bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and catalytic activity of adenine containing polyamines
Authors: Décout Jean‐Luc , Vergne Jacques , Maurel Marie‐Christine 
Published: April 2003

AbstractN6‐Ribosyladenine has been obtained as a major product in the condensation of adenine and ribose under presumably prebiotic conditions. This abnormal nucleoside exhibits a pronounced catalytic activity as compared to histidine, in the hydrolysis of p‐nitrophenyl acetate. The N6‐substituted adenine ring could be considered as a substitute for the imidazole moiety, which could have played a catalytic role in primitive enzymes. To study in more details the catalytic properties of such a group when placed in a favourable microenvironment, it was linked to poly(allylamine). The presence of one adenine ring in ten residues accelerated the p‐nitrophenyl butyrate hydrolysis at pH 8. The rate was increased two‐fold compared to the starting polymer and 100‐fold compared to free adenine. A remarkable, more than 400‐fold acceleration compared to free adenine was measured when long hydrophobic dodecyl side chains were attached as substrate binding sites on the polyamine containing adenine rings. Under mild basic conditions, the catalytic activity of the polymers in the hydrolysis of p‐nitrophenyl esters strongly increases with pH. A cooperative effect between the unprotonated aliphatic amino groups and adenine rings in proton transfers could explain these results. The imidazole ring of N6‐substituted adenine derivatives could act in catalysis with water as a proton‐relay system through a tautomeric equilibrium as the imidazole residue in actual enzymes.
Thermoplastic graft copolymer elastomers with chain‐folding or bifurcated side chains
Authors: Eisenbach Claus D. , Heinemann Torsten 
Published: April 2003

AbstractGraft copolymers with a poly(oxytetramethylene) main chain and molecularly uniform oligourethane grafts were synthesized by substitution polycondensation of a telechelic polyether and the corresponding α,α′‐bifunctional oligourethane macromonomer. The side chains were either characterized by a built‐in constitutional unit allowing a symmetrical chain fold or by bifurcation with two equally long oligourethane branches. Differential scanning calorimetry, small‐angle X‐ray scattering and dynamic mechanical analysis proved a microphase‐separated system with semicrystalline oligourethane hard domains, and the materials were thermoplastic elastomers. These data and the comparative study of model compounds for the specially structured grafts and of poly(ether‐urethane)s with symmetrically chain‐folded segments illustrated that the morphology and properties of these polyurethane elastomers could be perfectly mimicked by a graft copolymer with bifurcated side chains.
Cationic polymerization of hexamethylcyclotrisiloxane by trifluoromethanesulfonic acid and its derivatives, 2. Reaction involving activated trifluoromethylsulfonates
Authors: Toskas Georgios , Besztercey Gyula , Moreau Michel , Masure Michèle , Sigwalt Pierre 
Published: April 2003

AbstractSilyl trifluoromethanesulfonates are inactive for the polymerization of cyclosiloxanes in the complete absence of trifluoromethanesulfonic (triflic) acid, but polymerization occurs in its presence. Using a triflic ester as tagged silyl triflate (benzyldimethylsilyl triflate) the degree of polymerization (DPn) of the linear polymer formed with hexamethylcyclotrisiloxane (D3) in CH2Cl2 at 20°C is inversely proportional to the ester concentration and near to the theoretical value. The polymer contains one PhCH2(CH3)2 Si group per macromolecule, in agreement with a propagation occurring on the monoester PhCH2(CH3)2 SiD3x OTf. By comparison with experiments using the acid alone, polymerizations made in the presence of this ester lead to the suppression of the formation of macrocycles and to a strong decrease of that of D9 and D12. But the amount of D6 is only slightly reduced, which agrees with the hypothesis of its main direct formation on the active sites and not by ring closure of a silanol ester. The rate of D3 polymerization is internally 1st order in [D3] and externally proportional to both acid and ester initial concentrations, in agreement with a propagation involving silyl triflates activated by the acid, interconverting with transitory siloxonium ions leading to D6 formation by a ring expansion involving the polymer chain.
Main chain modification of aromatic polyamides by incorporation of kinked, flexible monomers
Authors: Maglio Giovanni , Palumba Rosario , Vignola Maria Carmela 
Published: April 2003

AbstractMultiring diamines and diacids containing ether and isopropylidene or hexafluoroisopropylidene bridges between phenyl groups were used alone or together with 1,4‐phenylenediamine and terephthalic acid to prepare flexible or semirigid aromatic polyamides by direct polycondensation using triphenyl phosphite and pyridine as condensing agents. All the polyamides are readily soluble in N,N‐dimethylacetamide, N‐methyl‐2‐pyrrolidone and N,N‐dimethylformamide. The wholly flexible polyamides are completely amorphous whereas those prepared from 1,4‐phenylenediamine or terephthalic acid are partially crystalline and melt in the temperature range from 276 to 330°C. Thermal analysis shows Tg's in the range from 204 to 216°C for the wholly flexible polyamides and in the range from 239 to 257°C for the semirigid ones. Both classes of aromatic polyamides show excellent thermal resistance which is comparable with that of rigid‐rod aramides.
Conformational properties of the amphipathic lytic polypeptide bombolitin II. A circular dichroism, NMR and computer simulation study
Authors: Battistutta Roberto , Pastore Annalisa , Mammi Stefano , Peggion Evaristo 
Published: April 2003

AbstractBombolitin II is a member of a family of five structurally related heptadecapeptides, originally isolated from the venom of a bumblebee, acting at the membrane level and able to increase the activity of phospholipase A2. The biological activity of bombolitins seems to be related to their ability to form amphipathic helical structures. To complete our systematic studies on this class of peptides, in the present work we synthesized bombolitin II by solid phase methodology. The secondary structure of this peptide was fully characterized by circular dichroism, 1H NMR, distance geometry and molecular dynamics simulation. The peptide tends to aggregate in aqueous solution at millimolar concentrations, with formation of bundles of amphiphilic helices. In dilute aqueous solution (10−5 mol/L) bombolitin II adopts an amphipathic helical structure in the presence of sodium dodecyl sulfate. The helical segment spans the sequence from residue 2 to residue 16. The results are in line with the hypothesis that this class of peptides modulate the acitivity of phospholipase A2 by altering the physical state of the aggregated substrate.
Synthesis of new polymers containing α‐(trifluoromethyl)‐acrylate units
Authors: Aglietto Mauro , Passaglia Elisa , di Mirabello Lorenzo Montagnini , Botteghi Carlo , Paganelli Stefano , Matteoli Ugo , Menchi Gloria 
Published: April 2003

AbstractFree radical polymerization of both α‐(trifluoromethyl)acrylic acid (TFMAA) and its methyl ester MTFMA is shown to be possible in the presence of bis(4‐tert‐butylcyclohexyl) peroxycarbonate (Percadox) as initiator and dioxane or THF as solvent. Also it is shown that copolymers of TFMAA with α‐olefins (1‐decene, 2‐methyl‐1‐hexene) and of methyl α‐(trifluoromethyl)acrylate (MTFMA) with vinyl ethers (butyl, 2‐ethylhexyl, and menthyl vinyl ether) can be simply obtained with AIBN as initiator; these copolymers have a predominantly alternating structure.
Novel types of polysaccharidic assemblies
Authors: Crescenzi Vittorio , Imbriaco David , Velàsquez Cristòbal Làrez , Dentini Mariella , Ciferri Alberto 
Published: April 2003

AbstractNew types of polysaccharidic assemblies based on chitosan and uncharged or charged derivatives of scleroglucan are presented. Macroscopic assemblies having a spherical skinlike shape were prepared by controlled mixing of two polyelectrolyte solutions. Hydrogels based exclusively on the above natural derivatized polysaccharides crosslinked via simple chemical processes, avoiding the use of extraneous reticulating agents and organic solvents, are also described. These biocompatible materials may, eventually, be used in drug release formulations or for the incapsulation of bioactive macromolecules. The interesting possibility exists to study the micelle formation of amphiphiles within the spherical skins.
A study for distinguishing mono‐ and bimetallic mechanisms in heterogeneous Ziegler‐Natta catalysis
Authors: Sacchi Maria Carmela , Forlini Fabrizio , Tritto Incoronata , Locatelli Paolo , Morini Giampiero 
Published: April 2003

AbstractThe results of 13C NMR analysis of chain end groups of poly(propylene) samples prepared with traditional δ‐TiCl3 and high yield TiCl4/MgCl2 catalysts in the presence of different 13C enriched alkylaluminium cocatalysts — Al(13CH2CH3)3, Al(13CH2CH3) (is‐o‐C4H9)2 and Al(13CH2CH3)(CH3)2 — have been compared. The data show that, while molecular weights and fraction distribution change from one cocatalyst to another, the mechanism of steric control is the same independent of the cocatalyst used. This supports the hypothesis that the role of the metal alkyls is that of activating the solid catalyst by alkylation of the titanium surface complexes, but they do not participate directly in the structure of the active center.
Synthesis and thermal properties of side‐chain liquid‐crystalline poly(glycidyl ethers) with racemic and chiral backbone
Authors: Taton Daniel , Le Borgne Alain , Spassky Nicolas , Noël Claudine 
Published: April 2003

AbstractOxiranes bearing a 4‐cyanobiphenyl‐4′‐oxy mesogenic group with spacers of different length have been synthesized from glycidyl p‐toluenesulfonate or epichlorohydrin (racemic or optically active). These monomers were polymerized with anionic initiators (CsOH, tBuOKtBu: tert‐butyl, Et: ethyl.
) or a chelate initiator (AlEt3/H2O/acetylacetone). A transfer of chirality from the polymer backbone to the mesophase is observed for polyethers with a short spacer. A cholesteric phase is observed for the optically active polymer while the racemic polymer is nematic. Increasing the length of the spacer leads to a smectic mesophase. However, in that case, the effect of the chiral centre of the polymer backbone on the mesomorphous properties is not detected.
Syndiotactic specific polymerization of styrene: driving energy of the steric control and reaction mechanism
Authors: Longo Pasquale , Proto Antonio , Zambelli Adolfo 
Published: April 2003

AbstractThe stereoregularity of polystyrenes prepared in the presence of different syndiotactic specific homogeneous catalysts, at different temperatures and monomer concentrations, has been evaluated by 13C NMR. It is confirmed that the statistical model of the stereospecific propagation is first‐order Markovian. The stereoregularity of the polymers decreases while increasing the polymerization temperature and is affected by the concentration of the monomer, by the ligands of the transition metal precursor of the catalyst, and is higher in the presence of titanium based catalysts. Polymerization of substituted styrenes is increasingly stereospecific in the order p‐chlorostyrene < styrene < p‐methylstyrene. The results strongly support the polyinsertion mechanism proposed in a previous paper by some of us.
Synthesis of polyurethanes by polycondensation of active biscarbonates of diols with hexamethylenediamine and its derivatives
Authors: Katsarava Ramaz , Kartvelishvili Tamara , Khosruashvili Tamara , Beridze Vakhtang 
Published: April 2003

AbstractA new synthesis pathway to polyurethanes (PURs) by polycondensation of active carbonates of diols with hexamethylenediamine was investigated in detail including model studies. It has been shown that high‐molecular‐weight PURs (ηred ≤ 3,8 dL/g) can be obtained under optimum reaction conditions. Salts of the diamine and its N,N′‐trimethyl‐silylated derivative were also used for the synthesis of film‐ and fiber‐forming PURs.
Linear non‐conjugated dienes from biomass as termonomers in EPDM synthesis, 1. Study of their reactivity in homo‐, co‐ and terpolymerizations
Authors: Dolatkhani Mohamad , Cramail Henri , Deffieux Alain 
Published: April 2003

AbstractThis paper deals with the use of 3,7‐dimethylocta‐1,6‐diene (3,7‐DMO) and 5,7‐dimethylocta‐1,6‐diene (5,7‐DMO), issued from terpene feedstock, as termonomers for the synthesis of ethylene‐propylene‐diene terpolymers (EPDM). Their reactivity is first compared to 7‐methylocta‐1,6‐diene (MOCD), an industrial linear diene, in homopolymerization and cross‐copolymerization. Two catalytic systems are used: TiCl3, 1/3AlCl3, 14 MgCl2 associated with Al(C2H5)3, and VOCl3 or VCl4 associated with Al(C2H5)2Cl. The influence of the diene structure on the observed order of reactivity is discussed. In a second part, the copolymerization and the terpolymerization of the different dienes with ethylene and propene are implemented. A drastic influence of the diene structure and concentration on the productivity (and activity) is observed. Potentiometric titrations of the vanadium, performed both in the absence and in the presence of dienes (and of other substituted olefins), indicate that the productivity loss mainly results from a reduction process of the vanadium, involving the di‐ or trisubstituted olefins
Dynamic viscoelastic properties of blends of poly(ethylene‐co‐vinyl acetate) and a modified starch
Authors: Jauregui Belén , Muñoz María Eugenia , Santamaria Anton 
Published: April 2003

AbstractWe report dynamic viscoelastic measurements of a series of binary blends of hydroxyethyl ether of starch and ethylene‐vinyl acetate copolymer (EVA), which are correlated with the granular arrangement of the starch derivative within the EVA matrix and the adhesion between both phases, studied by scanning electron microscopy. The rheological properties are similar to those of polymers filled with solid spheres, although we found a minimum in the Newtonian viscosity and a maximum in the elasticity at low starch derivative concentrations, which have been attributed to a change in the density of chain entanglements.
Synthesis and photobehaviour of hydrophilic acrylic polymers containing azobenzene groups
Authors: Altomare Angelina , Ciardelli Francesco , Solaro Roberto , Tirelli Nicola 
Published: April 2003

AbstractNew hydrophilic photochromic polymeric systems containing side‐chain azobenzene groups were synthesized by radical copolymerization of 4‐acryloyloxyazobenzene with hydrophilic acrylic comonomers containing in the side chain either amide or quaternary onium groups. In all cases copolymerization products characterized by an almost random distribution of monomeric units were obtained. On irradiation at 366 nm, azobenzene‐ containing copolymers underwent trans‐to‐cis photoisomerization of the side‐chain azo groups and in all cases monoexponential decay of the 320 nm absorbance was observed. Copolymer properties were investigated by DSC analysis, solubility measurements, UV spectroscopy and photoisomerization kinetics. The results obtained are discussed in terms of nature and content of hydrophilic comonomer and water content of the solvent used. The possibility of photomodulating copolymer solubility is also suggested.
A novel ferroelectric side‐chain liquid crystalline polysiloxane and its monomer with low transition temperature at the air/water interface
Authors: Xue Qing‐Bin , Chen Xiao , Yang Kong‐Zhang , Zhang Qi‐Zhen 
Published: April 2003

AbstractStable monolayers of a novel side‐chain liquid crystalline polysiloxane (PI) and its monomer (MI), both having low transition temperatures, are formed at the air/water interface at 20°C. In monolayer films mesogens are packed closely and their long axes are titled slightly to the water surface. Monomer molecules are thought to lie flat on the water surface when they are initially spread, and a possible model is presented to describe the conformational changes after compressing. Multilayer formations have been observed during isothermal compression of both the polymer and the monomer. Monomer monolayers cannot be deposited onto hydrophobic substrates, whereas polymer monolayers can be deposited at various surface pressures with Y‐type or Z‐type. UV‐Vis spectra of PI Langmuir‐Blodgett films indicate that H‐aggregates are formed during film formation. The absorption of Langmuir‐Blodgett films and cast films shows a distinct hypsochromic shift compared with that of PI chloroform solution.
The fast activation of ε‐caprolactam polymerization in quasi‐adiabatic conditions
Authors: Russo Saverio , Imperato Amalia , Mariani Alberto , Parodi Fabrizio 
Published: April 2003

AbstractTwo carbamoyl‐type activators of ε‐caprolactam (CL) anionic polymerization have been used in quasi‐adiabatic conditions with sodium caprolactamate as initiator, at different concentrations and relative ratios. The reaction products have been characterized in terms of high‐polymer content and extent of crosslinking. Correlations between the various polymerization parameters on one side, and amount of crosslinked fraction and resultant polymer properties on the other side, have been found. Potential implications on a fine control of PCL properties, exerted by the experimental conditions chosen for the anionic synthesis, are envisaged.
Synthesis and polymerization of 2‐cyano‐2‐methyltrimethylene carbonate
Authors: Kalbe Michael , Keul Helmut , Höcker Hartwig 
Published: April 2003

Abstract2‐Cyano ‐methyltrimethylene carbonate (CMTC, 2) was synthesized starting from 2‐methylacrolein (6), propionaldehyde (8) or 2‐hydroxymethyl‐2‐methyl‐1,3‐propanediol (9). A key position in this synthesis is held by 2,2‐bis(hydroxymethyl)propionitrile (3), which in a first step, is reacted — in conjunction with 2,2‐dimethyl‐1,3‐propanediol (200) — with diphenyl carbonate (17) to result in a statistical copolycarbonate. Ring‐closing depolymerization of this polymer, with a catalyst based on tin, yields in a second step the title monomer, CMTC (2), along with 2,2‐dimethyltrimethylene carbonate (DTC, 1b). Separation of the two monomers can be achieved by selective solubilization of the latter in toluene. Polymerization of CMTC is performed preferentially by using weak nucleophiles as initiators, such as Et2AlOEt, Al(O‐secBu)3 or MgBu2, since strong nucleophiles such as BuLi or ZnEt2 tend to give side reactions with the cyano group. Copolymerization of CMTC with DTC results in statistical copolymers. With Et2AlOEt as initiator copolymers with Bernoulli statistics are obtained, with a ratio of diads DTC/DTC : (DTC/CMTC + CMTC/DTC) : CMTC/CMTC equal to 1:2:1 for equimolar feed composition. With MgBu2 as initiator and the same feed composition, a copolymer with the diad ratio 1:5:1 is obtained. Poly(CMTC) is a crystalline polymer with a melting point of 132.9°C and a glass transition temperature of 68.8 °C.
Liquid crystalline polyfumarates, 2 Polymerization of fumarates with two mesogenic groups per unit
Authors: Jähnichen Klaus , Voigt Dieter , Jehnichen Dieter , Rätzsch Manfred 
Published: April 2003

AbstractThe paper describes synthesis and characterization of some new side‐chain liquid crystalline polymers (SCLCP) obtained by homo‐ and copolymerization of fumarates with two mesogenic groups per unit. The homopolymerization of spacerless bis[4‐(4‐butoxy‐benzoyloxy)phenyl] fumarate (1) did not take place due to steric hindrance of the propagation reaction by the bulky phenyl benzoate groups. The radically induced polymerization of the fumarates with spacer between fumaric unit and the mesogenic groups was performed in bulk. At the polymerization temperature the monomers were isotropic. During polymerization the mixtures became turbid due to phase separation of the isotropic monomer and the resulting polymerization products which formed a liquid crystalline (lc) phase. The molecular weights of the obtained homopolymers were relatively low and depended on spacer length. Transfer reactions to the monomer occurred to a considerable extent. The homopolymers showed an enantiotropic SA phase. This was confirmed by X‐ray measurements. A model for the arrangement of the polymer backbones in the smectic phase is given. Copolymerization of bis{6‐[4‐(4‐butoxybenzoyloxy)benzoyloxy]hexyl} fumarate (4) with styrene yielded copolymers 6 with different percentages of styrene. All copolymers formed an enantiotropic SA phase. With increasing percentage of styrene the transition to the isotropic state was shifted toward lower temperatures.
Terpolymerization of propene, ethylene and 1‐dodecene with highly efficient supported catalyst
Authors: Wen Yufeng , Han Shimin , Hu Youliang 
Published: April 2003

AbstractThe terpolymerization of propene, ethylene and 1‐dodecene (PED) with a highly efficient supported Ziegler‐Natta catalyst and the main physical and mechanical properties of PED terpolymers were investigated. It was found that, under equal polymerization conditions, the polymerization activities followed the order: PED terpolymerization > PE, PD copolymerizations > E, D homopolymerizations. The 13C NMR spectra of PED terpolymers indicated the existence of long propylene chain sequences. The content of ethylene and 1‐dodecene in PED terpolymers increased with the enhancement of the mole ratio of ethylene in the gas feed, whereas the effect of the concentration of 1‐dodecene in the reactor is much smaller. The intrinsic viscosity, density, melting temperature and crystallinity of the terpolymers decrease when the amount of comonomers in the feed increases. Compared with polypropene, the tensile and bending strenghts of PED terpolymers are reduced, but the elongation at break is over 700%, and the Izod impact is enhanced both at ambient and low temperatures.
Investigation of γ‐irradiated syndiotactic poly(2‐methylheptyl methacrylate) using NMR spectroscopy
Authors: Dong Limin , Hill David J. T. , O'Donnell James H. , Pomery Peter J. , Brereton Ian M. 
Published: April 2003

AbstractSyndiotactic poly(2‐methylheptyl methacrylate) which was γ‐irradiated at room temperature to a dose of 1600 kGy was investigated by NMR spectroscopy. The 1H and 13C resonances for the macromolecular chain were assigned by using the 2D and the DEPT (distortionless enhancement by polarization transfer) technique. The spin‐echo modified 2D NMR pulse sequence was used to investigate the small molecules and new structures which were formed during γ‐irradiation. The radiation mechanisms for cleavage of the side chain from the main chain and formation of double bonds from both the main chain and the side chain have been formulated based upon the NMR analysis.
Molecular design of biodegradable functional polymers, 4 Poly(vinyl alcohol) block as biodegradable segment
Authors: Matsumura Shuichi , Shimura Yukimasa , Toshima Kazunobu , Tsuji Masao , Hatanaka Tadashi 
Published: April 2003

AbstractThe minimum structure of a poly(vinyl alcohol) block as a biodegradable segment in the polymer chain was estimated with respect to block length and its stereochemical configuration. It was found that poly(vinyl alcohol) block with a chain length of more than 3 monomeric units and having an isotactic structure is quickly biodegraded, in contrast to an atactic block having the same chain length, by poly(vinyl alcohol) (PVA) assimilating microbes and PVA‐dehydrogenase. It was also found that the substrate specificity of PVA‐dehydrogenase obtained from both Alcaligenes faecalis KK314 and Pseudomonas sp. 113 P3 is quite similar.