bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the determination of methyl content in polyethylenes
Authors: Slowinski E. J. , Walter H. , Miller R. L. 
Published: April 2003

AbstractA method for the quantitative determination of the degree of branching (methyl content) in ethylene polymers is described. This method involves the use of a calibration curve prepared from hydrocarbons of known methyl content. Because of the importance to the calibration of having hydrocarbon with a methyl content roughly that of the polymers to be measured, the hydrocarbon, n‐C58H118, was prepared and its synthesis is given. The methyl contents of a series of polyethylenes, both commercial and experimental, were determined, and the results correlated with some physical properties of the polymers. A quantitative relationship was shown between the crystallinity of a polymer, as measured by the density, and the degree of branching. Qualitative relationships between molecular weight and branching and between mechanical properties and branching were also shown.
Polymers and group interactions. II. Friedel‐Crafts reactions on polyvinyl chloride, a route to poly‐1,3‐methyleneindans1
Authors: Teyssié Ph. , Smets G. 
Published: April 2003

AbstractPolyvinyl chloride was condensed with a series of aromatic compounds (benzene, toluene, m‐xylene, pseudocumene, and mesitylene) in the presence of aluminum chloride. These condensation reactions were carried out in several reaction media, in heterogeneous or semihomogeneous systems. The catalyst concentration exercises a determining effect on the over‐all rate of the reaction. The degree of substitution of the polymers obtained was evaluated by chemical determination of the residual chlorine content. The condensation proceeds through a two‐step reaction scheme: an alkylation reaction of the aromatic ring, according to the classical orientation rules (except for pseudocumene and mesitylene), followed by a fast intramolecular cyclization reaction yielding 1,3‐methyleneindan units. Nevertheless some “abnormal” substituted products were also detected in the end products. The structure of these polymers determined from their infrared absorption spectra by comparison with the spectra of the following reference compounds: polystyrene, poly‐m‐methyl‐ and poly‐p‐methylstyrenes, poly‐2,4‐dimethyl‐ and poly‐3,5‐dimethylstyrenes, poly‐2,4,6‐trimethylstyrene, 1,3‐dimethyl‐, 1,3,6‐trimethyl‐, and 1,1,3,3,4,6‐hexamethylindans. The condensation reactions of this type are always accompained by a strong decrease of the degree of polymerization, which was followed by both viscometric and osmotic measurements; this decrease of the degree of polymerization depends mostly on the amount of aromatic substitution on the polymers.
Diffusion and gelation in polyadditions. IV. Statistical theory of ring formation and the absolute gel point
Authors: Gordon Manfred , Roe Ryong‐Joon 
Published: April 2003

AbstractIn the model nonlinear polyaddition system methyl methacrylate/ethylene dimethacrylate (MMA/EDMA), the plot of the critical conversion against the rate of polymerization is a straight line. This is in accord with the classical theory of gelation, whose vindication is completed in this paper. To account quantitatively for the slope of the line, internal cyclization within the primary polymerization chains must be extensive. Thus of the order of half the pendent vinyls on such a chain fall to the radical on the same chain, in agreement with theoretical prediction on the basis of molecular models. The intercept of the critical conversion plot at zero rate can also be explained in terms of the internal cyclization reaction, while chain transfer makes at most a small contribution. The dependence of the gel point on the proportion ρ of EDMA unsaturation, over a 250‐fold range, is satisfactorily accounted for by the classical gelation theory. A statistical theory of internal cyclization suggests that a steady state is approached in the growth of a given radical chain. Pendent vinyls are then lost by cyclization as fast as they are added by polymerization. The limiting number of pendent vinyls on a primary chain is about 1000 ρ. A statistical theory of multiple crosslinking (cyclization involving more than one primary chain) suggests that it is unimportant. The number of pendent vinyls on a giant molecule grows proportionately to the number of primary chains of which it is comprised. Thus multiple crosslinking has little effect on the classical network theory of gelation, but makes a contribution to the parameter introduced into the theory to correct for internal cyclization. The interplay of kinetic and gelation measurements is useful in mechanistic studies of nonlinear polymerization.
Electron exchange polymers. VIII. The redox potentials of polymeric hydroquinones
Authors: Luttinger Lionel , Cassidy Harold G. 
Published: April 2003

AbstractThe redox potentials of linear and crosslinked polymeric hydroquinones were studied under a variety of experimental conditions. For aqueous systems a sulfonated copolymer was employed. The main features of these titrations were: (1) In aqueous solution the potentials were up to 200 mv. higher than that of a comparable monomer. (2) These potentials fell to about the expected value when the titration was carried out in 1 M KCI. (3) Titrations of the unsulfonated copolymer in 90% dioxane‐water indicated that a small but measurable enhancement of the potential (about 10–50 mv. over that of a comparable monomer) exists in this case. (4) Both the linear and crosslinked polymers yielded substantially the same results. (5) A smaller enhancement of the potential was observed when bromine rather than ceric sulfate was used as oxidant. (6) The reactions were very slow, but in the case of the oxidations with ceric sulfate the reaction rate was increased tenfold in the presence of 1 M KCl. The potentials are discussed in the light of current polyelectrolyte theory, which gives a plausible explanation of much of the observed effect, but direct experimental confirmation was not forthcoming. Various possibilities with regard to the catalysis by KCl are discussed. These polyelectrolyte phenomena are also shown to have important consequences for redox enzyme and other protein systems.
A rational measure for the heterogeneity of polymeric homologous substances
Authors: Hultin Eskil 
Published: April 2003

AbstractA rational measure of the heterogeneity of high molecular substances is obtained by comparison of their molecular weight distribution with the theoretical distribution arrived at if infinitely large molecules are depolymerized in such a way that all linkages between the basic molecules are broken with equal ease. This distribution differs noticeably from the error function, which was used by Lansing and Kraemer in measuring heterogeneity. A table is given, by which the distribution curve can be transformed to a straight line. These table values, called “dist” values, are logarithms of the degrees of polymerization in the theoretical distribution, expressed in per cent of the median degree of polymerization. For a fractionated sample, the table values corresponding to the various percentages of substance at which the fractions were obtained are plotted versus the logarithms of the molecular weights. If the molecular weight distribution of the sample is similar to that in depolymerization, a straight line fits the points. The inverse value of the inclination of this line is a measure of the heterogeneity, for which the name heterogeneity quotient is suggested.
Chain scission efficiency in the oxidation of natural rubber vulcanizates
Authors: Veith A. G. 
Published: April 2003

AbstractThe efficiency of the oxidative chain scission in natural rubber vulcanizates has been measured for a simple MBTS vulcanizate with and without antioxidants. This was accomplished by making concurrent measurements of the chain scission velocity and oxidation rate. The chain scission velocity was obtained from stress relaxation measurements which were corrected for the relaxation not due to oxygen by means of relaxation in vacuo. The reciprocal scission efficiency, defined as the number of molecules of O2 per chain scission, was found to be 1.5 as a mean for six vulcanizates both with and without antioxidant. The decrease in network chains was found to be first order. From the theoretical analysis by Bueche such behavior has been interpreted to indicate a nonrandom scission process with the scission occurring at the crosslinked site. The form of the dependence of the reciprocal scission efficiency on time, in vulcanizates with and without antioxidant, is consistent with nonrandom scission. Experiments on Butyl vulcanizates and the known effect of crosslink density or combined sulfur on oxidation rate further strengthen the concept of scission at the crosslinked site.
Anionic polymerization of isoprene: Effect of ionic character of the growing ion pair on polymer structure
Authors: Tobolsky A. V. , Rogers C. E. 
Published: April 2003

AbstractThe styrene content of styrene‐isoprene copolymers initiated by alkali metals in different solvents is correlated with the total 1,4‐adduct content of isoprene homopolymers initiated in the same manner. A very good linear relationship is obtained over the whole range which is dependent on the ionic character of the propagating species highly ionic systems (i.e., Na in ethers) give high styrene and low 1,4‐adduct contents, while less ionic systems, i.e., butyllithium in aromatic ethers and in hydrocarbons, give progressively lower styrene and higher 1,4‐adduct contents.
The apparent specific volume of polymers in dilute solution
Authors: Horth A. , Patterson D. , Rinfret M. 
Published: April 2003

AbstractApparent specific volumes φ2 of polymers in dilute solution (<5%) have been obtained with a magnetic float type densitometer for the following systems: polyvinyl acetate–chlorobenzene, polyisobutylene–benzene and –chlorobenzene, and polystyrene–chlorobenzene and –chloroform. Large variations of φ2 with concentration in very dilute solution have been reported in the literature, but could not be detected; preliminary results did show a variation, but this was found to be a nonequilibrium effect. The difference between φ2 and the specific volume of the pure polymeric liquid is found to be roughly proportional to the calorimetrically determined heat of mixing of polymer and solvent.
High pressure polymerization of ethylene. A kinetic study of polymerization initiated by 2,2′‐azobisisobutyronitrile
Authors: Kodama Shinjiro , Matsushima Yoshinori , Ueyoshi Akihito , Shimidzu Takeo , Kagiya Tsutomu , Yuasa Sachio , Fukui Kenichi 
Published: April 2003

AbstractThe polymerization of ethylene initiated by 2,2,‐azobisisobutyronitrile in water was studied at 70–120° C. and at 100–1500 kg./cm.2 pressure. The following relations between the reaction conditions and the properties of polyethylene produced were obtained (1) the density decreases with temperature, and (2) the molecular weight increases with pressure, independent of the amount of initiator. The reaction begins with an incubation period for which the overall rate Ri is represented by Ri = const. × I0P0, in which I0 and P0 are the amount of initiator used and the initial pressure, respectively. In the main period of reaction the overall rate was found to be R = k′I0 exp {−αt}P1.8. A reaction mechanism is proposed from which this rate equation can be derived. The proposed mechanism implies that the deactivation and the termination of radicals is first order with respect to the radical concentration.
Characterization of polyolefins by differential thermal analysis
Authors: Ke Bacon 
Published: April 2003

AbstractDifferential thermal analysis has been used to study the solid‐liquid transitions of four polyethylenes, an isotactic polypropylene, a series of ethylene‐propylene copolymers, and a physical mixture of polyethylene and polypropylene. The thermograms obtained directly yield the transition temperatures. By calibration, heats and entropies of fusion were also derived from the thermograms. From the heats of fusion, the degree of crystallinity of these polymers has been calculated. Differential thermal analysis can detect a physical mixture of polymers that melt sufficiently wide apart. The thermogram‐peak areas are proportional to the amounts of material present. Convenience and speed make differential thermal analysis a useful tool for characterizing polymeric materials when uniform conditions are maintained.
Characterization of counterion distribution in polyelectrolyte solutions by the rate of reaction of two charged species
Authors: Morawetz H. 
Published: April 2003

AbstractIt is shown that second‐order rate constants of reactions of two charged, small molecules yield parameters characterizing the counterion distribution in solutions of polyelectrolytes. The rates constant is larger than in conventional buffers if the reagents carry charges of the same sign and smaller if they carry charges of opposite sign.
Proton magnetic resonance of some polyamides
Authors: Woodward A. E. , Glick R. E. , Sauer J. A. , Gupta R. P. 
Published: April 2003

AbstractProton magnetic resonance of a number of polyamides has been investigated in the 80–410°K. range. Line width and second moment vs. temperature plots for dry specimens of poly(hexamethylene adipamide) and poly(hexamethylene sebacamide) are found to exhibit two transition regions. Saturation with H2O or D2O lowers the temperature of the principal line‐narrowing process for the above two polymers as well as for poly(decamethylene sebacamide) and shifts part of the second‐moment transition which occurs above room temperature to lower temperatures; in both cases H2O has a more pronounced effect than D2O. Exchange of the protons, presumably on the amide groups, for deuterium leads to small decreases in line width and second moment at temperature in and below the main transition. N‐methylation of poly(decamethylene sebacamide) up to 58% causes marked shifts of the principal line‐narrowing process and NMR second moment transition to lower temperatures. The NMR data are found to be in qualitative agreement with dynamic mechanical measurements on similar samples.
Polymerization in the crystalline state. I. Acrylamide
Authors: Fadner T. A. , Morawetz H. 
Published: April 2003

AbstractCrystalline acrylamide was irradiated at −78°C. with γ‐rays and the postpolymerization of the irradiated crystals was studied in the temperature range 0–60°C. The polymerization rate decays rapidly at low conversion, and the polymer yield is, for long polymerization times, linear in the logarithm of time. The activation energy for the polymerization is 25 kcal./mole. The molecular weight of the polymer depends at a given polymerization temperature on the polymerization time, but remains unchanged over a sixteenfold variation of the irradiation dose. The number of polymer chains, as deduced from the ratio of polymer yield and molecular weight, increases only slightly with conversion, probably due to chain transfer to monomer. The number of chains calculated in this way is in satisfactory agreement with the number of radicals estimated from electron spin resonance. The ESR signal changes very little during the postpolymerization. The presence of oxygen has little effect on the polymerization. Molten and shock‐cooled monomer yields about twice as much polymer as large slowly grown crystals, but the molecular weight of the product is the same, implying that crystal imperfections increase slightly the chain initiation efficiency, but are without effect on chain propagation. Propionamide is isomorphous with acrylamide and forms with it solid solutions over the entire concentration range. The polymerization of acrylamide in solid solutions containing up to 10% propionamide proceeds at a rate indistinguishable from that for pure acrylamide; at higher propionamide concentrations the rate falls off less rapidly than the concentration of the monomer. The molecular weights of polymers obtained from solid solutions approach a limiting value for long polymerization times which is determined by chain transfer to propionamide. Up to 10% propionamide concentration, the limiting polymer chain length is inversely proportional to the propionamide concentration and corresponds to a chain transfer coefficient of 0.022 at 25°C. and 0.0064 at 60°C. The high value of the chain transfer coefficient at 25°C. is ascribed to the directing influence of the crystal lattice which makes it difficult for a chain to “grow around” a site occupied by a propionamide molecule. The gradual loosening of the lattice restraints at higher temperatures explains the decrease in the chain transfer at higher temperatures. Acetamide is not isomorphous with acrylamide, but a limited amount of acetamide can be incorporated into the acrylamide lattice; the polymerization of such solid solutions exhibits, however, no chain transfer. X‐ray diffraction studies indicate that partially polymerized acrylamide contains separate monomer and polymer phases. Since the chain transfer behavior of propionamide and other evidence points to the importance of lattice control in solid‐state polymerization, it is suggested that the polymer chains grow at a monomer—polymer interface with the growing end anchored in the crystal lattice of the monomer.
Studies on polyoxypropylene glycols. Part IV. Elastic properties of derived elastomers
Authors: Conway B. E. 
Published: April 2003

AbstractThe stress‐strain behavior of three elastomers prepared from polyoxypropylene glycols has been examined, and the components of the elastic retractile force have been derived for one of the polymers. The data are used as a basis for interpretation of the swelling equilibrium behavior reported in the previous paper (Part III). The swelling volume ratios for the elastomers swollen in nonpolar solvents are related to the retractile forces at a given elongation in the manner expected theoretically. The degree of crosslinkage as determined by the number of elastic elements per cubic centimeter is discussed in relation to the retractile force and equilibrium swelling measurements.
A theory of the thermodynamic behavior of nonelectrolyte solutions. VI. Critical miscibility of polymer solutions
Authors: Maron Samuel H. , Nakajima Nobuyuki 
Published: April 2003

AbstractMaron's theory of the thermodynamics of nonelectrolyte solutions has been applied to the condition of critical miscibility in polymer solutions on the basis of an interaction parameter μ linearly dependent on the volume fraction v2, i.e., μ=μ°+σ°v2. The results yield expressions for μc, μc°, σc°and (μc° − σc°) at the point of critical miscibility which are related to the molar volume ratio, the critical volume v, and effective volume factors. For the limit of infinite molecular weight these equations yield σc°= 1/6, (μc° − σc°) = 1/2 and μc= μc°=2/3. These results differ from the χc=1/2 predicted by the Flory‐Huggins theory on the basis of an interaction parameter χ independent of concentration.
Anhydrous lithium perchlorate as an initiator of vinyl polymerization
Authors: Hodgdon Russell B. 
Published: April 2003

AbstractAnhydrous lithium perchlorate is an effective catalyst for the polymerization of certain vinyl monomers. Evidence shows that it behaves more as a cationic catalyst than a radical type, but is much milder in action than the better known representatives of this type of catalyst. Other perchlorates and lithium compounds show only a fraction or none of the activity of anhydrous lithium perchlorate in initiating vinyl polymerization.
Polyethylidene from diazoethane upon metal catalysts: Chromatographic analysis of evolved gases and mechanism of reaction
Authors: Nasini A. G. , Saini G. , Trossarelli L. , Campi E. 
Published: April 2003

AbstractIt has already been shown that many pure metals, as evaporated metal films, are suitable catalysts in giving polyethylidene from the decomposition of diazoethane in ethereal solution, whilst other metals (for instance Ag and Pd), although decomposing diazoethane, do not give polymer. The composition of the gases evolved during the reaction, as obtained by gas chromatographic analyses, is different in the two cases: besides nitrogen the 2‐butenes represent the main fraction of the gases evolved when polymer formation occurs; ethylene when no polymer is formed is the most important fraction of the light hydrocarbons evolved. A mechanism for the reaction of polymer formation from diazoethane is proposed, as derived from the results reported here.
Solid state polymerization of formaldehyde induced by ionizing radiation
Authors: Tsuda Yoshizo 
Published: April 2003

AbstractIrradiation with gamma rays or electrons of solid formaldehyde at −196°C. induces polymerization, which proceeds explosively on warming the irradiated solid monomer. The G value for conversion was much larger than those of any other radiation polymerizations. Polyoxymethylene of very high molecular weight was obtained in bulk and in solid solution irrespectively of dose rate and irradiation time. Acrylonitrile was found also to polymerize explosively on warming the solid monomer irradiated at −196°C. It was concluded that ions or highly excited molecules formed from the irradiation at −196°C. are trapped in the solid state and that they initiate the polymerization on warming the irradiated solid monomer.
Vinyl polymerization photosensitized by uranyl ions
Authors: Mahadevan V. , Santappa M. 
Published: April 2003

AbstractA systematic investigation of the kinetics of polymerization of the vinyl monomers methyl methacrylate, methyl acrylate, and acrylonitrile in aqueous solution, photosensitized by uranyl ions, was undertaken. Light of wavelengths 300–450 mμ was used for irradiation. Complex formation and ion‐pair formation was kept to the minimum. The course of the reactions was followed in terms of rates of monomer disappearance, rates of uranous ion formation, and the chain length of the polymer formed. Under controlled conditions of acidity and ionic strength, quantitative correlations between the various rates and chain length, and the variables (1) fractional light absorption, (2) uranyl ion concentration, (3) wavelength of incident radiation, (4) monomer concentration, (5) light intensity, and (6) temperature of the reaction were obtained. The influence on the reaction of uranous ion present initially in the system was studied. The quenching of the fluorescence of uranyl ions by vinyl monomers and by other standard quenchers was compared. The tentative mechanism proposed for the overall reaction is discussed in the light of these experimental results. Ratios of specific rate constants and activation energies for the various steps have been evaluated.