bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystallization of the γ‐form of isotactic poly(propylene), 2. Synchrotron radiation measurements
Authors: Marigo Antonio , Marega Carla , Zannetti Roberto , Paganetto Guglielmo , Schmidt Stephan , Zachmann Hans Gerhard 
Published: April 2003

AbstractSynchrotron radiation measurements were employed in recording wide‐ and small‐angle X‐ray diffraction patterns during the crystallization of isotactic poly(propylene) in γ‐form. In particular, crystallization phenomena of this form are reported for a fraction of a random propylene‐ethylene copolymer (4 wt.‐% of ethylene) previously investigated by traditional diffraction methods. On slow cooling from the melt, the main decrease in long period L occurs between 88 and 76°C where the degree of crystallinity is almost constant. This may be explained by a flattening of lamellae.
Synthesis of arylsubstituted monomers for high‐performance polymers
Authors: Land Horst Tore , Hatke Wilfried , Greiner Andreas , Schmidt Hans‐Werner , Heitz Walter 
Published: April 2003

AbstractThe arylation of monomers for high‐performance polymers is described. The reaction of dibenzoyl peroxide with various 1,4‐disubstituted benzene derivatives results in phenylation. Minimization of side reactions is discussed. The Ni‐promoted reaction of Grignard compounds with iodoarenes was used to introduce the phenyl, biphenyl, and naphthyl substituent.
Release of 5‐aminosalicylic acid from bioadhesive N‐(2‐hydroxypropyl)methacrylamide copolymers by azoreductases in vitro
Authors: Kopečková Pavla , Kopeček Jindřich 
Published: April 2003

AbstractN‐(2‐hydroxypropyl)methacrylamide (HPMA) copolymers (11a, b) containing side chains terminating in 5‐aminosalicylic acid (5‐ASA) and fucosylamine (10) were synthesized. A reactive polymeric precursor (9), a copolymer of HPMA (7) and N‐methacryloylglycylglycine p‐nitrophenyl ester (8), was consecutively aminolyzed with 5‐[4‐(2‐aminoethylcarbamoyl)phenylazo]‐salicylic acid (6) and fucosylamine (10). The latter renders the copolymers bioadhesive in the gastrointestinal tract. The release of 5‐ASA from 11a, b was studied in vitro by incubation with cell‐free extracts isolated from rat cecum, and factors influencing the degradation were determined. The rate of azo bond cleavage of 11a, b was similar to the rate of cleavage of low‐molecular‐weight substrates, methyl orange and compound 6. Addition of benzyl viologen, a low potential electron carrier, increased the rate of cleavage. At optimal benzyl viologen and substrate concentration ratios, a zero order release was observed. At higher substrate concentration, the rate of 5‐ASA release decreased.
Dynamics of photoinduced isomerization of azobenzene moieties in liquid‐crystalline polymers
Authors: Wiesner Ulrich , Antonietti Markus , Boeffel Christine , Spiess Hans Wolfgang 
Published: April 2003

AbstractForced Rayleigh scattering was used to investigate the dynamics of photoinduced isomerization of azobenzene involved in reversible holographic information storage. The studies were performed with statistical liquid‐crystalline side‐group copolymers having different concentrations of the dye, in a copolymer forming no mesophase and in a physical mixture of the dye in a liquid‐crystalline side‐group homopolymer. Two relaxation processes were found in the glassy state of these polymers, the faster one being distributed over a wide range of relaxation times ascribed mainly to reorientational relaxation of the dye as well as the glassy matrix. The second is a single exponential, ascribed to the relaxation of azobenzene back to its trans conformation. The two processes could be assigned through a control experiment using an irreversibly isomerizing dye. The results of a calculation of the angular dependence of azobenzene isomerization was compared with the experiment, in order to judge the influence of the anisotropic matrix on the relaxation process.
Solution properties of polystyrene‐block‐polybutadiene‐block‐polystyrene triblock copolymers
Authors: Küçükyavuz Zühal 
Published: April 2003

AbstractThe conformational behaviour of polystyrene‐block‐polybutadiene‐block‐polystyrenes, ABA‐type triblock copolymers, with 50 wt.‐% of A blocks were studied by light scattering, viscometric and osmometric methods over a wide range of molecular weight. Unperturbed dimensions were found directly by light scattering in the θ solvent methyl isobutyl ketone and also estimated by extrapolation methods from intrinsic viscosity and osmometric results in toluene, a thermodynamically good solvent. Osmometric and viscometric results showed that the block copolymers form a Gaussian coil in toluene, whereas light scattering results indicated some segregation of blocks for a low‐molecular‐weight sample in the θ solvent.
Chemical synthesis and properties of tetrabutylphosphonium‐ion‐doped polyacetylene
Authors: Ignatious Francis , Mathis Claude 
Published: April 2003

AbstractA direct method of introducing tetraalkylphosphonium ions into polyacetylene (PA) is described. The maximum doping levels achieved with reducing agents having various redox potentials were determined. The electrical and magnetic properties of resulting doped products were assessed. The thermal stability of this product was monitored by electrical conductivity measurements. An indirect ion‐exchange technique was devised to insert the phosphonium ion into PA. A similar method was found useful for the preparation of reduced β‐carotene, a soluble analogue of PA, containing tetraalkylphosphonium counterions. The stability of the resulting compound was also studied.
Coordination polymerization of lactides, 1. Structure determination of obtained polymers
Authors: Bero Maciej , Kasperczyk Janusz , Jedlinski Zbigniew J. 
Published: April 2003

AbstractRacemic lactide was polymerized with various initiators containing Zn and Al, and the structures of the obtained polymers were determined by means of 13C NMR spectroscopy. The extent of transesterification reactions was calculated on the basis of the analysis of the methine carbon signal in the polymer 13C NMR spectra. Three groups of initiators can be distinguished in view of their influence on transesterification: ZnCl2 exhibits the strongest transesterification activity, ZnEt2 and ZnEt2/Al(OiPr)3 are among those of medium activity, and Al(acac)3 does not show transesterification activity at all.
Poly(Ether/Ester)s based on poly(tetramethylene terephthalate) and poly(ethylene glycol), 3. Effect of thermal treatment and drawing on the structure of the poly(ether/ester)s
Authors: Fakirov Stoyko , Gogeva Tanya 
Published: April 2003

AbstractAnnealed drawn and undrawn bristles of poly(ether/ester)s based on poly(tetramethylene terephthalate) (PTMT) and poly(ethylene glycol) PEG 1000 (in various ratios) are studied by means of small‐angle X‐ray scatering and differential scanning calorimetry (DSC). The samples with the lowest PTMT content (49 wt.‐% PTMT) show on abrupt increase of the scattering intensity and the long spacing with increasing annealing temperature Ta, this increase becoming less pronounced with increasing fraction of hard segment (PTMT). The DSC heating scans are characterized by a low‐temperature glass transition due to the soft polyether segments and a multiple melting behaviour at about 200°C due to the crystalline hard PTMT segments. The data suggest a dependence of the thermal behaviour on the chemical composition, annealing temperature, and orientation. The characteristics of the undrawn samples are similar to those of the homopolyester PTMT and the copolymers based on PTMT and poly(tetramethylene oxide). Evidence is found for an increase of phase separation with an increase of the annealing temperature. The formation of larger amorphous regions of PEG with increasing Ta determines the thermal and scattering behaviour observed.
Enlargement of the glass transition range in compatible polymer blends
Authors: Schneider Hans Adam , Cantow Hans‐Joachim , Wendland Christina , Leikauf Bernhard 
Published: April 2003

AbstractAnalysis of glass transition temperature (Tg) ranges for compatible polymer blends defined by differential thermal analysis traces for the onset temperature (Tg, i) and the final temperature (Tg, f) of the glass transition shows the well‐known increase in width when compared with the Tg ranges of the blend components. This enlargement of the Tg range is generally attributed to local composition fluctuations; from a comparison of the effects in blends of polystyrenes (PS/PS) of different molecular weights the influence of an increase of the ratio of weight‐ to number‐average molecular weights M̄w/M̄n, because of interactions between the blend components (hetero‐interactions) has to be considered, too. Poly(methyl vinyl ether) (PVME)/PS blends are characterized by a peculiar behaviour, the increase in the width of the Tg range being at least three‐fold larger than for all other blends studied. This is valid for all blends with a molecular weight of the PS component higher than 10000. Local incompatibilities suggested by enthalpy relaxation and by dynamic mechanical measurements may be responsible for the observed unusual enlargement of the Tg range in the blends with 50–75 wt.‐% PS.
Functional monomers and polymers, 192. Synthesis of N‐nitrophenylchitosan derivatives and their electrochemical properties
Authors: Ohnishi Noriaki , Kondo Koichi , Takemoto Kiichi 
Published: April 2003

AbstractN ‐ Nitrophenylchitosan derivatives were prepared by the reaction of chitosan hydrochloride with 1 ‐ fluoro ‐ 4‐nitrobenzene, 1‐fluoro‐2,4‐dinitrobenzene and p‐nitrobenzaldehyde. The 2,4‐dinitrophenyl derivative, which is the only product soluble in dimethyl sulfoxide and dimethylformamide, was analyzed by two‐dimensional NMR spectroscopy. Its solution in dimethylformamide exhibits a remarkable change in color from yellow to red upon electroreduction, and the film cast from dimethylformamide solution shows similar electrochromic properties.
Computer simulation of the dynamics of branched polymers
Authors: Romantsova Irina , Taran Yurii 
Published: April 2003

AbstractThe dynamics of an isolated symmetrical four‐branched star‐shaped macromolecule is simulated for random (RW) and self‐avoiding walks (SAW) by a Monte Carlo algoritham. The motion of branching points is realized on a body‐centred cubic lattice by elementary moves, including 4–6 bonds of the chain. The average dimensions of the chain, the autocorrelation functions, and the translational diffusion are investigated. The algoritham for RW displays Rouse behaviour. Scaling exponents are found for SAW.
Evaluation of the equilibrium melting temperature and structure analysis of poly(ethylene oxide)/poly(methyl methacrylate) blends
Authors: Cimmino Sossio , Di Pace Emilia , Martuscelli Ezio , Silvestre Clara 
Published: April 2003

AbstractBy using optical microscopy, small‐angle X‐ray scattering and differential scanning calorimetry, the melting behaviour and the structural parameters of poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) blends are determined. The equation that relates the observed melting temperature, Tm′, to the lamellar thickness is used for the determination of the equilibrium melting temperature, Tm. In the case of blends a small depression in the equilibrium melting point is observed. The depression is dependent on composition. the interaction parameter obtained from the melting point degression, by using the Nishi and Wang equation, was found to be = −0,29. The superstructural parameters are dependent on blend composition, under cooling and sample preparation.
Graft copolymers, 2. The application of group‐transfer polymerisation to the synthesis of graft copolymers
Authors: Jenkins Aubrey D. , Tsartolia Eugenia , Walton David R. M. , Horská‐Jenkins Jitka , Kratochvíl Pavel , Stejskal Jaroslav 
Published: April 2003

AbstractA copolymer, containing a minor proportion of residues derived from a special monomer with particular structural features, has been synthesised and used in a subsequent grafting step in which functional groups belonging to the special monomer residues were converted into initiating centres from which grafts were grown by means of “group‐transfer” polymerisation. It is shown that this technique constitutes a satisfactory method for the synthesis of graft copolymers (or branched, i. e. comb‐like, homopolymers) free from linear homopolymer, and the procedure is applied to a specific system in which the principal backbone monomer is styrene, the special backbone monomer component is (2‐isobutyryloxy)ethyl methacrylate, and the grafting monomer is methyl methacrylate.
13C NMR analysis of poly[(m‐phenylene terephthalate)‐co‐oxybenzoate]s: Main‐chain and end‐group resonance assignments and sequence distribution
Authors: Komber Hartmut , Böhme Frank , Pospiech Doris , Rätzsch Manfred 
Published: April 2003

AbstractSamples of poly[(m‐phenylene terephthalate)‐co‐oxybenzoate] with different compositions were analyzed by 13C NMR spectroscopy. Diad and triad signals could be identified and assigned. Furthermore, the signals of acetoxy, carboxy and hydroxy end‐groups were assigned. The analysis of NMR substituent effects confirms the assignment. Comparison of the calculated statistical with the experimentally determined diad and triad contents shows a slight tendency for the formation of oxybenzoate blocks in the polymer chain.
Monte Carlo simulation of tetrahedral chains, 3. Star‐shaped polymers by pivot algorithm
Authors: Zifferer Gerhard 
Published: April 2003

AbstractBy use of the pivot algorithum, stars with F = 3–12 arms of length n, nF = 480, and linear chains (F = 2) are generated on a tetrahedral lattice in order to test the suitability of this algorithm for star‐shaped polymers. A new configuration is obtained by rotating that part of an arm which contains the chain end around a randomly selected bond by ±120°. If no double occupancies occur, the new configuration is accepted. Otherwise, the old one is restored. The (average) acceptance fraction decreases only slightly with increasing number of arms. The probability of obtaining a new self‐avoiding configuration by a move of an arm around a bond near the centre of the star is significantly higher than the probability for a successful combination of star with F‐1 arms with a further arm. The statistical error of global properties of stars with the same total number of segments is nearly independent of the number of arms, because an increase of the autocorrelation times is approximately compensated by a decrease of mean square deviations. In principle, comparison of the data with theoretical predictions yields the same results as found for other lattice models.
Détermination expérimentale des rapports de réactivité en copolymérisation: compariaison des méthodes d'Alfrey, Bohrer et Mark et de Tidwell et Mortimer
Authors: Bauduin Gérard , Boutevin Bernard , Belbachir Mohamed , Meghabar Rachid 
Published: April 2003

AbstractThe experimental methods for determining the copolymerization reactivity ratios r1 and r2 according to Tidwell and Mortimer (T.M.) on the one hand and according to Alfrey, Bohrer and Mark (A.B.M.), on the other hand are compared, using four examples. It is shown that they do not differ in principle: they are both curve‐fitting methods by the least‐squares technique. However, contrary to the systematical approach of A.B.M., the regression calculation of T.M. allows to estimate quantitatively the reliability of the numerical values of r1 and r2 determined.
Hydrodynamic properties of poly(1‐vinyl‐2‐pyrrolidone) molecules in dilute solution
Authors: Pavlov Georges M. , Panarin Evguenij F. , Korneeva Evgueniya V. , Kurochkin Constantin V. , Baikov Vadim E. , Ushakova Vera N. 
Published: April 2003

AbstractThe translational diffusion coefficient D0, the sedimentation coefficient S0, and the intrinsic viscosity [η] of samples and fractions of poly(1‐vinyl‐2‐pyrrolidone) were measured in a 0,1 M solution of sodium acetate in the molecular weight range 2 ≤ M · 10−3 ≤ 2200. For M > 4 · 104 the following relationships were obtained: [η] = 8,86 · 10−5 · M0,74, D0 = 2,42 · 10−4 · M−0,58, and S0 = 2,14 · 10−15 ·. M0,42. For M < 4 · 104 the corresponding relations are [η] = 5,0 · 10−4 · M0,56, D0 = 1,29 · 10‐4 · M−0,52 and S0 = 1,15 · 10−15 · M0,48. The hydrodynamic invariant is A0 = (3,2 ± 0,25) · 10−17 J · K−1 · mol−1/3 and the sedimentation parameter βs = (1,3 ± 0,17) · 107 mol−1/3. The temperature coefficient of the intrinsic viscosity is negative, viz. Δ ln[η]/ΔT = −6,3. 10M−3 K−1. The evaluation of the length of the Kuhn segment A and the hydrodynamic diameter d of chains representing the molecules of PVP in solution was conducted on the basis of the theory for the hydrodynamic properties of a wormlike necklace taking into account the excluded volume effects. The values of A agree with those obtained from the Burchard‐Stockmayer‐Fixman and Cowie‐Bywater equations, A = (2,1 ± 0,3) nm and d = (0,5 ± 0,13) nm.
Emulsion polymerization of styrene in the presence of poly(oxyethylene)‐poly(oxypropylene) block copolymers
Authors: Hergeth Wolf‐Dieter , Bloß Peter , Biedenweg Frank , Abendroth Peter , Schmutzler Klaus , Wartewig Siegfried 
Published: April 2003

AbstractPoly(oxyethylene)‐block‐poly(oxypropylene)‐block‐poly(oxyethylene) copolymers were applied as nonionic surfactants in styrene emulsion polymerization. The clouding phenomenon of the surfactant in the aqueous phase and the resulting characteristic partition of the block copolymer between aqueous and organic phase result in two particularities of this system compared with classical emulsion polymerization: (i) bimodal particle size distribution, and (ii) unusual dependence of reaction rate on temperature.
Side‐chain liquid‐crystalline polyacrylates containing heterocyclic mesogenic groups, 1. Influence of the substituent and the number of phenyl groups on the mesomorphous properties
Authors: Legrand Cécile , Bunel Claude , Borgne Alain Le , Lacoudre Nelly , Spassky Nicolas , Vairon Jean‐Pierre 
Published: April 2003

AbstractSynthesis and preliminary results on the characterization of liquid‐crystalline polyacrylates with trans‐1,3‐dioxane‐2,5‐diyl group in the side chain are presented. A stabilization of the mesophases occurs when two phenyl groups are present in the mesogenic moiety. All polymers with three rings exhibit SA mesophases except for poly(6‐[trans‐2‐(4‐(4‐methoxybenzoyloxy)phenyl)1,3‐dioxane‐5‐yl]hexyl acrylate) which presents a nematic phase over 200°C and is potentially useful as host matrix for applications in non‐linear optics.
Chirality of poly(vinyl compounds), 13. Sterical requirements in analogues of trityl methacrylate for the preparation of optically active, single‐sense helical polymers
Authors: Wulff Günter , Wu Yonghua 
Published: April 2003

AbstractTrityl methacrylate possesses two different substituents at the olefinic double bond. The larger one containing the trityl group forms the outside sphere of the helix in the corresponding polymers. In this paper the role of the second, smaller substituent is discussed. For this purpose four new monomers, methyl α‐(trityloxymethyl)acrylate (5), ethyl α‐(trityloxymethyl)acrylate (6), α‐(trityloxymethyl)styrene (7), and trityl α‐ethylacrylate (3), were prepared. Polymerization experiments showed that this substituent should be of minimum size to obtain a stable helix. More extended substituents though do not fit into the helical arrangement and therefore neither anionic nor radical polymerization was achieved.
Plastic‐rubber composite, 1. The polymer‐polymer interdiffusion at the phase boundary of poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) and polystyrene
Authors: Machate Christina , Lohmar Jörg , Dröscher Michael 
Published: April 2003

AbstractThe interdiffusion of poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) (PPE) and polystyrene (PS) sequences is the key step in the formation of the commonly called plastic‐rubber composite (Kunststoff‐Kautschuk‐Verbund, K&K‐V). This new process bonds PPE and poly(styrene‐co‐butadiene) rubber (SBR) during the vulcanization of the rubber, without the aid of any adhesive. As PPE and PS are fully mutually compatible polymers, polymer‐polymer interdiffusion takes place readily. PS was therefore used as a model system. Electron microscopy clearly demonstrates that the kinetics of the diffusion process are determined by the faster diffusing PS. This was studied in the temperature range of 180°C to 260°C. The interdiffusion coefficients are of the order of 10−13 to 10−10 cm2 · s−1. These are significantly higher than the selfdiffusion coefficients of PPE and PS, which are 10−15 and 10−12 cm2 · s−1, respectively. The interdiffusion coefficients are dependent on temperature and inversely proportional to the PS molecular weight, for PS molecular weights higher than the entanglement value. The diffusion process follows Fick's law. The interdiffusion coefficient is not, or is only weakly, dependent on the concentration. The interdiffusion of PS samples of molecular weights below the entanglement value is observed by a newly developed method based on Fourier transform infrared spectroscopy with attenuated total reflection technique (FTIR‐ATR). In this low‐molecular‐weight region, interdiffusion coefficients as high as 10−7 cm2·s−1 are obtained.
Plastic‐rubber composite, 2. Polymer‐polymer interdiffusion at the phase boundary of poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) and poly(styrene‐co‐butadiene)
Authors: Machate Christina , Lohmar Jörg , Dröscher Michael 
Published: April 2003

AbstractInterdiffusion of poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) (PPE) and polystyrene (PS) sequences is the key step in the formation of the so‐called plastic‐rubber composite (Kunststoff‐Kautschuk‐Verbund, K & K‐V). This new process links PPE and poly(styrene‐co‐butadiene) rubber (SBR) during the vulcanization of the rubber, without the aid of any adhesives. Polystyrene‐block‐polybutadiene (SB) is used as model for SBR. As PPE and polystyrene (PS) are fully mutually compatible polymers, polymer‐polymer interdiffusion occurs easily for PPE and the PS blocks. This is shown by electron microscopy. The thickness of the interdiffusion zone correlates to the PS block length. The respective butadiene block forms a layer on top of the interdiffusion zone. SBR with a high styrene content of at least 71 wt.‐% is also compatible with PPE. The interdiffusion kinetics of the system PPE‐SBR follows Fickian behaviour. The diffusion coefficients are smaller than for the system PPE‐PS. Although PPE and SBR with lower PS content, as it is used for the K & K‐V, are not compatible, interdiffusion occurs at the phase boundary. The thickness of the diffusion zone depends on the styrene content of the SBR. For SBR samples with 40 and 23,5 wt.‐% styrene, zones of 50 and 15 nm thickness are found.
Preparation of bisupported catalysts for ethylene polymerization
Authors: Pasquet Véronique , Spitz Roger 
Published: April 2003

AbstractSiO2‐MgCl2 supports were prepared thermally at moderate temperature. The preparation was improved by the use of an additive stabilizing MgCl2‐ammonium chloride. The best supports contain less than 5 wt.‐% Mg with about 2/3 of Mg as MgCl2 and keep most of the porous properties of the starting silica. Bisupported catalysts obtained after TiCl4 impregnation (2–4 wt.‐% Ti) present high activities and productivities in gas‐phase ethylene polymerization and copolymerization.