bluuebunny/crossref_metadata_2025_split huggingface dataset:
Equilibrium copolymerization of tetrahydrofuran‐3‐methyltetrahydrofuran
Authors: Guzman J. , Riande E. 
Published: April 2003

AbstractThe bulk cationic copolymerization of tetrahydrofuran and 3‐methyl‐tetrahydrofuran was studied at 0°C with acetylhexafluoroantimonate as initiator. The experimental equilibrium concentrations of both monomers were determined in all the intervals of composition, and the results obtained were compared with those calculated by different methods developed to study copolymerization systems in which depropagation reactions play an important role. In particular, very good agreement between calculated and experimental values was obtained by using Monte Carlo methods of simulation that allow the determination of the unknown cross‐propagation and cross‐depropagation rate constants, a necessary condition to calculate the equilibrium monomer concentrations.
Synthesis of polynucleotide analogs by grafting optically active nucleic acid base derivatives onto polyethylenimine
Authors: Overberger C. G. , Chen C. C. 
Published: April 2003

AbstractPolynucleotide analogs with a polyethylenimine backbone and optically active thymine‐ and adenine‐containing pendants and their model compounds were synthesized. The pendants were prepared by the addition reaction of the nucleic acid base to ethyl crotonate. The ammonium salt of 3‐(adenin‐9‐yl)butyric acid was employed to replace its free acid for the formation of diastereomeric salt with brucine. Fractional crystallization of the diastereomeric salt generates the partially resolved enantiomers. The solubility difference between the racemic mixture and its enantiomer was utilized to obtain the pure enantiomers. The active esters of the pendants were prepared. Grafting reactions were carried out by the reaction of active esters with PEI at room temperature. Completely grafted polymers were obtained.
Functional polymers and sequential copolymers by phase transfer catalysis. 25. Transformation of a monotropic mesophase into an enantiotropic one by increasing the molecular weight of the polymer and by copolymerization
Authors: Percec Virgil , Nava Hildeberto 
Published: April 2003

AbstractThe influence of molecular weight on thermal transitions and on the thermodynamic parameters was studied for two polymers based on 4,4′‐dihydroxy‐α‐methylstilbene with either 1,9‐dibromononane (HMS‐C9 polyethers) or 1,11‐dibromoundecane (HMS‐C11 polyethers). HMS‐C9 polyethers present an enantiotropic nematic mesophase over the entire range of molecular weights and a monotropic smectic mesophase for polymers of number average molecular weights higher than 17,000. The low molecular weight HMS‐C11 polyethers are only crystalline. On increasing their molecular weight, the polymers become monotropic nematics, and at higher molecular weights, enantiotropic nematics. Up to a composition containing as little as 20 mol % nonane structural units, the random copolyethers based on 1,9‐dibromononane, 1,11‐dibromoundecane, and 4,4′‐dihydroxy‐α‐methylstilbene (HMS‐C9/11 copolyethers) exhibit on cooling a phase diagram resembling that of HMS‐C9 polyether. HMS‐C9/11 containing about a 1/1 mole ratio between the two spacers presents both smectic and nematic enantiotropic mesophases. These results suggest that the phase diagram of random liquid crystalline copolymers is controlled by the shorter spacer. The thermodynamic parameters of isotropization for both polyethers and copolyethers are compared and suggest that copolymerization does not significantly decrease the degree of order of the mesogenic units in the mesomorphic phase.
Organic semiconductors—metal phthalocyanine sheet polymers
Authors: Achar B. N. , Fohlen G. M. , Parker J. A. , Keshavayya J. 
Published: April 2003

AbstractThis publication discusses the electronic, magnetic susceptibility, MS and GC–MS pyrolysis, X‐ray powder diffraction, and electrical conductivity studies on metal phthalocyanine sheet polymers. The magnetic measurements over the range of magnetic field strengths 1025–6144 gauss indicated the absence of the intermolecular cooperative effect. MS and GC–MS studies indicate that all these metal phthalocyanine sheet polymers give benzene, cyanobenzene, and dicyanobenzene on thermal degradation. The electrical conductivity measurements showed that these polymers are semiconductor in nature.
Kinetic studies of nonaqueous polymerization of methyl methacrylate initiated by ferric laurate–n‐hexyl amine system
Authors: Saha Sanjib Kumar , Chaudhuri Ajit Kumar 
Published: April 2003

AbstractThe polymerization of methyl methacrylate was studied in carbon tetrachloride medium with ferric laurate, a metal soap, in combination with n‐hexyl amine as the initiator system at 60°C. The rate of polymerization was found to be linear with the monomer concentration and proportional to the square root of both ferric ion and amine concentration. A reaction scheme involving initial complex formation between ferric ion and amine and subsequent reaction of the complex with the solvent molecule to produce free radicals responsible for initiation of polymerization has been postulated to account for the observed results.
Structure property correlation in crosslinkable copolyimides
Authors: Sen Debasish , Maiti Mrinal M. , Maiti Sukumar 
Published: April 2003

AbstractThree copolyimides containing crosslinkable alkyne groups either in the main chain backbone or as endgroups, have been synthesized and characterized in regard to their structure, molecular weight, solubility, film‐forming properties, crystallinity, crosslinking behavior, and thermal stability. A good correlation between the structure of the polymers and their properties has been established.
A comparison of heterogeneous and homogeneous kinetics in the formation of a polyurethane
Authors: Pearson R. G. , Williams E. L. 
Published: April 2003

AbstractThe extent of reaction between a liquid polyfunctional aromatic isocyanate and a diol was studied using infrared spectroscopy to follow the reduction in concentration of the isocyanate group. For the homogeneous conditions the reaction was performed in benzene solution. For the heterogeneous conditions the isocyanate was dispersed as droplets in the diol and the reaction proceeded interfacially.From a proposed model for the interfacial reaction based on the steady‐state diffusion theory the second‐order rate constant of the reaction can be evaluated. The values obtained were compared to the second‐order rate constants obtained for the solution method. For a range of temperature the heterogeneous rate constant was approximately six decades higher than that obtained for the homogenous conditions. However the activation energies obtained corresponded within a factor of 1.5.
Preparation of new blocked diisocyanate for dental application
Authors: Lei G. Y. , Angeli S. R. , Kristol D. S. , Snyder W. H. 
Published: April 2003

AbstractA novel two‐stage method of preparing 2‐hydroxyethyl methacrylate (HEMA) and methoxyphenol or cholorophenol blocked 2,4‐tolylene diisocyanate (TDI) was devised. The first stage reaction of TDI with HEMA was carried out in petroleum ether heterogeneously with the precipitation of the intermediate product, monoadduct, in the reaction solution, and followed by a second stage homogeneous reaction of monoadduct with the blocking agent, chlorophenol, or methoxyphenol, in ethyl acetate. In both reactions the inhibitor, chloranil, and the catalyst, dibutyltin dilaurate, were used. A total of eight products were achieved. Results of elemental analyses of these products along with their LC chromatograms, NMR, and IR spectra indicated that these materials were indeed the compounds expected. Testing results of these materials as dental adhesives will be reported in a separate paper.
Nematogenic block copolymers of rigid and flexible aromatic units. I. Synthesis and characterization
Authors: Krigbaum W. R. , Preston J. , Ciferri A. , Shufan Zhang 
Published: April 2003

AbstractThree types of wholly aromatic block copolymers were synthesized using the phosphorylation reactions of Yamazaki and Higashi. Each copolymer contained blocks of rigid and flexible units. The first copolymer, PBA/PABH‐T, contains blocks of poly(p‐benzamide) and the polyterephthalamide of p‐aminobenzhydrazide. The second copolymer, PBA/MPD‐I, contains blocks of poly(p‐benzamide) and poly(p‐phenylene isophthalamide), whereas the third, PPD T/MPD‐I, contains blocks of poly(p‐phenylene terephthalamide) and poly(m‐phenylene isophthalamide). Three synthetic routes were used for the preparation of the block copolymers. In the two‐step polycondensation (A), monomers of the flexible block are added to the rigid prepolymer. The multistep method (B) differs in that the rigid prepolymer is carboxy‐terminated prior to addition of the monomers of the flexible block. Carboxy‐terminated prepolymer of the rigid block is reacted with amine‐terminated prepolymer of the flexible block in the two‐pot condensation (C). The presence of a considerable amount of the flexible homopolymer is indicated by viscosity, extraction, and NMR studies, particularly when methods A and C were used. The flexible homopolymer can be extracted by using a nonsolvent for the rigid blocks. Extraction of the rigid homopolymer (which may also be presumed to be produced) entails a more elaborate procedure. In principle, one can use these methods to obtain pure block copolymer for study of mixtures with the rigid and flexible homopolymers. Phase studies of some of these systems will be reported in a following paper.
Influence of functional sulfonic acid groups on styrene–divinylbenzene copolymer pyrolysis
Authors: Matsuda Masami , Funabashi Kiyomi 
Published: April 2003

AbstractThe decomposition ratio of cation exchange resin (sulfonated ST‐DVB copolymer) after pyrolysis is only 50 wt%, while that of ST‐DVB copolymer is 90 wt%. Fundamental experiments were performed to investigate the reason for the low decomposition ratio of the former.The cation resin consists of base polymer (ST‐DVB copolymer) and functional sulfonic acid groups. Chemical analyses of the pyrolysis products showed that most of the functional groups decomposed at about 300°C and generated SO2 gas. However, only a small amount of the base polymer was pyrolyzed even at 600°C and the total decomposition ratio was only 50 wt%. The XPS studies on the residue showed that 35% of the functional sulfonic acid groups was converted to sulfonyl and sulfur bridges between the base polymers during pyrolysis. These bridges made the base polymers, namely ST‐DVB copolymer, thermally stable.
Characterization of cobalt‐modified polyimides
Authors: Boggess Robert K. , Taylor Larry T. 
Published: April 2003

AbstractModified polyimide films containing cobalt have been prepared by the addition of cobalt(II) chloride to a solution containing one of the diamines 4,4′‐oxydianiline (ODA) or 4,4′‐diaminodiphenylsulfide (DDS) and one of the dianhydrides 3.3′, 4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) or 4,4′‐bis(3,4‐dicarboxyphenoxy)diphenylsulfide dianhydride (BDSDA) and characterized by thermal methods, UV‐visible spectra, room‐temperature direct‐current electrical resistivity measurements, and X‐ray photoelectron and Auger electron spectroscopy. A principal goal of this work was to establish if there was coordination of the potential donor atoms of the polymide to cobalt. UV‐visible spectra of the modified polyamic acid solutions and polyimide films and a titration study of a model system do not show any appreciable coordination with either the polyamic acid or the polyimide; rather, the cobalt(II) appears to be coordinated to the solvent, N,N‐dimethylacetamide (DMAc), as [Co(DMAc)4]2+, until the temperature is raised above 200°C. X‐ray photoelectron spectra of films cured only to 200°C also do not show significant shifts in the binding energies of the potential donor atoms from those binding energies of the undoped polymers, confirming little direct coordination of the cobalt to atoms of the polyimide. Heating the films to 300°C in a forced‐air oven causes the formation of a cobalt oxide layer on the air side of the polymer. Direct‐current electrical resistivity measurements on this surface show a 104–106 reduction in resistivity due to this layer.
Theoretical basis and kinetic sense of covalent propagation in cationic polymerization
Authors: Matyjaszewski Krzysztof 
Published: April 2003

AbstractPolymerization of several vinyl and heterocyclic monomers was described recently as proceeding by covalent propagation. In this paper the theoretical basis of purely covalent multcenter propagation is discussed in terms of the orbital symmetry theory and the parity rules. A mechanism is considered in which ionic and covalent species are present simultaneously. Covalent species may react with monomers, forming intermediate ions. The kinetic sense of the rate of this elementary reaction is described.
Synthesis of polyformals from nitro‐ and fluordiols. Substituent and chainlength effects
Authors: Adolph Horst G. , Goldwasser Judah M. , Koppes William M. 
Published: April 2003

AbstractA series of primary and secondary diols carrying nitroalkyl, nitro, and fluoro substituents was reacted with formaldehyde under conditions of acid catalysis. Short‐chain primary diols gave cyclic formals while predominantly linear polymers were obtained beginning with pentane‐1,5‐diols and hexane‐1,6‐diols, depending upon the nature of the substituents. No polymers were formed from secondary diols with 1‐nitroalkyl substituents. The effect of monomer structure on polymer formation is discussed. The polymers obtained were characterized by GPC and end group analysis.
Synthesis and characterization of certain aromatic azopolyamides
Authors: Rajendran V. , Nanjan M. J. 
Published: April 2003

AbstractTwo new aromatic diamines, 2,2′‐dimethyl‐4,4′‐diaminoazobenzene [benzenamine‐(3,3′‐dimethyl‐4,4′‐azobis)] and 2,2′‐dichloro‐4,4′‐diaminoazobenzene [benzenamine‐(3,3′‐dichloro‐4,4′‐azobis)] were synthesized and their structures confirmed by IR, UV‐visible, 1H‐NMR, 13C‐NMR, and mass spectra. With these diamines, 16 aromatic polyamides were synthesized by both low‐temperature solution and phosphorylation polycondensation methods. The polymers were characterized by viscosity, solubility, IR, UV visible, TGA, and DTA studies.
Studies on poly(iminomethylenes)
Authors: King R. B. , Greene M. J. 
Published: April 2003

AbstractA variety of simple alkyl and aryl isocyanides have been polymerized using 0.5% NiCl2 in ethanol as a catalyst. The resulting poly(iminomethylenes) have been characterized by carbon‐13 NMR spectroscopy and their polystyrene‐equivalent molecular weights have been determined by gel permeation chromatography. Straight chain aliphatic isocyanides having from three to ten carbon atoms in the chain form readily solyble polymers having molecular weights (Mw) in the general range 10,000 to 30,000. Neopentyl isocyanide unlike tert‐butyl isocyanide forms an insoluble polymer. A number of new soluble aryl isocyanide polymers have been obtained. However, aryl isocyanides having a single alkyl substituent (CH3, C2H5, CF3) in the ortho position give only insoluble polymers, whereas aryl isocyanides having alkyl substituents in both ortho positions (e.g., 2,6‐(CH3)2C6H3NC and 2,4,6‐(CH3)3C6H2NC) fail to polymerize under these conditions. The highest molecular weight soluble aryl isocyanide homopolymer is obtained from 3‐CH3OC6H4NC(Mw = 26,000). The trimethylsilyl substituted isocyanide (CH3)3SiCH2CH2NC has been obtained from LiCH2NC and (CH3)SiCH2Cl and gives a brown soluble homopolymer with a molecular weight (Mw) of 19,000.
Magnesium chloride supported high mileage catalysts for olefin (decene‐l) polymerization XIV. Propagation and chain transfer
Authors: Chien James C. W. , Ang Tsunle 
Published: April 2003

AbstractDecene‐l was polymerized with the MgCl2/ethylebenzoate/p‐cresol/AIEt3/TiCl4‐AlEt3/methyl‐p‐toluate catalyst at 50° using an A/T ratio of 167 and a range of monomer concentration. The concentration of the two kinds of active sites are [Ti] = 12% and [Ti] = 4% of the total titanium. The rate constants of propagation are 24 M−1 s−1. Chain transfers to AIEt3, monomer, and by β‐hydride elimination have rate constant values of 1.7 × 10−3 M−1 s−1, 1.34 × 10−2 M−1 s−1, and 1.7 × 10−2 s−1, respectively. Poly(decene‐l) have relatively narrow MW which are unchanged during the course of a polymerization. Therefore, the active site concentrations in the CW catalyst for propylene and decene polymerization are identical and their rate constant values agree within a factor of 2. However, the rate of decene polymerization depends on fractional order of monomer concentration and decreases with the increase of activator concentration. Furthermore, the formation of metal polymer bonds has a rate independent of these concentrations. These kinetic behaviors are a manifestation of absorption processes of these species which are not seen in propylene polymerizations.
Cationic ring‐opening transfer polymerization of spiro ortho esters initiated by carbon black
Authors: Tsubokawa Norio , Ohshima Shingo , Sone Yasuo , Endo Takeshi 
Published: April 2003

AbstractThe ring‐opening transfer polymerization of spiro ortho esters (SOE) initiated by carbon black was investigated. In the absence of carbon black, no polymerization occurred at all. In the presence of channel black containing carboxyl group, the ring‐opening transfer polymerization of SOE was initiated at 50‐70°C. to give polyether ester, namely alternating copolymer of epoxide and lactone. The rate of polymerization of 1,4,6‐trioxaspiro[4.4]nonane and 1,4,6‐trioxaspiro[4.5]decane was considerably small compared with that of 1,4,6‐trioxaspiro[4.6]undecane. The activation energy of the polymerization of 2‐chloromethyl‐1,4,6‐trioxaspiro[4.6]undecane was estimated to be 6.0 kcal/mol. The initiating activity of carbon black increased with an increase in carboxyl group content of carbon black. Furnace black that contained no carboxyl group was unable to initiate the polymerization. Furthermore, the carbon black lost the initiating ability of the polymerization upon the blocking of carboxyl group on the surface by the treatment with potassium hydroxide or diazomethane. Based on these results, it was concluded that carboxyl group on carbon black plays an important role in the initiation. During the polymerization, a part of the polymer formed was grafted onto carbon black: the grafting ratio was 10–30%. The mechanisms of initiation and grafting were discussed.
Acidolysis of poly(4‐methyl‐1,3‐dioxolane)
Authors: Diab M. A. , Hseih D. T. , Lillya C. P. , Chien James C. W. 
Published: April 2003

AbstractThe onset of decomposition of poly(4‐methyl‐1,3‐dioxolane) was lowered to 70°C by 0.1 wt% p‐toluene sulfonic acid from 170°C in the absence of acid to produce more than 81% yield of monomer. Protonation forms cyclic oxonium ion followed by depolymerization. Minor products are isomers of hydroxymethyl‐2‐hydroxyl‐2‐methyl ethyl ether and bis(2‐hydroxyl‐2‐methyl ethoxyl)methane from rearrangements of the oxonium ions. The first order rate constant of acidolysis of poly(4‐methyl‐1‐1,3‐dioxolane) is about 8.5 kcal mol−1, which is much smaller than about 17 kcal mol−1 for the acidolysis of poly(1,3‐dioxolane).
Circular dichroism of copoly(γ‐stearyl‐L‐glutamate–γ‐methyl‐L‐glutamate)
Authors: Tsujita Yoshiharu , Ojika Ryoko , Tsuzuki Koji , Takizawa Akira , Kinoshita Takatoshi 
Published: April 2003

AbstractCopoly(γ‐stearly‐L‐glutamate‐γ‐methyl‐L‐glutamate)s with various compositions were synthesized by the ester exchange reaction of poly(γ‐methyl‐L‐glutamate). Circular dichroism studies were carried out for solution and solid film as a function of the degree of stearylation and temperature. The slight and gradual temperature dependence of molecular ellipticity was observed for solution of all the copolyglutamates studied here and for the solid film of the copolyglutamate with the degree of stearylation of 16%, indicative of no reversal in the helix sense. However the remarkable change in negative molecular ellipticity with temperature was detected for the solid film of the copolyglutamate with a low degree of stearylation, e.g., 52%, whereas the drastic change in molecular ellipticity from a negative to positive value appeared for that with a higher degree of stearylation. This is discussed in terms of the reversal in the helix sense from a right‐ to left‐handed α helix with the increase of temperature occurring at the melting temperature of the ordered side chain region.
Thermal decomposition processes in aromatic‐aliphatic polyamides investigated by mass spectrometry
Authors: Ballistreri Alberto , Garozzo Domenico , Maravigna Pietro , Montaudo Giorgio , Giuffrida Mario 
Published: April 2003

AbstractThe thermal decomposition processes of some aromatic‐aliphatic polymides, derived from terephthalic acid and aliphatic diamines, were studied by flash Pyrolysis‐GCMS and by direct Pyrolysis‐Mass Spectrometry, using both Chemical lonization and Electron Impact modes.The results indicate that the primary thermal decomposition proceeds via a β‐CH hydrogen transfer process, with formation of pyrolysis products containing amide and olefin end‐groups. Nitrile end‐groups are also formed by dehydration of the amide groups formed in the primary decompostion process.
Chemiluminescence of hydrocarbon polymers
Authors: Jirackova L. Audouin , Verdu J. 
Published: April 2003

AbstractThe thermal oxidation of some hydrecarbon polymers differing by their degree of branching was studied simultaneously by chemiluminescence and infrared spectrophotometry. In the case of isotactic polypropylene, measurements were made at various temperatures ranging from 140 to 180°C. The other polymers—ethylene–propylene copolymer, low and high density polyethylene—were studied only at 160°C. In all cases, the induction times of chemiluminescence coincide with those of carbonyl growth. The previously proposed mechanisms of light emission are not consistent with the kinetic data or with the structure effects on luminescence, which seems directly related with the presence of tertiary hydrogens. A hypothetical mechanism based on the β scission of tertiary alkoxyls is proposed.
Molecular factors affecting solubility in rigid‐rod polyamides
Authors: Gaudiana R. A. , Minns R. A. , Rogers H. G. , Sinta R. , Taylor L. D. , Kalyanaraman P. , McGowan C. 
Published: April 2003

AbstractThe solubility of a series of para‐linked, substituted phenyl, biphenyl, terphenyl, and quaterphenyl polyamides is reported. Most of these polymers are soluble in amide solvents without lithium chloride, and several are soluble in ethers and/or ketones. The results indicate that solubility in this class of polymers is affected by the position, polarizability and size of the substituents, enantiomeric purity, and the number of non‐coplanar biphenyl rings per repeat unit.
Study of the ceric ion behavior on the initiation of butyl acrylate polymerization onto amylose
Authors: Vázquez M. B. , Goñi I. , Gurruchaga M. , Valero M. , Guzmán G. M. 
Published: April 2003

AbstractA study of the Ce(IV) ion consumption during graft polymerization of butyl acrylate with amylose was carried out. The Ce(IV) consumed was ca. 80% and the ratio of Ce(IV) to anhydroglucose units was 1/15. Poly(butyl acrylate) (PBA) chains were isolated from the grafted copolymer by the perchloric acid hydrolysis method. The molecular distribution was obtained by gel permeation chromatography (GPC). The number‐average molecular weight (Mn) of the grafted chains was 276,000 and the weight‐average molecular weight (Mw) was 1,320,000. The total number of grafted chains (mmol) ranged from 0.4410−3 to 8.710−3 (amylose from 0.08 g to 1.23 g). Frequency of grafting ranged from 1042 to 704.