bluuebunny/crossref_metadata_2025_split huggingface dataset:
New polymer syntheses, 88. Thermosetting cholesterin oligocarbonates with propargyl endgroups
Authors: Kricheldorf Hans R. , Sun Shih‐Jieh 
Published: April 2003

AbstractThermosetting cholesteric oligocarbonates were prepared by polycondensation of mesogenic diphenols such as 4,4′‐dihydroxybiphenyl (DHB) or hydroquinone 4‐hydroxy‐benzoate (HQHB; system. name: 4‐hydroxyphenyl 4‐hydroxybenzoate) with methylhy‐droquinone and isosorbide. Trichloromethyl chloroformate served as condensing agent and propargyl alcohol (system. name of propargyl: 2‐propynyl), 4‐propargyloxybenzoyl chloride or 6‐propargyloxy‐2‐napthoyl chloride served as chain stoppers. Most oligocar‐bonates form a cholesteric phase over a broad temperature range. Depending on the mole fraction of isosorbide these oligocarbonates form Grandjean textures when sheared in the molten state.
A new theoretical formula for the determination of the copolymer composition distribution measured by gel permeation chromatography
Authors: Xu Jian , Wu Guanying , Sun Yufeng , Shen Yibing 
Published: April 2003

AbstractA new theoretical formula, used for the determination of the chemical composition distribution of copolymers, is proposed in this paper. The composition distribution of styrene in chlorinated butyl rubber/polystyrene comb graft copolymer was obtained by gel permeation chromatography utilising a combination of refractive index and ultraviolet detection. It is a more convenient and time‐saving method for the characterization of the molecular structure parameters of a copolymer compared to the conventional experimental method.
Synthesis of silsesquioxanes having photochromic diarylethene pendant groups
Authors: Nakashima Hisataka , Irie Masahiro 
Published: April 2003

AbstractSilsesquioxanes having 1‐(2‐methylbenzo[b]thien‐3‐yl)‐2‐[5‐(4‐butylphenyl)‐2,4‐dimethylthien‐3‐yl]perfluorocyclopentenes as the pendant groups were synthesized. Photochemical conversion from the open‐ring to the closed‐ring form of diarylethenes chemically bonded to polymers was by 15–25% lower than the conversion of the chromophores dispersed in the same matrix. No appreciable difference in the photoconversion of the fixed chromophores was observed below and above the glass transition temperature (Tg) of the polymer films.
Microsphere synthesis by dispersion copolymerization of methyl methacrylate with poly(acrylic acid) macromonomers: pH effect on microsphere formation
Authors: Ishizu Koji , Yamashita Masao , Ichimura Ayako 
Published: April 2003

AbstractThe pH effect on microsphere formation in the dispersion copolymerization of methyl methacrylate with vinylbenzyl‐terminated poly(acrylic acid) (PAA) macromonomers is studied. The diameter of poly(methyl methacrylate) (PMMA) microspheres is minimum around pH = 8. Dynamic light scattering data indicate that the shell thickness of PAA‐grafted chains shows a maximum around this pH. The degree of expansion of PAA chains drastically affects the particle size of PMMA microspheres during the dispersion copolymerization.
Gel permeation chromatographic determination of activation rate constants in nitroxide‐controlled free radical polymerization, 2. Analysis of evolution of polydispersities
Authors: Fukuda Takeshi , Goto Atsushi 
Published: April 2003

AbstractThe dissociation rate constant kd of the PS‐TEMPO adduct, where PS is polystyrene and TEMPO is 2,2,6,6‐tetramethylpiperidin‐1‐oxyl, was determined by the gel permeation chromatographic tracing of the evolution of polydispersities at an early stage of styrene polymerization with a model PS‐TEMPO adduct as initiator. The results agree with those obtained by the direct method in Part 1.
Chiral ethylenebis(4,5,6,7‐tetrahydro‐1‐indenyl) complexes of zirconium and hafnium: separation and application to asymmetric polymerization
Authors: Habaue Shigeki , Sakamoto Hiroshi , Baraki Hideo , Okamoto Yoshio 
Published: April 2003

AbstractOptical resolution of ethylenebis(4,5,6,7‐tetrahydro‐1‐indenyl) complexes of zirconium and hafnium was performed by using cellulose tris(3,5‐dimethylphenylcarbamate) coated on silica‐gel (Chiralcel OD) as a chiral stationary phase for HPLC. The biphenyl‐2,2′‐diolate complexes were completely resolved with the highest separation factor. The isolated enantiomerically pure hafnocenes were applied for the asymmetric cyclopolymerization of 1,5‐hexadiene.
Pressure effects on termination mechanisms during ethene polymerization catalyzed by dicyclopentadienylzirconium dichloride/methylaluminoxane
Authors: Thorshaug Knut , Rytter Erling , Ystenes Martin 
Published: April 2003

AbstractPolymerization of ethene catalyzed by dicyclopentadienylzirconium dichloride/methylaluminoxane was performed in toluene at 50°C under 0.38–8.95 bar ethene. Both Fourier‐transform infrared spectroscopy and gel‐permeation chromatography showed that the molecular weight is independent of the ethene pressure (concentration). The trans‐vinylene unsaturation content increased as the pressure decreased. Termination by β‐H transfer to a coordinated monomer and a kinetically controlled isomerization reaction are suggested, in order to explain the observations.
Preparation of amphiphilic networks by Diels‐Alder reactions between oligo(butyl methacrylate) with furan end‐groups and a poly(ethylene oxide‐co‐acetylenedicarboxylate)
Authors: Delerba Mark , Ebdon John R. , Rimmer Stephen 
Published: April 2003

AbstractA butyl methacrylate oligomer with furan end‐groups was synthesized by ozonolysing a poly(butyl methacrylate‐co‐butadiene) latex. The end‐groups of this oligomer were amidated with aminomethylfuran to give a coagulated mass of derivatized oligomers. This furan functional oligomer was then mixed with poly(ethylene oxide‐co‐acetylenedicarboxylate) and heated at 60°C or 125°C. The material cured at 125°C was found to contain a higher gel fraction (55 wt.‐%) than that cured at 60°C (30 wt.‐%).
Static density gradient centrifugation; extended Hermans‐Ende equation
Authors: Lechner M. Dieter 
Published: April 2003

AbstractAn extended Hermans‐Ende equation for real solutions has been derived in order to calculate the density as a function of the radial distance in a density gradient mixture (light/heavy medium) inside an ultracentrifugal cell. The equation has been tested with equilibrium density gradient measurements of the system water/metrizamide/polystyrene latex where metrizamide is the heavy medium. The solvent compositions were 8 to 15 mass‐% metrizamide (2‐(3‐acetamido‐5‐N‐methylacetamido‐2,4,6‐triiodobenzamido)‐2‐deoxy‐D‐glucose). The latex concentration was 0.03 mass‐%. It is demonstrated that the density gradient is highly influenced due to monideality effects with respect to the solvent composition and due to the pressure gradient in the ultracentrifuge.
Carboxy‐terminated homo‐ and copolymers of styrene using dicarboxylic acid‐functional azo initiator and 2,2,6,6‐tetramethyl‐1‐piperidyloxyl (TEMPO)
Authors: Baumert Martin , Mülhaupt Rolf 
Published: April 2003

AbstractCarboxy‐terminated polystyrene, poly(styrene‐co‐acrylonitrile), and polystyrene‐block‐poly(styrene‐co‐acrylonitrile) with ratios of weight‐ to number‐average molar masses M̄w/M̄n below 1.3 were synthesized via a controlled radical polymerization mechanism. The polymerizations were initiated with 4,4′‐azobis(4‐cyanopentane‐carboxylic acid) and 2,2,6,6‐tetramethyl‐1‐piperidyloxyl radical and conducted in bulk at elevated temperatures. The polymerization was monitored by nuclear magnetic resonance, size‐exclusion chromatography, end‐group titration and differential scanning calorimetry.
Study of molecular size in ethylene‐propene copolymerization with zirconocene and hafnocene catalysts
Authors: Naga Naofumi , Ohbayashi Yoshiaki , Mizunuma Kooji 
Published: April 2003

AbstractEthylene‐propene copolymerization was carried out with Cp2MCl2 (Cp = cyclopentadienyl), rac‐Et(Ind)2MCl2, rac‐Me2Si(Ind)2MCl2 (Et = ethylene, Me2Si = dimethylsilyl, Ind = indenyl, M = Zr or Hf)/methylaluminoxane. In the case of using ansa‐hafnocenes, the minimum molecular size (extended chain length) of ethylene‐propene copolymer was obtained at about 50 mol‐% of propene content in the copolymer. The polymerization activity decreased with increase of propene feed ratio in non‐bridged non‐specific metallocenes. Higher polymerization activities were observed for the copolymerization compared to ethylene and propene homo‐polymerization with ansa‐isospecific metallocenes. The factor of molecular size lowering was studied by the chain propagation and chain transfer reaction.
Enhanced velocity of surfactant binding after the volume collapse of an oppositely charged gel
Authors: Narita Tetsuharu , Gong Jianping , Osada Yoshihito 
Published: April 2003

AbstractThis paper is a kinetic study of the interaction between an ionic surfactant and an oppositely charged polymer gel. The volume collapse of the gel enhances substantially the velocity of surfactant uptake, despite the decreased free volume for diffusion. This indicates that the increased charge density of the polymer network accelerates the surfactant binding.
ESR study on SiO2‐supported half‐titanocene catalyst for syndiospecific polymerization of styrene
Authors: Xu Junting , Zhao Jian , Fan Zhiqiang , Feng Linxian 
Published: April 2003

AbstractMonocyclopentadienyltitanium trichloride (CpTiCl3) was directly immobilized on silica surface. The resulting CpTiCl3/SiO2‐MAO was investigated in view of its suitability for syndiospecific polymerization of styrene using ESR spectroscopy. Polymerization results show that both the syndiotacticity and the activity decrease upon immobilization. A possible explanation is that the active sites may become aspecific after immobilization and part of the immobilized active sites can be leached into the solution in the presence of MAO.
Alternating copolymerization of ethylene and 1‐octene with meso‐[dimethylsilylbis(2‐methyl‐1‐indenyl)]zirconium dichloride‐methylaluminoxane as catalyst system
Authors: Uozumi Toshiya , Miyazawa Kohji , Sano Tsuneji , Soga Kazuo 
Published: April 2003

AbstractCopolymerizations of ethylene and α‐olefins with homogeneous metallocene catalysts generally give the corresponding random copolymers with narrow molecular mass distributions. In this study, we have conducted the copolymerization of ethylene and 1‐octene with the meso‐Me2Si(2‐Me‐1‐Ind)2ZrCl2‐methylaluminoxane (MAO) catalyst system, and analyzed the microstructure of the resulting copolymers in detail. The content of the alternating [EO] sequence increases markedly with an increase in the feed ratio of 1‐octene to ethylene, reaching over 95% under appropriate copolymerization conditions. We have thus succeeded in preparing the first sample of alternating olefin copolymers.
End‐group evidence of zwitterionic species in the anionic polymerization of cyanoacrylates by Lewis bases
Authors: Costa Gianna , Loonan Conleth , Pepper David 
Published: April 2003

AbstractX‐ray fluorescence (XRF) spectra of poly(butyl cyanoacrylate) initiated, in tetrahydrofuran, by triphenylphospine and terminated by SO3, show the persistent presence of phosphorus and sulfur in the polymer, in near‐equivalent proportions, with the sulfur content partially removable by anion‐exchange. It is concluded that all chains have initial phosphonium groups, and, in abesence of any hydrolysis‐formed H2SO4, are macrozwitterions with terminal SO3−. Acid‐terminated chains should have proton‐capped ends and initial phosphonium+ · HSO4− ion‐pairs.
Simple methods for assessing the conformational sensitivity of infrared bands by dichroism
Authors: Ou‐Yang Wen‐Chung , Chen Hsin‐Lung 
Published: April 2003

AbstractIn characterizing the overall orientation of polymers by infrared (IR) dichroism, the orientation function must be obtained from the dichroic ratios of conformationally insensitive bands. Identification of such bands is thus necessary prior to the calculation of the orientation function. In this study, we devise two simple methods for evaluating the conformational sensitivities of IR bands from the measurement of the dichroic ratio. Both methods are based on the fact that the orientation function calculated by all conformationally insensitive bands should be identical, while this is not true for conformationally sensitive bands. Poly(ether ether ketone) (PEEK) is used as an example to demonstrate the use of these methods.
“Living” free radical copolymerization of styrene and N‐vinylcarbazole
Authors: Baethge Heike , Butz Sören , Schmidt‐Naake Gudrun 
Published: April 2003

AbstractPoly[styrene‐co‐(N‐vinylcarbazole)] copolymers with controlled molecular weights and narrow polydispersities were synthesized by nitroxide‐mediated “living” free radical copolymerization using an initiator/capping agent system consisting of benzoyl peroxide (BPO) and the stable nitroxyl radical 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO). The copolymerization behaves in a “living” fashion and allows the synthesis of poly[styrene‐co‐(N‐vinylcarbazole)]/polystyrene block copolymers via a controlled chain‐extension reaction of the prepared copolymers with styrene.
Saccharide modified silica particles by enzymatic grafting
Authors: Loos Katja , von Braunmühl Volker , Stadler Reimund , Landfester Katharina , Spiess Hans Wolfgang 
Published: April 2003

AbstractThe surface of silica particles has been chemically modified with oligo‐ or poly‐(α,1←4)‐D‐glucopyranose (amylose) chains of various length by covalently attaching maltoheptaose derivatives to the solid support and enzymatic polymerization of glucose‐1‐phosphate with potato phosphorylase (E.C. 2.4.1.1) as catalyst. The characterization of the products by solid‐state NMR spectroscopy showed an interesting dependence of the linewidth with the grafting density of the glucan chains. The modified silica particles showed chiral discrimination in liquid chromatography.
Structural effects in poly(3‐alkylthiophene)s on the exposition to poor solvent
Authors: Caronna Tullio , Catellani Marinella , Luzzati Silvia , Meille Stefano Valdo , Romita Valeria 
Published: April 2003

AbstractThe exposure to pentane vapour of poly(3‐alkylthiophene)s with different alkyl chains produces a modification in the optical properties of the thin films. The treatment induces a red‐shift of the electronic absorption maximum and the appearance of vibronic structure in the UV spectra. We have followed these changes with IR and Raman spectroscopies to monitor the modification of the backbone conjugation, and with X‐ray diffraction to evidence the structural order of the chains.
Novel amphiphilic linear polymer/dendrimer block copolymer: Synthesis of poly(2‐methyl‐2‐oxazoline)‐block‐poly(amido amine) dendrimer
Authors: Aoi Keigo , Motoda Aki , Okada Masahiko , Imae Toyoko 
Published: April 2003

AbstractNovel linear polymer/dendrimer block copolymers, poly(2‐methyl‐2‐oxazoline)‐block‐poly(amido amine) dendrimers (water‐soluble full‐generation type 4 (G = 4.0 and 5.0) and amphiphilic half‐generation type 5 (G = 3.5, 4.5, and 5.5)), were synthesized by divergent‐growth dendrimer construction with ω‐ethylenediamine‐terminated poly(2‐methyl‐2‐oxazoline), which was prepared by living ring‐opening polymerization of 2‐methyl‐2‐oxazoline. Assembly of the amphiphilic dendrimer‐based block copolymer (G = 5.5) was investigated by surface tension measurements (critical micelle concentration, 0.49 wt.‐%) and by small‐angle neutron scattering analysis (spherical particles; assembled number, ca. 103).
Chain‐length dependent termination in pulsed‐laser polymerization, 2. On the prospects of determining the bimolecular termination constant kt from the second moment of the chain‐length distribution
Authors: Olaj Oskar Friedrich , Kornherr Andreas , Zifferer Gerhard 
Published: April 2003

AbstractThe correct (event weighted) average of kt, 〈kt〉, has been calculated for pseudostationary laser‐induced polymerization for a kinetic scheme with chain‐length dependent termination and compared to the average k̄t obtained by formally solving for kt the expression for the second moment of the chain‐length distribution valid for chain‐length independent termination (represented by the product of rate of polymerization νp and weight average degree of polymerization P̄w). It is shown that there is a fair agreement between the two quantities. This may be used to recover experimentally the power‐law governing the dependence of kt on chain‐length, especially its exponent.
Quinoxaline‐based conjugated polymers containing ruthenium(II) bipyridine metal complex
Authors: Ng Po King , Gong Xiong , Wong Wing Tak , Chan Wai Kin 
Published: April 2003

AbstractA series of novel quinoxaline‐based conjugated polymers which contain a ruthenium(II) bipyridine complex were synthesized by the Suzuki coupling reactions. UV/VIS spectroscopy showed that the spectral features of the polymers are dependent on the amount of metal complex present. Results from excitation and emission spectroscopy suggest an energy transfer between the backbone and the metal complex. The polymers exhibit hole carrier mobilities of ≈ 10−5 cm2 · V−1 · s−1, which is comparable to organic photoconductors.
Synthesis of well‐defined azido and amino end‐functionalized polystyrene by atom transfer radical polymerization
Authors: Matyjaszewski Krzysztof , Nakagawa Yoshiki , Gaynor Scott G. 
Published: April 2003

AbstractMono and difunctional polystyrenes containing active halogenated end groups were prepared by atom transfer radical polymerization (ATRP). Substitution reactions were explored to convert the halogen termini to azido groups, followed by readuction to form the amino functional polymer. Quantitative conversion of the end groups was observed in each transformation reaction. 1H NMR demonstrated the formation of the azide from the bromide functionality without elimination. The difunctional α,ω‐diaminopolystyrene was reacted with terephthaloyl chloride in a condensation process to produce chain‐extended polystyrene containing amide bonds along the polymer backbone.
Preparation and characterization of cyclic poly(oxypropylene)
Authors: Yu Ga‐Er , Sinnathamby Prash , Sun Tao , Heatley Frank , Price Colin , Booth Colin 
Published: April 2003

AbstractPoly(propylene glycol) [α‐hydro‐ω‐hydroxypoly(oxypropylene)] of number‐average molar mass M̄n ≈ 2000 g · mol−1 (PPG2000) was cyclised with high conversion (ca. 75%) by reaction with dichloromethane in the presence of powdered KOH. The cyclic product was separated from chain extended polymer by preparative GPC, giving an overall yield of polymer (M̄n ≈ 2000 g · mol−1, narrow molar mass distribution) in excess of 50%. Characterisation by analytical GPC and 13C NMR spectroscopy confirmed cyclisation. DEPT and 1H‐coupled NMR spectra were used to show that the links in cyclic poly(oxypropylene) were 77% single acetal, 12% double acetal and 11% triple acetal (or higher). This complexity probably results from competitive reaction with water introduced with KOH.
Self‐organization of ionic surfactants controlled by oppositely charged polyelectrolytes
Authors: Kabanov Victor A. , Zezin Alexander B. , Kasaikin Victor A. , Zakharova Julia A. , Litmanovich Ekaterina A. , Ivleva Elena M. 
Published: April 2003

AbstractFormation and structure of water‐soluble complexes of poly(acrylic acid) (PA) and poly(diallyldimethylammonium chloride) (PDADMAC) with oppositely charged surfactants: tetradecyltrimethylammonium bromide and sodium dodecylsulfate correspondingly have been studied by elastic and quasi‐elastic laser light‐scattering, high‐speed sedimentation and viscometry techniques. It was shown that minimum aggregation number of the surfactant ions in the complex micelle is controlled by the chemical nature of the polymer. A shift from dilute to semi‐dilute solution regime with respect to a free polyelectrolyte results in drastic rearrangement in PDADMAC‐SDS complex structure.
Interplay of chemical and physical factors in reacting polymer blends. Theoretical considerations
Authors: Platé Nikolay A. , Litmanovich Arkady D. , Kudryavtsev Yaroslav V. , Govorun Elena N. 
Published: April 2003

AbstractVarious effects produced by copolymers in polymer blends are discussed, with an emphasis on the role of interchain interactions. Simple theoretical models are considered to study the following problems: the interplay of diffusion and macromolecular reaction in compatible and incompatible blends, the stabilizing effect of premade diblock copolymer on the system of minor phase particles in incompatible blends, the kinetics of transesterification in a homogeneous blend. The effect of diblock copolymer on the Ostwald ripening in a polymer blend is stated in more details; the possibility of narrowing the size distribution of minor phase particles is predicted.
Molecular order and dynamics in block copolymers of poly(oxybutylene) and poly(oxyethylene)
Authors: Fragiadakis Daniel , Bouga Maria , Kyritsis Apostolos , Pissis Polycarpos , Viras Kyriakos , Mingvanish Withawat , Booth Colin 
Published: April 2003

AbstractBroadband dielectric spectroscopy (10−2‐109 Hz) was employed to investigate the dynamics of poly(oxybutylene) chains in solid semicrystalline poly(oxybutylene)‐poly(oxyethylene)‐poly(oxybutylene) (BEB) triblock copolymers. The results are compared with those obtained for B homopolymers, EB diblocks and EBE triblocks. The B blocks were dipole‐inverted in the homopolymers and the EBE triblocks, however not in the EB and the BEB copolymers. The segmental α relaxation, caused by local chain motion, and the normal mode relaxation, due to chain motions of larger length scale, were studied in detail with respect to time scale, relaxation strength and shape of the response. The α relaxation in the BEB copolymers shows similar behavior to that in the other three systems, whereas the normal mode relaxation shows characteristic differences in the four systems.
A meanfield approach to the thermodynamics of a protein‐solvent system with application to the oligomerization of the tumor suppressor p53
Authors: Noolandi Jaan 
Published: April 2003

AbstractThe thermodynamic stability and oligomerization status of the tumor suppressor p53 tetramerization domain have been studied experimentally and theoretically. A series of hydrophilic mutations at Met‐340 and Leu‐344 of human p53 were designed to disrupt the hydrophobic dimer‐dimer interface of the tetrameric oligomerization domain of p53. Meanfield calculations of the free energy of the solvated mutants as a function of interdimer distance were compared with experimental data on the thermal stability and oligomeric state [tetramer, dimer, or equilibrium mixture of both] of each mutant. The calculations predicted a decreasing stability and oligomeric state for the following amino acids at residue 340: Met [tetramer] > Ser Asp, His, Gin, > Glu, Lys [dimer], whereas the experimental results showed the following order: Met [tetramer] > Ser > Gln > His, Lys > Asp, Glu [dimers]. For residue 344, the calculated trend was Leu [tetramer] > Ala > Arg, Gln, Lys [dimer], and the experimental trend was Leu [tetramer] > Ala, Arg, Gln, Lys [dimer]. The discrepancy for the lysine side chain at residue 340 is attributed to the dual nature of lysine, both hydrophobic and charged. The incorrect prediction of stability of the mutant with Asp at residue 340 is attributed to the fact that within the meanfield approach, we use the wild‐type backbone configuration for all mutants, but low melting temperatures suggest a softening of the α‐helices at the dimer‐dimer interface. This initial application of meanfield theory toward a protein‐solvent system is encouraging for the application of the theoretical model to more complex systems.