bluuebunny/crossref_metadata_2025_split huggingface dataset:
High molecular weight chitosan 6‐O‐sulfate. Synthesis, ESR and NMR characterization
Authors: Focher Bonaventura , Massoli Alberto , Torri Giangiacomo , Gervasini Antonella , Morazzoni Franca 
Published: April 2003

AbstractSelective sulfation of the primary hydroxyl group of chitosan was performed by means of the pyridine‐SO3 complex after the positions 2 and 3 of the aminoglucopyranosidic ring were protected by coordination with copper ions. The requirements for complexing copper ions were investigated as a function of the pH and Cu(II)/chitosan mole ratio of the starting solution. Cu(II)‐chitosan complexes were characterized by ESR and 13C NMR CP‐MAS investigations; two different paramagnetic Cu(II) species were observed, whose relative quantity changes by changing the pH of the starting solution. The g tensor values (species I: g1‖ = 2,28, g1‖ = 2,06, A2‖ = 160 G; species II; g2‖ = 2,24, g2‖ = 2,06, A2‖ = 160 G) are consistent with a CuN2O2 chromophore. The sulfation reaction was studied in the range of 25 to 75°C using 2 : 1 to 6 : 1 pyridine‐SO3/Cu(II)‐chitosan mole ratios. Under optimized reaction conditions, a selective 6‐O sulfation was obtained in more than 90% yield.
The characteristic ratio of poly(methacrylic acid) in organic solvents
Authors: Horský Jiří , Petrus Vladimír , Bohdanecký Miloslav 
Published: April 2003

AbstractParameters of the Mark‐Houwink equation for poly(methacrylic acid) (PMAA) in methanol at 25°C, [η] = 0,0224 · M0,679, were determined and found to differ markedly from those reported earlier for 26°C. The value of the exponent along with the high value of the second virial coefficient confirms that near to 25°C methanol is not a theta‐solvent for PMAA. By employing extrapolation according to Tanaka, the characteristic ratios C of PMAA in methanol (C = 12,0) and in 2‐ethoxyethanol (C = 9,7) were determined from viscosity data at 25°C. The unperturbed dimensions of PMAA depend on the solvent used. They are larger in organic solvents than in water, but the difference is not so high as assumed before. By using the Stockmayer‐Fixman extrapolation, the characteristic ratio for PMAA in 2‐ethoxyethanol was determined at 70°C, i.e. at a temperature not too far from theta‐conditions (Θ = 65°C, C = 8,2). A comparison with the value for 25°C shows that the unperturbed dimensions of PMAA decrease with increasing temperature.
Influence of termination and transfer on molecular weight distribution of polymers, 6. Chain transfer to monomer and spontaneous termination
Authors: Yuan Cui‐ming , Yan De‐yue 
Published: April 2003

AbstractIn the previous parts of this series, a mathematical procedure was developed for the derivation of molecular size distribution functions of polymers generated in several ionic polymerizations. This paper follows this mathematical procedure to treat theoretically the kinetics of cationic and anionic polymerizations with instantaneous initiation, chain transfer to monomer, and spontaneous termination. The expressions of molecular size distribution functions and other molecular parameters are derived rigorously. Moreover, the simultaneous influence of chain transfer to monomer and spontaneous termination on molecular size distribution is illustrated by means of several numerical examples.
On the preferential extraction of the more isotactic parts of PVC with acetone. A verification by 13C NMR analysis
Authors: Martínez Gerardo , Mijangos Carmen , Millán José Luis , Alemany Antonio 
Published: April 2003

AbstractAcetone‐soluble and ‐insoluble fractions were obtained from two different PVC samples: a polymer prepared in our laboratory at 60°C using 2,2′‐azoisobutyronitrile (AIBN) as initiator (sample A) and a commercial polymer prepared at 70°C (sample B). The content of isotactic, syndiotactic and heterotactic traids was accurately measured by high resolution 13C NMR. From the obtained data it follows that the isotactic triads accumulate preferably in the soluble fraction, the amount of which depends on the type of polymer. In agreement with earlier results, the soluble fraction is about 40% less stable than the insoluble fraction. The reasons for this behaviour are discussed in the light of the higher content of both isotactic triads and some defect structures, as found in the low molecular weight soluble extracts of PVC.
Photoreaktionen von Biscyclopentadienyltitandichlorid in einer monomerhaltigen polymethylmethacrylat‐matrix
Authors: Kopietz Michael , Lechner M. Dieter , Steinmeier Dietrich G. , Franke Hilmar 
Published: April 2003

AbstractIt could be demonstrated that methyl methacrylate (MMA) in a poly(methyl methacrylate) (PMMA)‐matrix can be polymerized by photoinduction with titaniumbiscyclopentadienyl dichloride (titanocene chloride). The photoinduced polymerized portion of MMA consists practically only of isotactic PMMA. The differences in polymerization by irradiation with laser light and with monochromatic light of a mercury light source with the same wavelength are discussed.
Copolymerization of 2‐chloro‐N,N‐dimethylacrylamide
Authors: Smets Georges , Samyn Celeste , Swaelen Kathleen 
Published: April 2003

Abstract2‐Chloro‐N,N‐dimethylacrylamide (CNA) does not homopolymerize easily (2% after 12 days) in contrast to 2‐chloroacrylic esters. Its copolymerization with styrene (St) and methyl methacrylate (MMA) is governed by the following copolymerization parameters: rCNA = 0,03 and rMMA = 3,4; rCNA = 0,2 ± 0,05 and rSt = 1,5 ± 0,2. The very low rates of copolymerization and the low molecular weights of the copolymers are interpreted on the basis of the formation of sterically hindered resonance stabilized radicals, and of high chain transfer constants.
Comparisons among some tetraalkoxysilanes in the hydrolytic precipitation of silica into elastomeric networks
Authors: Sur G. S. , Mark J. E. 
Published: April 2003

AbstractFour tetraalkoxysilanes Si(OR)4 were absorbed into networks of polydimethylsiloxane and then hydrolyzed, using a variety of catalysts, to give reinforcing silica particles. On the basis of the amount of silica precipitated and the extent of reinforcement, the (decreasing) order of effectiveness was found to be tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, and tetramethoxysilane.
Thermodynamics of gas solubility in polymeric liquids
Authors: Panayiotou Constantinos G. 
Published: April 2003

AbstractA modified fluid‐lattice model for mixtures of fluids is presented. Expressions for the basic thermodynamic quantities of mixing are given. From the equation for vapor‐liquid equilibrium, the expression for the Henry constant at low pressure is derived. Weight fraction Henry constants for gas‐polymer and gas‐polymer‐polymer systems are derived as limiting cases. Predictions of theory about the effect of temperature on the Henry constants are compared with experimental data for twenty two polymer‐organic vapor systems. In almost all cases the Henry constants are reproduced within the limit of experimental error. The effect of pressure on gas solubilities is considered. The effect of polymer‐polymer binary interaction parameter on the Henry constant in a gas‐polymer‐polymer mixture is also discussed.
Lyotropic mesophase of imogolite, 1. Effect of polydispersity on phase diagram
Authors: Kajiwara Kanji , Donkai Nobuo , Hiragi Yuzuru , Inagaki Hiroshi 
Published: April 2003

AbstractThe acidic aqueous solution of imogolite is proposed to be an ideal lyotropic system. No temperature dependence was marked on the two phase boundary concentrations (A and B points) of imogolite solutions as predicted by the theories of Flory and Onsager. A satisfactory quantitative agreement was observed with Onsager's theory. The polydispersity of rod lengths was found to shift the A point towards lower concentrations than expected from theory.
Synthesis and characterization of poly(dimethylsiloxane) based liquid crystals
Authors: Allen Richard C. , Wilkes Garth L. , Yilgor Iskinder , Wu Dshilian , McGrath James E. 
Published: April 2003

AbstractA novel set of low molecular weight copolymers have been synthesized which were based on the attachment of mesogenic groups to the terminal points of oligomer backbones. The placement of the groups at the end of the chains apparently allowed a second phase to form more easily than if the groups were attached along the backbone as pendant groups. The nature of the coupler or spacer was determined to influence whether the end groups crystallized or formed liquid crystallinity. The observation of liquid crystallinity was found to depend primarily on the relative concentration of mesogen to backbone molecular weight. Depending upon the specific coupler, there existed two critical values of molecular weight between which mesophase behavior was observed. Below a certain value, the end groups were found to crystallize. Above another critical value, there was no measureable second phase. Liquid crystallinity was only observed when the molecular weight was intermediate between the two critical values.
Second virial coefficient revisited, 3. Viscosity of dilute polymer solutions: Molecular weight dependence of the Huggins coefficient
Authors: Gundert F. , Wolf B. A. 
Published: April 2003

AbstractThe variation of the Huggins coefficient KH with the relative molecular mass M of the polymers was measured for solutions of polystyrene and of polyisobutylene and found to be most pronounced in the case of thermodynamically good solvents but vanishing at the theta‐temperature, where the individual curves kH (T; M) intersect with each other. The experimental results are interpreted as a consequence of the rheological inequality of inter‐ and intra‐molecular contacts between polymer segments. A model is presented according to which kH should be a linear function of M−(a−0,5), where a is the exponent of the intrinsic viscosity‐relative molecular mass relationship (Kuhn‐Mark‐Houwink). The evaluation of the present data, together with information from the literature, yields the individual effects from inter‐ and intra‐molecular intersegmental contacts, their interdependence, and their variation with the thermodynamic quality of the solvent. In thermodynamically poor solvents, were the polymer coils are nondraining, these effects are found to differ extremely; however, they approach each other as the goodness of the solvent improves and the coils become draining; their identity can be extrapolated for a = 1.
Study on the mechanism of 1‐cyanoguanidine cure of epoxy resins using model compounds
Authors: Galy Jocelyne , Gulino Danièle , Pascault Jean‐Pierre , Pham Quang Tho 
Published: April 2003

AbstractThe mechanism of the reaction of 2,3‐epoxypropyl phenyl ether (2), as a model compound, with 1‐cyanoguanidine (3), for which different pathways have been proposed, is investigated using HPLC and 1H NMR spectroscopy. The effect of stoichiometric ratio, temperature and catalytic reagent was studied. It was found that, independent on the stoichiometric ratio, at low temperature, etherification and addition at the primary amino group takes place and reaction of the cyano group only to a low extend. At higher temperature, HPLC diagrams show different peaks indicating a different mechanism.
Experimental evidence for the regiospecific primary mode of styrene insertion into metal‐carbon bonds of an isospecific Ziegler‐Natta catalyst
Authors: Benaboura Ahmed , Deffieux Alain , Sigwalt Pierre 
Published: April 2003

AbstractStyrene/1‐hexene copolymers of different chemical composition were prepared with a classical isospecific Ziegler‐Natta catalyst, TiCl3(H)‐AlEt3. Their structure and the distribution of the monomeric unites was analyzed by GPC double detection and 1H and 13C NMR. The chemical arrangement of isolated and blocked styrene monomeric units between sequences of hexene monomeric units was also investigated. 13C chemical shifts of carbon atoms in the copolymers and in addition in model molecules of the two modes of styrene addition indicate that styrene insertion into carbon‐metal bonds of the catalyst proceeds according to a primary mode. Mechanistic implications of these results are discussed.
Polymères porteurs de dérivés du glycérol, 7.. Synthèse d'esters d'époxy‐2,3 propyle
Authors: Soutif Jean‐Claude , Razermera Faly , Brosse Jean‐Claude 
Published: April 2003

Abstract2,3‐Epoxypropyl esters were obtained in two steps from carboxylic acids or in one step from their alkali salts by reaction with 1‐chloro‐2,3‐epoxypropane or from the acid chloride with 2,3‐epoxy‐1‐propanol. The kinetic parameters of these reactions were studied with acetic acid and sodium acetate to evaluate the optimal conditions for the synthesis of these esters with the intention to apply them to polymers containing carboxylic groups.
Additive rules for the 13C NMR shifts of methyl‐substituted alkanes and ethylene‐propylene copolymers
Authors: Cheng H. N. , Bennett Mark A. 
Published: April 2003

AbstractDetailed 13C NMR chemical shift rules are devised for ethylene and propylene polymers and for low‐molecular‐weight analogs. The rules are additive and account for substituent effects as well as for configurational sequences. The agreement between the observed and the predicted shifts is excellent. A computer program has been written to obtain the predicted shifts quickly and with minimum effort.
Influence of termination and transfer on molecular weight distribution of polymers, 7. Impurity transfer
Authors: Yan De‐yue , Yuan Cui‐ming 
Published: April 2003

AbstractA mathematical procedure is developed to deal with the kinetics of ionic polymerization with impurity transfer and instantaneous initiation. Besides the technique of variable transformation, the integration of an implicit function is applied. The expressions of the molecular size distribution function and other molecular parameters are derived regorously, and several examples for numerical computations are given.
Water‐soluble copolymers, 16. Studies of the behavior of acrylamide/N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide copolymers in aqueous salt solutions
Authors: McCormick Charles L. , Hutchinson Brewer H. , Morgan Sarah E. 
Published: April 2003

AbstractThe behavior of N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide more commonly known as diacetone acrylamide (DAAM) polymers and acrylamide/diacetone acrylamide copolymers in aqueous and non‐aqueous solutions has been examined. 13C NMR and IR studies do not support the formation of a six‐membered hydrogen‐bonded ring structure in the DAAM moiety as an explanation of the unusual increase in solution viscosity shown by these copolymers upon addition of salt. A 12‐membered hydrogen‐bonded structure involving the diacetone acrylamide side chain and an adjacent acrylamide unit is proposed which is consistent with the available data and which would explain the viscosity behavior. Another possible structure involves hydrogen bonding between adjacent comonomers through amide/imine resonance structures. Copolymer microstructure as indicated by calculated pentad and triad frequencies supports either of these proposed structures.
Polymerization of acetylene with Ti(OC4H9)4/butyllithium as catalyst system and silicone oil as reaction medium
Authors: Munardi Adriantono , Theophilou Nicolas , Aznar Raymond , Sledz Joseph , Schué François , Naarmann Herbert 
Published: April 2003

AbstractA polymerization reaction catalyzed by Ti(OC4H9)4/butyllithium in a reaction medium of silicone oil yields a homogeneous and highly conductive polyacetylene when doped with iron (III) chloride. The effect of the transition metal halide on polyacetylene was studied by solution doping with FeCl3/nitromethane as a function of time.
Graph theory of configurational and viscoelastic properties of polymers, 3. Cyclic and star‐shaped chains containing small copolymeric blocks
Authors: Yang Yuliang , Yu Tongyin 
Published: April 2003

AbstractGraph theory of configurational and viscoelastic properties of polymers has been extended to treat cyclic and star‐shaped chains containing small copolymeric blocks in the free‐draining limit. Analytical expressions of the zero‐shear‐rate viscosity η4 and the steady‐state recoverable compliance J of these types are obtained. In the Rouse theory of viscoelastic behaviour η0 and J are directly related to the moments of the radius of gyration 〈S2〉 and 〈S4〉, hence both can be obtained simultaneously. Particularly, the relaxation spectrum of cyclic alternating block copolymer chains can also be obtained. The results obtained in this paper indicate that the structures of these types of chains are altered locally by the incorporation of a small concentration of another type of segments; the variation in viscoelasticities cannot be ignored and shows a strong dependence on block configuration. The results obtained may prove useful for understanding and interpreting the rheological data of block copolymers.
Phase‐transfer catalysis of phosphonium ions derived from poly[(P‐phenyl)trimethylenephosphine]
Authors: Kobayashi Shiro , Suzuki Masato , Sakaya Tai‐ichi , Saegusa Takeo 
Published: April 2003

AbstractPolymeric phosphonium ion species having different content of phosphonium units (4a and 4b) were prepared from poly[(P‐phenyl)trimethylenephosphine] (3). Phase‐transfer catalysis of 4 was examined by means of a typical SN2 reaction (1) in a bi‐phase system. The apparent rate constant (kobs) was determined, its magnitude being smaller by about one order than that of the corresponding monomeric phosphonium ion 5. Crosslinked polymeric phosphonium ion species were coated on powdery alumina and used as a phase‐transfer catalyst for reaction (1) in a triphase system. Due to the inhomogeneous reaction, the kobs value was much smaller (1/5) than that in presence of 4.
Strictly alternating copolymers containing parabanic acid and amide or imide moieties
Authors: Bennett Cynthia , Heitz Walter 
Published: April 2003

Abstract1,3‐Bis(4‐aminophenyl)imidazolidinetrione dihydrochloride (1) was synthesized and used as starting material for the synthesis of strictly alternating copolymers. Fully aromatic copolymers containing parabanic acid and amide moieties (7a, b) were found to exhibit high glass temperatures and good thermal stability. Meltable copolymers with parabanic acid and amide moieties (7d–j) could be obtained by introducing flexible aliphatic spacers. The use of an unusually short, but symmetrically branched spacer was particularly effective. The strictly alternating, thermally stable copolymer 10 was synthesized from 1 and pyromellitic dianhydride. By using the trimethylsilyl ester of polyamic acid 11, the imidization temperature could be lowered by 100°C.
Determination of kinetic parameters of ethyl methacrylate polymerization by using the dead‐end procedure
Authors: Çatalgil Huceste H. , Baysal Bahattin M. 
Published: April 2003

AbstractKinetics of polymerization of ethyl methacrylate initiated by 2,2′‐azoisobutyronitrile (AIBN) was studied applying the “dead‐end” theory. This theory is appropriate to examine the solution polymerization of this monomer in benzene at θ > 60°C. Radical polymerizations of ethyl methacrylate were carried out at 60–110°C. By using the procedures of the dead‐end theory, the rate of decomposition and the initiator efficiency of AIBN were determined. Kinetic parameters of the solution polymerization of ethyl methacrylate were calculated and the results were compared with the literature values.
Cationic ring opening polymerization of 4,5‐dihydro‐2‐[2‐(9‐anthryl)ethyl]‐1,3‐oxazole
Authors: Simionescu Christofor I. , Onofrei Geta , Grigoras Mircea 
Published: April 2003

AbstractA new monomer, 4,5‐dihydro‐2‐[2‐(9‐anthryl)ethyl]‐1,3‐oxazole (5) was synthesized and polymerized by cationic ring‐opening isomerization. The polymerization was carried out in bulk or in solution, using methyl tosylate, ethylene ditosylate and α‐tosyl‐ω‐tosyloxypoly(oxyethylene) [poly(ethylene oxide)ditosylate] as initiators. The polymers were characterized by IR, 1H NMR and UV spectroscopy.
Polyacrylate graft polymers prepared by grafting of monomethoxypoly(ethylene oxide) homopolymers onto acrylic acid: Self‐gelling polymers
Authors: Gramain Philippe , Frere Yves 
Published: April 2003

AbstractPolyacrylates of monomethoxypoly(ethylene oxide)Systematic name for MePEO: α‐hydro‐ω‐methoxypoly(oxyethylene).
(MePEO) were prepared by grafting MePEO on prepolymerized acryloyl chloride polymers of different molecular weights. Copolymers with carboxyl groups were also prepared by the addition of both water and MePEO. The polymers spontaneously form irreversible gels in water as soon as the degree of polymerization exceeds a certain limit. This gel formation confirms preceding results on similar polymers obtained by polymerization of MePEO acrylate and methacrylate macromonomers. It is concluded that the gelification phenomenon is not due to chemical cross‐linking but rather to the presence of a high density of strongly interacting grafts of PEO on the polymer backbone. This new type of self‐gelling system is considered to be of special interest.
Method for the determination of the relative spherulite growth rate, 2. The shielding effect
Authors: Lednický František 
Published: April 2003

AbstractThe method for the evaluation of spherulite growth after completed crystallization is further refined by comparison of the predicted and real shapes of the more slowly growing spherulite encompassed by the faster‐growing one. The shielding effect (the effect of distorted growth of the faster‐growing spherulite behind the more slowly‐growing one) is theoretically described, compared with the observation, and used for the evaluation of the relative rate of spherulite growth. As an example, measurements are reported with samples of poly(vinylidene fluoride).
Der interferenzeffekt von gestreckten markoff‐ketten erster ordnung, 1. Einkettenrechnung unter vernachlässigung der atomistischen comonomerstrukturen
Authors: Bonart Richard , Mulzer Georg , Dietrich Johann 
Published: April 2003

AbstractThe previously derived so called Bonart‐Mulzer (BM)‐equation which gives the interference effect of fully elongated A/B block copolymers depending on the length distributions of the A‐ and B‐blocks, is specialized onto first‐order Markoff chains as characterized by the transition probabilities pAA, pBB and pAB, pBA for homo‐ and cross‐steps, respectively. The resulting interference function is illustrated by means of simple model calculations. The specilization is applicable to liquid‐crystalline block copolymers in order to analyse the statistical chain character.
Ring‐opening polymerization of cis‐3,4‐dimethoxyoxolane
Authors: Thiem Joachim , Häring Thomas 
Published: April 2003

AbstractThe reaction conditions for the ring‐opening polymerization of cis‐3,4‐dimethoxyoxolane (1,4‐anhydro‐2,3‐di‐O‐methyl‐D‐erythritol, 3) using fluorosulfonic acid as initiator are described. The resulting polyether 4, poly[oxy(2,3‐dimethoxytetramethylene)], is characterized by elucidation of M̄n and M̄w, elemental analysis, 1H NMR spectroscopy as well as terminal group determination. The optimum conditions for obtaining high molecular weight polymers 4 are established and discussed.
Ion exchange and ring‐opening reactions of telechelic poly(tetrahydrofuran)s containing terminal cyclic quaternary ammonium salts
Authors: Tezuka Yasuyuki , Goethals Eric J. 
Published: April 2003

AbstractAnion exchange and ring‐opening reactions of cyclic quaternary ammonium salt end groups of poly(tetrahydrofuran) [poly(THF)] were studied. The counter anion exchange reaction of the quaternary ammonium triflate to the sulfonate or to the carboxylate, was found to take place by precipitation of the starting poly(THF) prepolymer from an aqueous solution containing the corresponding sodium salt. The azetidinium salt 1 was found to undergo ring opening reaction with its carboxylate counter ion at ambient temperature, whereas the pyrrolidinium salt 2 needs heating up to 100°C. The ring‐opening reactivities of the cyclic ammonium salts of poly(THF) chain ends were compared with those of model systems.