bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of the structure on the photodegradation of poly(vinyl chloride), 3. Dependance of the quantum yield of dehydrochlorination on the isotactic content
Authors: Castillo Francisca , Martinez Gerardo , Sastre Roberto , Millán José Luis 
Published: April 2003

AbstractThe photodehydrochlorination of four poly(vinyl chloride) (PVC) samples of different tacticities, as studied previously, was compared with that of a PVC sample after being modified to various degrees by nucleophilic substitution with sodium benzenethiolate (NaBT). In order to separate the influence of substituted structures from that of the chromophoric group grafted onto the polymer, a series of PVC mixtures with sec‐butyl phenyl sulfide (BPT), of compositions similar to those of modified polymers was also studied. The evolution of HCl was found to be a linear function of the absorbed dose in all cases. The quantum yield of dehydrochlorination, ΦHCl, as obtained from the slopes, appeared to decrease with the isotactic content. The results suggest specific isotactic triads to be markedly reponsible for the photodehydrochlorination, which would account for a mechanism based on the occurrence of chlorines of low dissociation energy at such triads.
Anionic synthesis of chain‐end functionalized polymers using 1,1‐diphenylethylene derivatives. Preparation of 4‐hydroxyphenyl‐terminated polystyrenes
Authors: Quirk Roderic P. , Zhu Lin‐fang 
Published: April 2003

AbstractA new, general functionalization reaction for polymeric organolithium compounds was developed based on their quantitative reaction with 1,1‐diphenylethylene derivatives. The utility of this method was demonstrated by preparation of 4‐hydroxyphenyl‐terminated polystyrene (2b) by reaction of polystyryllithium in benzene at room temperature with 1‐[4‐(tert‐butyldimethylsiloxy)phenyl]‐1‐phenylethylene (1a) followed by hydrolysis with dilute hydrochloric acid. The course of the functionalization reaction was monitored by ultraviolet‐visible spectroscopy at 406 nm. Polystyrene 2b was characterized by size exclusion chromatography, thinlayer chromatography, membrane osmometry, end‐group titration and both 1H and 13C NMR spectroscopy. All experimental evidence is consistent with quantitative functionalization via the 1,1‐diphenylethylene derivative.
Kinetics of group transfer polymerization of tert‐butyl methacrylate in tetrahydrofuran
Authors: Doherty Martin A. , Müller Axel H. E. 
Published: April 2003

AbstractThe reaction kinetics for the group transfer polymerization (GTP) of tert‐butyl methacrylate (TBMA) using a silyl ketene acetal initiator and a nucleophilic catalyst are investigated. The reaction is shown to be of first order in both monomer and catalyst concentrations. The “livingness” of this system appears to be influenced by the reaction temperature. At temperatures above −20°C, deactivation is observed, with its severity increasing with increasing temperature. This deactivation is attributed to a depletion of catalyst by side reactions. It was demonstrated that reactivation is made possible by the addition of more catalyst. This result is in contrast to the anionic polymerization of TBMA, where no deactivation was observed even at ambient temperature. At temperatures below −20°C no deactivation is observed; however, at these temperatures, the reactions manifest induction periods with lengths increasing with decreasing temperature. The rate constants are lower than those for the GTP of methyl methacrylate (MMA) by a factor of 1,5 to 2. The following Arrhenius parameters were obtained for the propagation rate constants: activation energy, Ea = (19,1 ± 3) kJ/mol, preexponential factor, log10 A = (7,05 ± 0,3). These values are comparable with those obtained for MMA. The molecular weight distributions are similar to those obtained in the GTP of MMA, i.e. the ratio of weight‐to number‐average molecular weights is rather high for low monomer conversions and narrows to M̄w/M̄n ≥ 1,3 for full conversion. This is attributed to the rates of the catalyst exchange equilibrium.
Synthesis and structure of a “living” copolymer of propylene and 1,5‐hexadiene
Authors: Doi Yoshiharu , Tokuhiro Naoko , Soga Kazuo 
Published: April 2003

AbstractA soluble V(acac)3/Al(C2H5)2Cl system was found to polymerize 1,5‐hexadiene to give a living polymer in toluene at −78°C. Hydrogenation of poly(1,5‐hexadiene) was conducted to determine the chain microstructure. The 13C NMR analysis of hydrogenated poly(1,5‐hexadiene) indicated that the poly(1,5‐hexadiene) is composed of alternating units of 1,3‐cyclopentylenemethylene and 1‐vinyltetramethylene. In addition, living copolymers of propylene and 1,5‐hexadiene were prepared and characterized by analysis of the 1H and 13C NMR spectra. A chain propagation mechanism of living poly(1,5‐hexadiene) is proposed.
Synthesis of polypropylene with improved MgCl2‐supported Ziegler‐Natta catalysts, including silane compounds as external bases
Authors: Spitz Roger , Bobichon Charles , Guyot Alain 
Published: April 2003

AbstractThe new catalytic system comprising a diester as an internal Lewis base and a silane (triethoxyphenylsilane) as an external Lewis base presents important differences to the classical third generation catalyst with two esters in the system, i. e. a high isotacticity is obtained with a low ratio Al/Lewis base, the stereospecificity is stable with temperature and time, the sensitivity to hydrogen concerning the average molecular weight is high and the activity, which remains low without hydrogen, is greatly enhanced by the transfer agent. The selectivity of the system is controlled in a complex manner by the concentration and ratio of the cocatalytic system.
Chemical intercalation of tetraalkylammonium ions into polyacetylene
Authors: Ignatious Francis , François Bernard , Mathis Claude 
Published: April 2003

AbstractA novel class of carbanionic dopant systems was developed which facilitates the intercalation of tetraalkylammonium ions into polyacetylene (PA), which was considered impossible by chemical methods so far. The chemistry of the dopant system was discussed. The presence of [R4N]+ ions in PA was verified by elemental analysis and IR spectroscopy. The maximum doping levels were determined in the case of several carbanionic systems and also by systematically varying the size of the [R4N]+ ions. A correlation between maximum doping levels and the redox‐potentials of the carbanions was established.
Partitioned polymerization, 3. On the use of inhibitors partially soluble in the aqueous phase
Authors: Bartoň Jaroslav , Juraničová Viera 
Published: April 2003

AbstractThe partitioned emulsion polymerization of methyl methacrylate and acrylonitrile initiated by ammonium peroxodisulfate and/or 2,2′‐azoisobutyronitrile was studied in the presence of p‐benzoquinone, 2,2‐diphenyl‐1‐picrylhydrazyl, 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl, 4‐benzoyloxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl, 4‐methacryloyloxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl, 4‐acetoxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl and 4‐stearoyloxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl radicals. These compounds with the exception of 4‐stearoyloxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl inhibit the partitioned emulsion polymerization of methyl methacrylate. In the partitioned emulsion polymerization of acrylonitrile 4‐stearoyloxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl was also found to be effective. This fact was ascribed to the increased water solubility of this inhibitor in an emulsion polymerization system containing acrylonitrile.
Structural variations in ethylene‐tetrafluoroethylene copolymers as a function of composition and temperature
Authors: Iuliano Mauro , De Rosa Claudio , Guerra Gaetano , Petraccone Vittorio , Corradini Paolo 
Published: April 2003

AbstractEthylene‐tetrafluoroethylene copolymers, containing 50–80 mol‐% of tetrafluoroethylene (TFE) units, were investigated by wide‐angle X‐ray scattering (WAXS) and dynamic mechanical analysis (DMA). With increasing TFE content, a shift toward low temperatures of the crystalmesophase transition is observed; only the mesophase is observed for high TFE content (e.g., the 80 mol‐% TFE copolymer). On the basis of a conformational analysis, a gradual change, with the TFE content, of the chain conformation from a planar zig‐zag conformation to a conformation built up locally of very short helical stretches is indicated. For both the crystal and the mesophase structure the size of the domains in which the ordered disposition of the chain axes is maintained is larger for copolymers with higher TFE content, where a lower degree of local order is expected.
Tacticity and dielectric relaxation around the glass transition of poly(vinyl chloride). A thermally stimulated depolarization currents (TSDC) study
Authors: del Val Juan José , Colmenero Juan , Mijangos Carmen , Martínez Gerardo , Millán José Luis 
Published: April 2003

AbstractThe thermally stimulated depolarization currents (TSDC) technique has been used to study molecular motions around the glass transition in three different samples of poly(vinyl chloride) (PVC) varying in the contents of isotactic triads. The α‐relaxation mode associated with cooperative molecular motions taking part in glass transition appears to be strongly dependent on tacticity. A secondary relaxation mode α′, different from the β‐relaxation, has been detected just below the α‐relaxation and at temperatures depending on the content of isotactic triads. Above the glass transition temperature the TSDC curves show a ρ‐peak corresponding to the motion of free charges in the material. This process does not seem to be affected by tacticity. The results suggest that specific conformations of isotactic triads play an important role in the motion of chain segments in the polymer.
Plastic deformation and solid‐phase transformation in β‐phase polypropylene
Authors: Shi Guan‐yi , Chu Feng , Zhou Gui‐en , Han Zhe‐wen 
Published: April 2003

AbstractTensile specimens of isotactic polypropylene, initially crystallized in the β‐form with high purity, were tested at various temperatures. It was observed by WAXD that the most important phenomenon occurring in the course of a tensile test is the β‐smectic transformation for specimens drawn at lower temperature and β‐α transformation for specimens drawn at higher temperature, which takes place in the crystalline lamellae and is induced by plastic deformation. c‐Axis oriented β‐crystals have never been found in the drawn specimens. It was also shown that the β‐smectic transformation propagates inside the spherulites from the equatorial regions, in which the chain axes are nearly parallel to the drawing direction, towards the diagonal and polar regions. Finally, it was noted that microvoids are formed simultaneously during plastic deformation, which may be due to the volume contraction induced by the β‐α or β‐smectic transformation.
Heteropolyacids — new efficient initiators of cationic polymerization
Authors: Bednarek Melania , Brzezińska Krystyna , Stasiński Jacek , Kubisa Przemysław , Penczek Stanisław 
Published: April 2003

AbstractWe have found, that heteropolyacids (HPA) are efficient initiators of cationic polymerizations, including polymerizations of cyclic ethers and acetals, providing high‐molecular‐weight polymers. In several systems (e. g. THF, 1,3‐dioxolane) the degree of polymerization is given by the ratio of concentrations of monomer and initiator, as for the living system. In the polymerization of cyclic formaldehyde trimer: 1,3,5‐trioxane, the comparable polymerization rates may be obtained with ≈ 25 times less an initiator consumption on weight basis (≈ 103 times less on molar basis) than for typical initiators like BF3 · OR2.
Phthalocyanines on mineral carriers, 4. Low‐molecular‐weight and polymeric phthalocyanines on SiO2, γ‐Al2O3 and active charcoal as catalysts for the oxidation of 2‐mercaptoethanol
Authors: Wöhrle Dieter , Buck Thomas , Hündorf Uwe , Schulz‐Ekloff Günter , Andreev Atanas 
Published: April 2003

AbstractLow‐molecular‐weight phthalocyaninatocobalt compounds 2a–d and polymeric phthalocyaninatocobalt derivatives 4, 6a, b were prepared on the surface of the inorganic carriers SiO2 or γ‐Al2O3 and of active charcoal, the range of loading being 11,9 – 0,2 wt.‐%. The oxidation of 2‐mercaptoethanol in an aqueous solution at pH 9 was used as a model reaction for demercaptizations of petroleum fractions with phthalocyanines on carriers as heterogeneous catalysts. The catalytic activity, related to the phthalocyanine content, was found to increase with increasing dispersion of the complex on the carrier. The influence of the type of support on the activity is given by the following order: SiO2 < γ‐Al2O3 < Norit charcoal. Polymeric phthalocyanines exhibit a higher catalytic activity as compared with low‐molecular‐weight phthalocyanines. The mechanism of the oxidation of the thiol is discussed.
Rigid rod polymers with flexible side chains, 7. Synthesis and phase behaviour of polyimides prepared from pyromellitic anhydride and N,N′‐bis(1‐imidazolylcarbonyl)‐2,5‐bis(alkoxyalkoxy‐1,4‐phenylenediamines)
Authors: Helmer‐Metzmann Freddy , Ballauff Matthias , Schulz Rolf Christian , Wegner Gerhard 
Published: April 2003

AbstractPolymides 3a and 3b with stiff‐chains bearing trioxaoctyl or tetraoxaundecyl side chains were synthesized and characterized. The polycondensation was done with pyromellitic anhydride and N,N′‐bis(1‐imidazolylcarbonyl)‐2,5‐(1,4,7‐trioxaoctyl)‐ or 2,5‐(1,4,7,10‐tetraoxaundecyl)‐1,4‐phenylenediamine (2a or 2b). 3b, being sufficiently soluble, was characterized by 13C NMR spectroscopy. The results of IR and 13C NMR spectroscopy prove the presence of the correct imide structure. In solid state 3a and 3b form layered structures with the side chains being in a disordered state.
Effect of monomer diffusion in the polymerization of olefins over Ziegler‐Natta catalysts
Authors: Soga Kazuo , Yanagihara Hisayoshi , Lee Dong‐ho 
Published: April 2003

AbstractBy using an extremely high stereospecific catalyst, three kinds of copolymerizations were carried out with combinations of monomers which differ in the crystallinity of the homopolymers. Addition of a small quantity of comonomer to the homopolymerization systems producing very high crystalline polymers was found to cause a remarkable increase in the apparent polymerization rate as well as a marked decrease in the polymer crystallinity. Such an irregular increase in the polymerization activity was, however, not observed when a small amount of comonomer was added to the homopolymerization systems producing low‐crystalline or amorphous polymers. These observations have led to the conclusion that resistance of monomer diffusion through the polymer film should be one of the significant parameters for the apparent polymerization rate when very high crystalline polymers, like high density polyethylene, isotactic polypropylene etc., are produced.
Photoconductive polymers and copolymers of N‐(2‐propynyl) carbazole and N‐(2‐propynyl)phenothiazine
Authors: Kmínek Ivan , Cimrová Věra , Nešpůrek Stanislav , Vohlídal Jiří 
Published: April 2003

AbstractHomopolymers of N‐(2‐propynyl)carbazole, its copolymers with acetylene, and the homopolymer of N‐(2‐propynyl)phenothiazine were prepared using Ti(OBu)4/AIEt3 as the catalyst. The homopolymer of the carbazole derivative was also prepared by its metathetic polymerization catalyzed with the system WOCl4/Ph4Sn. Homopolymers of both monomers and the copolymer of N‐(2‐propynyl)carbazole with a small quantity of acetylene are photoconductive.
On the cationic polymerization of oxirane with triphenylmethylium salts
Authors: Libiszowski Jan , Szymanski Ryszard , Penczek Stanislaw 
Published: April 2003

Abstract1,4‐Dioxanium and other trialkyloxonium ions were observed by 1H NMR in the polymerization of oxirane initiated with the triphenylmethyl cation. The major product of polymerization is 1,4‐dioxane. Thus, the kinetic data for the same system previously published by other authors, refer to the propagation in which oxirane propagates with the participation of dioxanium and/or other unstrained trialkyl oxonium cations. Our present results, together with previous data of León et al., indicate that the rate constants of propagation with these two kinds of species are very close to each other. Propagation with participation of the oxiranium ion probably takes place only at the very beginning of polymerization.
Electrochemical preparation and properties of poly(3‐aryl‐2,5‐thienylene)s
Authors: Sato Masa‐aki , Tanaka Susumu , Kaeriyama Kyoji 
Published: April 2003

AbstractFilms of poly(3‐phenyl‐2,5‐thienylene) (1a), poly[3‐(4‐methoxyphenyl)‐2,5‐thienylene] (1b) and poly[3‐(4‐trifluoromethylphenyl)‐2,5‐thienylene] (1c) were electrochemically prepared. The conductivities of 1a, 1b and 1c were determined to be 140, 40, and 1,8 · 10−3 S/cm, respectively. The surfaces of 1a and 1b are considerably rough. The infrared spectra of electrochemically neutralized polymers showed that they have a regular structure. Cyclic voltammograms showed that the oxidation potential increases in the order 1b < 1a < 1c (in the neutral state). The results are discussed in terms of the electronic effect of the substituents. The visible spectra of these neutral polymers showed that the π‐π*‐transition occurs at lower energy than that of poly(2,5‐thienylene) (1d). This indicates that the pendant aryl groups are conjugated with the main chain. The effect of substituents on the peak positions of the π‐π* transition is hardly discernible. 1a is highly anode‐active as compared with 1d. The spectral change of 1a upon PF doping presumably is the indication of polarons at low doping levels. The changes during Et4N+ doping shows that cation doping took place.
Hydrogels based on N‐vinyl‐2‐pyrrolidinone and 2‐hydroxyethyl methacrylate
Authors: Koßmehl Gerhard , Volkheimer Jürgen , Schäfer Horst 
Published: April 2003

AbstractHydrogels (crosslinked polymers with a defined water content) based on N‐vinyl‐2‐pyrrolidinone and 2‐hydroxyethyl methacrylate of different compositions were prepared by radical copolymerization and swollen in buffered isotonic sodium chloride solution. The linear expansion to hydration, weight‐percentage of hydration, refractive index, extractables, percentage of transmission of visible light and oxygen permeability of the resulting hydrogel samples were examined.
Photo‐induced copolymerization of cyclohexene with maleic anhydride
Authors: Li Tong , Pan Jinshi , Zhang Zhongquan 
Published: April 2003

AbstractKinetics and mechanism of photo‐induced copolymerization of cyclohexene with maleic anhydride in chloroform were studied. The UV spectra suggested the formation of a chargetransfer complex between the comonomers. This complex was excited under irradiation and then underwent hydrogen abstraction to produce two kinds of radicals for initiation. The polymerization produces an alternating copolymer in the composition range of 25 to 75 mol‐% of either comonomer. The chain‐transfer role of cyclohexene was also investigated.
Electrosynthesis of poly(N‐ethyl‐3,6‐carbazolediyl) catalyzed by a Ni(0)‐based complex
Authors: Siove Alain , Adès Dominique , Chevrot Claude , Froyer Gérard 
Published: April 2003

AbstractPoly(N‐ethyl‐3,6‐carbazolediyl) was synthesized by electroreduction of the NiBr2/2,2′‐bipyridine/3,6‐dibromo‐N‐ethylcarbazole system in N,N‐dimethylacetamide. Both gel permeation chromatography analyses of the polymer formed and electrochemical studies of the system during the course of polymerization in homogeneous phase point at a constant efficiency of the catalytic complex. The latter generates potentially active species which contain the transition metal inserted into a CBr bond. Mechanisms of formation of the growing chains are proposed on the basis of the electrochemical behaviour of the catalytic system. Chemical doping of the polymer leads to a material the conductivity of which is in the range 10−4 < σ/(Ω−1 · cm−1) < 10−3.
Synthese und thermische eigenschaften von photosensiblen polyacrylsystemen mit zimtsäurehaltigen seitengruppen und deren verwendung in composite‐membranen
Authors: Koch Thomas , Ritter Helmut , Buchholz Norbert , Knöchel Friedrich 
Published: April 2003

AbstractThe synthesis of comb‐like polymers containing cinnamic acid derivatives in the side chains is described. The disappearance of thermal transitions after UV‐irradiation of the polymer samples was demonstrated by DSC measurements in the case of the liquid‐crystalline homopolymer poly[4‐propoxyphenyl 4‐(6‐acryloyloxyhexyloxy)cinnamate] and the side‐chain crystallizable copolymers poly[(4‐(6‐acryloyloxyhexyloxy)cinnamic acid‐co‐hexadecyl acrylate)]. A significant influence of UV‐irradiation on the permeation activation energy of 1‐butanol through polyamide composite membrance containing a film of the photosensible comb‐like polymers was observed.
Crystallization behavior of block copolyarylates synthesized via two‐step interfacial polycondensation
Authors: Lee Yu‐Der , Tsai Hong‐Bing 
Published: April 2003

AbstractDSC, X‐ray diffraction and solid‐state 13C NMR were used to investigate the crystallization properties of block copolyarylates prepared via two‐step interfacial polycondensation. The block copolyarylates obtained from 1,1,2,2‐tetrachloroethane solution were found to have low crystallinity. This could be explained as the influence of amorphous blocks on the crystalline blocks. When the block copolyarylates were redissolved in dichloromethane, the annealed, cast films exhibited considerably higher crystallinity. It was concluded that the crystallization behavior of block copolyarylates is very much dependent on their sample history.
Structural models for crystallographic disorder in poly(tetrafluoroethylene)
Authors: Marega Carla , Marigo Antonio , Garbuglio Carmine , Fichera Annamaria , Martorana Antonino , Zannetti Roberto 
Published: April 2003

AbstractSome structurally disordered models for poly(tetrafluoroethylene) were elaborated and the corresponding calculated X‐ray diffraction patterns compared with experimental patterns. This and differential scanning calorimetry results suggest some differences between the virgin powder and a sintered polycrystalline plate of poly(tetrafluoroethylene). These differences may be related to the crystal phase transitions that occur in a range of temperatures close to room temperature.
Ternary and partial ternary azeotropes
Authors: Quella Ferdinand 
Published: April 2003

AbstractA paper in 1983 of Ham postulating the non‐existence of ternary azeotropes resulting from ternary copolymerization is contradicted on the basis of mathematical solutions and further experimental results from other authors. A broader view of the problem of ternary azeotropy must include the partial azeotropes, which are almost absent from recent literature, although they contain the potential for hundreds of polymers with still largely unknown physical properties. Ham has hitherto been supported by the apparent necessity of using comparatively complex mathematical equations. However, it will be shown that many of these can be reduced to simple relationships.