bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymerization of cyclic monomers, 4. Synthesis and radical polymerization of bi‐ and trifunctional 2‐vinylcyclopropanes
Authors: Moszner Norbert , Zeuner Frank , Rheinberger Volker 
Published: April 2003

AbstractMultifunctional 2‐vinylcyclopropanes were synthesized by esterification of the 1‐methoxycarbonyl‐2‐vinylcyclopropane‐1‐carboxylic acid with ethylene glycol, 1,1,1‐trimethylolpropane or 1,4‐cyclohexanediol in the presence of 1,3‐dicyclohexylcarbodiimide (DCC). The structure of the new vinylcyclopropanes was confirmed by elemental analysis, IR, 1H NMR and 13C NMR spectroscopy. The radical polymerization of the 2‐vinylcyclopropanes in bulk with 2,2′‐azoisobutyronitrile (AIBN) results in transparent crosslinked polymers. The polymerization of the liquid monomers is accompanied by a low shrinkage in volume.
Polymerization of styrene to isotactic polymer with MAO‐Ni(acac)2. Examination of the factors that influence activity and stereospecificity
Authors: Crossetti Geraldo Lopes , Bormioli Carlotta , Ripa Alberto , Giarrusso Antonino , Porri Lido 
Published: April 2003

AbstractThe soluble catalyst system methylaluminoxane (MAO)‐Ni(acac), (acac: acetylacetonate) gives polystyrene consisting of an amorphous (aPS) and a crystalline isotactic (ips) fraction. Al(CH3)3, which is always present in commercial samples of MAO, decreases both polymer yield and stereospecificity. The polymer yield increases with increasing the MAO/Ni ratio but, at the same time, the iPS/aPS ratio decreases. Addition of N(C2H5)3 (mole ratio N/Ni = 1) increases the proportion of the isotactic fraction, while it decreases the polymer yield. A tentative interpretation of the stereospecificity is reported.
Polymerization of ϵ‐caprolactone using heterobimetallic lanthanocene complexes
Authors: Hultzsch Kai C. , Okuda Jun 
Published: April 2003

AbstractThe chiral heterobimetallic complexes Li[Ln(η5 : η1‐C5R41SiMe2NCH2CH2R2)2] (Ln = Y, Lu; C5R41 = C5Me4, C5H4, 3‐C5H3 t Bu; R2 = OMe, NMe2; Me: methyl; tBu: tert‐butyl) have been found to polymerize ϵ‐caprolactone to give a polymer of high molecular weight (M̄n < 20 000) and moderate polydispersity (M̄w/M̄n < 2.0). Failure to observe a correlation between monomer/initiator ratio and molecular weight suggests a polymerization mechanism different from a pseudo‐anionic mechanism.
A novel synthesis of semitelechelic functional poly(methacrylate)s through an alcoholate initiated polymerization. Synthesis of poly[2‐(N,N‐diethylaminoethyl) methacrylate] macromonomer
Authors: Nagasaki Yukio , Sato Yasuo , Kato Masao 
Published: April 2003

AbstractPotassium alcoholate was found to initiate the anionic polymerization of 2‐(N,N‐diethylaminoethyl) methacrylate (AMA) to form poly[2‐(N,N‐diethylaminoethyl) methacrylate] (PAMA). The molecular weight of the polymers was controlled by the monomer‐initiator ratio with a narrow molecular weight distribution. Increased reactivity of the initiator by chelation of the monomer to the cation may be important for the polymerization. Using potassium (4‐vinylbenzyl) alcoholate as an initiator, PAMA having a vinylbenzyl group was prepared which is a macromonomer having pH sensitive amino groups in each monomeric unit. By radical copolymerization with styrene, the PAMA macromonomer was incorporated as a graft chain.
Swelling behavior of ampholytic gels prepared by γ‐irradiation
Authors: Wada Seiichi , Satoh Mitsuru , Komiyama Jiro 
Published: April 2003

AbstractHeterogeneous ampholytic gels were prepared by two‐step γ‐irradiation of aqueous solutions of poly(vinyl alcohol)s having sulfonate and quaternary ammonium groups, respectively. A reference gel was prepared by one‐step irradiation. The heterogeneous gels turned out to swell to lesser degrees with increasing ionic strength of the immersing solution than the reference gel. However, the ion‐specific swelling and deswelling behavior, which had been found for the reference gel, was also observed for the present heterogeneous gel.
Water solubility of regioselectively 2,3‐O‐substituted carboxymethylcellulose
Authors: Liu Hai‐Qing , Zhang Li‐Na , Takaragi Akira , Miyamoto Takeaki 
Published: April 2003

AbstractA series of 2,3‐O‐carboxymethylcelluloses (CMC's), which are regioselectively substituted at the C‐2 and C‐3 position, were prepared and their water solubility was examined. It was found that the lower limit for the degree of substitution (DS) value of water‐soluble 2,3‐O‐CMC is about 0.3. This value was almost the same as that of CMC prepared in a slurry of isopropyl alcohol/water with isopropyl chloroacetate and sodium hydroxide, showing that the uniform alkylation is rather important to convert cellulose into water‐soluble derivatives.
A new polyphenylene derivative bearing two stable radicals
Authors: Zhang Ruifeng , Zheng Haipeng , Shen Jiacong 
Published: April 2003

AbstractHydroxylization of poly(N,N‐dimethylaniline) (PDMA) by using H2O2 in base medium gives rise to a new polyphenylene derivative containing a high concentration of stable phenoxy radicals in the solid state. In solution, hydroxylated PDMA can have two forms of stable radicals, phenoxy radical and radical cation, and these two forms can be converted reversibly into each other by adjusting the pH value of the solution.
Novel polyelectrolyte complexes based on diazo‐resins
Authors: Cao Wei‐xiao , Ye Shu‐jian , Cao Shu‐guang , Zhao Chao 
Published: April 2003

AbstractPolyelectrolyte complexes containing diazonium groups (PEC‐N2) with a high ionic crosslinking rate were prepared as a precipitate by mixing the diazo‐resin with polyanion solutions. The photochemical decomposition of the complexes from different polyanions was studied. It was shown that PEC‐N2 exhibit high photosensitive properties. Under irradiation of UV light, the complexes which can be dissolved in ternary mixtures such as H2O‐DMF‐LiCl,H2O‐DMF‐NaSCN or H2O‐DMF‐ZnCl2 (DMF: N,N‐dimethylformamide) become indissoluble since the crosslinking structure of the complexes changes from ionic to covalent.
The first approach to non‐aqueous solutions of carboxymethylcellulose
Authors: Heinze Thomas , Heinze Ute 
Published: April 2003

AbstractFormic acid was found to dissolve sodium carboxymethylcellulose (Na‐CMC) with comparatively slight chain degradation. The dissolution of Na‐CMC in a wide range of degree of substitution from 0.4 to 2.0 occurs under partial formylation of the remaining OH groups of the polymer, i.e., formic acid is the first non‐aqueous, so‐called derivatizing solvent. The Na‐CMC formyl esters, which can be isolated under water‐free conditions, are even soluble in dipolar‐aprotic solvents, and they can be regenerated to Na‐CMC by treating with aqueous solutions of NaOH.
Narrow‐polydispersity polystyrene/poly[styrene‐co‐(butyl methacrylate)] block copolymers by an N‐oxyl mediated free radical polymerization process
Authors: Butz Sören , Baethge Heike , Schmidt‐Naake Gudrun 
Published: April 2003

AbstractPolystyrene/poly[styrene‐co‐(butyl methacrylate)] block copolymers with controlled molecular weights and with polydispersities generally below M̄w/M̄n = 1,45 and partially as low as M̄w/M̄n = 1,19 were synthesized by a free radical bulk copolymerization using a 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO)‐capped polystyrene macroinitiator. The influence of the macroinitiator concentration on the block copolymerization was studied. The polymerization rates are independent of the macroinitiator concentration and are close to that of thermally self‐initiated styrene/butyl methacrylate copolymerizations showing the important role of self‐initiation for N‐oxyl mediated free radical polymerizations.
Bis‐macromonomers of 2‐alkyl‐2‐oxazolines–synthesis and polymerization
Authors: Christova Darinka , Velichkova Rumiana , Goethals Eric J. 
Published: April 2003

AbstractPoly(2‐alkyl‐2‐oxazoline)s having an acrylate group at both chain ends were synthesized by terminating living bifunctional poly(2‐methyl‐2‐oxazoline) or poly(2‐ethyl‐2‐oxazoline) with acrylic acid. These macromonomers have been polymerized to the corresponding polyoxazoline networks. Thermal as well as UV‐initiated free radical polymerization were applied and the influence of the polymerization conditions and molecular weight of the prepolymer used on the properties of the networks were investigated. Both methods of polymerization produced high fractions of soluble material, probably due to the low concentration of the acrylate end groups.
Cationic initiation of oligomerization of vinylformamide
Authors: Spange Stefan , Madl Alexander , Eismann Ulrike , Utecht Jens 
Published: April 2003

AbstractVinylformamide (VFA) is cationically polymerized in various solvents at 273 K and reaction temperature by the following initiators: iodine, bis(4‐methoxyphenyl)‐methyl chloride/silica, triphenylmethyl chloride/silica, and trimethylsilyl triflate. In every case defined oligomers with narrow molecular weight distribution are obtained in moderate yield (20–50%). Acid hydrolysis of the obtained oligomers yields well defined oligovinylamine products. The cationic initiation mechanism of VFA is discussed in terms of the HSAB‐conceptHSAB: Hard and soft acids and bases.
Threading of cyclodextrins onto a polyester of octanedicarboxylic acid and polyethylene glycol
Authors: Weickenmeier Meik , Wenz Gerhard 
Published: April 2003

AbstractA water‐soluble polyester was synthesized from dimethyl octane‐1,8‐dicarboxylate and polyethylene glycol (M̄n = 900). This polymer forms water‐soluble inclusion compounds with α‐, β‐ and hydroxypropyl‐α‐cyclodextrin as proven by surface tension measurements, 1H NMR spectroscopy and titration microcalorimetry. Mainly the octamethylene segments were covered by the cyclodextrins. This inclusion can be used to increase the solubility and the critical micelle concentration of the polyester in water.
Association thickener by host guest interaction of a β‐cyclodextrin polymer and a polymer with hydrophobic side‐groups
Authors: Weickenmeier Meik , Wenz Gerhard , Huff Jürgen 
Published: April 2003

AbstractA host polymer with pending β‐cyclodextrin side‐groups and a guest polymer with pending hydrophobic 4‐tert‐butylanilide side groups were synthesized by polymeranalogous reactions starting from poly[(maleic anhydride)‐alt‐(isobutene)] (M̄w = 60000). The inclusions of both polymers with complementary monomeric guests and hosts are proven by microcalorimetry. The interaction of the host polymer and the guest polymer in aqueous solution is accompanied by a tremendous increase in viscosity.
Elastomers with multimodal distributions of network chain lengths
Authors: Mark J.E. 
Published: April 2003

AbstractThe goal of primary interest in these investigations was the development of a novel method for preparing elastomeric networks having unusually good ultimate properties. The technique involves end linking mixtures of very short and relatively long functionally‐terminated chains to give bimodal networks. Such (unfilled) “bimodal” elastomers show very large increases in reduced stress or modulus at high elongations because of the very limited extensibility of the short chains present in the networks. This non‐Gaussian behavior also appears in compression or biaxial extension, shear, tearing, and cyclic fatigue tests. Non‐Gaussian theories taking into account this limited extensibility give a good account of the experimental results. Bimodal distributions also facilitate strain‐induced crystallization, and thus the reinforcement it provides. Suggestions are made for seeking additional advantages from multimodal distributions that are trimodal or higher.
The relaxation spectra of polymer networks with different types of topology, ordering, heterogeneity
Authors: Gotlib Yuli Ya. , Gurtovenko Andrew A. , Torchinskii Isaak A. , Shevelev Vladimir A. , Toshchevikov Vladimir P. 
Published: April 2003

AbstractMany characteristic features of the relaxation spectra of the different types of polymer networks (meshlike and tree‐like) manifesting in experimental behaviour are determined by manifold types of local and long‐range irregularities or inclusions existing even in the simplest network structures. These irregularities in the local topology, in the fluctuations of the local orientational order existing due to stretching of the chains in the bulk elastomers (even in the non‐ordered elastomers), also due to possible LC‐ordering, the distribution of chain lengths between junctions and possible existence of cross‐link agglomerations and domains at random cross‐linking and the influence of the position of the chain element relative to junctions lead to variety of relaxation spectra, frequency and time‐dependencies. The long‐range hydrodynamic effects in bulk network can also lead to drastic variation of relaxation spectra. The inclusion of elongated rigid particles in polymer gels and network leads to the appearance of new branches of relaxation spectra changing and overlapping the relaxation spectra of the primary network system.
Scale dependent diffusion in latex films studied by photoinduced grating relaxation technique
Authors: Bartsch Eckhard , Jahr Thilo , Eckert Thomas , Sillescu Hans , Veniaminov Andrei 
Published: April 2003

AbstractThe transition from an aqueous dispersion of polyacrylate latices into a homogeneous polymer film on drying has been studied by monitoring the diffusion of hydrophobia and hydrophilic photochromic molecular probes with the help of a holographic grating relaxation (forced Rayleigh scattering) technique. Experiments with the hydrophobic probe in wet films result in an unusual spatial scale‐dependence of the apparent diffusion coefficient that degenerates into a normal scale‐independent diffusion coefficient as the film dries. Employment of a two‐state diffusion model allows extracting the diffusion coefficients and mean displacements of the tracer in the polymer cores of the latex particles and in the hydrophilic interface meshes surrounding them. The cores were found to stay essentially intact, whereas the interfacial regions change dramatically with the residual water concentration. Its influence on diffusion disappears on drying but can be partially restored by remoistening the material. The interface can be efficiently controlled by varying the surfactant concentration. A water‐soluble tracer was found to diffuse in four different environments. In addition to the already known polymer cores and the hydrophilic interfacial regions, we found a large contribution of fast diffusion in a water rich region and a very small contribution of “ultraslow” diffusion in a state supposedly related with aggregated surfactant.
Interaction of dissolved proteins with spherical polyelectrolyte brushes
Authors: Wittemann A. , Haupt B. , Merkle R. , Ballauff M. 
Published: April 2003

AbstractWe consider the adsorption of bovine serum albumin (BSA) on spherical polyelectrolyte brushes (SPB). The SPB consist of a solid polystyrene core of 100nm diameter onto which linear polyelectrolyte chains (poly(acrylic acid), (PAA)) are grafted. The adsorption of BSA is studied at a pH of 6.1 at different concentrations of added salt and buffer (MES). We observe strong adsorption of BSA onto the SPB despite the effect that the particles as well as the dissolved BSA are charged negatively. The adsorption of BSA is strongest at low salt concentration and decreases drastically with increasing amounts of added salt. The adsorbed protein can be washed out again by raising the ionic strength. The various driving forces for the adsorption are discussed. It is demonstrated that the main driving force is located in the electrostatic interaction of the protein with the brush layer of the particles. All data show that the SPB present a new class of carrier particles whose interaction with proteins can be tuned in a well‐defined manner.
Novel diacetylene‐containing polymers for second order NLO applications: effect of main chains and structure property relationships
Authors: Hernández Susana , Miura Hirohiko , Beristain Miriam F. , Ogawa Takeshi , Watanabe Toshiyuki , Miyata Seizo 
Published: April 2003

AbstractIn order to obtain polymers having high second order nonlinear optical (NLO) response, various novel polymers that contain polar dye molecules in side chains and diacetylenic groups in the main chains were synthesized, and their second order NLO properties were studied. Some of these polymers consisting of para‐benzoate and para‐cinnamate main chains, showed extremely high NLO coefficients, d33 of 200 ‐ 350 pm/V, and the corresponding meta polymers showed much inferior NLO coefficients. The polymers having aliphatic main chains had very little NLO response probably because of their low glass transition temperatures and flexibility of main chains. The high SHG responses of these polymers are attributed to their facile orientation of both chromophores and main chains. In the case of para‐polymers, the main chain orientation of alkoxybenzoate and cinnamate along the chromophore is thought to be a reason for their high NLO coefficients.
Styrene copolymerization using diphenylzinc‐additive initiator systems: styrene/p‐substituted styrenes
Authors: Rabagliati Franco M. , Pérez Mónica A. , Cancino Rodrigo A. , Soto Marcelo A. , Rodriguez Francisco J. , Caro Carlos J. 
Published: April 2003

AbstractCombined systems including diphenylzinc (Ph2Zn), a metallocene, and methylaluminoxane (MAO), have been employed to initiate the copolymerization of styrene (S) with p‐alkylsubstituted styrenes and with α‐olefins. The copolymerization processes depend largely on the comonomer, the nature of the metallocene included in the initiator system, the presence of Ph2Zn, the polymerization temperature and the solvent used. Titanocenes produced true copolymers for S/p‐substituted styrene, but not in S/α‐olefin copolymerization. On the other hand zirconocenes either did not copolymerize S/p‐substituted styrene or produced very low conversions, while they succeeded in copolymerizing S/α‐olefin, depending on the particular zirconocene employed. A low p‐methylstyrene (p‐MeS) content in the S/p‐MeS copolymer and a low p‐tertbutylstyrene (p‐ButS) content in the S/p‐ButS copolymer decreased Tm, making them easier to process material than s‐PS.
Suppression of secondary PL emission by indirect photoexcitation
Authors: Byun H.Y. , Chung I.J. , Suh Y.‐S. , Shim H.K. , Kim D.Y. , Kim C.Y. 
Published: April 2003

AbstractA blend of a newly synthesized polyfluorene(PDHBF) and polyvinylcarbazole(PVK) exhibits a photoluminescence(PL) emission spectrum of PDHBF without an increase in the PL intensity on photoexcitation at 340 nm, the UV‐visible absorption maximum of PVK, despite of a substantial spectrum overlap. However, the indirect photoexcitation of the blend suppresses the secondary emission of the PL with the maximum at 520 nm. The chromophores generating the secondary emission are formed when the chromophores are photoexcited above the critical energy level of an excited state. The chromophores formed by the energy transfer have energy lower than the critical energy and fail to form the excimers. A low temperature PL study of the blend in a cryogenic chamber proves that the energy transfer in the system takes place mainly between the excimers of PVK generated by the partially eclipsed dimeric states of two carbazole units and the fluorophores of PDHBF.
Durable chiral sensor based on quartz crystal microbalance using self‐assembled monolayer of permethylated β‐cyclodextrin
Authors: Ng Siu‐Choon , Sun Tong , Chan Hardy S.O. 
Published: April 2003

AbstractA novel chiral sensor based on quartz crystal microbalance (QCM) with a self‐assembled monolayer of permethylated β‐cyclodextrin as the enantioselective coating has been derived which exhibit improved enantioselectivity and excellent long‐term environmental stability when used in gas phase sensing.
Core‐shell particles: building blocks for advanced polymer materials
Authors: Pham Hung H. , Kumacheva Eugenia 
Published: April 2003

AbstractPolymer particles with submicrometer dimensions show promising applications in “bottom‐to‐top approach” to fabrication of materials with periodic structure, function, and composition. A novel approach to producing such materials is proposed, which employs core‐shell particles with specific structures and compositions. We report on the synthesis of core‐shell particles using interfacial polymerization and heterocoagulation techniques. The compositions of core‐forming material and/or the shell‐forming polymers were selectively controlled to be make the cores or the shells rigid or fluid, fluorescent or non‐fluorescent, organic or inorganic. Several potential applications of nanocomposite materials obtained from these particles are demonstrated, including three‐dimensional optical data storage and optical limiting and switching.
Effects of external fields on macromolecular cholesteric phase
Authors: Wang Linge , Huang Yong 
Published: April 2003

AbstractEffects of external fields such as magnetic field and boundary conditions on supramolecular structure, molecular arrangement and the texture of the ethyl‐cyanoethyl cellulose cholesteric liquid crystalline solutions were investigated. It was found that the molecules of (E‐CE)C are oriented to perpendicular to the magnetic field and the diamagnetic anisotropy of (E‐CE)C is negative. With homeotropic anchoring boundary condition, the molecules are aggregated with focal‐conics arrangement the molecules are aggregated with planar arrangement with homogeneous anchoring boundary condition. The effects of the external field on the orientation of the cholesteric phase were influenced by the concentration of the solution because the twist power of the cholesteric was varied with the concentration. And the effects are also restrains by the surface tension of the interphase.
Structural evidence of grafting in electron beam irradiated starch‐allylurea blends
Authors: Olivier A. , Luna‐Carlos J. , Cazaux F. , Coqueret X. 
Published: April 2003

AbstractThe effectiveness of covalent grafting in mixtures of N‐allylurea (AU) and amorphized starch submitted to electron beam irradiation was studied for elucidating the chemical changes at the origin of the physical stabilization observed after radiation processing. FTIR and nmr analysis were used to quantify the progress of AU conversion upon irradiation of the mixtures and to gain information on the structure of the products. The grafting yield was determined by gravimetry after selective solubilization that extracts AU monomer and its homopolymer from the covalently modified polysaccharide. MALDI‐TOF spectrometry applied to irradiated mixtures of AU and maltotriose, as a model compound, affords unambiguous evidence of covalent grafting. The obtained data allow to estimate the size of the AU grafts and to propose mechanistic pathways for radiation grafting.
Surface thermal molecular motion of chain end‐modified polystyrenes
Authors: Kajiyama Tisato , Tanaka Keiji , Takahara Atsushi 
Published: April 2003

AbstractSurface glass transition temperature, Tgs, of three classes of monodisperse polystyrene, proton‐terminated (PS‐H), α,ω‐diamino‐terminated (α,ω‐PS(NH2)2) and α,ω‐dicarboxy‐terminated (α,ω‐PS(COOH)2), were studied by scanning force microscopy. Tgs of all samples was discernibly lower than the corresponding bulk glass transition temperature, Tgb. Also, Tgs value was strongly dependent on what the chemical structure of chain end groups was. Based on the time‐temperature superposition principle, apparent activation energy of the αa‐relaxation process corresponding to surface segmental motion was evaluated to be approximately 230 kJ·mol−1. This value was much smaller than the reported bulk ones, and was independent of the chemical structure of chain ends. This result implies that the cooperativity for the αa‐relaxation process at the PS surface is reduced in comparison with the bulk due probably to an existence of the free space presented to polymer segments at the surface. Hence, it was concluded that the surface αa‐relaxation process was activated by not only the chain end effect but also the reduced cooperativity at the surface.