bluuebunny/crossref_metadata_2025_split huggingface dataset:
Composite model calculation of the mechanical properties of polypropylene
Authors: Biswas Prabir K. , Sengupta Shyamal , Basu Asok N. 
Published: April 2003

AbstractThe theoretical interpretation of the anisotropic elastic properties of polypropylene is given. It was found that none of the existing models provide a unified description of the mechanical and optical properties of ultradrawn polypropylene. The composite model proposed by the authors, which takes into account the change in orientation and crystallinity on drawing, was applied to investigate the elastic moduli data of polypropylene for a wide range of temperature (−40 to 110°C) and over the entire drawing ratio range. The relationship between θ and θ′, the angles made by the C‐axis of the composite unit with drawing direction, was found to be adequately described by the relation tan θ = ϕ(n) tan θ′. It was further observed that ϕ(n) in the above relation obtained from birefringence data predicts the correct orientational changes on drawing for the temperature range −40 to 24°C. This makes the evaluation of mechanical properties possible without introducing any arbitrary parameter. However, it is noticed that a particular analytical form of ϕ(n) with two parameters is quite successful in interpreting the mechanical properties data over the entire temperature range. The abrupt changes of the parameters at certain temperatures seem to be correlated with the β‐relaxation and glass transition temperature.
Reusable heterogeneous catalysts of α‐amino acid racemization, 2. Factors affecting the activity of heterogeneous catalysts based on strongly basic anion exchangers in OH− form and 4‐hydroxy‐3‐formylbenzenesulfonic acid (5‐sulfosalicylaldehyde)
Authors: Belokon' Yuri N. , Tararov Vitali I. , Savel'eva Tatiana F. , Belikov Vasili M. 
Published: April 2003

AbstractThe kinetics of (S)‐Ala racemization on heterogeneous catalysts based on eight strongly basic anion exchangers modified with 4‐hydroxy‐3‐formylbenzenesulfonic acid (5‐sulfosalicylaldehyde) (SSA) in the presence of Cu(II) ions at 25 °C was studied. The “internal capacity” value f = mp/(V0 — Vp) was introduced to characterize the polymers, (mp : number of quaternary ammonium groups of the polymer sample, V0 : total volume of the swollen polymer, Vp : volume of the inert polymeric matrix). The correlation of the observed first‐order rate constants of (S)‐Ala racemization with the f values of the anion exchangers was established. According to this correlation the selected anion exchangers could be divided into two types with respect to the chemical nature of the groups attached to the quaternary nitrogen atom. The chemical nature, physical structure and the degree of cross‐linking of the polymeric matrix do not affect the correlation. Anion exchangers of the first type have at least one ß‐hydroxyalkyl substituent at the

Anion exchangers of the second type have

(CH3)3 cationic groups. Catalysts prepared with the first type anion exchangers have greater activity as compared with catalysts based on the second type anion exchangers with the same f values. The increase in activity of heterogeneous catalysts can be partially attributed to the 10 to 68 fold increase in OH− concentration in the internal phase of the catalysts as compared to the model homogeneous system, which contains the same amounts of the components as the heterogeneous one. Moreover, an additional acceleration is observed in the heterogeneous racemization as compared to the homogeneous one, ca. 5 fold for the second type anion exchangers and ca. 14 fold for the first type anion exchangers.
New polymeric phosphonato‐, phosphinato‐ and carboxybetaïnes, 1. Syntheses and characterization by IR spectroscopy
Authors: Hamaide Thierry , Germanaud Laurent , Perchec Pierre Le 
Published: April 2003

AbstractNeutral phosphonato‐, phosphinato‐, and carboxybetaïne moieties linked to various polymer supports, poly(styrene‐co‐4‐vinylpyridine) and poly(styrene‐co‐4‐dimethylaminomethylstyrene), were synthesized by a two step sequence. These products were characterized by means of FTIR analysis. Complexing properties towards transition metal salts are outlined.
Poly(ethylene glycol)s containing enzymatically degradable bonds
Authors: Ulbrich Karel , Strohalm Jiří , Kopeček Jindřich 
Published: April 2003

AbstractThe possibility to use poly(ethylene glycol) (PEG) as a synthetic, water‐soluble polymeric carrier of biologically active compounds was investigated. The relationship between structure of oligopeptide (amino acid)‐PEG conjugates and their hydrolysis catalyzed by chymotrypsin was studied. Two types of derivatives were synthesized: Derivatives of PEG 2000, containing an oligopeptide sequence terminating in p‐nitroaniline (drug model) and higher molecular weight derivatives of PEG 2000 containing in the main chain enzymatically and hydrolytically degradable bonds. The rates of chymotrypsin catalyzed release of p‐nitroaniline at pH 8,0 and 25°C were determined over a range of substrate concentrations to derive values for kcat and KM. The influence of the length and detailed structure of the oligopeptide sequence on the rate of hydrolysis was demonstrated. Comparison with copolymers of N‐(2‐hydroxypropyl)methacrylamide and poly(maleic anhydride‐co‐vinylpyrrolidone) showed that the sterical hindrance of the formation of the enzyme‐substrate complex is much less pronounced in the PEG‐oligopeptide conjugates. The latter conclusion is also valid in the case of cleavage of PEG derivatives which contain enzymatically degradable bonds in the main chain. The incorporation of a single amino acid residue (phenylalanine) into the main PEG chain is sufficient to make the polymer susceptible to chymotrypsin catalyzed hydrolysis.
Thermal properties of poly(2‐carboxyethylmethylsiloxane)‐poly(dimethylsiloxane) complexes
Authors: Ohyanagi Manshi , Kanai Hiroyuki , Takashima Tetsuo , Ikeda Koji , Sekine Yoshiro 
Published: April 2003

AbstractThe thermal properties of complexes between poly(2‐carboxyethylmethylsiloxane) and poly‐(dimethylsiloxane) are investigated. The results of DSC measurements indicate that the first‐order transition of the complexes is affected by the amount of poly(dimethylsiloxane) in the complex. From dynamic viscoelasticity measurements, it is inferred that the complex exhibits entropy elasticity due to a network structure maintained by hydrogen bonds.
Diffusion of TiO2 probe particles through a poly(ethylene oxide) melt
Authors: Lin Thy‐Hou 
Published: April 2003

AbstractQuasi‐elastic light scattering (QELS) spectroscopy was for the first time used to measure the mutual diffusion coefficient Dm of titanium dioxide (TiO2) particles of 0,37 μm and 0,31 μm diameters in a poly(ethylene oxide) melt (weight‐average mol. wt. 7 500) between 85 °C and 160 °C. Dm exhibits a strong dependence on the temperature. The effective shear imposed by diffusing particles on the polymer melt was estimated through a comparison of the viscosity obtained by a cone‐and‐plate viscometer with the microviscosity calculated from the diffusion coefficients and hydrodynamic radii of the particles through the Stokes‐Einstein equation. The rate of shear found was ≥ 104 · s−1.
Kinetics of the thermal degradation of anhydrous bisphenol‐A polycarbonate/alkali metal arylcarboxylate systems in the melt
Authors: Bailly Christian , Daumerie Michel , Legras Roger , Mercier Jean P. 
Published: April 2003

AbstractA kinetic study of the thermal degradation in the melt of bisphenol‐A polycarbonate in the presence of various anhydrous alkali metal arylcarboxylates is undertaken in order to assess the validity of the reaction mechanism previously established on a model system. The influence of the temperature, the concentration and the nature of the salt is studied. The results confirm the validity of the proposed kinetic model and suggest minor modifications to the reaction mechanism.
Study of the distributions of chemical composition and molecular weight in relation to the preparation method of vinyl alcohol/vinyl acetate copolymers
Authors: Arranz Félix , Sánchez‐Chaves Manuel , Riofrio Alicia 
Published: April 2003

AbstractThe chemical heterogeneity of two vinyl alcohol/vinyl acetate (VAL‐VAC) copolymers prepared by partial acetylation of poly(vinyl alcohol) and by partial alkaline hydrolysis of poly(vinyl acetate), respectively, was studied by cross‐fractionation. The used solvent/non‐solvent systems were selected on the basis of cloud‐point determinations. The chemical composition distribution (CCD) and the molecular weight distribution (MWD) curves were constructed from fractionation data. The observed chemical heterogeneity was correlated with the kinetic parameters of the two different methods used for the preparation of the VAL‐VAC copolymers. Thus, squared standard deviation values

= 2,90·10−4 and

= 7,42·10−4 were found for the two VAL‐VAC copolymers prepared by acetylation and hydrolysis, respectively. These results are in agreement with theoretical predictions. The cumulative data were fitted by the two‐parameters MWD functions of Tung and of Wesslau.
The effect of branching on the Huggins coefficient of statistical styrene/butadiene copolymers
Authors: Reddy Gandavarapu Venkataramana , Petrus Vladimír , Bohdanecký Miloslav 
Published: April 2003

AbstractThe Huggins coefficient kH of solutions of statistical styrene/butadiene copolymers in cyclohexane (at 25 °C) and 2‐pentanone (theta temperature 21 °C) is discussed. With an increase in branching the values of

(i. e. kH at the theta temperature) increase from 0,5 to 0,73. Lower values in cyclohexane (good solvent) correlate with the viscosity expansion factor αη3, and the dependence is well fitted by the equation

where

is a function of the degree of branching, whereas C″0 only slightly exceeds the value found for linear polymers.
On the nature of the active centres in the anionic polymerization of methacrylonitrile, 3. Interaction with lithium tert‐butoxide
Authors: Adler Hans‐Jürgen , Lochmann Lubomir , Dotcheva Dobrinka T. , Tsvetanov Christo B. 
Published: April 2003

AbstractThe interaction between lithium tert‐butoxide (t‐BuOLi) and the active centres in the anionic oligomerization of acrylonitrile was studied by IR spectroscopy and conductometrically. α‐Lithiated isobutyronitrile and 1,3,3‐trimethylglutaronitrile were used as model compounds. t‐BuOLi forms complexes with these active centres in a 1:1 and/or 2:1 stoichiometry.
Elastic and photoelastic properties of polyisoprene networks — applicability and bounds of theories
Authors: Gleim Wolfgang , Oppermann Wilhelm , Rehage Günther 
Published: April 2003

AbstractMeasurements of stress and birefringence of networks of natural rubber and cis‐1,4‐polyisoprene deformed by simple elongation are reported. The experimental results are compared with theoretical calculations. It is found that the stress‐strain relation is in accordance with the empirical Mooney‐Rivlin equation. The constants 2 C1 and 2 C2 increase linearly with temperature indicating that both reflect essentially entropic elasticity. From theories dealing with the origin of the Mooney‐Rivlin behaviour, neither the entanglement concept nor the fluctuation or packing concept alone may account for the elastic behaviour observed. The photoelastic investigations prove the well‐known proportionality of stress and birefringence.
The morphology and structure of undoped and I2‐doped polyacetylene‐polybutadiene graft copolymer films
Authors: Bolognesi Alberto , Catellani Marinella , Destri Silvia , Porzio William , Meille Stefano Valdo , Pedemonte Enrico 
Published: April 2003

AbstractThe morphological and structural aspects of a novel polyacetylene‐polybutadiene (PA‐PB) graft copolymer film were investigated by means of transmission electron microscopy (TEM), electron diffraction (ED), and wide angle X‐ray diffraction (WAXS). Moreover, the evolution of these properties upon I2‐vapour doping of the cast films was followed. Finally, correlations between morphology, structure, and conductivity were drawn, suggesting a possible mechanism of conduction in this material.
A new experimental device for sensitive birefringence measurements
Authors: Bühler Fritz , Stadler Reimund , Gronski Wolfram 
Published: April 2003

AbstractA double beam detection method for the measurement of birefringence in stretching experiments of polymers is developed. By this method a noise free intensity signal is measured allowing a sensitive determination of the absolute birefringence. The efficiency of the experimental device is tested using cis‐1,4‐polybutadiene and butyl‐rubber networks.
Orientation behaviour of rod‐like cross‐link molecules in elastomeric networks
Authors: Stadler Reimund , Bühler Fritz , Gronski Wolfram 
Published: April 2003

Abstractcis‐1,4‐Polybutadiene and butyl‐rubber were cross‐linked in solution by a tetrafunctional enophilic cross‐linking agent, 4,4′‐methylenebis(1,4‐phenylene)di‐1,2,4‐triazoline‐3,5‐dione, possessing a rod‐like structure. The stress optical coefficients of the networks vary linearly with cross‐link concentration. The smaller concentration dependence for polybutadiene shows that a high fraction of cross‐link molecules are incorporated into the network chains as elastically ineffective cross‐links by formation of loops during the cross‐linking reaction. By combination of the stress optical data of both kinds of networks, the orientation function of elastically effective cross‐linkages is shown to be greater by a factor of about 8 than the orientation parameter of elastically ineffective cross‐link molecules in chains. From the effectivity of the cross‐linking reaction and the Mooney Rivlin constants 2C1 the memory factors of the networks were determined. They show that the compression of the networks in the dry state is considerably smaller than calculated by the polymer concentration during cross‐linking.
Electrical properties of linear poly(ester‐urethane)s, 1. D.C. conductivity
Authors: Rehage Günter , Lamour Richard , Fuhrmann Jürgen , Wilhelm Thomas 
Published: April 2003

AbstractThe steady‐state D.C. currents of linear poly(ester‐urethane)s with different hard to soft segment ratios were investigated. With increasing hard to soft segment ratios, the conductivity was found to increase and the field strength, where ohmic currents change to space charge limited currents, is significantly lowered. Five distinct regions of different thermal activation energy were observed as a function of temperature. With increasing temperature, the thermal activation energy is decreased. Stretched poly(ester‐urethane)s show lower conductivity due to segregation of hard and soft segments. The results are discussed in terms of polymer structure and are correlated with well‐known morphological phenomena in polyurethanes.
Phase separation in mixed liposomes of dipalmitoyl phosphatidylcholine and di‐2,4‐octadecadiene phosphatidylcholine
Authors: Tsuchida Eishun , Seki Noriko , Ohno Hiroyuki 
Published: April 2003

AbstractMixed liposomes were prepared from a mixture of lipids having saturated acyl chains (1,2‐dipalmitoyl‐3‐phosphatidylcholine; DPPC) and unsaturated ones (1,2‐bis(2,4‐octadecadienoyl)‐3‐phosphatidylcholine; DODPC) in order to analyze their phase separation behaviours. The phase transition behaviour was analyzed by fluorescence depolarization and differential scanning calorimetry. Transition temperatures of DPPC and DODPC are 42 and 18°C, respectively. In mixed liposome systems, two transition temperatures were clearly observed by both techniques. These results strongly suggest that these two different kinds of lipids do not dissolve homogeneously but form clusters (phase separation). DODPC molecules are polymerized by UV‐irradiation. Polymerization was confirmed by the decrease of the characteristic absorption band for diene groups. Phase separation was also observed in the polymerized mixed membrane and was directly confirmed by freeze‐fracture transmission electron microscopy.
Dissociation constant of poly(ethylene oxide) macroion pairs in nitrobenzene
Authors: Martinez Armando , Mijangos Fernando , León Luis Manuel 
Published: April 2003

AbstractThe great stability of the cationic polymerization system, ethylene oxide/nitrobenzene, from an electrochemical point of view, was investigatd as well as the assumption that the stable salts of triphenylmethylium and the macroion pair have the same dissociation constant. The value was determined to be 9,4 · 10−3 mol · 1−1 at 293 K in nitrobenzene.
Microstructure of poly[polytetrahydrofuran‐block‐poly(sebacoylchloride‐alt‐hexamethylenediamine)] and its role in blood compatibility
Authors: Yui Nobuhiko , Kataoka Kazunori , Sakurai Yasuhisa , Keitoku Fumio , Sanui Kohei , Ogata Naoya 
Published: April 2003

AbstractThe microstructure of poly[polytetrahydrofuran‐block‐poly(sebacoyl chloride‐alt‐hexamethylenediamine)]s 1–4, containing polytetrahydrofuran (PTHF) blocks of various molecular weights, and their blood compatibility were studied. These multiblock copolymers were prepared by interfacial polycondensation. The characterization of these copolymers was carried out by means of transmission electron microscopy (TEM), differential scanning calorimetry (DSC), dynamic mechanical measurements, wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and electron spectroscopy for chemical analysis (ESCA). The TEM observation revealed the formation of a spherulitic structure at the copolymer surfaces, which is closely related to the homopolymer, polyamide (PA) 610. The DSC and dynamic mechanical measurements indicate the presence of distinct phase separation between PTHF and PA 610 blocks, and of the PTHF block in the copolymer being partially crystallized. The WAXD and SAXS indicate the formation of microstructures composed of crystalline and amorphous phases in the copolymer. Moreover, ESCA measurements verify that the surface chemical composition of the copolymer is identical to their bulk composition. Blood compatibility of these copolymers was evaluated by estimating platelet adhesion on the copolymer surfaces. Platelet adhesion was found to be affected by the PA 610 crystallinity, including the size and distribution of the crystalline phase in the case of the copolymers in which the PTHF blocks are completely amorphous (M̄n = 980). On the contrary, platelet adhesion at the copolymers in which the PTHF blocks are partially crystallized (M̄n ≥ 1560) depends upon the crystallinity of both PA 610 and PTHF, including the balance of crystalline (PA 610 and PTHF) and amorphous (mainly PTHF) phases. This result suggests that the balance of the crystalline and amorphous phase distribution in the copolymer is the most determinative factor for suppressing platelet adhesion at the copolymer surface.
Synthesis of liquid crystalline polyacrylates and their use in capillary gas chromatography
Authors: Naikwadi Krishnat P. , Jadhav Anita L. , Rokushika Souji , Hatano Hiroyuki , Ohshima Mitsuyosi 
Published: April 2003

AbstractNew enantiotropic liquid crystalline compounds based on 4‐(p‐substituted phenylazo)phenol and m‐cresol esters containing an acryloyloxy group were synthesized. Polyacrylates were prepared from these monomers by radical polymerization. The resulting polymers exhibit nematic enantioropic properties. The polyacrylates have broader nematic ranges and higher nematic to isotropic transition temperatures as compared to their corresponding monomers. The nematic range is dependent on both the lateral substituents and the terminal substituents. The laterally substituted polyacrylates gave a narrower nematic range than unsubstituted compounds. Increase in carbon number in the terminal alkyl group leads to a broader nematic range. The liquid crystalline polyacrylates could be coated uniformly on the inside of a glass capillary tubing. The coated capillary columns show an excellent selectivity in gas chromatography for the separation of isomeric compounds. The liquid crystalline stationary phases are highly stable up to 230°C without column bleeding.
Relationship between physical parameters of the solvent and its influence in stereocomplex formation
Authors: Katime Issa A. , Quintana Jose Ramon , Strazielle Claude 
Published: April 2003

AbstractAn extensive study on the influence of the solvent on the PMMA stereocomplex formation was made by means of laser light scattering and viscometry for the following solvents: nitroethane, cyclohexanone, aniline, 1,1,2,2‐tetrachloroethane, ethyl benzoate, 1,2‐dimethoxyethane, N,N‐dimethylacetamide, ethyl and propyl acetate, ethyl methyl and isobutyl methyl ketone, 1,2‐dichloroethane, 1,4‐dioxane, DMF, bromoform, chloroform, chlorobenzene, 1,2‐dichlorobenzene, 1,3‐dichlorobenzene, 1,1,1‐trichloroethane, and trans‐1,2‐dichloroethane. It was found that a variation in the polymer tacticity causes a change in the influence of the solvents on stereocomplex formation, e.g. in the case of chlorobenzene, 1,2‐dichlorobenzene and nitrobenzene. Further, the influence of the solvent was related with the non‐polar, polar and hydrogen bonding components of the solubility parameter, δd, δp and δh.
Study of the compatibility of poly(ethylene oxide) with polyitaconates
Authors: Quintana José R. , Radic Deodato , Cesteros Luis C. , Katime Issa A. 
Published: April 2003

AbstractThis paper reports on the compatibility of poly(ethylene oxide) (PEO) towards poly(monobenzyl itaconate) (PMBzl) and poly(dibenzyl itaconate) (PDBzl) in the bulk by analyzing the melting point depression of the crystalline component and the influence of the amorphous material on the crystallization kinetics of the former. The experimental data obtained suggest compatibility for the PEO/PMBzl blend and incompatibility for the PEO/PDBzl system. This behaviour is explained by specific interactions (hydrogen bonds) between the chains, and is compared with that of other polymers with similar chemical structure.
Lösungsmittel‐effekt bei der bildung von \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--} (\mathop {\rm C}\limits^{\rm |} \hbox{=} \mathop {\rm C}\limits^{\rm |} \rlap{--} )_{\rm n}$\end{document} doppelbindungssequenzen in polystyrol bei bestrahlung mit langwelligem uv‐licht
Authors: Turzyński Zbigniew , Woliński Leszek 
Published: April 2003

AbstractUpon irradiation with long‐wave range UV light of degassed chlorine‐containing solutions of polystyrene conjugated double bonds \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--} (\mathop {\rm C}\limits^{\rm |} \hbox{=} \mathop {\rm C}\limits^{\rm |} \rlap{--} )_{\rm n}$\end{document} are formed along the polystyrene chain. The kinetics of their formation and their sequence lengths depend on the solvent. Aside from isolated CC double bonds sequences of \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--} (\mathop {\rm C}\limits^{\rm |} \hbox{=} \mathop {\rm C}\limits^{\rm |} \rlap{--} )_{\rm n}$\end{document} with n = 2 to n = 5 are formed.