bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectric relaxation spectroscopy of amorphous and liquid‐crystalline side‐chain polycarbonates
Authors: Wübbenhorst Michael , Van Koten Ernout M. , Jansen John C. , Mijs Wim , van Turnhout Jan 
Published: April 2003

AbstractThe molecular dynamics of amorphous and liquid‐crystalline (LC) side‐chain polycarbonates was studied by dielectric spectroscopy at frequencies from 10−2 to 106 Hz and at temperatures from −160 to 180°C. ‘Model’ compounds containing no mesogenic side‐groups showed two relaxations, which originate from the carbonate group (α, βm‐relaxation). By contrast, in LC‐polycarbonates bearing a mesogenic nitrostilbene side group around and above the glass transition temperature Tg up to three relaxation modes were distinguished (α‐, λ1‐, λ2‐process); below Tg four secondary relaxations (γ‐, βm‐, βs‐, βsc‐relaxation) were observed. The γ‐relaxation was found only in compounds possessing an aliphatic spacer linked to the backbone by an ether bond. Apart from βm‐, two additional β‐processes were identified as relaxations associated with the mesogenic unit in the glassy (βs) or in the crystalline state (βsc).
Synthesis of polymeric organic‐inorganic hybrid materials. Partially deacetylated chitin‐silica hybrid
Authors: Retuert Jaime , Nuñez Alicia , Martínez Francisco , Yazdani‐Pedram Mehrdad 
Published: April 2003

AbstractThis work reports the synthesis of a novel polymeric organic‐inorganic hybrid. The inorganic component is a silica network obtained by controlled hydrolysis of tetraethyl orthosilicate via sol‐gel process and the organic counterpart is partially deacetylated chitin (CHI). The resulting polymer hybrids were homogeneous transparent film forming glassy materials being compatible through a wide composition range. Simultaneous thermal analysis of a CHI/silica 1:1 mixture confirms the intermolecular complex formation between organic and inorganic polymers.
Refractive index decrease during photocrosslinking in photopolymers suitable for holographic recording
Authors: Nagata Akira , Sakaguchi Toru , Ichihashi Taichi , Miya Masaru , Ohta Koji 
Published: April 2003

AbstractPhotosensitive polymers of cyclobutane formation type have been found to show a decrease in their refractive indices with progress of photocrosslinking, when studied by the waveguide method. The decrease in refractive index is considered to be due to a decrease of exaltation in molar refraction. This phenomenon is of potential importance in holographic recording.
Synthesis and liquid crystal properties of bipyridine‐containing aromatic polyamides
Authors: Yu Sze Chit , Chan Wai Kin 
Published: April 2003

AbstractA series of novel aromatic polyamides containing 2,2′‐bipyridine moiety were synthesized by polycondensation of 2,2′‐bipyridine‐5,5′‐dicarboxylic acid (2) with various aromatic diamines in hexamethylphosphoramide (HMPA) containing lithium chloride. The resulting polyamide solutions in 98% sulfuric acid and in HMPA‐LiCl exhibited lyotropic liquid crystal phases. The phase transition behaviors were studied by polarizing microscopy and X‐ray diffraction. The polyamides also formed metal complexes with cis‐dichlorobis(bipyridine)ruthenium dihydrate [cis‐Ru(bpy)2Cl2 · 2H2O] which was supported by changes in electronic spectra.
Imaging of a pH‐sensitive polymer brush on a porous membrane using atomic force microscopy in aqueous solution
Authors: Ito Yoshihiro , Park Yong Soon , Imanishi Yukio 
Published: April 2003

AbstractPoly(methacrylic acid) was grafted on a nanoporous polycarbonate membrane using the glow‐discharge method. Atomic force microscopy showed that the pore size is dependent upon pH in such a way that a low pH the graft chains are protonated and contracted to open the pore, whereas at high pH, the graft chains became extended, thus reducing the pore size. Water permeation through the graft membrane is regulated by the pH value. The permeation rate is low at high pH value and high at low pH. This phenomenon corresponds to the pore size.
Synthesis of well‐defined polystyrene with multi‐functional end groups utilizing cyclotriphosphazene
Authors: Inoue Kenzo , Negayama Sadao , Itaya Tomoyuki , Sugiyama Minoru 
Published: April 2003

AbstractTelechelic polystyrenes with five benzyl chloride moieties at the polymer end (PSt‐E) were prepared by coupling reaction of polystyryllithium with hexakis(4‐chloromethyl‐phenoxy)cyclotriphosphazene (4). The coupling reaction occurs almost quantitatively and unfavorable side reactions were not operative. When a mole ratio [4]/[sec‐BuLi] = 9.3 was used, polystyrenes with cyclophosphazene carrying five benzyl chloride moieties at the polymer end (PSt‐E) were obtained in more than 90% yield, which have narrow and predictable molecular weights (Mw/Mn = 1.05). A star shaped polystyrene with phosphazene core could also be prepared by using excess polystyryl anions.
Hyperbranched polycarbosilane macromonomers bearing oxazoline functionalities
Authors: Lach Christian , Müller Philipp , Frey Holger , Mülhaupt Rolf 
Published: April 2003

AbstractSynthesis of hyperbranched polycarbosilanes by hydrosilylation of triallylsilane is reported. Soluble high molecular weight polymer was obtained in an uncontrolled bulk reaction. Addition of 2‐(10‐decen‐1‐yl)‐1,3‐oxazoline (i) afforded control over degree of polymerization (DP) and (ii) resulted in hyperbranched macromonomers. 17000 ≥ Mw ≥ 800 (GPC (PS)) was obtained. 29Si NMR spectroscopy allowed identification of dendritic, branched, linear, and terminal silicon branch‐points. A modified definition for the degree of branching yielded a value of 0.48 ± 0.05 (theory: 0.44).
New metallomesogenic polymers built by self‐assembly of non‐mesomorphic stilbazole dimers and CF3SO3Ag through coordination bonds
Authors: Kihara Hideyuki , Kato Takashi , Uryu Toshiyuki 
Published: April 2003

AbstractSupramolecular liquid‐crystalline main‐chain polymers have been obtained by self‐assembly of non‐mesomorphic bifunctional ligands and a transition metal ion. Stibazole dimers, bis[2‐(2‐{4‐[2‐(4‐pyridyl)vinyl]phenoxy}ethoxy)ethyl] ether (1) and 1,2‐bis[2‐(2‐{4‐[2‐(4‐pyridyl)vinyl]phenoxy}ethoxy)ethoxy]benzene (2) have been synthesized and complexed with silver trifluoromethanesulfonate (CF3SO3Ag). The metallomesogenic polymeric complexes formed by coordination bonds between the pyridyl groups of the stilbazole dimers and the silver ion exhibit smectic phases.
Polyelectrolyte‐surfactant complexes containing photolabile diazosulfonate chromophores
Authors: Antonietti Markus , Kublickas Rimantas , Nuyken Oskar , Voit Brigitte 
Published: April 2003

AbstractLow‐molar‐mass surfactants (S) and polyelectrolytes (PE) containing diazosulfonate chromophores which are photo‐labile and electrically charged were used for the formation of polyelectrolyte/surfactant complexes (PESC) in combination with commonly used polyelectrolytes and surfactants. The stable complexes are no longer water‐soluble and were characterized by means of nuclear magnetic resonance spectroscopy and in some cases by means of gel‐permeation chromatography measurements. Complexes with a 1 : 1 stoichiomctry with respect to charge are formed. Ultraviolet irradiation of the photo‐labile PESC resulted in the loss of the ionic interactions.
Amphiphilic derivatives of poly(acrylic acid) as stabilizer in emulsion polymerisation
Authors: Antonietti Markus , Weißenberger Markus C. 
Published: April 2003

AbstractPoly(acrylic acid)s of various molecular weights and different degree of hydrophobic modification have been synthesized by a polymer analogous reaction with tetradecylamine or copolymerization with styrene. Testing these amphiphilic polymers as stabilizers for the emulsion polymerization of styrene reveals that well stabilized latices are obtained within a certain range of molecular weight and hydrophobicity. As an example, the addition of 1 wt.‐% polymer with respect to the monomer allows the synthesis of polystyrene latices with a radius of about 100 nm in the absence of ionic initiators or polar comonomers.
Reversible local melting in polymer crystals
Authors: Okazaki Iwao , Wunderlich Bernhard 
Published: April 2003

AbstractThe melting of poly(ethylene terephthalate) is analyzed by quasi‐isothermal, temperature‐modulated differential scanning calorimetry. The measurement is done by sinusoidally changing the temperature in the melting range (± 1.0 K). In the melting range a small portion of the sample melts reversibly. This observation is taken as a direct observation of the reversibility of melting of specific macromolecules as long as they are melting only partially and need no molecular nucleation for recrystallization.
Alternating terpolymerization of three non‐homopolymerizable monomers
Authors: Braun Dietrich , Schacht Matthias , Elsässer Hartmut , Tüdős Ferenc 
Published: April 2003

AbstractThe free‐radical terpolymerization of maleic anhydride (MSA), isobutyl vinyl ether (VIBE) and anethol (ANE) at 60°C is described. These three monomers do not homopolymerize under the conditions used. Binary copolymers are only obtained from MSA and one of the two investigated donor monomers, whereas the binary copolymerization of VIBE with ANE is not possible. In all terpolymers from these three non‐homopolymerizable monomers the MSA content amounts to about 50 mol‐%; VIBE is about twice as reactive as ANE. The terpolymerization can formally also be described under the assumption that two binary complexes (MSA/ANE (I) and MSA/VIBE (II)) are copolymerized. For this case the reactivity ratios rI = 0,9 and rII = 1,7 are obtained.
Liquid‐crystalline main‐chain elastomers
Authors: Bergmann Gerd H. F. , Finkelmann Heino , Percec Virgil , Zhao Mingyang 
Published: April 2003

AbstractA main‐chain elastomer was synthesized for the first time by a cross‐linking hydrosilylation of a cyclosiloxane with a new main‐chain liquid crystalline semiflexible polyether. Imposing a uniaxial mechanical field to the unstretched nematic polydomain sample results in a macroscopic alignment of the director. For this process the sample has to be stretched by a factor of about 5, which considerably exceeds the effect observed for nematic side‐chain elastomers.
An effective etching technique for polycarbonate/core‐shell poly(butyl acrylate)‐poly(methyl methacrylate) blend
Authors: Lu Dan , Dong Lisong , Feng Zhiliu 
Published: April 2003

AbstractTwo etching techniques are used to reveal the morphology of PC/PBA‐cs‐PMMA blend. One is based on acetic acid (CH3COOH) solutions, whereas the other uses CCl4/C2H5OH (3/1 v/v). The latter approach shows to be more appropriate and successful for revealing the morphology of PC/PBA‐cs‐PMMA blend.
Polymerization of ethylene by using zirconocene catalyst anchored on silica with trisiloxane and pentamethylene spacers
Authors: Lee Dong‐ho , Yoon Keun‐byoung , Noh Seok‐kyun 
Published: April 2003

AbstractNew supported catalysts on the basis of cyclopentadienylindenylzirconium dichloride (CpIndZrCl2) anchored on silica with a trisiloxane spacer (ZATS) and a pentamethylene spacer (ZAPM) were prepared and used for ethylene polymerization with modified methylaluminoxane (MAO) as cocatalyst. ZATS and ZAPM produce polyethylene with lower molecular weight but show higher activity than silica‐supported CpIndZrCl2 which was prepared by reacting zirconocene directly with silica, i.e., the activity of silica‐supported CpIndZrCl2 is enhanced by introducing a spacer between silica surface and metallocene species.
Self‐assembled second order nonlinear optical multilayer azo polymer
Authors: Wang Xiaogong , Balasubramanian Srinivasan , Li Lian , Jiang Xinli , Sandman Daniel J. , Rubner Michael F. , Kumar Jayant , Tripathy Sukant K. 
Published: April 2003

AbstractAn epoxy based polymer with nonlinear optical azo chromophores was designed to contain anionic groups to induce water solubility and self assembly. Using this polyanion with a polycation, multilayers were prepared on a glass substrate by alternating adsorption from dilute aqueous solutions. The azo chromophores in the confined layer of the polyanion in the multilayer films self‐assemble into a noncentrosymmetric alignment and demonstrate second order optical nonlinearity (d33 = 19 pm/V).
Lipase‐catalyzed ring‐opening polymerization of lactide
Authors: Matsumura Shuichi , Mabuchi Kimihiro , Toshima Kazunobu 
Published: April 2003

AbstractThe six‐membered lactide was polymerized using the ring‐opening polymerization with lipase as a catalyst at a temperature between 80 and 130°C in bulk to yield the corresponding polylactide with weight‐average molecular weights of up to 126000. The most preferable conditions with respect to the molecular weight of the polylactide are the bulk polymerization using lipase PS at a temperature of 100°C. The D,L‐lactide gave higher molecular weight compared to the D,D‐ and L,L‐lactide.
Interactions of di‐ and trivalent anionic azo dyes with polycations of integral type
Authors: Dragan Stela , Cristea Mariana , Airinei Anton , Simionescu Bogdan C. 
Published: April 2003

AbstractThe spectral changes of Crystal Ponceau 6R and Ponceau 4R induced by the interaction with polycations having N,N‐dimethyl‐2‐hydroxypropane‐1,3‐diylammonium chloride units in the main chain were followed. The stoichiometry of the polycation‐dye complex related to the dye structure was elaborated by UV‐VIS spectrophotometry and viscosimetric measurements. Formation of a tricomponent complex between the polycation/dye complex and poly(sodium acrylate) was also revealed.
Graft copolymers of poly(ethylene glycol) (PEG) and chitosan
Authors: Saito Hiroshi , Wu Xiangdong , Harris J. Milton , Hoffman Allan S. 
Published: April 2003

AbstractGraft copolymers of poly(ethylene glycol) (PEG) on a chitosan backbone (PEG‐g‐chitosan) have been synthesized and their aqueous solution properties were investigated. At pH 6.5 the graft copolymers are 100% soluble, while chitosan phase separates from solution at those conditions. These interesting graft copolymers may be especially suitable as carriers for delivery of anionic drugs, such as proteins, glycosaminoglycans, and DNA plasmids or oligonucleotides.
Lipase‐catalyzed ring‐opening polymerization of 1,3‐dioxan‐2‐one
Authors: Kobayashi Shiro , Kikuchi Hirofumi , Uyama Hiroshi 
Published: April 2003

AbstractEnzymatic ring‐opening polymerization of a 6‐membered cyclic carbonate, 1,3‐dioxan‐2‐one, was investigated by using lipase as catalyst in bulk. Supported lipase derived from Candida antarctica catalyzed the polymerization to give the corresponding aliphatic polycarbonate. Unchanged monomer was recovered in the absence of the enzyme or using an inactivated enzyme, indicating that the present polymerization proceeds through enzymatic catalysis.
Effect of co‐catalyst system on α‐olefin polymerization with rac‐ and meso‐[dimethylsilylenebis(2,3,5‐trimethyl‐cyclopentadienyl)]zirconium dichloride
Authors: Naga Naofumi , Mizunuma Kooji 
Published: April 2003

AbstractPropene, 1‐butene and 1‐hexene polymerization was conducted with a mixture of rac‐ and meso‐[dimethylsilylenebis((2,3,5‐tetramethyl‐cyclopentadienyl))]zirconium dichloride (Me2Si(2,3,5‐Me3Cp)2ZrCl2) (1) combined with methylaluminoxane (MAO), triethylaluminium (AlEt3)/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)4) (2) and triisobutylaluminium (AliBu3)/Ph3CB(C6F5)4, respectively, as co‐catalyst systems. The ratios of polymerization rates Rp(rac)/Rp(meso) were changed with the combined cocatalysts. It was found that in the case of using trialkylaluminium/2 as co‐catalyst Rp(rac)/Rp(meso) is lower than when using MAO in any kind of α‐olefin polymerization.
Liquid crystalline, highly luminescent poly(2,5‐dialkoxy‐p‐phenyleneethynylene)
Authors: Steiger Daniel , Smith Paul , Weder Christoph 
Published: April 2003

AbstractA high‐molecular‐weight poly(2,5‐dialkoxy‐p‐phenyleneethynylene) derivative has been prepared by the Heck reaction of 1,4‐bis(2‐ethylhexyloxy)‐2,5‐diiodobenzene and 1,4‐diethynyl‐2,5‐dioctyloxybenzene. The highly luminescent polymer exhibits excellent solubility and can readily be processed into high‐optical‐quality films. The weight‐average molecular weight M̄w was 240000 g · mol−1, with a polydispersity index of 2.9. Thermal analysis revealed a glass transition around 90°C, and an onset of chemical crosslinking at 130°C. The high M̄w and the remarkable solubility enabled the preparation of liquid crystalline solutions of the new PPE.
End‐group dynamics of fluorescently labeled dendrimers
Authors: Wilken Ralph , Adams Jörg 
Published: April 2003

AbstractThe molecular dynamics of dendrimer branches were studied by observing the excimer formation of pyrenyl end‐groups. By a selective synthesis only one pyrene moiety per dendron was attached, resulting in a dendrimer with 3 fluorophors per molecule. The first 3 generations of the dendrimer were synthesized by the convergent‐growth approach. By time resolved measurements of the eximer and monomer fluorescence an increased mobility of the end‐groups was observed.
Effect of stereoregularity on the thermo‐oxidative degradation of poly(propylene)s estimated by chemiluminescence
Authors: Osawa Zenjiro , Kato Masahide , Terano Minoru 
Published: April 2003

AbstractThe effect of stereoregularity on the thermo‐oxidative degradation of poly(propylene)s, isotactic (IPP) and syndiotactic (SPP), was compared with that of high density polyethylene (HDPE) by means of chemiluminescence (CL). SPP is extremely stable to thermal oxidation and CL signals appeared much later than in IPP and even later than in HDPE. For example, at 160°C the maximum intensity of CL was measured after only 13 min for IPP, 60 min for HDPE and 260 min for SPP. IR spectroscopic results support the conclusions drawn from CL results.
Gel permeation chromatographic determination of activation rate constants in nitroxide‐controlled free radical polymerization, 1. Direct analysis by peak resolution
Authors: Goto Atsushi , Terauchi Tomoya , Fukuda Takeshi , Miyamoto Takeaki 
Published: April 2003

AbstractThe dissociation rate constant kd related to the homolytic cleavage of the CON bond formed between a polystyrene (PS) and 2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPO) is determined by adopting the gel permeation chromatography peak‐resolution method to the styrene polymerization with a PS‐TEMPO adduct as a probe and the radical initiator tert‐butyl hydroperoxide. The result was given by the Arrhenius equation, kd = A exp(−E/(RT)) with A = 3.0 × 1013 s−1 and E = 124 kJ · mol−1.
Alternating copolymers of tetramethylene urea with 2,2‐dimethyltrimethylene carbonate and ethylene carbonate; preparation of the corresponding polyurethanes
Authors: Schmitz Frank , Keul Helmut , Höcker Hartwig 
Published: April 2003

AbstractCopolymerization of tetramethylene urea (TeU, 1) with the cyclic carbonates 2,2‐dimethyltrimethylene carbonate (DTC, 2) and ethylene carbonate (EC, 3) results in the polyurethanes 4 and 5 with an approximate number‐average molecular weight of 20 000 and a polydispersity index of two. Polyurethane 4 is an amorphous material with a glass transition temperature of 26.3°C; polyurethane 5 is a semicrystalline material with a melting temperature of 208°C. Distinct copolymerization mechanisms are proposed for the formation of polyurethane 4 and 5, respectively.
Processing‐induced chromism in thin films of polythiophene derivatives
Authors: Leclerc Mario , Lévesque Isabelle , Goldenberg Leonid , Petty M. C. 
Published: April 2003

AbstractLangmuir‐Blodgett films of amphiphilic poly[3‐oligo(oxyethylene)‐4‐methylthiophene] have been obtained. The resulting thin films are poorly conjugated, with a maximum of absorption at 405 nm which remains almost constant upon heating or cooling. In contrast, cast thin films of this polymer exhibit a maximum of absorption at 550 nm and show interesting thermochromic effects. These results to indicate that the method of preparation of thin films can have a significant influence on the conformational structure of the polymer at room temperature and, consequently, on its thermochromic behaviour.
Synthesis of a new siloxane‐crown ether polyamide
Authors: Ardeleanu Rodinel , Voiculescu Nicolae , Marcu Mihai , Roman Gheorghe , Buchidau Carmen , Sacarescu Liviu , Sacarescu Gabriela 
Published: April 2003

AbstractThe synthesis of a siloxane‐crown ether polyamide by solution polycondensation of 4,4′‐diaminodibenzo‐18‐crown‐6 with a carboxypropyl‐terminated siloxane oligomer is presented. The polymer is characterized by IR and 1H NMR spectroscopy as well as by differential thermal analysis and differential scanning calorimetry.
Synthesis and structure of crosslinked poly[(methylsiloxane)‐co‐(oxymethylene)] copolymers
Authors: Rodríguez‐Baeza Mario , Zapata Melcy , Yoshida I. Valeria P. 
Published: April 2003

AbstractA series of new crosslinked copolymers was obtained by cationic ring‐opening copolymerization of 1,3,5,7‐tetramethylcyclotetrasiloxane and 1,3,5‐trioxane. The poly[(methylsiloxane)‐co‐(oxymethylene)] copolymers are white crystals or glassy. Crosslinking reactions take place in the reaction medium. The degree of crosslinking increases with a higher concentration of the methylsiloxane units in the copolymers. The combination of solid‐state magic‐angle spinning nuclear magnetic resonance of 29Si and 13C and Fourier‐transform infrared spectroscopy provided a quantitative description of the copolymer microstructure.
Studies on microgels, 3. Synthesis using living free radical polymerization
Authors: Abrol Simmi , Kambouris Peter A. , Looney Mark G. , Solomon David H. 
Published: April 2003

AbstractMicrogels which are soluble crosslinked polymer networks have been prepared using the nitroxide living free radical polymerization methodology. When heated in the presence of tert‐butylstyrene and 1,4‐divinylbenzene, the alkoxyamine 1 derived from 2,2′‐azoisobutyronitrile (AIBN) afforded a high molecular weight soluble polymer which was shown by size exclusion chromatography in conjunction with an on‐line multi angle laser light scattering (MALLS) detector to have microgel properties.
Alternative molecularly imprinted polymeric membranes from a tetrapeptide residue consisting of D‐ or L‐amino acids
Authors: Yoshikawa Masakazu , Izumi Jun‐ichiro , Kitao Toshio , Sakamoto Shunji 
Published: April 2003

AbstractAlternative molecularly imprinted polymeric membranes were prepared from a polystyrene resin bearing tetrapeptides consisting of D‐amino acids or L‐amino acids. The membrane prepared from a DLDE derivative (H‐Asp(OcHex)‐Leu‐Asp(OcHex)‐Glu(OBzl)CH2) consisting of D‐amino acids and imprinted by Boc‐D‐Trp recognizes the D‐isomer in preference to the corresponding L‐isomer and vice versa. The amino acid preferentially adsorbed by the membrane was selectively permeated by applying electrodialysis.
Ring‐opening polymerization of chloromethylthiirane with SO42−/TiO2/Nd3+ as initiator
Authors: Shen Zhiquan , Li Weishi , Zhang Fuyao , Zhang Yifeng , Shen Lianfang , Yuan Hanzhen 
Published: April 2003

AbstractA new type of solid superacid (SO42−/TiO2/Nd3+) was used for the ring‐opening polymerization of chloromethylthiirane (CMT). TiO2 · H2O immersed in a sulfuric acid solution containing Nd3+ ions and calcined at 600°C gave the solid superacid for initiating the polymerization of CMT. The effects of polymerization temperature and amount of the initiator on the CMT polymerization were studied. Poly(CMT) obtained has higher molecular weight (M̄w = 52 000) than ever reported.