bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sequence distribution of poly(ether‐sulfone)/poly(ether‐ketone) copolymers by mass spectrometry and 13C NMR
Authors: Montaudo Giorgio , Montaudo Maurizio S. , Puglisi Concetto , Samperi Filippo 
Published: April 2003

AbstractThe sequence distributions of four poly(ether‐sulfone)/poly(ether‐ketone) (PES/PEK) copolymer samples were determined by means of fast atom bombardment mass spectrometry (FAB‐MS) and by 13C NMR spectroscopy. The controlled partial degradation of the copolymer chains to produce oligomers suitable of FAB‐MS analysis was performed with sodium methoxide in dimethyl sulfoxide solution at 130°C, and the experimental conditions were optimized. The sequential arrangements of ether‐sulfone/ether‐ketone units present in these materials were estimated by a best‐fit minimization method using the MACO4 computer program which compares the experimental FAB‐MS spectral intensities with theoretical intensities. Random PES/PEK copolymer samples showed quite the same sequence arrangements as expected from monomer feed‐ratios used in the syntheses. Instead, a PES/PEK copolymer sample expected to be exactly alternating (from the synthesis procedure) showed 44% of random sequences owing to the transetherification reaction which occurred in the synthesis. The results of sequential analysis obtained from 13C NMR data compare well with the data obtained by the FAB‐MS analysis.
Initiation of polymerization with substituted ethanes, 13. Free radical polymerization of methyl methacrylate and styrene with substituted succinonitriles
Authors: Braun Dietrich , Skrzek Thomas , Steinhauer‐Beißer Susanne , Tretner Hartmut , Lindner Hans Jörg 
Published: April 2003

AbstractTetraarylsuccinonitriles 2 were synthesized via oxidative dimerization of diarylacetonitriles 1 in basic media. The thermal decomposition of 2 results in two identical diarylcyanomethyl semi‐radicals 3. The dissociation energy (Ea) measured using the thiophenol radical scavenging technique was found to amount to 94,3 ± 9,2 kJ/mol in the case of tetraphenylsuccinonitrile 2a. Tetraarylsuccinonitriles 2 show an atypical “stepwise” initiation mechanism in free‐radical polymerization, particularly in the case of methyl methacrylate (MMA) as monomer. In the initial phase of the polymerization reaction a very high concentration of diarylcyanomethyl primary radicals 3 leads to the formation of short‐chain telechelics with both end groups originating from the initiator. In the further course of the polymerization these MMA telechelics are able to re‐form radicals by the scission of thermolabile carbon‐carbon bonds and by the release of initiator end groups, and so the MMA telechelics ‘re‐initiate’ the free‐radical polymerization (“resuscitable free‐radical polymerization”). In styrene polymerization, tetraarylsuccinonitriles 2 indeed cause a pronounced primary radical termination effect, but the styrene telechelics formed in contrast to MMA telechelics are thermostable, and therefore no “re‐initiation” effect occurs. The X‐ray structure determination of the styrene telechelic 2,2,3,5,5‐pentaphenyladiponitrile 4a exhibits a bond length of the thermolabile carbon‐carbon bond of 158,7 pm as compared to 162,8 pm of the corresponding MMA telechelic 2,2,5,5‐tetraphenyl‐3‐methoxycarbonyl‐3‐methyladiponitrile and emphasizes the higher thermal stability of 4.
Polymerizable tautomers, 11. Tautomerism and polymerization of p‐vinylbenzoylacetone
Authors: Masuda Seizo , Tomida Tahei , Tanaka Masami , Asahi Yutaka 
Published: April 2003

AbstractSolvent effects on tautomerism and polymerization of p‐vinylbenzoylacetone (1) were studied. 1 exhibits the coexistence of the ketonic and enolic forms (the latter is pedominant), and the tautomeric equilibria shift with the solvents. Multiparametric regression analysis of the tautomeric constants reveals that the equilibria depend on polarity and hydrogen bond donor acidity of the solvents. On the other hand, the polymerization of 1 is not affected by the solvents. The polymerization of 1 conforms to the conventional model (rule of square root). Monomer reactivity ratios r1 = 2,56 and r2 = 0,32 were obtained in the copolymerization of 1 (M1) and styrene (M2) in benzene.
Characterization and kinetics of mesophase transition for naphthalene‐based thermotropic polyesters with polymethylene spacers
Authors: Liu Shur‐Fen , Lee Yu‐Der 
Published: April 2003

AbstractMain‐chain thermotropic polyesters containing naphthalene rings and flexible spacers with 2 ≤ n ≤ 10 methylene groups were prepared in this study. Their thermotropic properties were investigated by means of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The nematic mesophase dominates the anisotropy of the prepared polymers except for the polymers with n = 7 and n = 9. Moreover, the nematic domain size depends upon the number n. On the other hand, the naphthalene ring in the mesogen has a strong effect on the mesomorphic properties of the prepared polyesters. The polymers with n = 7 and n = 9 exhibit cooling rate‐dependent anisotropic behavior of nematic and smectic phases. The crystallization for the investigated polymers is strongly influenced by the anisotropic behavior. The kinetics of crystallization at higher temperatures does not satisfy the Ozawa theory, while it does at lower temperatures. Nucleation begins to occur in the nematic shreads and the crystal growth proceeds toward liquid‐crystalline domains from the observation by POM. Thus, the Avrami exponent a is dependent upon the polymethylene spacer with n being even or odd and high or low. In addition, the parameters of crystallization obtained from DSC and X‐ray diffraction were consistent with the results of non‐isothermal crystallization kinetics and the observation by POM.
Synthesis and properties of liquid‐crystalline AB‐block copolymers poly[6‐(4′‐methoxy‐4‐biphenylyloxy)hexyl methacrylate]‐block‐polystyrene
Authors: Van de Velde Kathleen , Van Beylen Marcel , Ottenburgs Raoul , Samyn Celest 
Published: April 2003

AbstractLiquid‐crystalline AB‐block copolymers poly[6‐(4′‐methoxy‐4‐biphenylyoxy)hexyl methacrylate]‐block‐polystyrene were synthesized by direct coupling of the homopolymers with functional end groups. Like the liquid‐crystalline homopolymer with mesogenic units in the side chain, all block copolymers show a nematic mesophase. The transition temperatures are hardly affected by the composition and molecular weight of the block copolymers.
Synthesis and characterization of alternating copolyimides containing two different diimide units
Authors: Rhee Suh Bong , Park Ji‐Woong , Moon Bong Seok , Lee Myong‐Hoon , Chang Ji Young 
Published: April 2003

AbstractSoluble and stable precursors of aromatic imidodiamines were prepared and employed in polymerization reactions with aromatic dianhydrides to yield poly(amic acid ester)s. Thermal imidization of the polymers produced strictly aromatic copolyimides. The reaction of pyromellitic dianhydride (PMDA, 1c), 3,3′,4,4′‐ biphenylteracarboxylic dianhydride (BPDA, 1a), or 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA, 1b) with isopropyl alcohol produced a mixture of isomeric esters. These isomer mixtures were employed in amidation reactions without further separation. Direct amidation with ethyl chloroformate was employed. The acids were reacted with ethyl chloroformate in tetrahydrofuran and the resulting solutions were added slowly to solution of excess 1,4‐ or 1,3‐phenylendediamine in tetrahydrofuran. The reaction of diamines 5a–f with dianhydrides yielded poly(amic acid ester)s. The poly(amic acid ester)s were more stable against depolymerization during storage in solution compared with the corresponding poly(amic acid)s. Alternating copolyimides 6–11 had two different diimide units derived from PMDA (1c), BPDA (1a), or BTDA (1b). In differential scanning calorimetry (DSC) analyses, alternating copolyimides 7,9 and 11 containing 1,3‐phenylenediamine units exhibited distinct and reproducible glass transition temperatures, which were a little lower than the average values of corresponding homopolyimides and those of random copolyimides. But alternating copolyimides 6, 8, and 10, which contain 1,4‐phenylenediamine units, showed very weak glass transitions.
Influence of branch length on the dynamic fatigue properties of short‐chain branched polyethylenes
Authors: Yeh Jen‐taut , Hong Huei‐song 
Published: April 2003

AbstractAn investigation of the influence of the short‐chain branch length on the dynamic fatigue behavior of short‐chain branched polyethylenes (SBPE) is reported. The number of fatigue failure cycles (Nf) increases significantly with increasing branch length at temperatures above the β‐transition of SBPE polymers. In addition, an examination of the fracture surfaces of these specimens indicates a transition to a more ductile‐type behavior when specimens are associated with larger branch lengths. Detailed characterization shows that these SBPEs have approximately the same molecular weight, molecular weight distribution, branch frequency, crystallinity or microstructure but different branch length. The difference in branch length is suggested to be responsible of the dramatic change in Nf and in the morphology of the fracture surface at temperatures above the β‐transition of SBPEs. In contrast, no significant change in Nf and in the morphology of the fracture surface were found with increasing branch length at temperatures near or below the β‐transition. This dramatic change in the effect of short‐chain branches on Nf and on the morphology of the fracture surface are attributed to the change in the molecular relaxation motion at temperatures near the β‐transition of SBPE polymers.
Sequence ordered copoly(arylester‐carbonate)s: synthesis and characterization
Authors: Shaikh Abbas‐Alli G. , Sivaram Swaminathan 
Published: April 2003

AbstractA new class of ester‐carbonate monomers was prepared by reaction of monomethylcarbonate of bisphenol‐A with tere/isophthaloyl chloride. Self polycondensation of these monomers in presence of titanium tetraisopropoxide as catalyst resulted in the formation of copoly(arylester‐carbonate)s having an ester to carbonate ratio of 2: 1. Copoly(arylester‐carbonate)s rich in either carbonate groups were also prepared by copolymerization of ester‐carbonate monomer with dimethyl terephthalate and the bismethylcarbonate of bisphenol‐A. The polymer structure was established by 1 H NMR and IR spectroscopy. The ordered sequence of estercarbonate groups in the polymer was established by 13C NMR spectroscopy.
Miscibility and morphology of AB/C‐type blends composed of block copolymer and homopolymer or random copolymer, 1. Polyisoprene‐block‐poly(methyl methacrylate)/modified polystyrene blends
Authors: Jiang Ming , Huang Tianzi , Xie Jingwei 
Published: April 2003

AbstractThe miscibility and morphology of AB/C‐type blends composed of polyisoprene‐block‐poly(methyl methacrylate) [PI‐b‐PMMA] and a modified polystyrene with hydroxyl‐containing units [PS(OH)] has been studied by transmission electron microscopy (TEM). In the blends the density of hydrogen bonding between C and B block is adjustable. The miscibility and morphology of the blends cast from toluene, which is inert to hydrogen bonding, are found to depend on the hydroxyl content in PS(OH). Immiscibility between PMMA blocks and PS(OH) alters to miscibility when the hydroxyl content in PS(OH) reaches 1,6 mol‐%. Little effect of the relative molecular weight of PS(OH) to that of the PMMA block is found, which is different from that for AB/A‐type blends. An apparent effect of the casting solvent on the miscibility and morphology is observed. Being a proton‐acceptor solvent, tetrahydrofuran (THF) considerably decreases the miscibility, and a homogeneous microphase structure appears only when the hydroxyl content reaches 10 mol‐%. This implies that the main driving force for the miscibility between PS(OH) and PMMA blocks is hydrogen bonding between hydroxyl groups of PS(OH) and carbonyl groups of PMMA.
Miscibility and morphology of AB/C‐type blends composed of block copolymer and homopolymer or random coploymer, 2. Blends with random copolymer effect
Authors: Jiang Ming , Huang Tianzi , Xie Jingwei 
Published: April 2003

AbstractThis work is an extension of the concept of miscibility window in homopolymer/random copolymer blends to blends containing block copolymers. The miscibility and morphology of THF‐cast blends composed of the block copolymer polyisoprene‐block‐poly(methyl methacrylate) (Pl‐b‐PMMA) and the random copolymer poly(styrene‐ran‐acrylonitrile) (SAN) (22 wt.‐% AN) has been studied by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). Most blends show miscibility between PMMA blocks and SAN, presenting a homogeneous microdomain structure. Coupling of macrophase separation occurs only when the ratio of molecular weights of SAN to the PMMA bock is very large and SAN becomes the dominant component. The excellent miscibility in the block copolymer/random copolymer blends can be understood by considering that the monomer unit composition of SAN is within the miscibility window in PMMA/SAN blends. The main driving force for the miscibility is repulsion between S and AN units rather than hydrogen bonding between SAN and PMMA, since a proton‐acceptor type solvent does not show any effect on the miscibility in the blends. Apparent broadening of the glass transition of the ‘hard phase’ is observed and explained with the aid of the segment density gradient model.
Rheo‐optical FT‐Raman study of uniaxially stretched poly(vinylidene fluoride)
Authors: Rodríguez‐Cabello José Carlos , Merino Juan Carlos , Pastor José María , Hoffmann Uwe , Okretic Stephano , Siesler Heinz Wilhelm 
Published: April 2003

AbstractA Fourier‐transform Raman‐sepectroscopy‐based rheo‐optical system was used to study the process of uniaxial stretching of poly(vinylidene fluoride) (PVF2). This rheo‐optical system made possible to reduce the rate of stretching and favoured the acquisition of a higher number of spectra in different mechanical stages during the stretching process. Those can be the eleastic zone or the formation of the neck. Thus, it has been possible to establish that the stretching‐induced phase transition in PVF2 takes place in the beginning of the neck formation. Shortly after the neck development that transition has reached its maximum extent. The performance of the transition was highly temperature dependent. As the temperature of stretching increases, the extent of the transition decreases. Along with this permanent modification of the sample structure, other transient modifications were found. High resolution spectra of the phase β of loaded PVF2 showed a wavenumber shift of specific absorption bands. These band shift have been interpreted as a deformation of the geometry of the bonds reflected by the absorption band. This bands with high contribution of skeletal CC bonds suffered the highest band shift, suggesting that these bonds were most sensible to the applied load. This band shift and, consequently, bond deformation immediately vanished after removal of the load.
Anisotropy in electrical conduction of polypyrrole/polyethylene composite films by drawing
Authors: Kurachi Kouichirou , Kise Hideo 
Published: April 2003

AbstractPolypyrrole/polyethylene composite films were prepared by vapor phase polymerization of pyrrole on porous polyethylene films using iron(III) chloride as an oxidant. By drawing the films before or after the polymerization of pyrrole, anisotropy in electrical conduction was observed parallel and perpendicular to the drawing direction. The effects of drawing on the conductivity and the mechanism of conduction are discussed in terms of the temperature dependence of the conductivity.
Mass spectrometric characterization of a 2,2‐bis[4‐(2,3‐epoxypropoxy)phenyl]propane‐aniline addition polymer and its telechelic prepolymers
Authors: Klee Joachim E. , Hägele Klaus , Przybylski Michael 
Published: April 2003

AbstractFast‐atom bombardment (FAB) and plasma desorption mass spectrometry of high molecular weight addition polymers of 2,2‐bis[4‐(2,3‐epoxypropoxy)phenyl]propane (DGEBA) and aniline show protonated molecular ions of the intact polymer and oligomer molecules. The oligomeric products consist mainly of cyclooligomers. Their formation can be observed during the polymerization reaction. Telechelic prepolymers having epoxide end groups as well as telechelics containing amino end groups were found with lower degree of polymerization in the mass spectra. Side reactions such as ether formation or epoxide polymerization were not observed. Telechelic DGEBA‐aniline prepolymers are shown to consist of a series of oligomers as shown by highpressure liquid chromatography (HPLC) analyses. Consequently, the FAB mass spectra of the prepolymers show molecular ions of the different oligomers. Furthermore, under the conditions of the FAB mass spectrometric analysis fragmentation of the prepolymers to iminium fragment ions was observed.
Ring‐opening metathesis polymerization of 7‐phenylnorbornadiene and benzonorbornadiene
Authors: Hamilton James G. , Rooney John J. , Snowden David G. 
Published: April 2003

AbstractRing‐opened metathesis polymers of 7‐phenylnorbornadiene and benzonorbornadiene have been prepared using a variety of catalysts based on Ru, Os, Ir, W and Mo chloride salts and complexes. Detailed 13C and 1H NMR spectra of these materials and their corresponding hydrogenated derivatives have been obtained and analysed for information concerning tacticities and fractions of cis double bonds (σc). The behaviour of 7‐phenylnorbornadiene is similar to that of 7‐methylnorbornadiene in that a strong preference for the anti over the syn mode of monomer insertion is observed in contrast to 7‐tert‐butoxynorbornadiene which shows little or no regioselectivity. Pronounced effect on σc are also observed using the OsCl3 catalyst as expected from previous experience of ring‐opening metathesis polymerization (ROMP) systems containing chelating dienes and this catalyst. Weaker effects of this type due to complexation of monomer as a spectator ligand are also indicated for the polymerization of benzonorbornadiene; these are also compared to the effects of using Michael acceptor additives in metathesis systems.
Tensions superficielles de copolymères méthacryliques perfluoroalkylés
Authors: Guery‐Rubio Claudine , Viguier Michel , Commeyras Auguste 
Published: April 2003

AbstractThe surface properties of methacrylic copolymers with a random distribution of perfluoroalkyl pendent groups were studied by a tensiometric method and were found to depend on the concentration of fluorinated units (2‐hydroxy‐4,4,5,5,6,6,7,7,8,8,9,9,9‐tridecafluorononyl methacrylate (1)), and the nature of the non‐fluorinated methacrylic ester (methyl, butyl, stearyl). The surface tensions estimated by various approaches (critical surface tension, geometric and harmonic mean approximations) are very low (11 mN · m−1 < y < 12 mN · m−1). The surface tension of the copolymers drops drastically when a few percent of fluorinated units are incorporated into the polymeric chain. The wetting hysteresis, observed particularly in the case of water, could be due to the mobility of macromolecular chains at the interface, leading to a reorganization of fluorinated groups in order to minimize the interfacial energy.
Ordering of liquid crystalline solutions of rigid‐rod aramids using mechanical shearing and electric‐field poling
Authors: Weder Christoph , Glomm Bernhard H. , Neuenschwander Peter , Suter Ulrich W. 
Published: April 2003

Abstract2′,5′‐Diamino‐4‐(dimethylamino)‐4′‐nitrostilbene was polymerized with terephthaloyl dichloride and 2,6‐difluoroterephthaloyl dichloride in a low‐temperature solution polycondensation to give two novel, fully aromatic rigid‐rod polyamides. Nematic solutions of these polymers were processed into fibers and films that were characterized by wide‐angle X‐ray diffraction measurements. A post‐spin annealing process was employed to enhance the chain orientation in the fibers. The dominating crystal structure was found to be similar to “modification II” of the fibers from poly(p‐phenyleneterephthalamide), but the fibers do not suffer a comparable structural transformation upon heat treatment. A corona‐discharge poling process gave rise to a remarkable gain in average chain orientation in the films. Again the crystal structure was found to be similar to “modification II”. The aramids investigated in this work represent a new approach to the design of liquid‐crystalline rigid‐rod polymers, where different mechanisms of orientation can be combined. In the nematic phase, the rigid‐rod molecules form highly oriented domains that can be oriented using mechanical processes such as shearing. In addition the stilbene units that are fixed in the polymer backbone with their dipole moments oriented transverse to the main chain can be oriented in an electric field. The combination of both orientation mechanisms seems to cause a synergistic effect, probably since each affects different levels of the polymer microstructure in the solid.
Radical ions of poly(phenylsilyne) and poly(phenylgermyne)
Authors: Watanabe Akira , Komatsubara Tadaharu , Matsuda Minoru , Yoshida Yoichi , Tagawa Seiichi 
Published: April 2003

AbstractPoly(phenylsilyne) and poly(phenylgermyne), which have a network Si‐ and Ge‐skeleton, were synthesized by electrochemical reduction of trichlorophenylsilane and trichlorophenylgermane, respectively. The poly(phenylsilyne) showed broad absorption and emission bands that are characteristic of silicon network polymers. Similarly broad absorption and emission bands were observed for the poly(phenylgermyne). Radical anions and radical cations of poly(phenylsilyne) and poly(phenylgermyne) were produced by pulse radiolysis. The radical ions of these network polymers showed broad transient absorption bands from the UV to the IR region. Within 200 ns after pulse radiolysis, the absorption band of the radical cation in the UV region decreased, whereas the band in the IR region increased. The time‐dependent spectral change of the radical cation suggests the formation of a change resonance band of the delocalized positive charge on the σ‐conjugated polymer chain. In contrast to the radical cation, the radical anion of the network polymers did not show a spectral change.
Concentration quenching of photoluminescent Ru(bpy) dispersed in a polysiloxane film containing 2,2′‐bipyridine pendant groups in dependence of molecular distribution
Authors: Nagai Keiji , Ueno Yukihiko , Takamiya Nobuo , Kaneko Masao 
Published: April 2003

AbstractThe photoluminescent Ru(bpy) complex was dispersed in a polysiloxane film containing 2,2′‐bipyridine (bpy) pendant groups. The unusually long photoluminescence lifetime of the Ru(bpy) (1,94 μs at 25°C) and the blue‐shifted photoluminescent wavelength suggest a rigid polymer matrix. The fluorescence yield becomes lower with higher probe concentration, indicating concentration quenching. According to the analysis based on Stern‐Volmer plots, the quenching obeys a mechanism composed of both static and dynamic processes. A statistical intermolecular distance distribution between the probes was used to interpret the results in terms of static and dynamic quenching. It is shown that in the present system the dispersed complexes diffuse slightly during the excited state.