chemical modifications, such as nucleophilic substitutions with cyanide ions or nucleophilic addition of butyllithium, were studied.
Poly(vinylsaccharide)s, 7 New surfactant polymers based on carbohydrates
Authors: Klein Joachim , Kunz Markwart , Kowalczyk Jörg 
Published: April 2003

AbstractNew amphiphilic poly(vinylsaccharide)s (poly(7) and poly(8)) were synthesized. Various alkylamino substituted mono‐ and disaccharides 3 and 5 were obtained by reductive amination of reducing mono‐ and disaccharides with alkylamines. The reaction of these monofunctionalized sugar derivates with 2‐isocyanatoethyl methacrylate (2) leads to well‐defined monomers (7 and 8) of the urea type. The monomers were polymerized in aqueous solution to high‐molecular‐weight polymers, using the redox initiator system (NH4)2S2O8/Na2S2O5. The influence of structural variations by changing the hydrophilic sugar moiety or the lipophilic alkyl part was studied by viscometry, light scattering and measurements of the surface tension.
Synthese und polymerisationsverhalten neuer spirocyclischer methacrylate
Authors: Haase Ludwig , Klemm Elisabeth 
Published: April 2003

AbstractNovel 2‐substituted 9‐methacryloyloxy‐8,8‐dimethyl‐1,4,6‐trioxaspiro[4,4]nonanes 3a–e were synthesized by O‐acylation of the corresponding 9‐hydroxyspiroorthoesters 2a–e with methacrylic acid. Its radical homopolymerization in solution results in film‐forming, soluble polymers with intact spiroorthoester groups, which can be crosslinked by cationic ring‐opening reaction. On the other hand, insoluble polymers are formed by radical polymerization of these methacrylic spiroorthoesters 3a–e in bulk. Crosslinking is traced back to a radical ring‐opening reaction as a consequence of a chain transfer reaction at the spirocyclic part of the molecule.