bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photooxidative degradation of cellulose: Reactions of the cellulosic free radicals with oxygen
Authors: Hon David N.‐S. 
Published: April 2003

AbstractPhotooxidative degradation of cellulose resulted in decreases of degree of polymerization (DP) and α‐cellulose content, concurrently producing chromophoric groups; namely, carbonyl, carboxyl, and hydroperoxide groups within the polymer. Electron spin resonance (ESR) studies revealed that cellulosic carbon free radicals readily reacted with oxygen molecules at 143–160 K to produce peroxy radicals, whereas cellulosic oxygen free radicals were inert toward oxygen molecules throughout the photooxygenation reactions. At 77 K it is feasible that only photoexcited oxygen molecules reacted with cellulosic carbon free radicals to produce peroxide radicals. These radicals were themselves stabilized at 273 K by abstraction of hydrogen atoms from cellulose to produce polymer hydroperoxides. Simultaneously, new radical sites, which exhibited three‐line ESR spectra, were generated in cellulose.
Polymerization of coordinated monomers. XV. 13C‐NMR study on the alternating copolymers of methyl methacrylate with styrene
Authors: Hirai Hidefumi , Koinuma Hideomi , Tanabe Tsuneaki , Takeuchi Kazuhiko 
Published: April 2003

AbstractBy the use of various metal halides methyl methacrylate and styrene were copolymerized to produce equimolar alternating sequences and different cotacticities. The 13C‐NMR spectra of these copolymers were simple in comparison to those of random copolymers because of the fixed monomer sequence which yielded sharply split triplets for carbonyl, methoxy, and quaternary carbons. The relative intensities in these split peaks varied according to the metal halide used. A comparison of the intensities made it possible to obtain clear‐cut and quantitative information on the methyl methacrylate‐centered triad cotacticity of the copolymers. The spectral assignment with respect to the methoxy carbon was definitely justified by the combined use of partly relaxed Fourier transform and selective decoupling techniques. The spectrum of aromatic C1 carbon in styrene units also split into three main peaks. From their relative intensities the splitting was attributed to styrene‐centered triad cotacticity. The assignment of this carbon was compared with two other assignments made for random copolymers of methyl methacrylate with styrene; they were contradictory, however. Furthermore, an apparent discrepancy was observed between methyl methacrylate‐and styrene‐centered tactic triads of these alternating copolymers. The origin of this discrepancy suggests a close relationship with the copolymerization mechanism.
Polymerization of acrylamide with persulfate–thiomalic acid initiator
Authors: Misra G. S. , Dubey S. L. 
Published: April 2003

AbstractThe redox system of potassium persulfate–thiomalic acid (I1–I2) was used to initiate the polymerization of acrylamide (M) in aqueous medium. For 20–30% conversion the rate equation is

where Rp is the rate of polymerization. Activation energy is 8.34 kcal deg−1 mole−1 in the investigated range of temperature 25–45°C. Mn is directly proportional to [M] and inversely to [I1]. The range of concentrations for which these observations hold at 35°C and pH 4.2 are [I1] = (1.0–3.0) × 10−3, [I2] = (3.0–7.5) × 10−3, and [M] = 5.0 × 10−2–3.0 × 10−1 mole/liter.
Peroxide‐initiated crosslinking of maleic anhydride‐modified low‐molecular‐weight polybutadiene. II. Crosslinking degree and thermal degradation of cured polymers
Authors: Gancarz I. , Łaskawski W. 
Published: April 2003

AbstractThe crosslinking density and thermal properties of peroxide‐crosslinked low‐molecular‐weight polybutadiene and its modification products with maleic anhydride were studied. It was shown that the Flory‐Rehner equation may be used for describing the equilibrium swelling of the studied systems. The molecular weight between crosslinks calculated from this equation has values from 117 to 216. It was found thermogravimetrically that the thermal stability of modified polybutadiene is lower than the unmodified material. The thermal destruction of the polymers studied is a step‐by‐step reaction, the first being of zero order, with activation energy of 76.6–112.6 kJ/mole, the second, a first‐order reaction with an Ea of 286.8–363.4 kJ/mole.
Maleimide‐terminated amide‐imide prepolymers: Synthesis and basic properties
Authors: Kruh Daniel , Jablonski Richard J. 
Published: April 2003

AbstractRepresentatives of a family of soluble, imidized maleimide‐terminated amide‐imide precursors for molding and composite applications were prepared and characterized. The key step was the preparation of an amine‐terminated amide‐imide intermediate that was needed in order to introduce the maleimide groups. Trimellitic anhydride (TMA) and its monoacid chloride (TMAC) were each investigated for utility in reaction with molar excesses of methylenedianiline. With TMA the limiting factor was the time‐consuming amidation reaction, which, although catalyzed with triphenyl phosphite, required 24 hr to bring to completion in hot N‐methylpyrrolidone (NMP). The use of TMAC provided a more facile route to the intermediate and, as shown by gel permeation chromatography (GPC), resulted in a narrower molecular weight range than with TMA for the final maleimide‐terminated products. The reactions were followed by carboxyl titration, and the resulting products were characterized by IR, NMR, DTA, GPC, and inherent viscosity. The relative thermal capabilities were compared by isothermal aging as thin films (250°C) and as molded bars (316°C). Physical properties were assessed on glass laminates and molded bars. Although soluble in polar solvents, the products were viscosity unstable at ambient conditions. A solution to this problem was demonstrated by the preparation of the cyclopentadiene adduct, which was viscosity stable.
Radiation‐induced bulk polymerization of vinyl chloride under centrifugation
Authors: Carenza M. , Tavan M. , Palma G. 
Published: April 2003

AbstractRadiation‐induced bulk polymerization of vinyl chloride has been carried out under centrifugation at 21°C. The polymerization rate and the molecular weight of the polymer produced were found to remain constant in the low‐conversion region and to be equal to the corresponding values that were obtained by extrapolation at zero conversion in normal polymerization. This was at variance with the case of normal polymerization in which both quantities exhibit a continuous increase from the start of the polymerization. Such an increase is to be associated with the presence of large agglomerates, formed through flocculation of initially originated particles, in the liquid monomer phase during the polymerization under quiescent conditions. For the constancy of the kinetic parameters in the polymerization under centrifugation it should be assumed that in the system there remain dispersed only particles not yet flocculated.
Kinetic studies on the formation of cyclic oligomers in poly(ethylene terephthalate)
Authors: Ha Wan Shik , Choun Young Kwan 
Published: April 2003

AbstractThe mechanism of cyclic oligomer formation has been kinetically studied by determining the rate of the formation of cyclic oligomers during melt of poly(ethylene terephthalate) (PET) at several levels of average molecular weight, which were obtained by fractionation and did not initially contain oligomers. The experimental rate equation of cyclic oligomer formation was introduced and then compared with the rate equation derived theoretically. The close agreement between the two equations suggested that the cyclic oligomer formation takes place according to cyclodepolymerization by the action of hydroxyl end groups in PET. The relation is represented as [C] = m·[OH]0·t1–n, where [C] is the concentration of cyclic oligomers, [OH]0 is the initial concentration of hydroxyl end groups, m and n are constants, and t is melting time. A method has also been developed for separating cyclic oligomers from PET using dimethylformamide (DMF) as a solvent.
Cationic polymerization of α‐methylstyrene from polydienes. I. Synthesis and characterization of poly(butadiene‐g‐α‐methylstyrene) copolymers
Authors: Ambrose R. J. , Newell J. J. 
Published: April 2003

AbstractThe preparation of poly(butadiene‐g‐α‐methylstyrene) copolymers was investigated with three different alkylaluminum coinitiators. The alkylaluminum compounds in conjunction with polybutadiene which contained a low concentration of labile chlorine atoms initiated the polymerization of α‐methylstyrene to produce graft copolymers. Trimethylaluminum gave higher grafting efficiencies than diethylaluminum chloride at comparable monomer conversions. Triethylaluminum produced only very low monomer conversions (<5%), even at long reaction times, and for this reason was not studied extensively. The number of grafts per polybutadiene backbone was determined for a number of copolymers and found to increase slightly as the allylic chlorine concentration in the polybutadiene backbone was increased. In all cases, however, only a low percentage of the available labile chlorine sites along the polybutadiene backbone resulted in grafted α‐methylstyrene side chains. The addition of small quantities of water to the polymerization solvent greatly enhanced the grafting rate and ultimate monomer conversion during the synthesis of these poly(butadiene‐g‐α‐methylstyrene) copolymers. The mechanistic role of water during these grafting reactions is unknown at the present time.
Polychlorinated polyamides. II. Synthesis and characterization of polyamides derived from 2, 5‐dichloroterephthaloyl dichloride and perchloroterephthaloyl dichloride
Authors: Díaz F. R. , Gargallo L. , Lizana C. , Gilbert S. 
Published: April 2003

AbstractNew thermally stable polyamides were prepared by interfacial polymerization of the title compounds and various aliphatic and aromatic diamines. The polymers were characterized by infrared spectrometry, elemental analysis, and differential scanning calorimetry. The molecular weights of the polymers were estimated by viscosity measurements. The influence of the halogen content on the thermal properties and degree of polymerization of the polymers was studied. One of the polyamides was fractionated to determine the degree of polydispersity.
New carbazole‐containing monomers and polymers
Authors: Simionescu C. I. , Percec V. 
Published: April 2003

AbstractFive novel vinyl monomers, all of which contain 3‐substituted carbazolyl groups [i.e., N‐(9‐ethyl‐3‐carbazolyl)‐maleimide, 9‐ethyl‐3‐carbazolyl acrylamide, 9‐ethyl‐3‐carbazolyl methacrylamide, 9‐ethyl‐3‐hydroxymethylcarbazolyl acrylate, and 9‐ethyl‐3‐hydroxymethylcarbazolyl methacrylate], and their corresponding polymers were synthesized. Two methods were used for the synthesis of the last two monomers.
Malonic ester‐blocked aliphatic isocyanates
Authors: Kostyk Barry W. , Wicks Zeno W. 
Published: April 2003

AbstractProducts formed on pyrolysis of malonic ester‐blocked aliphatic isocyanates depend on the enolizability of the blocked isocyanate. Previous work reported that diethyl malonate‐blocked aliphatic isocyanates on pyrolysis yield predominantly “abnormal” products rather than the expected isocyanates. It has now been shown that this behavior results from the reactions of the enol forms. A nonenolizable diethyl methylmalonate‐blocked isocyanate has been synthesized. On pyrolysis essentially quantitative conversion to isocyanate and diethyl methylmalonate occurs. Significant differences in reactivity with amines and alcohols also result from the difference in enolizability.
Synthesis and thermal characterization of some novel phenol carbonates
Authors: Gibson Harry W. , Bailey F. C. , Pochan John M. 
Published: April 2003

AbstractA total of 16 carbonates, all but one new compounds, have been synthesized. These include bis‐(phenyl carbonate)s of 13 bisphenols and 3 bis(substituted phenyl carbonate)s of 2,2‐bis(p‐hydroxyphenyl) butane. The present report characterizes them in terms of melting points Tm, elemental analyses, glass transition temperatures Tg, and enthalpies and entropies of fusion and relates the thermal properties to structure on a comparative basis. A number of the carbonates have what seem to be two distinct crystal structures as deduced from differential scanning calorimetry and x‐ray patterns. In keeping with data for polycarbonates, these bis(phenyl carbonate)s show abnormally high Tg/Tm relative to most polymers.
Copolymers of vinyl and vinylidene chlorides with alkyl acrylates
Authors: Logothetis A. L. 
Published: April 2003

AbstractHigh‐molecular‐weight copolymers of vinyl chloride and ethyl or butyl acrylate were prepared in high conversion and yield in the presence of boron trifluoride as the acrylate ester complexing agent. When the vinyl chloride monomer is in excess of equimolar amounts, the resulting copolymers are alternating; and when the alkyl acrylates are in excess, acrylate‐rich copolymers are obtained. Ethylene–vinyl chloride–ethyl acrylate and propylene–vinyl chloride–ethyl acrylate terpolymers were also obtained with an ethyl acrylate content of 50 mole %. The relative reactivities of propylene, vinyl chloride, and ethylene in these polymerizations were 5.4, 3.8, and 1.0, respectively. Vinylidene chloride–ethyl acrylate copolymers that are nearly alternating and rich in acrylate or in vinylidene chloride have also been prepared. The monomer reactivity ratios for vinylidene chloride and ethyl acrylate in the presence of boron trifluoride are considerably lower than in its absence.
Mechanism of inhibitory action of metal dithiocarbamates. II. Autooxidation of tetralin and cumene and decomposition of tetralin hydroperoxide in the presence of zinc bisisobutyldithiocarbamate
Authors: Kateva J. , Ivanov S. K. 
Published: April 2003

AbstractIn the initial moment of the tetralin oxidation in the presence of tetralin and cumene hydroperoxides (THP, CHP) as well as of zinc diisobutyldithiocarbamate (ZDTC) an intensive absorption of oxygen‐prooxidation effect was observed. A pulsation absorption of oxygen during the oxidation of tetralin with ZDTC and AIBN was established. It has been proved that the stoichiometric coefficient of inhibition (f) is a function of the ZDTC concentration. A probable scheme of the decomposition of the THP with ZDTC which includes the formation of SO2 as possible decomposition agent of ROOH according to the ionic mechanism was suggested.
Biphenylene as a crosslinking unit in polyaromatic ether–ketone and ether–ketone–sulfone resins. XVI
Authors: Swedo Raymond J. , Marvel C. S. 
Published: April 2003

AbstractBiphenylene units have been incorporated into polyaromatic ether–ketone and polyaromatic ether–ketone–sulfone resins as useful crosslinking sites. Crosslinking is achieved by heating the resins to 300–400°C. The keto polymers are soluble only in sulfuric acid before curing, but the sulfone polymers are soluble also in some aprotic solvents. Molded “I beams” of the cured keto polymer are stronger than those of the sulfone polymer. Both classes of polymer are quite thermally stable. Curing can be hastened by catalyzing with rhodium compounds.
Polymerization of vinyl fluoride initiated by the system silver nitrate–tetraethyl lead
Authors: Raucher Daniel , Demiel Arieh , Levy Moshe , Vofsi David 
Published: April 2003

AbstractThe initiator system AgNO3–tetraethyl lead was used for the polymerization of vinyl fluoride. Dimethyl sulfoxide was found to have a specific effect on the half‐life of the initiating system, which leads to long reaction times and high conversions at ambient temperatures. This effect was explained by the complexing power of DMSO on silver ions, which slows down the rate of formation of AgEt and permits the polymerization to proceed for longer periods than in other solvents. The kinetics of the polymerization agreed with the scheme developed earlier. Tetraethyl lead acts as a powerful chain transfer agent and determines to a large extent the resulting polymers.
A novel metal alkyl‐free catalyst for the ring‐opening polymerization of cycloolefins
Authors: De Figueiredo Cecilia M. C. 
Published: April 2003

AbstractA new catalytic system based on tungstic acid (H2WO4) and aluminum trichloride (AlCl3) polymerizes cyclopentene and 1,5‐cyclooctadiene through a ring‐opening mechanism in high yields and high molecular weight.
Linear polythioesters. III. Products of interfacial polycondensation of 1,4‐, 1,5‐di(mercaptomethyl)‐naphthalene, and their mixture with adipoyl and sebacoyl chlorides
Authors: Podkościelny Wawrzyniec , Charmas Władysław 
Published: April 2003

AbstractNew polythioesters of naphthalene derivatives by polycondensation of 1,4‐di(mercaptomethyl)‐naphthalene, 1,5‐di(mercaptomethyl)naphthalene, as well as their mixture with adipoyl and sebacoyl chlorides have been obtained. Low‐temperature and high‐temperature solution polycondensation as well as interfacial polycondensation have been used. Interfacial polycondensation proved to be the most useful. To define the optimal conditions of interfacial polycondensation, the following factors influencing the process have been studied: ratio of aqueous to organic phase, concentration of hydrochloride acceptor, temperature of reaction and rate of addition of acid chloride, contribution of emulsifier and catalyst. Yield for all reaction products and reduced viscosity have been found. The structure of polythioesters of high‐value viscosity and good yield was determined from elementary analysis, infrared spectra, x‐ray, and thermogravimetric analysis. Some mechanical and electrical properties of the polythioesters obtained from the mixture of 1,4‐ and 1,5‐di(mercaptomethyl)naphthalene have been studied after pressing in increased temperature. The molecular weight was not determined because of very low solubility.
Alternating copolymerization of 1‐ and 2‐vinylnaphthalene with methyl methacrylate by using diethylaluminum chloride
Authors: Hirabayashi Tadamichi , Nishikawa Yoshikazu , Yokota Kenji 
Published: April 2003

AbstractThe alternating copolymerization of 1‐ and 2‐vinylnaphthalene (1‐VNap and 2‐VNap) with methyl methacrylate (MMA) by using diethylaluminum chloride (Et2AlCl) in toluene at 0°C has been studied. No polymerization could occur without Et2AlCl, and alternating copolymers were obtained only when an equimolar amount of Et2AlCl with MMA was supplied. Through 1H‐NMR analyses on both dyad and triad of alternating deuterated 1‐ and 2‐α‐d‐VNap–MMA copolymers, each configuration could be described successfully by a single parameter, coisotacticity σ, whose value was estimated as 0.41 for the former and 0.56 for the latter copolymer, respectively. A rather low coisotacticity of copoly(1‐VNap–MMA) was explained in the terms of steric effect (peri effect) of 1‐VNap monomer.
The mobility profile around polymer segments as calculated from microviscosity data on polymer solutions and gels
Authors: Elmgren Hans 
Published: April 2003

AbstractA mobility profile describes the change of the solvent mobility with the distance from the surface of a suspended particle. By means of numerical integration on a computer, a relationship was found between such profiles and the concentration dependence of microviscosity in suspensions of cylinders (models for polymer segments in polymer solutions and gels) and spheres (e.g., protein molecules).The obtained relationship was used to calculate the mobility profile in aqueous solutions of hydroxyethyl cellulose and ribonuclease A. The influence of the macromolecules on the water mobility was found to change as the inverse distance to the power of 1.6 and 2.2, respectively. At a distance of 40 Å from the cellulose segment, or from the surface of the ribonuclease molecule, the mobility is reduced by 10% from that in bulk solvent.
Thermodynamics of binding methyl orange and its homologs by polyvinylpyrrolidone: The effect of hexamethylenetetramine
Authors: Takagishi Toru , Kuroki Nobuhiko 
Published: April 2003

AbstractHexamethylenetetramine (HMT) has been examined for its effect on the binding of methyl orange homologs, methyl orange, ethyl orange, propyl orange, and butyl orange by polyvinylpyrrolidone (PVP). In the presence of HMT the entropy changes associated with the binding tend to become more positive and the absolute magnitude in the enthalpy changes becomes smaller compared with those in the absence of HMT. These tendencies are accounted for in terms of the water‐structure‐promoting effect of HMT, hence the enhancement of hydrophobic interactions in the binding. PVP undergoes changes in conformation on the addition of HMT and its conformation becomes more compact. This also increases the contribution of the hydrophobic interactions to the macromolecule‐small molecule interaction. Some other effects exerted by the added HMT on the binding system are also described.
Plasma polymerization. III. An ESCA investigation of polymers synthesized by excitation of inductively coupled RF plasmas in perfluorocyclohexa‐1,3‐ and 1,4‐dienes, and in perfluorocyclohexene
Authors: Clark D. T. , Shuttleworth D. 
Published: April 2003

AbstractThe plasma polymers prepared from perfluorocyclohexa‐1,3‐diene, perfluorocyclohexa‐1,4‐diene, and perfluorocyclohexene have been investigated by ESCA. The carbon‐to‐fluorine stoichiometries of the diene‐derived polymers are similar and close to that of the starting material. The polymer prepared from perfluorocyclohexene is depleted in fluorine compared to the fluorine content of the “monomer.” The polymers prepared in nonglow regions are also studied and shown to be high in CF2 derived species. The results are compared with those for perfluorobenzene and perfluorocyclohexane, and the polymerization rates are in the order C6F6 > C6F8 1,3 ∼ 1,4 > C6F10 ∼ C6F12. The variations in composition of the plasma polymer as revealed by ESCA as a function of the polymerization conditions are discussed.
Studies of the polymerization of diallyl compounds. XXVI. Enhanced polymerizability by the hydroxyl group in the polymerization of diallyl hydroxydicarboxylates
Authors: Ohata Tetsuji , Matsumoto Akira , Oiwa Masayoshi 
Published: April 2003

AbstractIn order to elucidate the effect of the hydroxyl group on the polymerization of diallyl hydroxydicarboxylates, we investigated in detail the radical polymerizations of diallyl succinate (DASu), diallyl malate (DAMa), and diallyl tartrate (DATa), each of which have similar structure differing only in the number of hydroxyl groups present. The rate of polymerization (Rp) was quite enhanced in the order DASu < DAMa < DATa, in accord with the increase in the number of hydroxyl groups within a monomer unit. The enhanced ability of the allylic monomer radical to reinitiate chain growth was also in the same order, as was clear from the dependence of Rp on the initiator concentration. The dependence of the residual unsaturation of the polymer on the monomer concentration in the polymerizations of DAMa and DATa was abnormal in terms of cyclopolymerization. These results are discussed in connection with the formation of the intermolecular hydrogen bond through the hydroxyl groups.
High‐molecular‐weight polyterephthalamide by direct polycondensation reaction in the presence of poly(ethylene oxide)
Authors: Higashi Fukuji , Nakano Yoshimasa , Goto Mitsuyoshi , Kakinoki Hideo 
Published: April 2003

AbstractPolyterephthalamides of high molecular weight (ηinh up to 1.9) were obtained by the direct polycondensation reaction of terephthalic acid and aromatic diamines in the presence of poly(ethylene oxide) (PEO) with triphenyl phosphite in a N‐methylpyrrolidone (NMP)–pyridine solution that contained lithium chloride. The molecular weights of the polymers produced varied with the amount and molecular weight of PEO, which showed maximum values when PEO with a molecular weight of 2.0 × 104−5.0 × 105 was used in a concentration of about 0.5 wt % in the solvent. The polycondensation reaction was significantly affected by the level of pyridine in a mixed solvent of NMP and pyridine and by the concentration of the lithium chloride added.