bluuebunny/crossref_metadata_2025_split huggingface dataset:
All‐trans oligomers of 2,5‐dialkyl‐1,4‐phenylenevinylenes–metathesis preparation and characterization
Authors: Thorn‐Csányi Emma , Kraxner Peter 
Published: April 2003

AbstractOligomers of 2,5‐dialkyl‐1,4‐phenylenevinylenes (DR‐OPV, R = C4H9, C7H15, C10H21 and C6H11) (CyH) were prepared via metathesis polycondensation of the respective 2,5‐dialkyl‐1,4‐divinylbenzenes. The synthesis of the monomers is described. The highly active metal‐alkylidene complex Mo(NAr)(CHCMe2Ph)[OCMe(CF3)2]2 (Ar = 2,6‐dimethylphenyl) serves as a catalyst. The degree of polymerization can be controlled by variation of the solvent and by the length of the side chains, since the reaction proceeds as a precipitation polycondensation. The DR‐OPVs are bilious‐green products and, depending on the molecular weight, soluble in various solvents like toluene, THF and CHCl3. The solutions are highly fluorescent and coloured. The DR‐OPVs have vinylic end groups. The vinylene double bonds are of all‐trans configuration. Due to their rigid‐rod structure, the DR‐OPVs synthesized have a distinct tendency to crystallize in a highly ordered state, forming a sanidic layer structure.
Determination of the transfer constant of α‐thioglycerol in methyl methacrylate free‐radical polymerization
Authors: Fernández‐García Marta , Delgue Michel , Madruga Enrique López 
Published: April 2003

AbstractUsing the Mayo and the Clay‐Gilbert method, the transfer rate coefficient of α‐thioglycerol (TG) was determined at 50°C for the polymerization of methyl methacrylate (MMA) in a 3 mol · L−1 tetrahydrofuran solution using different amounts of 2,2′‐azoisobutyronitrile (AIBN) as initiator. The transfer rate coefficient was found to be independent of the initiator concentration and higher by a factor of 1.6 when obtained according to the Clay‐Gilbert method compared to the Mayo method.
Synthesis and characterization of poly‐L‐lysine with controlled low molecular weight
Authors: Van Dijk‐Wolthuis Wendelmoed N. E. , van de Water Leon , van de Wetering Petra , Van Steenbergen Mies J. , Kettenes‐van den Bosch Jantien J. , Schuyl Wijnand J. W. , Hennink Wim E. 
Published: April 2003

AbstractN‐Carboxy‐(Nϵ‐benzyloxycarbonyl)‐L‐lysine anhydride (Z‐L‐lysine NCA) was polymerized in dimethylformamide with triethylamine, diethylamine or hexylamine as initiator, at varying molar ratios of NCA to initiator (M/I ratio). After removal of the protecting Z‐group the resulting poly‐L‐lysine was characterized with 1H NMR and MALDI TOF MS. Both diethylamine‐ and hexylamine‐initiated polymerization yielded poly‐L‐lysine in which the initiators were incorporated at the carboxylic end of the polymer. This indicates that the NCA polymerization occurred exclusively via nucleophilic attack of the initiator on the monomer. On the other, hand, when triethylamine was used as the initiator, poly‐L‐lysine was obtained in which no triethylamine‐derived end group could be detected by MS. These polymer chains are most likely end‐capped with an N‐acyl‐2,5‐dioxopiperazine group at the carboxylic end of the polymer. Incorporation of diethylamine and hexylamine allowed determination of the degree of polymerization (DP) of the obtained polymers by 1H NMR. The DP depended linearly on the M/I ratio, for both diethylamine and hexylamine, with higher DPs for the diethylamine‐initiated poly‐L‐lysine at equal M/I ratio.
Generation of a spin polymer through a charge‐transfer complex of a ferrocenyl mesogen with tetracyanoethylene in the solid state
Authors: Tanaka Hitoshi , Mizota Kazuya 
Published: April 2003

AbstractSome disubstituted ferrocenes and a polymer with flexible pendant ferrocenyl mesogens were found to form a complex with tetracyanoethylene to give a spin molecule even in the solid state at ambient temperature.
Selective synthesis of 4,4′‐biphenyldicarboxylic acid using cyclodextrin as catalyst
Authors: Hirai Hidefumi , Shiraishi Yukihide , Saito Kazuhiro 
Published: April 2003

AbstractThe selective carboxylation of 4‐biphenylcarboxylic acid with carbon tetrachloride in aqueous alkali to obtain 4,4′‐biphenyldicarboxylic acid was achieved by the use of ß‐cyclodextrin and copper powder II under mild conditions.
Command surfaces, 10. Novel polymethacrylates with laterally attached azobenzene groups displaying photoinduced optical anisotropy
Authors: Akiyama Haruhisa , Kudo Kazuaki , Ichimura Kunihiro 
Published: April 2003

AbstractPolymethacrylates with laterally attached azobenzenes were prepared to cause molecular reorientation of this chromophore in their thin films by linearly polarized irradiation with an exposure energy of less than ca. 100 mJ/cm2. A homogeneous alignment was induced by assembling a nematic liquid crystal cell using a substrate plate covered with the photoirradiated films. The alignment direction of the cell was controlled by changing the electric vector of the actinic light.
Morphology of single‐chain single crystals of poly(ethylene oxide)
Authors: Shi Songhua , Chen Erqiang , Hu Hanjie , Bu Haishan , Zhang Ze 
Published: April 2003

AbstractSingle‐chain particles of poly(ethylene oxide) (PEO) were prepared by spreading a 10‐4 wt.‐% solution of PEO in benzene on a hot water surface. After isothermal crystallization at 317,2 ± 0,1 K for 10 h, regular‐shaped single‐chain crystals were observed. A variety of typical morphologies were also found, and some of them are discussed on the basis of the habit of PEO crystals and various twin modes.
Curing of a rigid rod epoxy resin with an aliphatic diacid: an example of a lightly crosslinked liquid crystalline thermoset
Authors: Giamberini Marta , Amendola Eugenio , Carfagna Cosimo 
Published: April 2003

AbstractBy reacting a rigid rod epoxy terminated molecule (p‐bis(2,3‐epoxypropoxy)‐α‐methylstilbene) with an aliphatic carboxylic acid (decanedioic acid), a lightly crosslinked liquid crystalline network is obtained. This network exhibits a smectic‐like phase. While the mesophasic structure resulted “frozen” by the crosslinks in the case of higly crosslinked liquid crystalline epoxy resins, in this case a reversible transition from the liquid crystalline to the isotropic phase is observed. Moreover, while curing the same rigid rod epoxy molecule with amines resulted in a thermoset with a nematic structure, in this case a more ordered mesophase can be obtained. Preliminary results show that it is possible to orient macroscopically the mesogenic chains by stretching thin films above the glass transition temperature (Tg) and then quickly cooling down to the glassy state. This makes this material very attractive in the field of optical applications.
Pulsed laser terpolymerization of styrene, methyl methacrylate and methyl acrylate
Authors: Schoonbrood Harold A. S. , van den Reijen Bram , de Kock John B. L. , Manders Bart G. , van Herk Alex M. , German Anton L. 
Published: April 2003

AbstractThe propagation rate coefficient of the terpolymerization of styrene, methyl methacrylate and methyl acrylate in bulk was successfully determined at three different monomer compositions. The temperature was varied between 18 and 80°C. The resulting data at 50°C were not in agreement with predictions according to the terminal model with binary reactivity ratios that have been determined by fitting copolymer composition data with the terminal model. This indicates that here also the penultimate unit affects the kinetics.
Temperature‐induced phase transition behaviors of random vs. graft copolymers of N‐isopropylacrylamide and acrylic acid
Authors: Chen Guohua , Hoffman Allan S. 
Published: April 2003

AbstractGraft copolymers of poly(N‐isopropylacrylamide) (PNIPAAm) on a poly(acrylic acid) backbone retain the temperature‐induced phase transition behavior of PNIPAAm over a wide range of compositions even at pH 7,4 and should be useful for sustained‐release, bioadhesive drug delivery systems at physiologic conditions.
Applying principles of polymer miscibility for thermal imaging
Authors: Schild Howard G. 
Published: April 2003

AbstractKnowledge of polymer‐polymer interactions is employed to design an improved media for dye diffusion thermal transfer (D2T2). Selecting the donor and receiver sheet binder polymers to be an immiscible pair results in acceptable images free from the “sticking” during printing that is observed if these two polymers are miscible. This approach has the potential to improve upon the dye density and surface characteristics of current commercial systems.
Poly(organophosphazenes) containing azo dyes
Authors: Facchin Giacomo , Gleria Mario , Minto Francesco , Bertani Roberta , Guglielmi Massimo , Brusatin Giovanna 
Published: April 2003

AbstractIn this paper we describe a method for the functionalization of catenapoly[bis(4‐hydroxyphenoxy)‐λ5‐phosphazene] with diazonium salts to form new, deeply‐coloured, phosphazene copolymers containing variable amounts of azo dyes attached to the polyphosphazene skeleton. The degree of functionalization in these substrates is regulated in order not to exceed 20% of the sites available in the pristine polyphosphazene and to maintain a high percentage of unreacted, free, hydroxy groups, in the final, coloured copolymers. These species are still very reactive and able to undergo further functionalization reactions.
Liquid‐crystalline polyimides, 16. Chiral thermotropic copoly(ester‐imide)s based on isosorbide and N‐(4‐carboxyphenyl)trimellitimide
Authors: Kricheldorf Hans R. , Probst Nicolas 
Published: April 2003

AbstractA series of chiral copoly(ester‐imide)s was prepared by polycondensation of N‐(4‐carboxy‐phenyl)trimellitimide with mixtures of isosorbide and phenylhydroquinone. All copolyesters are non‐crystalline. They form a cholesteric melt, when containing more than 50 mol‐% of phenyl‐hydroquinone. Containing 5 or 10 mol‐% of isosorbide a “Grand‐Jean” texture is detected above 300°C and 350°C, respectively.
Rigid rod polymers with regularly spaced silicon‐centered phthalocyanine units in the backbone
Authors: Lauter Ulrich , Schulze Margit , Wegner Gerhard 
Published: April 2003

AbstractWe describe the synthesis of new rigid rod polymers possessing a backbone of silicon phthalo‐cyanine units and stiff 4,4′‐dioxybiphenyl or 2,6‐dioxynaphthalene spacers. These modified phthalocyaninato‐polysiloxane derivatives are characterised by mass, absorption and 13C‐CPMAS spectroscopies, differential scanning calorimetry and X‐ray powder diffractometry. UV/VIS spectra show only slight differences to the corresponding phthalocyanine monomers, which indicates the absence of excited state interactions between the chromophores within the polymer backbone.
Polymerizations of ethylene and styrene initiated with trisiloxane‐bridged dinuclear titanium metallocene/MMAO catalyst systems
Authors: Lee Dong‐ho , Yoon Keun‐byung , Lee Eok‐hyung , Noh Seok‐kyun , Byun Gyu‐gum , Lee Chul‐soo 
Published: April 2003

AbstractTwo kinds of the trisiloxane‐bridged dinuclear titanium metallocene‐type complexes were synthesized. They are monocyclopentadienyl and biscyclopentadienyl dinuclear titanocenes with trisiloxane bridges. The above complexes with modified methylaluminoxane (MMAO) cocatalyst initiate the polymerizations of ethylene and styrene to produce high‐density polyethylene and syndiotactic polystyrene. In addition, a copolymer of ethylene and styrene was obtained.
Pressure and temperature dependence of the propagation rate coefficient in free‐radical polymerization of butyl methacrylate
Authors: Bergert Ute , Buback Michael , Heyne Joachim 
Published: April 2003

AbstractThe propagation rate coefficient in free‐radical bulk polymerization of butyl methacrylate has been studied at temperatures between −10°C and 60°C up to a maximum pressure of 2 000 bar. The data were obtained by means of the PLP‐GPC technique which combines pulsed‐laser polymerization with product analysis by gel‐permeation chromatography.
Poly[2,4‐bis(chloroamino)‐6‐vinyl‐1,3,5‐triazine] as a recyclable oxidizing agent of alcohols
Authors: Kondo Shuji , Kawasoe Shinya , Ohira Mari , Atarashi Tadashi , Ikeda Kazahisa , Kunisada Hideo , Yuki Yasuo 
Published: April 2003

AbstractA polymer containing dichlorotriazine moiety was prepared readily by the reaction of poly(2,4‐diamino‐6‐vinyl‐1,3,5‐triazine) with tert‐butyl hypochlorite. This polymer oxidizes various primary and secondary alcohols to the corresponding carbonyl compounds under mild conditions, while the reaction of the monomeric analogue N,N′‐dichloroacetoguanamine with alcohols does not proceed. The polymer reagent can be handled easily and recycled for further use.
The structure of azomethine block copolymers from X‐ray powder diffraction data
Authors: Brückner Sergio , Destri Silvia , Porzio William 
Published: April 2003

AbstractThe crystal structure of a block copolymer, constituted by the periodic alternation of three thienyl‐ and two phenyl fragments separated by azomethine residues, has been determined and refined on powder X‐ray diffraction data. Polymers of this kind are particularly interesting because of some evidences of electronic confinement, i. e. possible realization of multiple‐quantum‐dot sequences have been detected. Although the quality of the measured profile was poor, a molecular model is proposed giving a satisfactory agreement with the observed data.
Effect of catalyst aging on catalyst activity and stereospecificity for MgCl2/ethyl benzoate or dioctyl phthalate/TiCl4‐triethylaluminium for propene polymerization
Authors: Yang Chun B. , Hsu Cheng C. 
Published: April 2003

AbstractThe aging of the MgCl2/dioctyl phthalate (DOP) or ethyl benzoate (EB)/TiCl4 catalyst was studied. Because of the strong complexation of DOP with the catalyst, only a small fraction of DOP was extracted by cocatalyst triethylaluminium (TEA) during aging, resulting in converting some highly isospecific sites into aspecific ones. No change of the overall number of sites was detected. EB, on the other hand, could be readily removed by TEA, resulting in a large increase in aspecific sites. Clustering of those sites facilitated catalyst deactivation.
Syndiospecific polymerization of styrene with arene titanium(II) complexes as catalyst precursors
Authors: Kaminsky Walter , Park Young‐Whan 
Published: April 2003

AbstractThe divalent titanium compounds [(η6‐C6H5Me)Ti(Cl2AlCl2)2] (1) and [(η6‐C6Me6)Ti(Cl2AlCl2)2] (2) are syndiospecific catalysts in the polymerization of styrene when activated with methylaluminoxane. The polystyrene is of exceptionally high molecular weight.
Heterogeneity of active species in metallocene catalysts
Authors: Soga Kazuo , Uozumi Toshiya , Arai Takashi , Nakamura Shuji 
Published: April 2003

AbstractFrom a detailed analysis of poly[ethylene‐co‐(1‐hexene)] obtained with typical metallocene catalysts, it was found that metallocene catalysts give two kinds of copolymers which differ in crystallinity. It may be thus plausible to assume that there are two kinds of active species in metallocene catalysts.
Solubilization of polyaniline in water by interpolymer complexation
Authors: Liao Yun‐Hsin , Levon Kalle , Laakso Jukka , Österholm Jan‐Erik 
Published: April 2003

AbstractWater solubility of electro‐active polymers in their doped state may provide a possibility for environmentally feasible manufacturing processes. Because previous results in this direction require expensive modifications or impractical template polymerization methods, we created a simple method of mixing components with a large molecular weight difference. The polymer which acts as an acidic dopant and provides water solubility, has to have the higher molecular weight. The formed complex resembles a block copolymer but in this case the polyaniline block is attached to the sulfonated polystyrene chain by strong physical interactions instead of chemical end‐to‐end linkage.
The effect of mixing time on the morphology and physical properties of liquid crystalline polymer based blends
Authors: Zaldua Ane M. , Muñoz M. Eugenia , Peña Juan J. , Santamaría Anton 
Published: April 2003

AbstractRheological and thermal analysis results of blends of a thermotropic copolyesteramide and polyarylate of bisphenol A depend on the thermo‐mechanical treatment during mixing. The changes observed as mixing time increases are the following: (a) melt viscosity and loss factor increase, (b) glass transition temperature decreases. The morphological analysis of the blends shows the inability of the treated blends to form an oriented liquid crystalline polymer (LCP) phase, which explains the observed viscoelastic properties.
A fast catalyst system for the ring‐opening polymerization of cyclosiloxanes
Authors: Molenberg Aart , Möller Martin 
Published: April 2003

AbstractMethanol, in combination with a non‐ionic phosphazene base, was used to initiate the polymerization of octamethylcyclotetrasiloxane. In bulk, an instantaneous and large increase in viscosity was observed upon addition of the initiator. In toluene solution, the equilibrium state was reached in approximately 1 min. In addition to its high polymerization rate, another advantage of this system, as compared with e.g. alkali metal hydroxides, is that it is homogeneous.
A method for the prediction of metallocene‐type catalyst activity in olefin (co)polymerisation reactions
Authors: Pieters Paul J. J. , van Beek Johannes A. M. , van Tol Maurits F. H. 
Published: April 2003

AbstractThe use of ultraviolet/visible spectroscopy (UV‐Vis) for the prediction of metallocene catalyst potential for the polymerisation of olefins is described. Upon addition of methylaluminoxane (MAO) to rac‐[C2H4(1‐indenyl)2ZrCl2] ([Al]/[Zr] = 200) the ligand‐to‐metal charge transfer band shows a hypsochromic shift while a bathochromic shift is observed when more MAO is added ([Al]/[Zr] = 2000). These shifts can be explained by assuming that methylation of the zirconocene by MAO occurs in the case of [Al]/[Zr] = 200 while a cationic complex, the active catalytic system, is formed upon addition of more MAO, e.g., [Al]/[Zr] = 2000.
A novel synthesis of linear high‐molecular‐weight poly(4‐vinylphenol) and poly[styrene‐co‐(4‐vinylphenol)]
Authors: Xiang Maoliang , Jiang Ming , Feng Linxian 
Published: April 2003

AbstractA novel synthesis of linear high‐molecular‐weight poly(4‐vinylphenol) (PVPh) and poly[styrene‐co‐(4‐vinylphenol)] (STVPh, 2) via demethylation reaction is developed. The parent polymers, poly(4‐methoxystyrene) and poly[styrene‐co‐(4‐methoxystyrene)] produced by free‐radical polymerization, are converted to PVPh and STVPh (2), respectively, by being treated with trimethylsilyl iodide (TMSI) at room temperature. Both 1H NMR and 13C NMR data show that methoxy is completely cleaved and converted to hydroxy after hydrolysis without crosslinking and other side reactions. In addition, size‐exclusion chromatography data show that no chain scission occurs during group conversion.
Evidence of interchange reaction in a poly(ethylene 2,6‐naphthalenedicarboxylate)/poly(bisphenol‐A carbonate) blend
Authors: Fernandez‐Berridi Maria Jose , Iruin Juan Jose , Maiza Iñaki 
Published: April 2003

AbstractThe existence of interchange reactions in a poly(ethylene 2,6‐naphthalenedicarboxylate)/poly(bisphenol‐A carbonate) blend (PEN/PC) has been proven by means of solubility tests, DSC and FTIR and NMR spectroscopies. In addition, DSC results reveal that these interchange reactions are responsible for the miscibilization of the initially immiscible system.
Polymerization of ethylene over metallocenes confined inside the supercage of a NaY zeolite
Authors: Woo Seong Ihl , Ko Young Soo , Han Taek Kyu 
Published: April 2003

AbstractMetallocene catalysts entrapped inside the supercages of NaY zeolite were prepared by reacting NaY with methylaluminoxane (MAO) or trimethylaluminium (TMA) and then with Cp2ZrCl2 (Cp: cyclopentadienyl) or Cp2TiCl2. NaY/MAO/Cp2ZrCl2 and NaY/MAO/Cp2TiCl2 catalysts could polymerize ethylene. The amount of additional MAO for the polymerization was lowered to a mole ratio of Al/Zr of 186. Molecular weights and melting points of polyethylene polymerized with NaY‐supported catalysts were higher than those of polyethylene obtained with homogeneous metallocene catalysts. It could be confirmed by extraction experiments that the metallocene catalyst was confined securely inside the supercage of the NaY zeolite.
Polymeric substitution in a pH oscillator
Authors: Giannos Steven A. , Dinh Steven M. , Berner Bret 
Published: April 2003

AbstractThe iodate pH oscillator, which oscillates between pH 6.5 and 4.0, is reproducible in a semibatch reactor. pH oscillations of similar period and amplitude were observed when poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) was substituted for sulfuric acid. Therefore, a polymer may be used as an alternative reagent, where the polymer actively participates in the reaction instead of serving as an inert reaction medium.
Silica‐supported metallocenes: stereochemical comparison between homogeneous and heterogeneous catalysis
Authors: Sacchi Maria Carmela , Zucchi Debora , Tritto Incoronata , Locatelli Paolo , Dall'Occo Tiziano 
Published: April 2003

AbstractPropylene was polymerized in the presence of the isospecific Et(Ind)2ZrCl2 (Et: ethylene, Ind: indenyl) and the aspecific (Ind)2ZrCl2 complexes in solution and anchored to SiO2 and SiO2/MAO (MAO: methylaluminoxane) supports. From the stereochemical analysis of the polypropene samples obtained it can be deduced that (i) the same active species is formed when a metallocene is in solution and when it is anchored to the SiO2/MAO support and (ii) a completely different active species is formed when the metallocene is anchored to the silica. The fact that both systems Et(Ind)2ZrCl2SiO2 and (Ind)2ZrCl2SiO2 produce the same prevailingly isospecific polymer suggests that only isospecific centers are formed in this case, independently of the metallocene stereochemical structure.
Study of polystyrene‐poly(tert‐butyl acrylate) heteroarm star copolymers in dilute solutions
Authors: Tsitsilianis Constantinos , Kouli Ourania 
Published: April 2003

AbstractHeteroarm star copolymers with polystyrene and poly(tert‐butyl acrylate) arms are studied in dilute solutions by means of viscometry and static light scattering. In a weakly selective solvent a segregated‐nonsegregated conformational transition is observed induced by temperature change. In a strongly selective solvent association phenomena take place and the heteroarm star molecules form multimolecular micelles.
Study of the chain transfer reaction by hydrogen in the initial stage of propene polymerization
Authors: Mori Hideharu , Tashino Kunihiko , Terano Minoru 
Published: April 2003

AbstractThe chain transfer reaction by hydrogen in the initial stage of propene polymerization with MgCl2‐supported Ziegler catalyst was studied by means of the stopped‐flow polymerization. The yield and molecular weight of polypropene produced in the initial stage were not affected by hydrogen. Thus, the method was successfully applied to find the region in which hydrogen does not act as a chain transfer reagent. On the other hand, a chain transfer reaction proceeded in the initial stage of polymerization by using Zn(C2H5)2. Furthermore, when the catalyst was treated with Al(C2H5)3 before polymerization, the molecular weight of the produced polymer was decreased by using hydrogen, indicating that it acted as a chain transfer agent for the catalyst modified by pre‐treatment.
Ferroelectric liquid‐crystalline elastomers with short switching times
Authors: Brehmer Martin , Zentel Rudolf 
Published: April 2003

AbstractThe crosslinking of ferroelectric liquid‐crystalline (LC) polysiloxanes — performed within the region of microphase separation — allows the preparation of LC‐elastomers which combine macroscopic form stability (insolubility) with nearly unchanged switching time (compared to the uncrosslinked polymers).