bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and crystallization kinetics of poly(L‐lactic acid)
Authors: Marega Carla , Marigo Antonio , Di Noto Vito , Zannetti Roberto , Martorana Antonino , Paganetto Guglielmo 
Published: April 2003

AbstractA structural investigation is described of poly(L‐lactic acid) by best fitting of powder X‐ray diffraction patterns. The examined sample shows the already known pseudo‐orthorhombic α‐form, and it was possible to determine the location of the two 103 polymeric helices in the unit cell and the size distribution of the crystallites. Furthermore, a study is reported of the crystallization kinetics of the above cited polymer by light depolarization measurements in an optical microscope. The crystallization kinetic constants in bulk were evaluated in a temperature range (70–165°C) wider than that previously resulting from measurements of radial growth of spherulites.
Particle formation in emulsion polymerization, 2. Aggregation of primary particles
Authors: Hergeth Wolf‐Dieter , Lebek Werner , Stettin Enrico , Witkowski Konrad , Schmutzler Klaus 
Published: April 2003

AbstractThe formation and aggregation of primary particles in the beginning of emulsion polymerization was monitored by surface tension measurements, viscometry, electron microscopy, and static and dynamic light scattering. The dimensions of the primary particles in the emulsion polymerizations of vinyl acetate and methyl methacrylate are of the order of 3 – 5 nm. Immediately after the formation of primary particles these begin to aggregate. The stability of these particles is discussed and conclusions are drawn concerning the formation of new particles in the course of polymerization or in seeded polymerization experiments.
Reactive blending of poly(ethylene terephthalate) and polycarbonate, 1. A reappraisal of the reactions occuring during melt‐mixing
Authors: Berti Corrado , Bonora Virna , Pilati Francesco , Fiorini Maurizio 
Published: April 2003

AbstractThe reactions occurring during melt‐mixing of poly(ethylene terephthalate) and bisphenol‐A polycarbonate have been reconsidered. Certain evidence leads us to conclude that two reactions, usually disregarded in the literature, occur, which have to be considered in the general scheme along with the already described exchange reactions. These reactions lead to the formation of cyclic ethylene carbonate and of aromatic‐aliphatic ether moieties, and therefore introduce significant modifications in the chemical structure of the polymeric material resulting from melt‐mixing. An increase in the amount of aromatic‐aromatic ester groups and the formation of a significant amount of aromatic‐aliphatic ether moieties can be obtained depending on reaction conditions.
Reactive blending of poly(ethylene terephthalate) and polycarbonate, 2. A novel route to copoly(ester‐ether)s
Authors: Berti Corrado , Bonora Virna , Pilati Francesco , Fiorini Maurizio 
Published: April 2003

AbstractCopoly(ester‐ether)s have been prepared by reacting poly(ethylene terephtalate) (PET) and bisphenol A polycarbonate (PC) at high temperature, under vacuum, in the presence cf titanium tetrabutoxide as catalyst. The polymeric materials obtained in this way, which contain terephthalate, bisphenol A and ethylene glycol moieties, are the result of exchange reactions followed by the elimination of cyclic ethylene carbonate and by a decarboxylation reaction. These copolymers have a higher glass transition temperature and thermal resistance than PET, and a better solvent resistance than PC; their dynamic mechanical spectra are similar to that of PC in the −150 to +50°C temperature range.
Chain dimensions, entanglement molecular weights and molecular weight distributions of poly(aryl ethers). A combined rheological and MNDO analysis
Authors: Herrmann‐Schönherr Otto , Schneller Arnold , Seifert Andreas M. , Soliman Maria , Wendorff Joachim H. 
Published: April 2003

AbstractThe viscoelastic melt properties of a series of different poly(aryl ethers) were analyzed to obtain information on the corresponding chain statistics, i. e. entanglement molecular weights and characteristic ratios C∞. The consistent result is that all chain molecules behave as freely rotating chains with values of C∞ of the order of two to three. MNDO‐calculations were used to obtain a detailed insight into the origin of such a behaviour. The relationship between chemical structure and the corresponding rotational potentials was analyzed. Finally, using a combination of rheological and MNDO (Modified Neglect of Diatomic Overlap) studies, information was derived on the molecular weight distribution of the poly(aryl ethers).
Studies on silicone‐grafted copolyimides, 4. Synthesis and properties of branching copolyimides with fluoroalkyl and poly(dimethylsiloxane) side chains
Authors: Akiyama Ei‐ichi , Takamura Yuriko , Nagase Yu 
Published: April 2003

AbstractSoluble copolyimides containing fluorinated alkoxy (FA) groups and poly(dimethylsiloxane) (PDMS) side chains were prepared by means of polycondensation of 2,2,2‐trifluoro‐1‐(trifluoromethyl)ethylidene diphthalic anhydride (6FDA) with 4,4′‐oxydianiline (ODA), 3‐(3,5‐diamino‐benzyloxy)propyl‐terminated poly(dimethylsiloxane) (DAB‐PDMS) and 3,5‐diaminobenzyl fluoroalkyl ether (DAB‐FA) followed by imidation. Tough menbranes were prepared from the copolymides by a solvent casting method. The introduction of FA groups and PDMS side chains remarkably increases the hydrophobicity of the copolyimide film, the contact angle of water being raised to 124°C. Introduction of FA groups in the copolyimide resulted also in an increase of the permselectivity of oxygen toward nitrogen of the membrane. Furthermore, the selective permeation of organic liquids was observed in the pervaporation of aqueous organic solutions through the membrane.
Partial swelling of latex particles with monomers
Authors: Maxwell Ian A. , Kurja Jenci , Van Doremaele Gerard H. J. , German Anton L. , Morrison Bradley R. 
Published: April 2003

AbstractTwo methods are described for experimentally determining the concentrations of monomer in both the aqueous phase and the latex particle phase during partial swelling of latex particles, and therefore also during intervall III of an emulsion polymerization. The ratio of the monomer concentrations in the aqueous phase, both below and at saturation, can be related to the volume fraction of polymer in the latex particles via the Vanzo equation. Comparison of theory and experiments for the methyl acrylate and poly(methyl acrylate‐co‐styrene) system shows that the monomer partitioning is insensitive to temperature, latex particle radius, polymer composition, polymer molecular weight and polymer cross‐linking. Thermodynamic treatment of these and previously published partitioning results shows, at higher volume fractions of polymer, that the conformational entropy of mixing of monomer and polymer is the significant term determining the degree of partial latex particle swelling by monomer. Theoretical predictions of experimental results are quite insensitive to values of the Flory‐Huggins interaction parameter and to the latex particle‐water interfacial tension. A simple model is developed for the estimation of monomer partitioning which requires only the saturation monomer concentrations in the particle and aqueous phases.
Thermodynamics of swelling of latex particles with two monomers
Authors: Maxwell Ian A. , Kurja Jenci , Van Doremaele Gerard H. J. , German Anton L. 
Published: April 2003

AbstractThe partitioning of two monomers between the latex particle, monomer droplet and aqueous phases of an emulsion polymer latex are measured at saturation swelling of the latex particle phase (corresponding to intervals I and II of an emulsion polymerization). The monomer and polymer types are varied systematically and the experiments are performed at two temperatures. The results of these experiments correspond well to a simplified thermodynamic theory of the saturation swelling of an emulsion polymer with two monomers, in which it is realized that the fraction of one monomer is equivalent in the latex particle and monomer droplet phases. Further, it is shown that Henry's law holds for monomers, both in the absence and in the presence of swollen latex particles. A simple empirical relationship is developed whereby the concentration of two monomers at any ratio can be calculated from the individual saturation concentration of the two monomers in the latex of interest.
Synthesis of polyradicals by the oxidative coupling copolymerization of 2‐(3,5‐diethynylphenyl)‐4,4,5,5‐tetramethyl‐3‐oxo‐2‐imidazolin‐1‐yloxyl and 1,3,5‐triethynylbenzene catalyzed by CuCl/O2, and their magnetic properties
Authors: Miura Yozo , Inui Kunihiko 
Published: April 2003

AbstractThe present paper describes the synthesis of polyradicals by the oxidative coupling polymerization of 2‐(3,5‐diethynylphenyl)‐4,4,5,5‐tetramethyl‐3‐oxo‐2‐imidazolin‐1‐yloxyl (1) and 1,3,5‐triethynylbenzene (2) catalyzed by CuCl/O2, and their magnetic properties. The polyradicals obtained are dark blue and insoluble in all solvents examined. The ESR measurements of the polyradicals give a broad single‐line spectrum indicating that spin‐exchange narrowing takes place. The spin concentrations determined by the ESR spectroscopic method are 1,17 · 1021 to 1,28 · 1021 spins/g. The vibrating sample magnetometer (VSM) measurements of the polyradicals afford a linear magnetic moment vs. magnetic field dependence with a positive slope, suggesting that the copolymer has predominant paramagnetic properties within the limits of experimental error.
Side reactions during the initiation step in oligomerization of methacrylic esters by electron transfer reaction
Authors: Catala Jean‐Marie , Clauss Margot 
Published: April 2003

AbstractAnionic oligomerization of methacrylic esters (methyl (MMA), ethyl (EMA), butyl (n‐BMA), tert‐butyl (t‐BMA) methacrylates) was conducted in a one‐step process by mixing, in tetrahydrofuran, the monomer, an alkali metal (sodium) and a deactivating agent (sulfur or tert‐butyl alcohol). The formation of alcohol due to a nucleophilic attack of the ester group by the methacrylic carbanion was quantified and related to the monomer structure, temperature and nature of the living ends. It was shown that this side reaction is not limited to the propagation step but can occur during the initiation step. From mass spectra and nuclear magnetic resonance (NMR) spectroscopy of the protonated oligomers (tert‐butyl alcohol as deactivating agent), it was concluded that this side reaction led to five‐membered cyclic β‐keto esters during the initiation step of MMA, EMA and n‐BMA monomers only. This implies an intramolecular reaction between one carbanion of the dianionic dimer and the penultimate ester group. It was found that this reaction involves primarily dianionic tail‐to‐tail dimer, even though head‐to‐tail dimer was also formed.
Asymmetrically branched alkyl spacers in liquid‐crystalline poly(alkylene 4,4′‐terephthaloyldioxydibenzoate)s
Authors: del Pino Javier , Rocha Carlos Marco , Gómez Marián A. , Fatou Jose G. 
Published: April 2003

AbstractPoly[oxy‐(1,4‐dimethyltetramethylene)oxycarbonyl‐1,4‐phenyleneoxyterephthaloyloxy‐1,4‐phenylenecarbonyl] (1) was synthesized for the first time, and its thermal behaviour was studied by differential scanning calorimetry, thermooptical microscopy, and X‐ray diffraction. The crystal to liquid‐crystal and the mesophase to isotropic transition temperatures are lower by ca. 100°C than the values reported for the unsubstituted polymer. Moreover, the formation of a three‐dimensional order is hindered in the case of the polymer with lateral substituents and can only be achieved by long annealing times.
Copolymérisation du dicyanure de propène‐1 ylidène‐1 avec l'acétate de vinyle et des styrènes substitutés. Calcul des taux de réactivité et étude de l'effet pénultième
Authors: Monthéard Jean‐Pierre , Boinon Bernard , Raihane Mustapha , Pham Quang‐Tho 
Published: April 2003

Abstract1‐Propen‐1‐ylidene dicyanide was copolymerized in bulk with vinyl acetate and five substituted styrenes. The reactivity ratios of these copolymerizations were calculated by the Fineman‐Ross or the Kelen‐T¨︁udős method. The penultimate model describes satisfactorily the deviation from the terminal model in the copolymerization reactions between 1‐propene‐1‐ylidene dicyanide and the substituted styrenes.
Cationic polymerization of α‐pinene with the binary catalyst AlCl3/SbCl3
Authors: Higashimura Toshinobu , Lu Jiang , Kamigaito Masami , Sawamoto Mitsuo , Deng Yun‐Xiang 
Published: April 2003

AbstractOligomers of α‐pinene (1) with relatively high molecular weight (number‐average molecular weight Mn = 1140, weight‐average molecular weight Mw = 2590) were obtained with the binary catalyst AlCl3/SbCl3 in toluene at − 15°C ([AlCl3]0 = 42,5 mmol · L−1, mole ratio SbCl3/AlCl3 = 0,50). The yield was higher than 90%, and the dimer content was as low as 5 wt.‐%. In contrast, AlCl3 alone gave predominantly dimers and lower oligomers in poor yield, whereas SbCl3 had no catalytic activity for 1. 1H NMR analysis reveled that the structure of the higher‐molecular‐weight fraction (Mn = 2920, Mw = 3690) of the oligomers obtained with AlCl3/SbCl3 is 6, which consists of a cyclohexene ring with an endo‐olefin group, most likely derived from the cationic monomer isomerization of α‐pinene via the ring‐opening of the cyclobutane unit. Effects of the reaction conditions on the polymerization rate and molecular weight were also investigated.
Investigations of the crystallization of polyethylene by means of simultaneous small‐angle and wide‐angle X‐ray scattering
Authors: Bark Michael , Zachmann Hans Gerhard , Alamo Rufina , Mandelkern Leo 
Published: April 2003

AbstractThe isothermal crystallization of linear polyethylene fractions was studied by means of simultaneous measurements of wide‐angle X‐ray scattering (WAXS) and small‐angle X‐ray scattering (SAXS) employing synchrotron radiation. From WAXS the overall degree of crystallinity xc was determined. From SAXS, the scattering power Q was evaluated and compared with several different models for the crystallizing system. When the scattering arises solely from the supermolecular structures, such as spherulites, Q is proportional to xs·xcL·(1 − xcL), where xs is the fraction of material transformed into such structures and xcL is the degree of crystallinity within these structures. By comparing xc with Q it was possible to separate the primary and secondary crystallization and to show that secondary crystallization takes place within the lamellar stacks where the crystals become thicker and the amorphous layers become thinner. The process of recrystallization during annealing of crystalline samples was studied in the same way. Other models were treated in a similar manner.
Reexamination of the Michelson reaction leading to poly(glycerol phosphate). Its functionalization
Authors: Merle Liliane , Boukobza Alain , Spach Gérard 
Published: April 2003

AbstractFractionation of the products obtained by the Michelson polyaddition of glycerol 2‐phosphate with diphenyl phosphate chloride gives a definite poly(glycerol phosphate) (PGP) of a molecular weight of about 1000. The exact structure was determined by 31P NMR spectra from which the existence of a random copolymer containig 1,3‐ and 1,2‐PGP sequences can be inferred. The free hydroxyl groups of PGP were grafted with a 1‐thymineacetic acid derivative to an extent of about 40% as determined by 1H NMR.
FTIR spectra and chain conformations in the crystalline forms and clathrates of syndiotactic poly(p‐methylstyrene)
Authors: Guerra Gaetano , Poggetto Francesco Dal , Iuliano Mauro , Manfredi Carla 
Published: April 2003

AbstractInfrared spectra of syndiotactic poly(p‐methylstyrene) (s‐PPMS) samples, exhibiting various crystalline forms and clathrate structures, are reported in this contribution. Bands due to the syndiotactic stereostructure, bands typical of the two different chain conformations observed in the crystalline structures and bands sensitive to intermolecular interactions typical of the different modes of packing of chains are pointed out. The observed similarities with the case of syndiotactic polystyrene are alos indicated. A complete assignment, via FTIR analysis, of the chain conformations, is presented for all the known crystalline forms and clathrates of s‐PPMS.
Vapour‐liquid equilibria and segment‐molar excess gibbs free energies of concentrated poly(butyl methacrylate) solutions
Authors: Wohlfarth Christian , Zech Birgit 
Published: April 2003

AbstractSolvent activities were measured by an isopiestic sorption technique for solutions of poly(butyl methacrylate) and poly(tert‐butyl methacrylate), respectively, in various solvents between 323 K and 373 K (or 403 K). The experimental data were reduced to segment‐molar excess Gibbs free energies and to χ‐functions. There is a clear difference in the thermodynamic behaviour of both polymers in their corresponding solutions due to the steric effect of the tert‐butyl group. The chain‐of‐rotators equation‐of‐state model was used to calculate the thermodynamic quantities applying a group‐contribution approach. In general, good agreement can be observed between experimental and calculated results.
New polymer syntheses, 57. Thermotropic polyesters based on 2‐(4‐carboxyphenyl)benzoxazole‐5‐carboxylic acid
Authors: Kricheldorf Hans R. , Thomsen Sven A. 
Published: April 2003

Abstract2‐(4‐Carboxyphenyl)benzoxazole‐5‐carboxylic acid was prepared from silylated 3‐amino‐4‐hydroxybenzoic acid and methyl 4‐chloroformyl‐1‐benzoate in an “one‐pot procedure”. In addition to the free dicarboxylic acid the acid chloride was prepared and used as monomer. Polycondensations were conducted with the acetates or trimethylsilyl derivatives of phenylhydroquinone, phenylthiohydroquinone, 2,5‐bis(phenylthio)hydroquinone and 4,4′‐oxydiphenol. Furthermore, a copolyester containing 4‐hydroxybenzoic acid was prepared. The resulting polyesters were characterized by elemental analyses, inherent viscosities, differential scanning calorimetry (DSC) and wide‐angle X‐ray scattering (WAXS) measurements and optical microscopy. The polyesters derived from monosubstituted hydroquinones and the copolyester were found to form nematic melts, whereas all other polyesters only form isotropic melts. The structure/property relationships are discussed by comparison with those of the corresponding poly(ester‐imide)s.
Compositional microstructure of polymer prepared by partial hydrolysis of isotactic poly(methyl methacrylate)
Authors: Doskočilová Danica , Mikeš František , Pecka Jan , Kříž Jaroslav 
Published: April 2003

AbstractThe compositional microstructure of partial hydrolyzates of isotactic poly(methyl methacrylate) was analyzed by means of 1H and 3C NMR spectroscopy. The placement of hydrolyzed units was found to be essentially random, and no neighbouring group effect was detected. Thus, at low degrees of hydrolysis, most carboxyl groups are expected to be isolated.
Anionic polymerization of 6‐hexanelactam, 62. Fast catalytic systems in the anionic polymerization of 6‐hexanelactam
Authors: Stehlíček Jaroslav , Puffr Rudolf 
Published: April 2003

AbstractWith magnesium 6‐hexanelactamate bromide (LMgBr) as a catalyst and the N‐acyllactam as initiator an exceptionally high rate of polymerization of 6‐hexanelactam is observed. Side reactions decreasing the concentrations of growth centres and activated monomer (lactam anion) are not affected to such an extent as to explain this acceleration. In the presence of poly(propylene oxide), the side reactions are largely suppressed with LMgBr. The results corroborate the assumption that the reactivity of the N‐acyllactam growth centre is increased by coordination of a magnesium bromide ligand.
Photoreactive polyanhydrides with cinnamic acid units in the main chain
Authors: Pinther Peter , Hartmann Manfred , Wermann Kurt , Günther Wolfgang , Ritter Helmut 
Published: April 2003

Abstract4,4′‐(Octamethylenedioxy)di‐trans‐cinnamic and 4,4′‐(sebacoyldioxy)di‐trans‐cinnamic acid were synthesized and converted into mixed anhydrides by the reaction with acetic anhydride. Subsequent melt polycondensation produced soluble polyanhydrides having weight‐average molecular weights (Mw) of ca. 11000. The DSC measurements of the polymers exhibited endotherms indicating normal melting processes. On UV‐irradiation of solid films of the polyanhydrides, photocrosslinking of the cinnamoyl moieties in the main chain took place.
Solution‐grown crystals of poly(dimethylphosphazene)
Authors: Kojima Mario , Magill Joseph H. 
Published: April 2003

AbstractPoly(dimethylphosphazene) crystals have been grown by two techniques, namely: (a) dilute‐solution crystallization and (b) from the supercooled melt. An orthorhombic crystal form with a = 1,390 nm, b = 0,598 nm and c = 0,473 nm was deduced from electron and X‐ray diffraction. There are four monomers per unit cell of density 1,267 g/cm3. Streaks connecting the (hk0) reflections in electron diffraction are suggestive of lattice defects along the [b] axis. Whenever crystals are annealed just below Tm where sufficient mobility exists, the “streaks” are absent when the specimen is cooled to room temperature. Differential scanning calorimetry (heating) exhibits two endothermic peaks at 142°C and 146°C, corresponding to T(1) and Tm transitions, respectively. A mesophase exists between these closely spaced peaks. A wider mesophase range is encountered in poly(oxyphosphazenes).
Novel silicones for transdermal therapeutic system, 4. Modified route to prepare oligodimethylsiloxane containing a cationic end‐group, and its property as transdermal penetration enhancer
Authors: Aoyagi Takao , Akimoto Tomoko , Nagase Yu 
Published: April 2003

AbstractA modified route to prepare oligodimethylsiloxane (ODMS) containing a quaternary salt at the one chain end was investigated, for the development of a silicone‐based transdermal penetration enhancer. p‐(Chloromethyl)phenethyl‐terminated ODMS (CMP‐ODMS) was prepared by hydrosilylation of p‐chloromethylstyrene with hydrosilyl‐terminated ODMS, as an intermediate. Then, CMP‐ODMS was reacted with pyridine or ethyldimethylamine to afford a quaternary ODMS salt quantitatively. The enhancing activity of drug penetration was evaluated by measuring the amount of indomethacin permeating through the skin, using a two‐chamber diffusion cell having an isolated rabbit abdominal skin mounted between half cells. The obtained polymers effectively enhanced the drug penetration through the skin, whereupon the permeation coefficients were 2 to 15 times that measured without enhancer. Also, the enhancing activities were influenced by the chemical structure of polar and non‐polar end‐groups.
Synthesis of an angularly annulated Diels‐Alder ladder polymer
Authors: Packe Rainer , Enkelmann Volker , Schlüter Arnulf‐Dieter 
Published: April 2003

AbstractThe synthesis of a soluble, angularly annulated Diels‐Alder ladder polymer is described. Its molecular structure is proven by an analysis of the high‐resolution 13C and 1H NMR spectra. Model studies including the structures in the crystal of 9a, 9c, and anti‐4 provide some insight into stereochemical features.