bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of the effects of additives in homogeneous anionic polymerization of α‐methylstyrene by n‐butyllithium (to prepare polymers having narrow molecular weight distribution)
Authors: Fujimoto Teruo , Ozaki Noriyoshi , Nagasawa Mitsuru 
Published: April 2003

AbstractPolymerization of α‐methylstyrene with n‐butyllithium was carried out in the presence of some additives such as LiBr, LiOH, LiOBu, and LiN(Et)2 in THF. The change in the color of the α‐methylstyryl anion with amount of the additives, the activity of n‐BuLi, the average molecular weights, and the molecular weight distributions of polymers obtained were observed to clarify the interaction of n‐BuLi (or of α‐methylstyryl anion) with these additives. It was concluded that LiBr and LiOH deactivate the initiator in the mole ratio of 1:1 and only the remaining part of n‐BuLi participates in polymerization, while LiOBu and LiN(Et)2 do not. The order of the additives in the capacity to form deactivating centers (possibly by complex formation) follows the order of nucleophilicity and is opposite to the order of activity for initiating the polymerization. The molecular weight distribution of the polymer obtained with pure n‐BuLi in the absence of additives was extremely sharp.
Photodegradation of poly(α‐methylstyrene) in solution
Authors: Fox R. B. , Price T. R. 
Published: April 2003

AbstractApparent quantum yields for the random scission of poly(α‐methylstyrene) in solution by 2537 A. radiation were shown to be solvent‐dependent, indicating that processes other than the direct photolysis of the polymer are taking place. Quantum yields on the order of 10−3 scissions per quantum absorbed by the polymer were found in benzene, dioxane, cyclohexane, and methylene chloride and about 0.2 in chloroform and carbon tetrachloride; the quantum yields were unaffected by oxygen. In carbon tetrachloride, the quantum yields decreased slightly with increasing polymer concentration. Ethanol and cyclohexane were inhibitors for the photolysis in carbon tetrachloride, while the latter solvent acted as a sensitizer in cyclohexane. By comparison with model compounds irradiated in carbon tetrachloride, it was shown that an early step in the photolysis of poly(α‐methylstyrene) in this solvent involves reaction with a main‐chain methylene group and eventual substitution with a trichloromethyl group.
Redox kinetics of the peroxydisulfate–iron–sulfoxylate system
Authors: Andersen H. M. , Proctor S. I. 
Published: April 2003

AbstractInhibition kinetics were used to study the peroxydisulfate–iron–sulfoxylate redox initiation system. Onset of polymerization was detected by a thermometric technique permitting accurate measurement of short inhibition periods. Rate constants were derived from the inhibition periods by using an analog simulation. A good fit of calculated to observed results was obtained, based on a simple model, for experiments in ammonia buffer (pH ca 10). In bicarbonate buffer (pH ca 8.5), however, the same simple model was inadequate; additional involvement of iron is indicated. Evidence was found that the reduction of ferric versenate by sulfoxylate yields a free radical, tentatively (HCHO)SO2·. Absolute rates of radical generation were calculated.
Synthesis of polyhydrazones and polypyrazoles by a polycyclization reaction
Authors: Korshak V. V. , Krongauz E. S. , Berlin A. M. 
Published: April 2003

AbstractBy the interaction of linear or branched bis(β‐diketones) and dihydrazides of dicarboxylic acids or dihydrazines unknown high molecular compounds with pyrazole rings in the chain have been prepared. Polypyrazoles of the second type (with a free NH‐group in the pyrazole ring) were prepared by the interaction of bisdiazoalkanes and diacetylenes. Some features of the polycyclization reaction as well as the structure and properties of polymers obtained are discussed.
Alkaline hydrolysis of polyacrylamide
Authors: Nagase Kunihiko , Sakaguchi Kahei 
Published: April 2003

AbstractPolyacrylamide has been reported to show an abnormal behavior on alkaline hydrolysis, that is, the reaction rate is quite high at the initial stage and decreases rapidly with increasing conversion. This phenomenon has been attributed to the polymer structure. We have found that the low molecular weight diamides show essentially the same behavior and concluded that this abnormality is due to the polyfunctionality and is not necessarily specific to polymers.
Studies on melt spinning. I. Fundamental equations on the dynamics of melt spinning
Authors: Kase Susumu , Matsuo Tatsuki 
Published: April 2003

AbstractThe dynamics of melt spinning was analyzed by deriving a set of simultaneous partial differential equations.Equation of heat balance:

Equation of force balance:

Equation of material balance:

In the above equations, the distance x from the spinneret and time τ are the independent variables; temperature t, local velocity v, and cross‐sectional area A are the dependent variables. It is assumed that tensile viscosity β is a function of temperature t alone, and the spinning tension F is a pure time function. Steady‐state (∂/∂τ = 0) solutions of the above equations showed a fairly good agreement with the experimentally measured values of temperature t(x) and thickness A(x).
Potentiometric study of the conformational transition in poly(acrylic acid)
Authors: Mathieson A. R. , McLaren J. V. 
Published: April 2003

AbstractDetailed potentiometric titration curves have been obtained for poly(acrylic acid) (Mn = 2.6 × 106) in solution at four different ionic strengths at 25°C. When plotted as pH + log [(1 − α)/α] versus α (where α is the degree of dissociation), they reveal the presence of two different molecular conformations, denoted PAA(a) and PAA(b), with a transition between them. The proportion of the material present in the two conformations has been calculated for different degrees of dissociation and is found to be independent of ionic strength. PAA(a) is intact up to α = 0.22 and is completely converted into PAA(b) by α = 0.75. The free energy of transition from PAA(a) to PAA(b) when both forms are uncharged decreases numerically from −275 to −157 cal./mole monomer residues as the ionic strength increases from 0.02 to 0.20. The increase of the pH of solutions of the PAA(a) from over those of the PAA(b) form at a given value of α, is largely independent of α. This makes it possible to calculate the free energy of transition from PAA(a) to PAA(b) when both forms are charged to the same extent. This free energy is proportional to α and decreases numerically from −944α to −561α (cal.) as ionic strength increases from 0.02 to 0.20. The charge‐independent part of the free energy of transition is a constant fraction of the total, at a given value of α, independent of the ionic strength. The PAA(a) form is the more compact, less contractile, and more ordered structure. The possibility is suggested that this conformation may be partly helical in nature.
Cationic polymerization α,β‐disubstituted olefins. Part I. Cationic copolymerization of β‐methylstyrenes
Authors: Mizote A. , Tanaka T. , Higashimura T. , Okamura S. 
Published: April 2003

AbstractSteric and electronic effects of the β‐methyl group on monomer reactivity have been studied by copolymerization of styrenes and β‐methylstyrenes. Steric hindrance of the β‐methyl group in the transition state of homopolymerization is so great that the rate of the propagation reaction is considered to be depressed by as much as 1/10−1/20 of the corresponding styrene derivatives. In contrast to this, steric hindrance of the β‐methyl group in cross propagation reactions with styrene is found to be very small. The monomer reactivity itself of β‐methylstyrenes is a little lower than that of corresponding styrenes. This lowered reactivity of β‐methylstyrenes is considered to be due to the electronic effect of the β‐methyl group.
Effect of crosslinking density on the viscoelastic properties of unsaturated polyesters
Authors: Shibayama K. , Suzuki Y. 
Published: April 2003

AbstractViscoelastic properties of unsaturated polyesters were investigated in the glass‐rubber transition region in relation to the temperature dependence of specific volume. Polyesters which are homologous with respect to crosslinking density were prepared by using mixtures of succinic and fumaric acid as the dibasic acid component. The temperature dependence of the specific volume was determined by refractive index measurement, the specific refractivity being assumed to be independent of temperature. The temperature dispersion of dynamic viscoelasticity was measured at a constant frequency. Results are summarized as follows. Specific volume and glass temperature are linearly related to the logarithm of crosslinking density. The thermal expansion coefficient and steepness of viscoelastic dispersion decrease with increasing crosslinking density. Fractional free volume and expansion coefficient of free volume, both of which were calculated by WLF equation, are in good agreement with the temperature dependence of specific volume. The results indicate that the effect of crosslinking is largely attributable to the change in amount and distribution of free volume in polymer networks.
Polymerization of adsorbed monolayers. II. Thermal degradation of the inserted polymer
Authors: Blumstein Alexandre 
Published: April 2003

AbstractMonomolecular layers of methyl methacrylate inserted between the lamellae of montmorillonite clay were polymerized. Finely divided complexes of poly(methyl methacrylate)–montmorillonite were suspended in boiling hydrocarbons and subjected to thermal degradation at 215°C. and above, under air and nitrogen, with constant vigorous stirring. Aliquots were regularly withdrawn, centrifuged, and extracted with appropriate solvents. The weight losses upon calcination at 1000°C. were determined, and from them the rates of reversal to monomer were followed. Complexes containing inserted and external polymer were studied. The inserted polymer was found to resist thermal degradation under conditions at which complete degradation of the external polymer was found. This effect seems to be due to steric factors hindering the thermal motion of the segments of the polymer sandwiched between the lamellae of the crystallites. The insertion polymer isolated from the polymer–clay complex, had a greater thermal stability than poly(methyl methacrylate) made in a conventional free radical system without the presence of clay.
Copolymerization of acrylonitrile and sodium p‐styrenesulfonate in dimethyl sulfoxide solution
Authors: Izumi Z. , Kiuchi H. , Watanabe M. , Uchiyama H. 
Published: April 2003

AbstractThe copolymerization of acrylonitrile (AN) with sodium p‐styrenesulfonate (SSS) in dimethyl sulfoxide solution has been investigated. Monomer reactivity ratios at 45°C., for AN and SSS are found to be r1 = 0.15 ± 0.02, r2 = 0.55 ± 0.03. From these data Price Q and e values for SSS of 0.44 and −0.38, respectively, are calculated. The values are found to be different from those in aqueous solutions, which may be attributed to the different electron distributions in all solvents. Initial rates of copolymerization at 45°C. with azobisisobutyronitrile as initiator were determined over the entire range of composition from pure AN to pure SSS. It was found that there is a slight rise in copolymerization rates in the range of 90–95 mole‐% SSS in the monomer feed; this is attributed to the coexistence of liquids of different optical density. Homopolymerization of AN and SSS in dimethyl sulfoxide was also investigated and δ = (k/kp) for AN and SSS found to be 6.55 (mole‐sec./1.)½ and 2.46 (mole‐sec./1.)½, respectively. From these values the cross‐termination constant φ is calculated to be 6.5.
Polymer–solvent interactions of bisphenol a polycarbonate in different solvents
Authors: Sitaramaiah Gullapalli 
Published: April 2003

AbstractBisphenol A polycarbonate (Lexan, General Electric) was fractionated from methylene chloride by progressive precipitation with methanol and the fractions were characterized by osmometry, light scattering, and viscometry. Intrinsic viscosities of eight fractions in the molecular weight range 10,000–70,000 were obtained in five solvents at different temperatures to study the molecular expansion of polycarbonate. Light‐scattering molecular weights, measured for the three high viscosity fractions, agreed within ±5% with the Mv values. The Mv/Mn ratio of the fractions was between 1.1 and 1.3, as compared to 2.7 for the unfractionated polymer. This indicates a relatively narrow distribution of the fractions. The exponent, a, in the Mark‐Houwink equation showed no appreciable change with temperature. Values of d[η]/dT were generally negative. The unperturbed dimensions of polycarbonate, evaluated by the relation [η] = KM½‐α2.43, suggest a stiff molecule. Values of K and d log α3/dT indicate increased chain flexibility at higher temperatures. Experimental data demonstrate that the Kurata‐Stockmayer‐Roig expression, based on the equivalent ellipsoidal model of a linear polymer molecule, is well suited to interpret the molecular expansion of polycarbonate. The Flory relation, α5 − α3 versus M½, is found to be of limited applicability.
Polymerization of acrylonitrile by electron transfer initiation
Authors: Tsukamoto Akira 
Published: April 2003

AbstractThe homogeneous polymerization of acrylonitrile by electron transfer initiators is investigated. In a rigorously purified system at low temperatures it is demonstrated that “living” polyacrylonitrile is formed, and that its molecular weight can be predetermined. The number‐average molecular weight of “living” polyacrylonitrile is approximately given by 2M/I, where M represents grams of monomer and I is the number of moles of the initiator. For polyacrylonitrile prepared by homogeneous anionic polymerization with an electron‐transfer initiator, it is found that the viscosity average molecular weight calculated by using the conventional values of K and α in the Mark‐Houwink equation is considerably smaller than the osmotic number‐average molecular weight. This clearly indicates a structural difference between the free‐radical and anionic polyacrylonitrile; the anionic polyacrylonitrile appears to have a highly branched structure formed by a chain transfer process to the polymer.
Copolymerization studies. VI. Spontaneous copolymerization of bicyclo[2.2.1]hept‐2‐ene and sulfur dioxide. Evidence for propagation by biradical coupling
Authors: Zutty N. L. , Wilson C. W. , Potter G. H. , Priest D. C. , Whitworth C. J. 
Published: April 2003

AbstractThe alternating copolymerization of bicyclo[2.2.1]hept‐2‐ene and sulfur dioxide has been found to be quite unusual for a free‐radical polymerization: (1) the initiation of copolymerization is spontaneous, even at −40°C.; (2) solution copolymerization is extremely fast, yielding very high molecular weight polymer within a few seconds; (3) conversions are high (up to 93% within a minute); (4) molecular weight during copolymerization increases at essentially constant conversion; (5) the reaction is incapable of being chemically inhibited indefinitely, short of exhausting one of the constituent monomers; (6) at elevated temperatures, the monomers and copolymer appear to be in equilibrium; (7) large concentrations of free radicals have been detected by electron paramagnetic resonance to be associated with the bulk copolymerization; and (8) the copolymerization appears to result in “living” free‐radical polymers. A copolymerization mechanism is proposed to explain these observations. Bicycloheptene and sulfur dioxide initially form a 1 : 1 molecular charge transfer complex which rearranges to a biradical; subsequent coupling of biradicals with each other (and possibly also with the molecular complexes themselves) leads to rapid propagation to high molecular weight, alternating copolymer. Speculations that similar mechanisms may be important in other copolymerization reactions are also made.
Ziegler polymerization of olefins without added metal alkyls
Authors: Matlack A. S. , Breslow D. S. 
Published: April 2003

AbstractEthylene has been polymerized under mild conditions by (1) transition metals plus alkyl halides, (2) transition metal hydrides, (3) certain transition metals alone, and (4) certain divalent transition metal halides and oxides. Propylene has been polymerized to mixtures of amorphous and crystalline polymer in low conversions by (1) transition metals plus alkyl halides and (2) certain divalent transition metal halides. A vibratory ball mill was used as the polymerization vessel to provide a continuous supply of fresh catalyst surface during the polymerizations. The transient existence of transition metal alkyls is postulated to account for the observed catalysis. This work provides one of the most direct proofs that polymerization occurs on the transition metal, rather than on aluminum, zinc, or other metals usually associated with it in typical Ziegler catalysts.
Variation of crystallinity with temperature for homopolymers and random copolymers
Authors: Krigbaum William R. , Uematsu Ichitara 
Published: April 2003

AbstractAn earlier treatment assumed that crystallization places portions of the polymer molecule between tie‐points under strain, which limits the equilibrium crystallinity at any temperature. If these strained chains can be treated in the Gaussian approximation, (1 – ω)−2 should be a linear function of T−1, where ω is the degree of crystallinity. This prediction is unchanged by inclusion of the crystal surface energy. The degree of crystallinity is primarily governed by the deformation entropy at high supercoolings, while near the apparent melting point the crystal surface energy dominates, hence the Hoffman and Weeks procedure for evaluating thermodynamic melting point remains valid. Random introduction of comonomer lowers the apparent melting point and increases the tie‐point density. The latter limits both the degree of crystallinity and the initial Young's modulus of a random copolymer at high supercoolings. Values obtained for N (the number of statistical links between tie‐points) by fitting crystallinity data near the melting points for isothermally crystallized isotactic polypropylene and linear and branched polyethylene by using the Gaussian approximation, are identical to those previously obtained at high supercoolings by using inverse Langevin statistics. In fact, if the effects of crystal surface energy and the presence of a comonomer are included and the amorphous chains are treated by inverse Langevin statistics, one obtains a satisfactory representation of the variation of crystallinity with temperature over the entire range studied. Finally, the predicted linear variation of ω at high supercoolings with N−½ is verified for polyethylene.
Effect of thiourea on the radical polymerization of vinyl monomers. Part I. Polymerization of acrylonitrile with the hydrogen peroxide–thiourea catalyst system
Authors: Sugimura Takaaki , Yasumoto Noboru , Minoura Yuji 
Published: April 2003

AbstractThe polymerization of acrylonitrile (AN) was studied in aqueous solution with hydrogen peroxide (H2O2) as catalyst and thiourea (TU) as cocatalyst at 30°C. Since the polymerization was carried out at a relatively low temperature, AN was not polymerized by hydrogen peroxide alone. Upon addition of TU to the reaction system, polymerization occurred immediately, and the rate of polymerization increased with increasing TU concentration. In order to obtain the overall polymerization equation, the dependence of polymerization rate on H2O2 and AN concentration was studied kinetically. It was found that the overall polymerization rate Rp was represented by the equation: Rp = K[TU]frac12;[H2O2]frac12;[AN], where K is the rate constant. The acceleration in the presence of TU might be attributed to a redox reaction between H2O2 and TU which would produce free radicals rapidly. The effect of substituents was investigated by use of various N‐substituted derivatives of TU. The polymerization rate increased linearly with the σ* constants of the substituents as electron‐withdrawing substituents were added. The polymerization mechanism is discussed on the basis of the results.
Effect of reaction medium on copolymerization of acrylonitrile and sodium allyl sulfonate
Authors: Izumi Zenzi , Kiuchi Hiroshi , Watanabe Masamoto 
Published: April 2003

AbstractThe copolymerization of acrylonitrile (AN) with sodium allyl sulfonate (SAS) in dimethyl sulfoxide (DMSO) at pH 7, aqueous DMSO solution (6% H2O), DMSO at pH 1.5, and aqueous solution at pH 7 has been investigated. Monomer reactivity ratios at 45°C. for AN and SAS are found to be r1 = 1.00 ± 0.01, r2 = 0.38 ± 0.02 in DMSO at pH 7; r1 = 1.25 ± 0.01, r2 = 0.28 ± 0.02 in aqueous DMSO; r1 = 1.85 ± 0.01, r2 = 0.43 ± 0.01 in DMSO at pH 1.5. From these values Price Q and e values, respectively, calculated for SAS were 0.19 and 0.22 in DMSO at pH 7, 0.14 and 0.18 in aqueous DMSO, and 0.18 and 0.70 in DMSO at pH 1.5. The large differences in reactivity of SAS may be attributed to the different electron distributions in SAS in each solvent which are caused by the poor solvating power of dimethyl sulfoxide and by the addition of protons. In copolymerization in aqueous solution, the physical condition depends upon the content of SAS in the monomer feed, and SAS is copolymerized to only a small extent in the range of heterogeneous systems, whereas SAS is copolymerized rather well in the range of homogeneous systems. Homopolymerization of SAS shows a first‐order dependence on initiator concentration and a three‐halves‐order dependence on monomer concentration; this is attributed to degradative chain transfer of SAS. Rates of copolymerization of AN and SAS decrease with increasing SAS content.
Coupling of xylylene dihalides with divalent chromium. Aspects of copolymerization and mechanism
Authors: Lunk H. E. , Youngman E. A. 
Published: April 2003

AbstractCopolymers of p‐ and m‐xylylene have been prepared by coupling of the corresponding dihalides with chromous chloride. A stepwise mechanism is proposed for the formation of polyxylylenes, and evidence is given for the occurrence of free radicals in the decomposition of the intermediate organochromium complex.
Crystallization kinetics of polypropylene fractions
Authors: Hoshino S. , Meinecke E. , Powers J. , Stein R. S. , Newman S. 
Published: April 2003

AbstractThe overall crystallization rate of polypropylene fractions was studied dilatometrically, and the crystallization behavior was considered in relation to the stereoregularity of the samples. The study includes a photomicroscopic analysis of the nucleation, formation, and growth of spherulites, as well as an evaluation by means of rapid x‐ray scanning techniques of the increase of crystallinity within the spherulites. A theory was applied to the discussion of crystallization behavior in which two stages of growth were introduced: (a) growth at the spherulite interface, and (b) secondary crystallization within the spherulite. These were described in terms of Avrami‐type equations with differing parameters.
Modified avrami equation for the bulk crystallization kinetics of spherulitic polymers
Authors: Hillier I. H. 
Published: April 2003

AbstractAn explanation of the anomalous fractional values of the Avrami exponent found for the crystallization of a number of polymers is presented. The interpretation is based on a model which postulates the constant radial growth of spherulites, followed by an increase in crystallinity within them by a first order process. The model is supported by direct microscopic observations of other workers. Crystallization isotherms for polymethylene, poly(ethylene oxide), and poly(decamethylene terephthalate) are fitted to this model. Apart from the removal of the fractional values of the Avrami exponent, which have no physical meaning, this model gives a considerably better fit than the Avrami equation to most isotherms analyzed. The temperature dependence of the rate constants found for the two rate processes of this model is also discussed. An interpretation of the results of seeded experiments is presented in terms of this model.