bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polylactones, 8. Mechanism of the cationic polymerization of L,L‐dilactide
Authors: Kricheldorf Hans R. , Dunsing Ruth 
Published: April 2003

AbstractVarious acidic compounds were tested as potential initiators of the cationic polymerization of L,L‐dilactide. Regardless of solvent and temperature only trifluoromethanesulfonic acid and methyl triflate proved to be useful initiators. With methyl triflate as initiator L,L‐dilactide polymerizes faster than diglycolide, whereas diglycolide is more reactive when anionic or complexing initiators are used. Initiation with methyl triflate yields poly(L‐lactide) with methyl ester endgroups indicating that the chain growth proceeds via cleavage of the alkyl‐oxygen bond. At polymerization temperatures > 100°C the resulting poly(L‐lactide) is 100% optically active indicating that the chain growth does not proceed via free carbenium ions, but via triflate ester endgroups. All attemps to identify cyclic dioxocarbenium ions as reaction intermediates failed, because propagation is much faster than initiation. However, in nitromethane oligomers with triflate ester endgroups were detected. For comparison the reaction of γ‐valerolactone with methyl triflate was studied by means of IR and 1H NMR spectroscopy. Methylation of the exocyclic oxygen yielding a cyclic dioxocarbenium ion was found to be the sole reaction.
Synthesis of a new antithrombogenic block copolymer containing fluorinated segments: poly(nonafluorohexyl acrylate‐b‐styrene)
Authors: Akemi Hitoshi , Aoyagi Takao , Shinohara Isao , Okano Teruo , Kataoka Kazunori , Sakurai Yasuhisa 
Published: April 2003

AbstractTwo types of block copolymers, 3a and 3b, were synthesized from α‐hydro‐ω‐(2‐hydroxyethylthio)poly[1‐(3,3,4,4,5,5,6,6,6‐nonafluorohexyloxycarbonyl)ethylene] (1a) or α‐hydro‐ω‐(2‐aminoethylthio)poly[1‐(hexyloxycarbonyl)ethylene] (1b) and α,ω‐bis(4‐cyanatophenylthio)‐poly(1‐phenylethylene) (2), respectively, and the adhesion of blood platelets to these polymer surfaces was evaluated. Adhesion and activation of platelets were found to be effectively suppressed at the lamellar‐microdomain surface of block copolymer 3a, having a surface free energy gap between microdomains of about 20 dyn/cm, whereas no such a suppression was observed for the microdomain structured surface of block copolymer 3b with a small surface free energy gap between the microdomains. Further, a random copolymer from nonafluorohexyl acrylate and styrene without microdomain structure does not suppress the adhesion and activation of platelets. From these results, it was concluded that the microdomain morphology and the surface free energy gap between microdomain is important to produce antithrombogenicity.
Rheological properties of liquid‐crystalline side‐group polymers in the isotropic, nematic, and smectic states
Authors: Zentel Rudolf , Wu Jishan 
Published: April 2003

AbstractThe melt viscosity of seven liquid‐crystalline side‐group polymers with polyacrylate and polysiloxane main chains is measured as a function of shear rate and temperature. In the isotropic and also in the nematic phase none or only a very small dependence of the melt viscosity on shear rate is observed for the shear rates investigated. The melt viscosity in the nematic phase is higher than that in the isotropic phase. This is contrary to the results for liquid crystalline mainchain polymers and points to the fact, that there is no resulting orientation in shear flow of liquid‐crystalline side‐group polymers in the nematic phase. In the smectic phase the melt viscosity is very high and strongly shear‐rate dependent. These results are compared with dielectric relaxation measurements on polymethacrylates and a polychloroacrylate.
Dynamic mechanical behaviour and phase separation of mixtures of polysulfone with bis[4‐(4‐ethynylphenoxy)phenyl]‐sulfone or poly(phenylene sulfide)
Authors: Zeng Hanmin , Mai Kancheng 
Published: April 2003

AbstractThe dynamic mechanical behaviour and microphase‐separation structure of polysulfone blends with bis[4‐(4‐ethynylphenoxy)phenyl]sulfone and with poly(phenylene sulfide) were investigated using torsional braid analysis and scanning electron microscopy. The experimental results showed that the size and shape of dynamic mechanical damping peaks and the structure characteristics of polysulfone blends with sulfur‐containing polymers do not only depend on the chemical and physical nature and the weight fractions of the two components but also on conditions of thermal treatment leading to cross‐linking reactions. In these multi‐component polymer systems, the initially compatible mixture turns into an incompatible two‐phase system during heating.
Shrinkage force and molecular orientation in polyacrylonitrile fibers
Authors: Henrici‐Olivé Gisela , Olivé Salvador , Frushour Bruce G. 
Published: April 2003

AbstractA correlation between sonic modulus and shrinkage force was found for fibers spun from copolymers of acrylonitrile and other vinyl monomers. Using this correlation, the orientation factor as defined by Moseley can be calculated from a single shrinkage force measurement, permitting a fast and reliable characterization of fibers and spinning conditions. Equipment and modus operandi are described.
13C NMR characterization of a new ethylene‐propene copolymer obtained with a high yield titanium catalyst
Authors: Abis Luigi , Bacchilega Giancarlo , Milani Federico 
Published: April 2003

AbstractA detailed microstructural characterization of ethylene‐propene copolymers, obtained with a high yield Ti‐catalyst and showing elastomeric properties, was carried out by 13C NMR spectroscopy. These copolymers show no inversions in propene insertion, a tendency to form blocks of ethylene and propylene, and the presence of both isotactic and atactic blocks of propylene. Furthermore, in these polymers the reactivity ratio product (r1 · r2) and the experimental versus calculated triad distribution point to the presence of components which are heterogeneous with respect to the monomer distribution and composition. 13C NMR analysis of fractions, separated by hexane and ether, supports the above hypothesis.
Liquid crystalline elastomers based on liquid crystalline side group, main chain and combined polymers
Authors: Zentel Rudolf , Reckert Gertrude 
Published: April 2003

AbstractCovalently crosslinked liquid crystalline networks with elastic properties were prepared in isotropic solution from linear liquid crystalline polymers. As linear precursors for the networks were used: (i) polymers with the mesogenic groups in the side groups (polyacrylates and polymethacrylates), (ii) polymers with the mesogenic groups in the main chain (polymalonates) and (iii) polymers with the mesogenic groups in main chain and side groups (“combined liquid crystalline polymers”). In all crosslinked polymers the liquid crystalline phases of the linear polymers are retained. For low degrees of crosslinking (≤2 mol‐%) the phase transition temperatures remain nearly unchanged. These elastomers are very soft above Tg and can be easily stretched for more than 100%. For higher degrees of crosslinking the phase transition temperatures are reduced.
Radical polymerization of methyl methacrylate and methyl acrylate in the presence of an oligomer of 2‐methoxy‐4‐vinylphenol
Authors: Ito Katsukiyo 
Published: April 2003

AbstractMethyl methacrylate (MMA) and methyl acrylate (MA) were polymerized in the presence of an oligomer of 2‐methoxy‐4‐vinylphenol (OMVP) with a double bond at its end. It is shown by means of the UV spectra and the kinetic treatment that the double bond disappears by hydrogen transfer from the growing polymer chain to OMVP and that the OMVP radical formed propagates further. In the polymerization of MMA, the transfer rate is comparable with the termination rate if [OMVP] ≤ 0,52 mol · 1−1. In the polymerization of MA, the transfer rate is very much higher than the termination rate for [OMVP] ≥ 0,016 mol · 1−1. It is suggested that each PMA chain carries one OMVP unit at the end.
Exciplex laser‐induced polymerization of pure ethylene at high pressure
Authors: Brackemann Holger , Buback Michael , Vögele Hans‐Peter 
Published: April 2003

AbstractPure ethylene is photo‐polymerized with an exciplex laser on the KrF line (248 nm) at temperatures from 190°C to 230°C and for pressures up to 3 200 bar. The radical reaction is directly monitored via quantitative high‐pressure high‐temperature near infrared spectroscopy. Toward higher densities and temperatures, the overall quantum yield increases and up to several thousand ethylene molecules are polymerized by one absorbed laser photon. A kinetic scheme is presented which adequately describes the polymerization kinetics as a function of temperature, overall density, laser pulse energy, and conversion. Termination rate coefficient kt is found to decrease in the initial polymerization period, whereas a single value of kt is sufficient to represent kinetic data in the extended conversion range from 20% to 70%.
Influence des conditions de fusion et de cristallisation sur la morphologie superstructurale du polypropylène isotactique cristallisé au dessus de 130°C
Authors: Idrissi Mohamed Oulad Bouyahya , Chabert Bernard , Guillet Jacques 
Published: April 2003

AbstractThe morphology of polypropylene samples cooled from the melt and then isothermally crystallized above 130°C, was studied by optical polarization microscopy. If the temperature of the melt is raised above 175°C, the spherulitic superstructure is fully destroyed. Isothermal crystallization involves negative or positive birefringence which mainly depends on the temperature of crystallization (above or below 130°C). If the temperature of the melt is raised to 172°C, that is to say at a temperature at which no birefringence is detectable, isothermal crystallization leads to negative spherulites above 155°C and to positive ones below 155°C. If the melt is heated between 172°C and 175°C, crystalline lamellae are partially destroyed and they further lead to crystallization of small positive spherulites, which are located inside the initial spherulitic superstructure. These observations are explained in terms of a quadritic arrangement of the lamellae of crystallized polypropylene. Moreover, the crystallization temperature of 155°C appears as a true transition temperature beyond which tangential lamellae cannot exist; this always implies negative birefringence of the spherulites, whatever the melting conditions are.
Synthesis of high‐molecular‐weight polysuccinamides by polycondensation of active succinates with diamines
Authors: Katsarava Ramaz D. , Kharadze Darejan P. , Avalishvili Lamara M. 
Published: April 2003

AbstractHigh‐molecular‐weight, film‐ and fiber‐forming polysuccinamides were synthesized by polycondensation of active diesters of succinic acid with hexamethylenediamine or dodecamethylenediamine under mild conditions. By kinetic investigations it was established that the formation of high‐molecular‐weight polysuccinamides is connected with a low rate of chain‐terminating formation of a cyclic imide and its nearly complete suppression by chain‐growth aminolysis reaction.
Precursors of hydrophilic polymers, 6. Preferential sorption of water on poly[2‐(dimethylamino)ethyl methacrylate] in ethanol/water mixtures
Authors: Přádný Martin , Ševčík Stanislav 
Published: April 2003

AbstractThe study deals with the kinetic behaviour of atactic and isotactic poly[2‐(dimethylamino)‐ethyl methacrylate] (PDAEM) and of low‐molecular‐weight tertiary amines in the quaternization by low‐molecular‐weight alkyl iodides (Mentschutkin's reaction) in water/ethanol solution at 60°C. Unlike quaternization of PDAEM with methyl iodide and 2‐iodoethanol, in the cases of the other alkyl iodides the rate constant of quaternization depends on the initial concentration of the alkyl iodide. The rate constant decreases with increasing concentration of the alkyl iodides. The effect becomes more pronounced in a reaction medium containing 43 wt.‐% of water in a mixture with ethanol as compared to azeotropic ethanol. Such behaviour is attributed to the fact that in solution of a water/ethanolic mixture the tertiary amines investigated in this study are preferentially solvated by water.
Nuclear magnetic resonance studies on polymer carbanions, 5. Polystyryl carbanion with lithium as counter cation and its dimer model compounds
Authors: Matsuzaki Kei , Ishihara Ken , Shinohara Yoshinao , Kanai Taiichi 
Published: April 2003

AbstractOligostyryllithium was synthesized by the reaction of sec‐butyllithium with styrene in diethyl ether at −40°C. Dimer model anions (counter cations: Li and K) of the growing chain ends were synthesized by metallation of 1‐methoxy‐1,3‐diphenylpropane. The structures of the lithium compounds were corroborated by 13C NMR spectroscopy and compared with those of the potassium compounds. As for polystyryllithium and its model compounds, the charge density on the α‐carbon increased and that on the phenyl ring of the growing end decreased with increasing molecular weight, while, in polystyrylpotassium and its model compounds, the charge density on the α‐carbon increased and the one on the phenyl ring did not change with increasing molecular weight. The temperature change of the 1H NMR spectrum of oligostyryllithium in diethyl ether indicated rotation around the C‐1Cα bond at lower temperatures than in tetrahydrofuran, but the activation energy was the same in both solvents. T1 values of the phenyl carbons in model compound 2b were one to two orders of magnitude shorter than those of the protonated compound.
Molmassenabhängigkeit der Geschwindigkeitskonstanten der Adsorption von Polybutylmethacrylat aus Cyclohexan
Authors: Wochnowski Horst , Dzeick‐Pickuth Astrid 
Published: April 2003

AbstractThe kinetics of adsoprtion of poly(butyl methacrylate) on iron powder from cyclohexane as solvent is determined by measuring the polymer concentration during adsorption for different molecular weights. There is an inverse relationship between the rate constant of adsorption k and the molecular weight of polymer. This corroborates theoretical results, which involve the quality of solvent: k ∼ 1/M2a where a is the Kuhn‐Mark‐Houwink exponent. Thus it is possible to determine the quality of solvent by investigations of adsorption using polymers of various molecular weight. Good coincidence with the a‐value received from viscosity data via the Kuhn‐Mark‐Houwink relationship is achieved in the case of cyclohexane.
On the entropy of single flexible polymer chains
Authors: Cifra Peter , Romanov Andrej 
Published: April 2003

AbstractThe existence of a new universal exponent λ in the expression for the number of possible configurations of a flexible self‐avoiding polymer chain is connected to the excluded volume in the chain and rationalized on the basis of loop exlcusion in stepwise growth, N→N + 1, of the chain consisting of N segments. An approximative analytical expression is given for λ. For three‐dimensional chains the theoretical expression gives the value of the exponent obtained from analysis of enumeration data on the number of self‐avoiding chains, while for twodimensional chains λ is underestimated.
Are there covalent active species in the polymerization of styrene initiated by trifluoromethanesulfonic acid?
Authors: Matyjaszewski Krzysztof , Sigwalt Pierre 
Published: April 2003

AbstractPolymerization of styrene by perchloric and trifluoromethanesulfonic acids has been assumed previously to proceed via a pseudo‐cationic mechanism. We found that for the latter system the trifluoromethanesulfonate ester is not stable. Attempts to observe the model 1‐phenylethylester were unsuccessful even at −78°C. In the reaction between 1‐phenylethyl bromide and AgSO3CF3 a very rapid alkylation of the aromatic rings occurs. In the reaction between 1‐phenylethanol and (CF3SO2)2O a very rapid reaction between the intermediate ester (or ion) and the alcohol leads to the formation of the corresponding ether. A reaction carried out with the optically active alcohol indicates that no more than 4% of the intermediate species might have reacted with the alcohol as ester before racemization (i.e. ionization). The macromolecular ester does not seem to be much more stable and in 19F NMR spectra only the acid was observed. An attempt at the formation of a block copolymer with N‐tert‐butylaziridine give zero or very low yield, contrarily to results previously observed with perchloric acid. An analysis of some former results on polymerization kinetics and of the new data given in this paper show no real evidence in favor of the pseudo‐cationic polymerization of styrene in CH2Cl2, initiated by CF3SO3H. The various data may be explained more satisfactorily by a more classical ionic mechanism. Triflic acid can reversibly protonate olefins due to the affinity of the triflate anion being higher for a proton than for a secondary or tertiary carbon atom; this is sufficient to explain the extremely low concentration of ionic species.
Investigation of the polymerization of the N‐carboxyanhydride of γ‐benzyl L‐glutamate, initiated by low‐molecular‐weight and polymeric initiators
Authors: Ovsiannikova Lujdmila A. , Rudkovskaya Galina D. , Vlasov Gennadii P. 
Published: April 2003

AbstractN‐carboxyanhydride of γ‐benzyl L‐glutamate (N‐CA‐γ‐BG) was polymerized with the lowmolecular‐weight initiators 2,2′‐dithiodiglycinanilide (1) and 2,2′‐azo‐2,2′‐dimethyldipropionohydrazide (2) and with poly(methyl methacrylate) (PMMA) of different molecular weights containing amino and hydrazide end groups, exhibiting different nucleophilicities. For comparison, the N‐CA was also polymerized with initiators described in the literature. It could be shown that the induction period depends on the nucleophilicity of the end groups of the initiator. In contrast to the low‐molecular‐weight initiators, the polymerization of the N‐CA with PMMA proceeds without acceleration.
Microstructure of styrene‐methacrylic acid and styrene‐acrylic acid copolymers, 1. 1H NMR study of methylated styrene‐methacrylic acid copolymers
Authors: S̀witała Maria , Wojtczak Zbigniew 
Published: April 2003

AbstractCopolymers of styrene and methacrylic acid were obtained in emulsion, benzene solution, and by grafting. 1H NMR measurements were carried out on the methoxy proton region of their methylated derivatives. From these measurements mole fractions of methacrylic acid centered triads, run numbers, number‐average sequence lengths of methacrylic acid and styrene, and the probability of finding a sequence of n methacrylic acid units were determined. All these quantities are very similar for the emulsion and random copolymers of similar composition. Emulsion styrene‐methacrylic acid copolymers can therefore not be regarded as block copolymers.
Microstructure of styrene‐methacrylic acid and styrene‐acrylic acid copolymers, 2. 1H NMR study of methylated styrene‐acrylic acid copolymers
Authors: S̀witała Maria , Wojtczak Zbigniew 
Published: April 2003

AbstractThe microstructure of styrene‐acrylic acid copolymers prepared in emulsion was studied and compared with the structure of copolymers prepared in benzene solution and by grafting. An analysis of the 1H NMR spectra in the methoxy proton region of methylated copolymers was carried out and mole fractions of acrylic acid centered triads, run numbers, number‐average sequence lengths of acrylic acid and styrene, and the probability of finding a sequence of n acrylic acid units were determined. From these data it is found that the difference in microstructure of emulsion and random copolymers is not great if the copolymers contain up to 30 mol‐% of acrylic acid units, but increases with increase in the acid content of copolymers.
Dielectric relaxation of poly(tolyl methacrylate)s
Authors: Kihira Yasuharu , Sugiyama Kazuo 
Published: April 2003

AbstractThe dielectric relaxation of poly(phenyl methacrylate) and of poly(o‐, m‐, andp‐tolyl methacrylate)s was studied over a wide frequency and temperature range. These samples show three relaxation processes termed α, β, and γ within the temperature ranges 130 to 160°C, 50 to 120°C, and −60 to −20°C, respectively. The α‐ and β‐processes are attributed to the micro‐Brownian motion of the main chain and of the entire side chain, respectively. The γ‐process is suggested to be associated with the relaxation of the tolyl group at the end of the side chain.
Molecular and crystal structure of bis(4‐mercaptophenyl) sulfide as a model compound for poly(1,4‐phenylene sulfide)
Authors: Garbarczyk Józef 
Published: April 2003

AbstractThe molecular and crystal structure of bis(4‐mercaptophenyl) sulfide (3) was determined by means of an X‐ray diffraction analysis. The crystals are monoclinic, P21 /n with four molecules in the unit cell of the dimensions: a = 5,752 (1), b = 25,767 (9), c = 7,954 (2) Å and β = 95,2 (1)°. The structure was solved by direct methods and refined by least‐squares techniques up to R = 0,075 for 1 280 independent reflections. The molecules of 3 do not have own symmetry and are arranged in the unit cell in chains along the 21 axes. Between sulfur atoms of neighbouring molecules hydrogen bonds are formed. From investigations of 3 and poly(1,4‐phenylene sulfide) (2) at low temperatures (down to 90 K) similarities of changes in the crystal structures of both substances were evidenced.
Polymeric bound porphyrines and their precursors, 3. Photoredox properties of combined moieties of porphyrine and phthalocyanine, covalently bound to polystyrene
Authors: Wöhrle Dieter , Krawczyk Gerhard 
Published: April 2003

AbstractCopolymers containing covalently bound phthalocyanine moieties (4) or tetraphenylporphyrine moieties (5) were prepared by the reaction of partially chloromethylated polystyrene (3) with the low molecular substituted phthalocyanine 1b and tetraphenylporphyrine 2b, respectively. Combined binding of moieties of 1b and 2b yielded polymer 6. The photoredox behavior of 1, 2, 4, 5 and 6 was investigated under irradiation with visible light in the presence of a donor and an acceptor. Mixtures of sensitizers (1 + 2 and 4 + 5) resulted in reduced photocatalytic properties. Only in the case of 6, due to reduced intermolecular interactions, higher yields of photochemical reaction products were obtained.
N‐carboxyanhydride of 4‐amino‐4‐carboxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl, a new paramagnetic monomer
Authors: Seidemann Rolf , Dulog Lothar 
Published: April 2003

AbstractN‐carboxyanhydride of 4‐amino‐4‐carboxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (5), a new paramagnetic monomer, was synthesized, starting from 2,2,6,6‐tetramethyl‐4‐oxo‐piperidine (1), which was oxidized to 2,2,6,6‐tetramethyl‐4‐oxo‐piperidine‐1‐oxyl (2). Applying the Bucherer‐Bergs synthesis, 4‐amino‐4‐carboxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (4) was obtained. The key step in the synthesis of 5 is the reaction of the derived amino acids 4a and 4c with phosgene. From the two procedures which were considered the reaction of 4c with phosgene affords the N‐carboxyanhydride 5 in good yield. 5 is suited for spin labeling.