bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural analysis of poly(3‐alkylthiophene)s
Authors: Leclerc Mario , Diaz Francisco Martinez , Wegner Gerhard 
Published: April 2003

AbstractPoly(3‐hexylthiophene) (PT6), poly(3‐octylthiophene) (PT8), poly(3‐decylthiophene) (PT10) and poly(3‐dodecylthiophene) (PT12) were synthesized by electrochemical and chemical polymerization. Investigation of these polymers by means of gel permeation chromatography indicates that the polymers prepared from the different monomers under similar conditions do not differ substantially considering molecular weight and molecular weight distribution. Bimodal distributions were found for electropolymerized polymers, and with increasing polymerization time, the high‐molecular‐weight and probably highly branched fraction increased relatively to the low‐molecular‐weight fraction. The microstructure of the polymers was investigated by nuclear magnetic resonance, and it has been found that the polymers exhibit more types of structural units than expected from a simple coupling of adjacent thiophene moieties in 2,5′‐positions. Chemical oxidation with iron trichloride in chloroform gave soluble, high‐molecular‐weight poly(3‐alkyl‐thiophene)s with a rather low amount of irregular couplings, and these more regular polymers exhibited a higher degree of crytallinity. Room temperature conductivities of the oxidized polymers were between 0,1 and 30 S/cm depending on the polymerization conditions, but these values were rather independent of the length of the alkyl substituent.
Graft polymerization onto a polystyrene resin containing thermolabile azo groups and the effect of the grafted resin on asymmetric reduction of oxime ethers
Authors: Inoue Kenzo , Takemoto Hidemi , Tanigaki Teiichi 
Published: April 2003

AbstractGraft polymerization of various vinyl monomers onto a polystyrene resin (6) containing azo groups having the ability to initiate the radical polymerization was performed. The graft efficiency of vinyl monomers onto 6 increases with time of polymerization and achieves more than 85%. The swelling of 6 affects remarkably the graft efficiency. Scanning electron microscopy (SEM) shows that considerable amounts of graft copolymers are located at the surface of 6. The graft copolymer of chloromethylstyrene onto 6 was treated with (S)‐(−)‐2‐amino‐3‐(p‐hydroxyphenyl)‐1,1‐diphenyl‐1‐propanol to yield a resin (9) carrying chiral amino alcohol functions. Resin 9/borane was used for asymmetric reductions of acetophenone oxime O‐methyl and O‐benzyl ethers, leading to 1‐phenylethylamine with 43% and 46% enantiomeric excess (e.e.), respectively. These values are higher than those obtained with the generally used polystyrene resin, suggesting that the enantioselectivity can be improved by modification of the support resin.
Effect of hydrogen on propene polymerization with solvay‐type TiCl3/Cp2 TiMe2 catalyst
Authors: Sun Lixin , Soga Kazuo 
Published: April 2003

AbstractPolymerization of propene with a highly isospecific Solvay‐type TiCl3/Cp2TiMe2 catalyst in the presence and absence of hydrogen was investigated. It was found that hydrogen exerts almost no effect on the molecular weight and the stereoregularity of the resulting polypropylene. Furthermore, the H2/D2 exchange reaction hardly proceeds over the catalyst. To discuss this unusual behavior, plausible mechanistic explanations on the basis of the structure of active species are proposed.
Stabilization of polystyrene/poly(methyl methacrylate) blends by in situ compatibilization with graft copolymers
Authors: van Ballegooie Peter , Rudin Alfred 
Published: April 2003

AbstractCopolymers of styrene and ortho‐vinylbenzaldehyde (o‐VBA) are useful precursors to multicomponent polymer systems. Graft copolymers of poly(styrene‐stat‐o‐VBA) can be produced by free‐radical chain transfer to methyl methacrylate monomer to yield materials that display some potential as interfacial agents with binary blends of polystyrene and poly(methyl methacrylate). Significant improvements in ultimate tensile strengths and energy to rupture values have been witnessed for polystyrene/poly(methyl methacrylate) mixtures that contain various levels of the graft component. Scanning electron microscopy of representative fracture surfaces demonstrate a decrease in the particle size of the dispersed phase; it is suggested that this morphological factor contributes to the superior mechanical properties of these composites. In this regard, both the isolated and the crude graft copolymers are able to compatibilize, and thereby enhance, the material properties of polystyrene/poly(methyl methacrylate) blends.
Orientational behaviour of polymer blends containing a liquid‐crystalline component
Authors: Uzman Mehmet , Kühnpast Kurt , Springer Jürgen 
Published: April 2003

AbstractThis paper describes the orientational behaviour of polymer blends containing a side‐group liquid‐crystalline polymer (LCP). The macroscopic orientation of the LC phase in these blends, and the possibility to freeze in this state are of technical interest. The orientation of LCP‐containing blends through mechanical forces depends on a variety of structural, thermal, energetical and also morphological properties, which are strongly dependent on the kinetical and thermal history. This report describes the optical‐ and scanning electron microscopy (SEM), X‐ray diffraction and interfacial tension studies of the liquid‐crystalline polyacrylate 1a and the poly(methacrylate) 1b in poly(methyl methacrylate) (PMMA) and polycarbonate matrices. 1a droplets in thermoplastic matrices can be oriented macroscopically during fibre‐drawing, but, as a result of higher interfacial tension between the components, 1b‐containing blends can not.
Tacticity and dielectric relaxation around the glass transition of poly(vinyl chloride), a dynamic‐dielectric study
Authors: del Val Juan José , Alegría Angel , Colmenero Juan , Mijangos Carmen , Martínez Gerardo , LuisMillán José 
Published: April 2003

AbstractMolecular motions of poly(vinyl chloride) (PVC) in the glass transition range were studied by means of dielectric spectroscopy. The measurements were carried out with three different PVC samples obtained at different polymerization temperatures (0, 60 and 90°C) showing strong variations in their contents of syndiotactic, heterotactic and isotactic triads. The results show that all parameters (relaxation strength, temperature of the maxima of loss curves, evolution of the shift factors, master curves) characterizing the dielectric α‐relaxation in the liquid state of PVC are strongly affected by the tacticity. These facts are interpreted in terms of the role of specific local conformations in the motion of chain segments in the polymer molecules. These conclusions are in agreement with those outlined from the results previously obtained on PVC for the molecular motions in the glassy state just below the glass transition temperature.
Nematic elastomers: The influence of external mechanical stress on the liquid‐crystalline phase behavior
Authors: Schätzle Joachim , Kaufhold Wolfgang , Finkelmann Heino 
Published: April 2003

AbstractThe influence of external mechanical stress on the nematic‐isotropic phase transformation of nematic elastomers was investigated. The experimental results of IR‐dichroism measurements in the nematic phase and stress‐optical measurements in the isotropic phase are in good agreement with the theoretical predicitions of the phenomenological Landau‐de Gennes theory. This is for the first time that a significant influence of an external field on the nematic‐isotropic phase transformation temperature and on the nematic order parameter S has been proved.
Rigid rods with flexible side chains — A route to molecular reinforcement?
Authors: Heitz Thomas , Rohrbach Peter , Höcker Hartwig 
Published: April 2003

AbstractLiquid‐crystalline main‐chain polyesters with polystyrene side chains of different length and number per main chain were synthesized using aromatic hydroxyfunctional polystyrene (PS) macromonomers, terephthalic acid derivatives and tert‐butylhydroquinone as co‐diol. The molecular weight of the polystyrene side chain was varied in the range from 1000 to 20000. The influence of this novel type of substituent on the solubility, thermal behaviour and miscibility with PS as a flexible matrix polymer is discussed. The properties of the new compounds are compared to those of the respective homopolyester. The graft copolyesters are, depending on the characteristics of the polymeric substituent, soluble in common organic solvents and their thermal transition points are lowered compared to the homopolyester. Compared to blends of the homopolyester, the improvement of miscibility of the polymer‐substituted rigid rods with PS as an example for a flexible matrix polymer can be valued as a step to molecular reinforcement.
Cyclization versus polymerization in phase transfer catalyzed polytioetherification
Authors: Shaffer Timothy D. , Kramer Michael C. 
Published: April 2003

AbstractSome unexpected results were observed in the phase transfer of catalyzed (PTC) (two phase, aqueous‐organic) polymerization of α,ω‐dibromoalkanes with sodium sulfide. Alkane dielectrophiles containing fewer than six methylene units give rise to large, and sometimes quantitative, amounts of cyclic thioethers. These cyclic sulfides are formed under “polymerization” conditions and can be minimized by using only the monomer as the organic phase. Alkane dielectrophiles containing more than six methylene units yield only polymer. When a comonomer system composed of a 1:1 mixture of 1,4‐dibromobutane (DBB) and 1,8‐dibromooctane (DBO) is employed, the resulting copolymer's molecular weight and polydispersity are vastly improved compared to the corresponding homopolymerizations. Microstructurally, this copolymer is formed by complete consumption of DBO and partial incorporation of DBB. The remaining DBB forms tetrahydrothiophene (THT). These two odd and seemingly conflicting results could not be explained by “normal” or “inverse” PTC extraction mechanisms. Support of this new mechanism is given in the PTC polymerization of DBO with sodium sulfide in the presence of a catalytic amount of THT. The resulting polymer is of very high molecular weight and narrow polydispersity; it also does not contain tetramethylene sequences. Using this new mechanism, all results suggest the participation of cyclic sulfides either facilitates cyclic formation or enhance polymer reactivity as controlled by the length of the alkane dielectrophile.
Effect of ethyl benzoate on the microstructure distributions of olefin homopolymers and copolymers prepared with supported titanium catalyst
Authors: Wu Qing , Yang Nan‐Loh , Lin Shangan 
Published: April 2003

AbstractThe microstructure distributions of ethylene‐propene(EP) copolymers and propene homopolymers prepared with supported titanium catalyst were analyzed by 13C NMR spectroscopy. A two‐site model with an isospecific site and a non‐stereospecific site was used to describe the stereospecific polymerization of propene. A second two‐site model with individual r1r2 = 1 was applied to the analysis of the ethylene‐propene copolymerization. The addition of an external base, ethyl benzoate (EB), alters the relative concentrations of catalytic sites. Based on the comparison of the results from the homopolymers and copolymers prepared under different EB concentrations, the correlations between the stereospecificity and the activity toward the monomers were established: the isospecific site produces the copolymer with lower ethylene content; the non‐stereospecific site gives the copolymer with higher ethylene content.
Kinetic study of the polymerization of N,N′‐methylenebis(acrylamide) in aqueous dispersion systems
Authors: Capek Ignác , Funke Werner 
Published: April 2003

AbstractThe aqueous‐phase polymerization of N,N′‐methylenebis(acrylamide) initiated by potassium peroxodisulfate in the absence and in the presence of the anionic emulsifier sodium dodecylsulfate was kinetically investigated at 50°C by conventional gravimetric and dilatometric methods. The rate of polymerization is found to be proportional to the 0,75 and 0,24 oder with respect to potassium peroxodisulfate and N,N′‐methylenebis(acrylamide) concentrations, respectively. On the other hand, it is independent of the concentration of sodium dodecylsulfate. This agrees with the polymerization of a monomer soluble in water. Therefore, the equations for a homogeneous polymerization were applied to evaluate the experimental results. The calculated ratio kp/kt0,5 of the rate constants of propagation kp and termination kt for the N,N′‐methylenebis(acrylamide) polymerization at zero conversion in the absence of emulsifier are scattered in the interval between 3,1 and 3,4 dm1,5 · mol−0,5 · s−0,5 and in the presence of emulsifier in the interval between 2,4 and 3,5 dm1,5 · mol−0,5 · s−0,5. They are close to those obtained for the homogeneous polymerization of acrylamide in the aqueous phase. The lower values of kp/kt0,5 ≈ 0,3–0,6 dm1,5 · mol−0,5 · s−0,5 determined for the polymerization of N,N′‐methylenebis(acrylamide) for conversions between 30 and 60% follow from the hindered termination reaction within the polymer particles. The polymer dispersions formed are unstable. The growth of the polymer particles proceeds predominantly by coalescence. This suggests a kinetics which does not follow the Smith‐Ewart theory but is characterized by a continuous particle nucleation and agglomeration. The interval 1 occurs at the beginning of the dispersion polymerization when polymer particles are being formed. Interval 2 follows, once the number of polymer particles has been fixed.
UV and IR studies of the photolysis of poly(alkylsilane)s
Authors: Devaux Jacques , Sledz Joseph , Schué François , Giral Louis , Naarmann Herbert 
Published: April 2003

AbstractUV and IR spectroscopy were used to follow the photolysis of poly(syclohexylmethylsilane) (1) and poly(hexylmethylsilane) (2). Striking correspondences were found between wavelengths at maximum absorption and absorbance in UV region and particular IR bands which undergo bleaching in parallel. New IR band assignments are proposed. In addition, there is some evidence of a random scission of the chains with no significant contribution of an unzipping process.
The molecular weight effect on the mesomorphic behaviour of liquid‐crystalline poly(ester‐β‐sulfide)s
Authors: Laus Michele , Angeloni Annino S. , Galli Giancarlo , Chiellini Emo 
Published: April 2003

AbstractA DSC study is reported on the dependence of thermal properties on molecular weight in two series of thermotropic liquid‐crystalline poly(ester‐β‐sulfide)s, 9S4 and 9S5. The molecular weights range from approximately 1 600 to 14 000. All of the polymers exhibit a nematic phase preceded, at lower temperature, by a smectic A phase which is monotropic in the majority of the cases. The nematic‐isotropic transition temperatures and relevant entropy changes were found to be practically insensitive to molecular weight variations. In contrast, the smectic A‐nematic transition temperatures and entropy changes increase with increasing molecular weight and reach a plateau value at an average chain length of 6–7 repeating units. It is suggested that in the nematic phase of these polymers the flexible segment plays a role of diluent of the rigid groups, whereas at the nematic‐smectic A transition a cooperative increase in chain stiffness takes place.
Hydrophobic water‐soluble polymers, 1. Dilute solution properties of poly(1‐vinyl‐2‐piperidone) and poly(N‐vinylcaprolactam)
Authors: Eisele Michael , Burchard Walther 
Published: April 2003

AbstractPoly(vinyllactams) form a class of non‐ionic water‐soluble polymers from which only poly‐(1‐vinyl‐2‐pyrrolidone) (PVP) is well known and has been investigated extensively. The homologues poly(1‐vinyl‐2‐piperidone) (1, poly[1‐(2‐oxo‐1‐piperidyl)ethylene]) and poly(N‐vinylcaprolactam) (2, poly[1‐(2‐oxoperhydroazepin‐1‐yl)ethylene]) which are still soluble in water at room temperature have not yet been studied in aqueous solution. In this work the synthesis of these two polymers by radical polymerization in solution and the investigation of the dilute aqueous solution properties of these polymers by static and dynamic light scattering measurements are presented. Special attention is paid to the influence of the increasing hydrophobicity of these polymers on coil dimensions and structures in aqueous solution.
Effect of crosslinker on properties of copolymeric N‐vinyl‐2‐pyrrolidone/methyl methacrylate hydrogels and organogels
Authors: Davis Thomas P. , Huglin Malcolm B. 
Published: April 2003

AbstractThe γ‐ray initiated copolymerisation of N‐vinyl‐2‐pyrrolidone with methyl methacrylate in the presence of crosslinker has been effected to high conversion. At two fixed compositions of the principal monomers, the inclusion of different concentrations of the tetrafunctional crosslinkers ethylene dimethacrylate and a low molar mass poly(ethylene glycol) dimethacrylate produced crosslinked xerogels, which were subsequently swollen in water and 1,4‐dioxane to yield hydrogels and organogels, respectively. These gels were characterised by determinations of sol fraction, equilibrium solvent content and uniaxial compression stress/strain measurements. Differences among the swelling and mechanical properties according to the nature and concentration of crosslinking agent and according to the nature of the swelling medium are noted and discussed.
13C NMR studies of thermotropic liquid crystalline poly(γ‐alkylaryl L‐glutamate)s
Authors: Yamamoto Ryôta , Araki Kazuo , Imamura Yoshio , Asakura Tetsuo , Iizuka Eisaku , Iida Shûji 
Published: April 2003

AbstractThe molecular motions of three kinds of poly(γ‐alkylaryl L‐glutamate)s (1–3) having a phenylene or a biphenylylene group and alkyl groups with various length, containing 6 to 22 carbon atoms, were investigated by means of 13C NMR spectroscopy as a function of temperature. The observed range of temperature covers the “crystal‐to‐liquid‐crystal” phase transition temperature, Tm. It was found that these phase transitions are caused by an increase of the motions of aromatic or alkyl groups in the side chain, depending on the samples, and that the motion of main chains of polymers 1–3 with α‐helical conformation does not occur on the NMR time scale at least up to 160°C. The degree of the mobility of the alkyl chain in the side chain of 1–3 depends on their length above Tm.
Gradient high performance liquid chromatography of polymers, 1. Characterization of the products obtained by grafting methyl methacrylate onto ethylene‐propene‐diene rubber by SEC‐HPLC cross fractionation using evaporative light scattering detection
Authors: Augenstein Michael , Stickler Manfred 
Published: April 2003

AbstractThe products of the grafting reaction of methyl methacrylate (MMA) onto ethylenepropene‐diene rubber (EPDM) were characterized by size exclusion chromatography (SEC) and gradient HPLC to give detailed information about the grafting parameters. Evaporative light scattering detection (ELSD) was used for the quantitative evaluation of the HPLC runs. Gradient elution was shown to fractionate the grafting products according to chemical composition. By means of SEC‐HPLC cross fractionation the two‐dimensional distribution of chemical composition and molecular weight (CCMWD) was established qualitatively.
The use of low‐molecular‐weight model compounds in an investigation of polyelectrolytes, 2. Potentiometric properties of poly[(methacrylic acid)‐co‐(2‐dimethylaminoethyl methacrylate)] and its quaternary ammonium salt
Authors: Přádný Martin , Holata Jan , Ševčík Stanislav 
Published: April 2003

AbstractThe potentiometric behaviour of two polyampholytes, poly[(methacrylic acid)‐co‐(2‐dimethyl‐aminoethyl metharylate)] and poly{(methacrylic acid)‐co‐[2‐(methacryloyloxy)ethyltrimethyl‐ammonium iodide]} is described. The dissociation constants of low‐molecular‐weight compounds modelling the structural units and diads of polyampholytes are reported, and effects of adjacentgroups on the potentiometric behaviour of the copolymers are discussed.
Synthesis of polyorganosiloxanes with imidazolyl groups in the side chain
Authors: Nemoto Nobukatsu , Yotsuya Tadashi , Aoyagi Shigenobu , Ueno Yukihiko , Ikeda Koji , Takamiya Nobuo 
Published: April 2003

AbstractAn imidazolyl ring was introduced into the side chain of poly(3‐chlorocarbonylpropylmethyl‐siloxane) (4) by esterification with 4(5)‐hydroxymethylimidazole (1), the imino group being protected during esterification by the 2‐nitrobenzyl group which can be easily cleaved by UV light irradiation without attacking the main chain. The photolytic cleavage of the 2‐nitrobenzyl group was completed with a yield of ≈ 100% after 2 h without any remarkable side reaction. The polyorganosiloxanes (6), with a high content of imidazolyl groups in the side chain, are slightly soluble in hot DMSO and DMF. From this fact, in addition to the result of the measurement of Tg, it is suggested that very strong intermolecular hydrogen bonds are operating.
Liquid‐crystalline polyimides, 1. Thermotropic poly(ester‐imide)s derived from 4‐hydroxyphthalic acid, 4‐aminophenol and various aliphatic α,ω‐diacids
Authors: de Abajo Javier , de la Campa José , Kricheldorf Hans R. , Schwarz Gert 
Published: April 2003

AbstractPoly(ester‐imide)s with a regular sequence of aliphatic spacers and aromatic imide mesogens were prepared in two ways. Either aliphatic α,ω‐diacids were condensed with an acetylated diphenol derived from 4‐hydroxyphthalic acid and 4‐aminophenol, or aliphatic α,ω‐diacid dichlorides were condensed with the silylated diphenol. The resulting poly(ester‐imide)s were characterized by elemental analyses, viscosity measurements, microscopy under polarized light, DSC‐ and WAXS measurements. All poly(ester‐imide)s are crystalline materials with a layered supermolecular structure in the solid state. Above the melting point a nematic mesophase exists over a broad temperature range. A pronounced odd‐even effect was found for the temperature of isotropization, but not for the melting points.
Studies on the kinetics and initiation mechanism of acrylamide polymerization using persulfate/aliphatic diamine systems as initiator
Authors: Guo Xin Qiu , Qiu Kun Yuan , De Feng Xin 
Published: April 2003

AbstractThe effects of various aliphatic diamines on vinyl polymerization using ammonium persulfate as initiator were studied. It was found that diamines with two amino groups separated by an ethylene unit possess higher promoting activities than those with two amino groups linked by other α,ω‐alkylene units such as methylene or propylene. The promoting activities of diamines on vinyl polymerization are in the order: tertiary diamine > secondary diamine > primary diamine. The methyl group is a preferred substituent at the amino groups of the diamine, being faster oxidized by persulfate (to produce the dialkylaminomethyl free radical) than the α‐methylene groups. The primary free radicals produced through redox‐reaction of persulfate and aliphatic diamines were studied using the spin trapping technique and ESR spectroscopy. An initiation mechanism of persulfate/aliphatic diamine systems is proposed.