bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of reaction of living polymers with linking agents resulting in ring closure
Authors: Szwarc Michael 
Published: April 2003

AbstractReaction of a living polymer endowed with two reactive end‐groups with a bifunctional linking agent results in ring closure as well as in chain extension. These competing reactions are described by a kinetic scheme involving dimensionless rate constants which gives the fractions of the initial reagents converted into products as functions of a dimensionless “time”. The treatment leads to 9 coupled differential equations solved numerically. The results are discussed and the approximation involved in this treatment was shown to be reliable.
Melt elongation of a commercial poly(methyl methacrylate) product and a commercial polystyrene
Authors: Linster Jean‐Jacques , Meissner Joachim 
Published: April 2003

AbstractMelts of a commercial poly(methyl methacrylate) product and a commercial polystyrene were elongated homogeneously up to Hencky strains of ε > 4 by means of the rotary clamp technique. For this purpose, certain modifications to the rheometer were necessary which are described in detail. Both polymer melts show strain hardening, i. e. the elongational viscosities are higher than the threefold of the linear viscoelastic limiting viscosity measured in shear. The degree of hardening is very different: For the poly(methyl methacrylate) product the hardening is only small, and so are the recoverable portions of the total strains, whereas for the polystyrene the opposite is true. This different behaviour is connected with a difference of the linear viscoelastic relaxation spectra at long relaxation times. The test results can be described efficiently by the Lodge‐Wagner rubberlike liquid constitutive equation.
Polymers from multifunctional isocyanates, 3. Synthesis and polyaddition reactions of (liquid‐crystalline) fully aromatic diisocyanatoesters
Authors: Mormann Werner , Brahm Martin 
Published: April 2003

AbstractThe regioselective reaction of aliphatic ω‐isocyanatoacyl chlorides with silyl‐protected hydroxy‐nucleophiles was extended to aromatic isocyanatoacyl chlorides. Starting with 3‐ or 4‐isocyanatobenzoyl chloride and 3‐ or 4‐trimethylsiloxyphenyl isocyanate, the four isomeric isocyanatobenzoic acid isocyanatophenyl esters were synthesized in high yields. From terephthaloyl chloride and two moles of a siloxyphenyl isocyanate or from 1,4‐bis(trimethylsiloxybenzene) and two moles of an isocyanatobenzoyl chloride, diesterdiisocyanates were obtained containing 3 benzene rings. The para‐substituted diisocyanates show liquid‐crystalline behaviour. Polyaddition reaction with various diols led to poly(esterurethane)s with a regular sequence of urethane and ester groups. The poly(urethane)s from the para‐substituted diisocyanates have very high melting points (225–350°C). Liquid crystallinity could not be proven unambiguously due to the instability of the urethane linkage at these temperatures.
Préparation de microlatex acryliques par polymérisation photochimique de solutions micellaires et de microémulsions
Authors: Schauber Claude , Riess Gérard 
Published: April 2003

AbstractMicrolatices of acrylic monomers, in the particle size range of 10–30 nm, were prepared by photopolymerization of micellar systems (monomer‐surfactant) and of microemulsions based on monomer‐surfactant‐cosurfactant. Formation of monomer containing microemulsions is shown for various surfactants in combination with alcohols as cosurfactants and the corresponding phase diagrams are given. Photopolymerization, in the presence of oil‐soluble initiators, was investigated for such systems based on cyclohexyl methacrylate (CHMA) and on tetramethylene dimethacrylate (BDMA). Crosslinked and non‐crosslinked colloidal polymer particles could be obtained, with a 5–10% solid content of polymer. The variation of particle size, and the molecular weight for non‐crosslinked systems, was studies as a function of initiator concentration, and monomer/surfactant ratio. The smallest particles (10–15 nm) are obtained for the system BDMA/lauryl sulfate (LS).
Partitioned polymerization, 2. Simultaneous transfer of monomer and of initiator
Authors: Bartoň Jaroslav , Juraničová Viera 
Published: April 2003

AbstractThe kinetics of the 2,2′‐azoisobutyronitrile (AIBN)‐initiated emulsion polymerization of methyl methacrylate and butyl methacrylate was studied in the presence or in the absence of 4‐stearoyloxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl radical (STMPO) situated in the oil (monomer) phase. The polymerization was initiated and oligomeric radicals were formed in the aqueous phase to which methyl methacrylate (butyl methacrylate) and AIBN were transferred. Polymerization does not take place in the oil phase because of the inhibitor present. Relatively short inhibition periods of polymerization observed in systems containing STMPO confirm that a small part of STMPO was transferred from the oil to the water phase. The length of the inhibition period in the emulsion polymerization is determined by a competition between the addition reaction of primary radicals with monomer and the termination reaction of primary radicals with STMPO as well as by the rate of STMPO scavenging by oligomer‐monomer and polymer‐monomer particles. The polymerization system studied belongs to a group of partitioned polymerization systems characterized by simultaneous transfer of monomer and initiator from the oil to the water phase, where the initiation of polymerization takes place.
Synthesis and properties of poly(L‐glutamic acid)s containing covalently bound 4‐hydroxyphenylporphyrin moieties
Authors: Hanabusa Kenji , Sogabe Seiji , Koyama Toshiki , Shirai Hirofusa , Hayakawa Tadao , Hojo Nobumasa , Kurose Akio 
Published: April 2003

AbstractPoly(L‐glutamic acid)s with various contents of 4‐[10,15,20‐tris(4‐hydroxyphenyl)‐5‐porphyrinyl]phenoxy groups (polymers 3a–e) prepared by reaction of poly(L‐glutamic acid) (1) and 5,10,15,20‐tetrakis(4‐hydroxyphenyl)porphyrin (2) in the presence of dicyclohexylcarbodiimide. The structures of 3a–e in ethanol were studied by CD spectroscopy and it was found that the introduction of large amounts of porphyrin moieties into 3 tends to prevent the α‐helix formation. The IR dichroic ratios of films of 3a–e, obtained by rubbing the concentrated ethanol solution on an NaCl plate with a spatula into a constant direction, gave informations about the orientation of the α‐helix rod. X‐ray diffraction photographs suggest that the crystalline packing of the α‐helix is more disordered with increasing content of porphyrin moieties in 3. Polarizing microscopy indicates that 3a–d form lyotropic liquid crystals in concentrated DMF solution.
Characterization of ethylene‐propene copolymers prepared with heterogeneous titanium‐based catalysts
Authors: Kakugo Masahiro , Naito Yukio , Mizunuma Kooji , Miyatake Tatsuya 
Published: April 2003

AbstractEthylene‐propene (EP) copolymers prepared with various heterogeneous titanium‐based Ziegler‐Natta catalysts, i. e., δ‐TiCl3, β‐TiCl3, and MgCl2‐supported titanium catalysts were fractionated by successive solvent extraction. Wide composition distributions were observed for all samples. Composition distributions of some samples were investigated precisely by temperature‐programmed elution column fractionation. The fractionation data showed that these copolymers are a mixture of polyethylene and of copolymers with different structures, i. e., random and block copolymers. In every sample random copolymers were found most abundantly, the propylene sequences being present only as mmmm pentads. These data suggest that random copolymer is formed on an isospecific site.
Infrared spectroscopic investigation of solution‐crystallized trans‐1,4‐polybutadiene copolymers
Authors: Wang Pei‐guo , Woodward Arthur E. 
Published: April 2003

AbstractFourier transform infrared spectra were obtained for solution‐crystallized samples of two polybutadiene copolymers, one containing 10% cis‐, 1,5% 1,2‐ and 88,5% trans‐ and the other 1% cis‐ and 99% trans‐polybutadiene. Measurements were made at room temperature, at temperatures above the crystal transition temperature, but below the melting temperature, and at temperatures above the melting temperature. Spectra for 100% crystalline samples were obtained by subtraction of the spectrum for the melt from that for the semicrystalline sample. Infrared spectra were also obtained for suspension epoxidized samples; these showed the presence of an unreacted crystal core and completely reacted lamellar surfaces.
Effect of dilution during network formation on the sol fraction and elasticity of polyurethane networks
Authors: Ilavský Michal , Bouchal Karel , Dušek Karel 
Published: April 2003

AbstractThe effect of dilution at network formation (polymer volume fraction v(0) = 1 − 0,4) on the fraction and equilibrium photoelastic behaviour of polyurethane networks was investigated. The networks were prepared from poly(oxypropylene)triol and 4,4′‐methylenedi(phenyl isocyanate) with various mole ratios of reactive groups 1 ≤ rH = [OH]/[NCO] ≤ 1,5. From a comparison between the experiments and the theory of branching processes we find that: (a) with both increasing ratio rH and increasing dilution the fraction of bonds lost in elastically inactive cycles increases from 0,02 to 0,06; (b) the experimental reduced equilibrium moduli Gr of the predominant majority of samples are higher than those theoretically predicted by the Flory junction‐fluctuation theory for the front factor A = 1. Also the decrease of Gr with dilution (expressed as volume fraction of diluent during network formation v(0)) is very steep, thus supporting the contribution of permanent interchain constraints to the overall Gr value.
Chitosan gels, 3. The formation of gels by reaction of chitosan with glutaraldehyde
Authors: Roberts George A. F. , Taylor Kathryn E. 
Published: April 2003

AbstractThe effects of several variables on the gelation behaviour of the chitosan/glutaraldehyde system have been studied. The rate of gelation is increased by increase in concentration of either chitosan or glutaraldehyde, or by an increase in temperature, and reduced by an increase in the concentration of acetic acid. Addition of a number of neutral electrolytes also causes an increase in the rate of gelation, the increase being larger the greater the activity coefficient of the electrolyte. UV/visible and NMR spectra of glutaraldehyde, acetaldehyde and crotonaldehyde, together with those of their 2,4‐dinitrophenylhydrazine derivatives, indicate that only a very small proportion (<0,15%) of the aldehyde groups have undergone an aldol condensation reaction leading to α,β‐unsaturated aldehyde groups. This, together with other evidence, suggests that the cross‐linking mechanism involves formation of Schiff's base structures rather than Michael‐type adducts as previously postulated.
Hydrogen peroxide generation from reduced polymer nitroxyls and oxygen
Authors: Seidemann Rolf , Dulog Lothar 
Published: April 2003

AbstractFor producing hydrogen peroxide the suitability of stable polymeric nitroxyls as reaction carriers was investigated. These can be hydrogenated to the corresponding hydroxylamines, which are oxidized by oxygen exclusively to hydrogen peroxide and nitroxyls. The yield of hydrogen peroxide was determined in different solvents, at different reaction times and temperatures. Possible side reactions for the decomposition of hydrogen peroxide were investigated. The activation energy for the oxidation of polymeric hydroxylamine with oxygen in DMSO was calculated to be 67 kJ/mol.
Thermodynamics of ternary mixtures of random copolymers
Authors: Dafniotis Petros , Karayianni Eleni , Panayiotou Constantinos 
Published: April 2003

AbstractA most general formalism based on the Lattice‐Fluid theory of polymer solutions is presented for multicomponent mixtures of random copolymers which may consist of any number of different types of monomers. Particular emphasis is given to the phase stability in these mixtures. Equations for the spinodals and the critical points are presented. The formalism is subsequently applied to a number of interesting cases of ternary (co)polymer mixtures such as: mixtures of three random copolymers with the same monomers A and B but in different proportions (A B + A B + A B) mixtures of homopolymers Am and Bn with the random copolymer Ai Bj, and mixtures of the random copolymers (A B + A B + A C). The effect of temperature on the phase behavior of these systems is discussed. The agreement of theoretical predictions with available experimental information is satisfactory. Because of its simplicity, the model may be used as a tool for studying multicomponent mixtures exhibiting lower or upper critical solution temperature behavior.
Characterization of isotactic polypropylene obtained with ethylenebis(4,5,6,7‐tetrahydro‐1‐indenyl)zirconium dichloride as catalyst
Authors: Tsutsui Toshiyuki , Mizuno Akira , Kashiwa Norio 
Published: April 2003

AbstractPolypropylene (PP) prepared with ethylenebis(4,5,6,7‐tetrahydro‐1‐indenyl)zirconium dichloride in conjunction with methylaluminoxane yields 58 wt.‐% of material insoluble in boiling heptane (C7). The C7‐soluble and the C7‐insoluble fraction exhibit high isotacticity, viz. 97,2% and 98,2%, respectively, relatively narrow molecular weight distribution (weight‐ to number‐average molecular weight M̄w/M̄n = 2,19 for the whole polymer), a small amount of regioirregular units arranged with meso‐placements and relatively low melting points, i.e., 151,3°C for the C7‐soluble and 153,2°C for the C7‐insoluble fraction in spite of high isotacticity.
Emulsion polymerization of styrene using phospholipid as emulsifier. Immobilization of phospholipids on the latex surface
Authors: Yamaguchi Kazuo , Watanabe Shinji , Nakahama Seiichi 
Published: April 2003

AbstractEmulsion polymerization of styrene using polymerizable and non‐polymerizable phospholipids with double alkyl chains (1a, 1b), and their single‐chain analogues (2a, 2b) as emulsifier gave polymer latices with narrow size distribution. The resulting latices, which were subjected to acid and enzymatic hydrolysis, and reprecipitation with methanol, were characterized by phosphorus analysis and X‐ray photoelectron spectroscopy (XPS). The phospholipids remained mainly on the surface of the latices. The non‐polymerizable emulsifiers were physically adsorbed on the latices, but the polymerizable emulsifiers were chemically bound to the latices. Phospholipid 1b on the latex prepared with a lipophilic radical initiator was hydrolyzed by phospholipase C.
Oligomerization of oxetane and synthesis of polyterephthalates derived from 1,3‐propanediol and 3,3′‐oxydipropanol
Authors: González César Carlos , Bello Antonio , Pereña José Manuel 
Published: April 2003

AbstractThe oligomerization of oxetane (trimethylene oxide) initiated by sulfuric acid in methylene chloride in the presence of 1,3‐propanediol (trimethylene glycol) leads to the formation of α‐hydro‐ω‐hydroxyoligo(oxytrimethylene)s. The effect of adding different amounts of trimethylene glycol was studied, and the dimer, 3,3′‐oxydipropanol, could be isolated. Polymers from dimethyl terephthalate and 3,3′‐oxydipropanol and copolymers from 1,3‐propanediol, 3,3′‐oxydipropanol and dimethyl terephthalate were synthesized. The influence of the chemical structure on their thermal transitions was analyzed.
A chemical modification of a grafted synthetic polymer under cellulose hydrolysis conditions
Authors: Casinos Ismael , Fernández María Jesús , Guzmán Gonzalo Martín 
Published: April 2003

AbstractThe current cellulose hydrolysis methods were applied to cellulose‐graft‐poly(vinyl acetate‐co‐methyl acrylate) giving rise to a residual solid that showed IR absorptions at 3 600 – 3 000 and 1775 cm−1 and partial insolubility in the solvents of poly(vinyl acetate‐co‐methyl acrylate). Some model experiments showed that hydrolysis of the acetoxy and methoxycarbonyl groups takes place and subsequent γ‐lactonization and crosslinking in the grafted synthetic polymer, parallel to the cellulose hydrolysis. It became evident that the competition between lactonization and crosslinking and their extent are controlled by the sequence‐length distributions of the monomeric units in the copolymer and by the conversion in the hydrolysis reaction, respectively. Both esterification reactions were eliminated when the experiment was performed at sufficiently low temperature.
Polymerization of bicyclic acetals, 18. Propagation processes in the cationic ring‐opening polymerization of 6,8‐dioxabicyclo[3.2.1]octane derivatives having a 3(e)‐benzyloxy group as a common substituent
Authors: Okada Masahiko , Hirasawa Takahito , Sumitomo Hiroshi 
Published: April 2003

AbstractPolymerizations of two bicyclic acetals, rac‐2(a), 3(e)‐bis(benzyloxy)‐6,8‐dioxabicyclo‐[3.2.1]octane (1d) and the D‐enantiomer of 2(a),3(e),4(a)‐tris(benzyloxy)‐6,8‐dioxabicyclo[3.2.1]octane (1,6‐anhydro‐2,3,4‐tri‐O‐benzyl‐β‐D‐allopyranose) (1e) were investigated in dichloromethane as solvent at different temperatures ranging from −90 to −30°C. The polymerization of 1d gave polyacetals containing both the trans‐ and cis‐2,6‐linked tetrahydropyran units (2d and 3d) over the entire temperature range. The proportion of 3d increased up to 73% with decreasing initial monomer concentration at higher polymerization temperature. On the other hand, the polymerization of 1e gave rise to polymers exclusively or predominantly composed of trans units (2e), the content of cis units (3e) being at most 25%. On the basis of these results, along with the previous experimental results on the polymerizations of three other relevant bicyclic acetals (1a – c), the marked substituent effect as well as the influence of polymerization temperature and initial monomer concentration on the stereochemical course of the polymerization are discussed in terms of a propagation mechanism involving an oxonium exchange reaction at the penultimate unit of a growing chain.
Transient effects in diffusion‐controlled polymer cyclization
Authors: Xu Huelin , Martinho José M. G. , Winnik Mitchell A. , Beinert Gérard 
Published: April 2003

AbstractFluorescence decay measurements were carried out to study the kinetics of intramolecular exciplex formation in two low‐molecular‐weight samples of polystyrene (1) with narrow molecular weight distribution capped on one end with a pyrene moiety and on the other with an N,N‐di‐methylaminophenyl group. Monomer and excimer decay profiles, IM(t) and IE(t), resp., were inconsistent with the predictions of the simple two‐state (Birks) model, but could be well‐fitted by assuming that the diffusion‐controlled rate coefficient for exciplex formation, k1(t), is time dependent. Using a Smoluchowski formulation for this rate coefficient k1(t) = a(1 + bt−1/2), we could use the a and b parameters to calculate values for the chain‐end diffusion coefficient characterizing the reaction for samples of the polymers in cyclopentane and cyclohexane solutions.
Preparation and crystalline structure of random copolymers of glycine and β‐alanine
Authors: Puiggalí Jordi , Muñoz‐Guerra Sebastián 
Published: April 2003

AbstractCopolymers of glycine and β‐alanine within a range of amount‐of‐substance compositions from 3:1 to 1:9 were prepared by polycondensation of mixtures of the respective pentachlorophenyl ester hydrobromides. Number‐average molecular weights between 2 500 and 9 000 were obtained, the lower values corresponding to those copolymers with a higher content in glycine. Sequence distributions were evaluated by means of 50,3 MHz 13C NMR spectroscopy and the crystalline structure was examined by wide‐angle X‐ray diffraction. Random copolymers having similar contents in glycine and β‐alanine were found to crystallize in a bidimensional hexagonal lattice (a = 4,79 Å) with chains packed in a similar manner as they do in the crystalline structure of polyglycine II. On the contrary, a heterogeneous product consisting of homopolymer and random copolymer fractions results from mixtures which are enriched in one of the two amino acids. The random copolymer poly(glycine‐ran‐β‐alanine) adopts a packing scheme similar to that found for the helical form of the alternating copolymer nylon 2/3. Chains are hexagonally arranged and interlinked by a three‐dimensional network of hydrogen bonds as described for the well known model of polyglycine II, although in the present case no order along the chain axis should be expected.
Low temperature modification of polymers by triazolinediones. Electrophilic substitution of poly(oxy‐2,6‐dimethyl‐1,4‐phenylene)
Authors: Stadler Reimund , de Araujo Macro A. , Kuhrau Martin , Rösch Joachim 
Published: April 2003

AbstractPoly(oxy‐2,6‐dimethyl‐1,4‐phenylene) (PPE, 8) is reacted with substituted 1,2,4‐triazoline‐3,5‐diones 1 to give the partially substituted poly[oxy‐2,6‐dimethyl‐3‐(1,2,4‐triazoline‐3,5‐dione‐1‐yl)‐1,4‐phenylene]9. The reaction occurs via electrophilic substitution of the electron‐rich PPE with the highly electron deficient triazolinediones 1. For low degrees of substitution, the reaction readily occurs at room temperature. The inherent viscosity decreases with increasing substitution. The results are compared to similarly substituted polybutadiene. The glass transition temperature of the substituted PPE's decreases with the content of triazoline groups, a result which is interpreted by a distortion of the packing in glassy PPE.
Determination of the number of active centers in Ziegler‐Natta polymerization of propene using sulfur‐containing terminating agents, 1. Application of carbon disulfide
Authors: Vozka Pavel , Mejzlík Jiří 
Published: April 2003

AbstractPolymerization of propene catalyzed with TiCl3 · 1/3(AlCl3)/AlEt2Cl or TiCl3 · 1/3(AlCl3)/AlEt3 systems in heptane at 323,2 K in the presence of CS2 was studied. It was demonstrated that the sharp decrease of rate, observed upon addition of CS2, is not due to a decrease of the organometal concentration, although some consumption of the organometal was evidenced by means of IR measurement. Tagging of the growing chains was monitored by determination of the sulfur content in the polymer. Side reactions of CS2, leading to a blank content of sulfur in polypropylene, were observed in the presence of catalytical components even after their deactivation. Thus, a thorough washing of the polymer was necessary. A substantial increase of heptane solubles observed upon addition of larger amounts of CS2 was found to be due to a much lower molecular weight of the polymer, while stereospecificity of the catalytical system was virtually preserved. It was concluded that CS2 behaves as a suitable terminating and tagging agent.
Synthesis of poly(α‐malic acid) and its hydrolysis behavior in vitro
Authors: Ouchi Tatsuro , Fujino Atsushi 
Published: April 2003

AbstractBiodegradable poly(α‐malic acid) (7) was synthesized by means of ring‐opening homopolymerization of malide dibenzyl ester (5), which is a cyclic dimer of β‐benzyl malate. In order to obtain a high‐molecular‐weight biodegradable lactic acid type polyester having pendent modifiable groups, ring‐opening copolymerization of malide dibenzyl ester with L‐dilactide was applied to give poly(α‐malic acid‐co‐lactic acid) (10). It was found from the results of hydrolysis of poly(α‐malic acid) that the main‐chain ester bonds were cleaved randomly and slowly in vitro.
Thermotropic para‐linked aromatic polyesters containing 1,1′‐binaphthyl‐4,4′‐ylene units
Authors: Hohlweg Martin , Schmidt Hans‐Werner 
Published: April 2003

AbstractSynthesis, thermal properties and solubility behaviour of para‐linked aromatic homopolyesters containing non‐coplanar 1,1′‐binaphthyl‐4,4′‐ylene units are described. By combining such binaphthylylene units with monosubstituted phenylene units, crystallization can be suppressed and thermotropic liquid‐crystalline polyesters with glass transition temperatures (Tg) up to 190°C are obtainable. The liquid‐crystalline order is maintained below Tg in an anisotropic glass. The polyesters show good solubility in common organic solvents, such as chloroform or tetrahydrofuran.