bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pressure‐induced crystallization in polyethylene
Authors: Matsuoka Shiro 
Published: April 2003

AbstractThe kinetics of crystallization of a high density polyethylene melt under hydrostatic pressure have been studied dilatometrically. The isotherms for the crystallization thus found are not superimposable by a shift along the logarithmic time axis. A mathematical model for the crystallization process of polymers has been developed by modifying the existing theory of kinetics of phase transition in nonpolymeric materials. The comparison of the experimental results with the above model shows that the two are in very good agreement.
Polyethylene specific volume, crystallinity, and glass transition
Authors: Swan Paul R. 
Published: April 2003

AbstractIn all polymer crystallinity determinations, the basic assumptions are made that there exist only two well‐characterized phases and that the volumes of those phases are additive. For the case of polyethylene, the specific volume of the amorphous phase cannot be measured directly and is usually obtained as a linear extrapolation of the melt specific volume. This is shown to be invalid for the particular case of a high density polyethylene studied here. A new approach is proposed which utilizes temperature dependent determinations of total specifiac volume and of crystalline specific volume. The results indicate that the specific volume of the amorphous phase is less than the extrapolated liquid specific volume, and this is attributed to the restraining effect of the crystalline regions. The crystallinity of the particular high density polyethylene studied is found to have a constant value of about 70% up to 80°C., where melting commences. During this work, the glass transition of polyethylene has been detected as a 15% increase in the slope of the total specific volume‐temperature curve at −130°C.
Cationic polymerization in liquid sulfur dioxide. II. Cationic polymerization of styrene with the friedel‐crafts‐type and other acid catalysts
Authors: Asami Ryuzo , Tokura Niichiro 
Published: April 2003

AbstractCationic polymerization of styrene in liquid sulfur dioxide was carried out at 0° using Friedel‐Crafts‐type metal chlorides, and inorganic and organic acids as catalysts. All catalysts of the Friedel‐Crafts‐type possessed excellent abilities to affect cationic polymerization, and gave polystyrenes of high molecular weight in quantitative yield. Catalytic activity decreased in the order: FeCl3, BF3(C2H5)2O, SnCl4, AlCl3, ZnCl2, SbCl5, TiCl4. The molecular weight of the polystyrene formed decreased by the use of a catalyst in order: ZnCl2, BF3(C2H5)2O, SnCl4, FeCl3, AlCl3, TiCl4, SbCl5. The polymerization of styrene in liquid sulfur dioxide with BF3(C2H5)2O, from among this type of catalyst, seemed to be a cationic polymerization of the “living polymer” type, similar to the case of SnCl4 reported in the preceding paper. Of the acid reagents employed, H2SO4, HSO3Cl, C6H5SO3H, P2O5, and HClO4 showed ability to affect cationic polymerization. Polystyrene was formed quantitatively, although the molecular weight of the polymers was not so large.
Kinetics of radical termination in irradiated polyamides
Authors: Zimmerman Joseph 
Published: April 2003

AbstractThe rate of decay of free radical concentration in irradiated polyamides has been measured by observing the changes in transient optical density of polyamide films at the wavelength of maximum absorption. The dependence of initial radical concentration and of the initial rate constant for radical decay on radiation dose has been interpreted as resulting from the nonhomogeneous placement of radical “spurs” at low doses. The results are consistent with a “spur” diameter of 30–40 A.
The kinetics of the polymerization of methyl methacrylate. II. The crosslinked and heterogeneous reaction
Authors: Hayden P. , Melville Harry 
Published: April 2003

AbstractA thermocouple method of following the nonstationary state of chemical reactions has been used to study the kinetics of the crosslinked and heterogeneous polymerization of methyl methacrylate. The crosslinked reaction exhibits to an enhanced degree those characteristics of the linear polymerization which have been ascribed to diffusion control of the elementary steps. Conversion ceases prematurely due to the occlusion of monomer within the crosslinked reaction medium. Polymerization of methyl methacrylate in cyclohexane solutions flocculates the polymer formed. With about 50% cyclohexane, the reaction assumes the kinetic characteristics of a polymerization terminating by a unimolecular process.
Gelation in condensation reaction of partially N‐methylolcarbamoylethylated polyvinyl alcohol
Authors: Negishi M. , Nakamura Y. , Koide T. 
Published: April 2003

AbstractGelation velocity and reaction rate for the acid‐catalyzed condensation reaction in the aqueous solution (10–22%) of partially N‐methylolcarbamoylethylated polyvinyl alcohol (about 20 mole‐% degree of methylolcarbamoylethylation) have been investigated by the falling ball viscosity method and the chemical analysis of methylol groups including the effects of kinds of acid, concentrations of acid and polymer, and temperatures of reaction. For the reciprocal gel point, 1/tg, and the hydrogen ion concentration, [H+], the following equation holds:

where α and c are constants independent of the kind of acid; also α is independent of temperature and polymer concentration, while c increases with increasing temperature or polymer concentration. The 1/tg is approximately proportional to the concentration of polymer in the range of a concentrated polymer solution above about 15% by weight. From this fact, it is suggested that, in a concentrated polymer solution, the intermolecular crosslinking proceeds predominantly as a bimolecular reaction with respect to methylol groups. Assuming that the increase of the apparent viscosity of the reacting system is mainly due to that of the structural viscosity which should be increased by a bimolecular crosslinking reaction, the following expression was derived for the gelation velocity:

in which,

where η0 and ηt are the apparent viscosities at time 0 and t, respectively, A is a measure of gelation velocity, a is the initial number of methylol groups, xg is the number of crosslinked methylol groups at the gel point, and k is the bimolecular rate constant. The experimental results of viscosity changes have shown a fairly good agreement with the above expression except in the early stage of condensation. The extent of reaction at the gel point (xg) has been estimated to be about 0.03–0.05 regardless of concentration of polymer and acid, kinds of acid, and temperature. Also, it has been observed that the rate constant of reaction is independent of the concentration of polymer and is proportional to the concentration of hydrogen ions. The above expression and estimation have been verified by the chemical analysis of methylol groups in the condensation processes. However, the extent of reaction at the gel point is about ten times that predicted by Flory's theory. This discrepancy may presumably be attributed to the fact that all of the methylol groups on the polymer chains which are coiled, entangled, and strongly solvated prior to the crosslinking are not equally reactive sterically and a certain extent of intramolecular crosslinking occurs. The activation energy of reaction has been estimated to be about 21 kcal./mole.
The mechanism of vinyl polymerization initiated by metal alkyls: Copolymerization studies
Authors: Zutty N. L. , Welch F. J. 
Published: April 2003

AbstractMonomer reactivity ratios have been determined for the copolymerization of methyl methacrylate (M1) and acrylonitrile (M2) catalyzed by alkyl derivatives of lithium, sodium, beryllium, magnesium, boron, aluminum, zinc, and cadmium. Lithium, sodium, beryllium, and magnesium alkyls gave reactivity ratios averagingr1= 0.34,r2= 6.7, while alkyls of boron, aluminum, zinc, and cadmium gaver1= 1.24,r2= 0.11. These values compare favorably with published reactivity ratios for anionic copolymerization (r1= 0.25,r2= 7.9) and free‐radical copolymerization (r1= 1.35,r2= 0.18). Therefore, alkyl derivatives of groups Ia and IIa metals propagate by an anionic mechanism, while those of groups IIb and IIIa do so by a free‐radical mechanism. Confirmatory experiments were run using styrene (M1)–acrylonitrile (M2) solutions. For groups Ia and IIa alkyls the reactivity ratios averaged,r1= 0.20,r2= 12.5; and for Groups IIb and IIIar1= 0.33,r2= 0.03. The published values for free‐radical catalysts arer1= 0.41,r2= 0.04. The formation of free radicals from the groups IIb and IIIa metal alkyls probably arises from oxidation of the metal alkyls by chance traces of oxygen.
Melting point depression study of polyacrylonitrile
Authors: Krigbaum W. R. , Tokita Noboru 
Published: April 2003

AbstractMelting point depressions were determined by dilatometric and microscopic measurements for polyacrylonitrile in dimethylformamide and in γ‐butyrolactone. These data give for the glass transition and melting point of the pure polymer 104 and 317°C., respectively. Both the heat and entropy of fusion are low. This suggests that the high melting point of polyacrylonitrile is due to its extended molecular conformation rather than to strong attractions between the molecules in the crystalline state.Average crystallization rates measured dilatometrically indicate that the optimum temperature for crystallization from solutions in the concentration range 17–27% is only 21°C. above the glass transition temperature. On either side of the optimum temperature the rate decreases sharply, and although crystallization then continues for a longer time the amount of crystallinity finally developed is less.For 15–20% solutions the viscosity increases abruptly as the glass transition is approached, and decreases rapidly at about 25°C. below the true melting point. The shear dependence is large at low temperatures but appears to vanish at 25°C. below the melting point. As the temperature is raised a narrow region is observed for each concentration in which the viscosity exhibits an anomalous increase. These temperatures stand in good agreement with the optimum temperature for crystallization as determined dilatometrically. The foregoing observations suggest the presence of molecular aggregates which are held together by regions of small and imperfect crystallites.In addition to the low entropy of fusion, additional evidence for the extended shape of polyacrylonitrile molecules is provided by estimates based on dilute solution measurements. The interaction between nearest‐neighbor nitrile dipoles was investigated in an attempt to correlate large unperturbed dimensions with the molecular structure. This dipolar interaction is repulsive, and its magnitude depends upon the rotational position of the two nitrile groups. By adding a further contribution representing the steric repulsion the total rotational potential is estimated for isotactic and syndiotactic sequences. The dipolar interaction is much larger than the steric repulsion, and the rotation about successive chain bonds must be cooperative to avoid certain high energy conformations. This requirement probably explains the low flexibility and high extension of polyacrylonitrile molecules. The total rotational potential for an isotactic sequence favors the same helical conformation observed in crystalline isotactic polyolefins, while for a syndiotactic sequence some type of helical conformation appears to be preferred rather than the extended planar zigzag.
Thermally stable polymers from condensation polymerization of perfluoroalkylamidines
Authors: Brown Henry C. 
Published: April 2003

AbstractPerfluoroalkyldiamidines and cyclic perfluoroalkylimidines undergo condensation polymerization with the liberation of ammonia to produce infusible polymers that are stable to heating in air at 350° and are not attacked by strong oxidizing agents. Copolymerization of perfluoroalkyldiamidines or perfluoroalkylimidines with perfluoroalkylmonoamidines produces polymers that are equally stable at high temperatures and that range in physical characteristics from viscous liquids to elastomeric gums. A probable structural unit for this new polymer system consists of s‐triazine rings linked by perfluoroalkyl chains.
Molecular weight distributions of vinyl polymers grafted to a solid polymeric substrate by irradiation (theoretical)
Authors: Zimmerman Joseph 
Published: April 2003

AbstractThe molecular weight distributions of vinyl polymers grafted by irradiation have been deduced theoretically. The derivations are rigorous for cases where chain transfer is not important or in all cases where the radiation dose is high (>1 Mrad). In the absence of chain transfer, the width of the distribution depends mainly on conversion of monomer to grafted polymer and on the ratio of the rate constant for propagation to that for termination (kp/2kt). As this ratio gets smaller, the molecular weight distribution becomes broader. For relatively small values of kp/2kt (e.g., 0.5 or less), the width of the distribution increases markedly with increasing conversion. In such cases, the occurrence of chain transfer tends to make the distribution narrower. For a monomer grafted to a substrate where kp/2kt = 0.9 (for example), the ratio of weight to number average molecular weight is ca. 2. In general, monomers which have lower rates of propagation should form grafted polymers with broader molecular weight distributions.
Solid state polymerization of acrylamide initiated by gamma radiation
Authors: Baysal B. , Adler G. , Ballantine D. , Colombo P. 
Published: April 2003

AbstractThe solid‐state polymerization of acrylamide, both in a radiation field and after removal from the field, is shown to proceed by an unusual kinetic mechanism. The usual steady state assumption is found to be inadequate because there seems to be no free radical termination (in the normal sense) involved. These results are consistent with the view that the solid‐state polymerization proceeds by a nucleation mechanism in which the free radicals are probably trapped by overlapping of the reactive sites.
Sequence length distributions in vinylene carbonate‐vinyl acetate copolymers
Authors: Marder Herman L. , Schuerch Conrad 
Published: April 2003

AbstractPolyvinylene carbonate is a linear polymer which can be dissolved with saponification in cold alkali. After precipitation the resultant amorphous polyvinylene glycol can only be dissolved in fused urea. Vinylene carbonate (M1)–vinyl acetate (M2) copolymers are higher melting than polyvinylacetate, and at 55° the reactivity ratios are r1 = 0.0579, r2 = 3.71. Expressions are derived relating periodate consumption and formic acid formation by hydrolyzed vinylene carbonate copolymers to the number‐average sequence lengths predicted by copolymerization theory. Periodate consumption by the homopolymer and copolymers is complicated by the overoxidation of the intermediate malondialdehyde to carbon dioxide. When this side reaction is taken into account, periodate consumption and formic acid liberation are in reasonably good semi‐quantitative agreement with theoretical predications of number‐average sequence length.
Polyesters from expoxides and anhydrides
Authors: Fischer R. F. 
Published: April 2003

AbstractThe reaction of monoanhydrides and terminal epoxides to give linear polyesters is 98–99% specific in the presence of tertiary amines. Products with molecular weights up to 18,400 have been obtained; the only termination reaction detected (within the limits of analytical accuracy) has been due to hydroxyl‐containing impurities in the reagents. With most epoxides the products are mixtures of stereoisomers which soften below 100°. Ethylene oxide, however, gives highly crystalline products melting at 110° to 163–165°, depending on the anhydride. Cyclohexene oxide also gives products softening higher than 110°. The use of functional epoxides gives polyesters with side‐chains modifying their physical and chemical properties. Up to 30 mole‐% of maleic anhydride has been incorporated, giving styrene‐compatible structural polyesters. Within limits, the rate, molecular weight, and product composition are independent of the monomer concentrations. The degree of specificity drops to ca. 80% with cyclohexene oxides and to ca. 60% with alkyl epoxy stearates.
Graft copolymerization by a preirradiation method
Authors: Shinohara Y. , Tomioka K. 
Published: April 2003

AbstractFree radicals as well as peroxides are formed when irradiation of polyethylene is accomplished with the use of cobalt‐60 or a Van de Graaff electron accelerator, as radiation sources, even in the presence of air. The free radicals are able to induce graft copolymerization under low temperatures, in which peroxide grafting cannot occur. When the irradiated polymer is stored in air, the trapped free radicals disappear monomolecularly, probably combining with oxygen. The activation energy for this reaction is 20 kcal./mole. In graft copolymerization by free radicals, the percent grafting is proportional to the square root of the free radical content, and the higher the grafting temperature, the faster the initial rate of graft copolymerization. There occurs, however, a saturation phenomenon of the per cent grafting with a grafting time, especially in high temperatures, and the higher the grafting temperature, the smaller the saturation value. It is believed that the kinetic theory of vinyl polymerization in a homogeneous system is applicable for graft reaction in spite of its apparent heterogeneous character.
Electron spin resonance studies of free radical decay in gamma‐irradiated polyethylene
Authors: Loy Billy R. 
Published: April 2003

AbstractPolyethylene was irradiated in vacuo at liquid nitrogen temperature and allowed to warm up. The concentration of free radicals, as observed by electron spin resonance (ESR) spectroscopy, decays very quickly to a relatively stable value which is temperature dependent. This behavior is interpreted to mean that these reactive radicals are relatively close to one another as opposed to random distribution. The cold‐irradiated sample was exposed to air, and the formation of the peroxy radical was observed at −80°C. Only 40–45% of the radicals reacted. This was interpreted to mean that 90–95% of the radicals trapped at −195°C. are in the amorphous phase
Morphology of n‐alkanes, linear polyethylene, and isotactic polypropylene crystallized from solution
Authors: Rånby B. G. , Morehead F. F. , Walter N. M. 
Published: April 2003

AbstractThe morphology of two n‐alkanes (n‐C44H90 and n‐C82H166, prepared by E. Stenhagen, et al. ) and linear polyethylenes (Ziegler‐type of low and Marlex 50 of high molecular weight, respectively), crystallized from dilute solution by slow cooling, have been studied by electron microscopy and small‐angle x‐ray scattering. A series of solvents were used with cloud points for polyethylene from about 120°C. (poor solvents, e.g., diphenyl ether) to 65–75°C. (good solvents, e.g., tetrachloroethylene). All samples crystallized with basically the same morphology, showing large, thin flakes or lamellac with the chains perpendicular to the plane of the flakes. This involves chain folding for all polyethylenes studied, as proposed by Keller. In most cases, the large flakes were overgrown with or accompanied by diamond‐ or lozenge‐shaped single crystals (as reported by Jaccodine and Till) containing from 2 to about 20 lamellae and developed as pyramids, sometimes as spirals and sometimes as consecutive layers. Isotactic polypropylene crystallized with a similar morphology. The nucleation and growth mechanisms of the large flakes are not clear. They seem to grow without dislocations, while the diamond‐shaped crystals seem to form according to Frank's screw‐dislocation growth concepts. Crystallization of polyethylene at high temperatures give thicker lamellae (165 A. at 120°C.) than crystallization at low temperatures (103 A. at 60°C.), as measured by small‐angle x‐ray scattering, regardless of molecular weight. When heated, the lamellae recrystallized to larger thickness. This would imply that the folding length of the polyethylene chains and the related thickness of stable lamellae are primarily a function of the crystallization temperature. The lamellae of n‐alkanes showed a thickness which agreed with the extended chain length of each sample within a few angstroms.
Dilatometric measurements on poly(4‐methyl‐1‐pentene) glass and melt transition temperatures, crystallization rates, and unusual density behavior
Authors: Griffith Joe H. , Rånby B. G. 
Published: April 2003

AbstractDilatometers were used to measure the volume‐temperature curves of seven poly(4‐methyl‐1‐pentene) (PMP) samples between −30 and +270°C., and to measure crystallization rates on one sample between 220 and 236°C. A glass transition temperature of 18–29°C. was found, and the crystalline melting point was found to be 250°C. The value of dV/dT above and below the glass temperature was used to measure the degree of crystallinity. The results indicate that the crystalline PMP is less dense at room temperature than the amorphous polymer. However, because of different rates of expansion, the normal positive volume change on melting is observed. A density value of 0.828 ± 0.002 g./ml. at 20°C. is calculated for the PMP crystal.
The action of oxygen corona and of ozone on polyethylene
Authors: Cooper Glenn D. , Prober Maurice 
Published: April 2003

AbstractFilms of low‐density polyethylene which were exposed to a corona discharge in oxygen at a pressure of 1 atm. lost weight and decreased in thickness due to oxidation of the surface to volatile products (principally carbon dioxide and water). The weight loss was directly proportional to the time of exposure and was independent of film thickness. The infrared spectra of the films after exposure to the discharge showed a strong band at 1717 cm.–1 due to carbonyl groups. After a short time in the discharge, the formation of new carbonyl groups in the polymer was balanced by their destruction by oxidation to volatile products at the surface. The intensity of the carbonyl band initially increased rapidly with increasing exposure, but reached a maximum value after 4 hr. and then showed no further change for 90 hr., during which time the thickness of a film originally 4 mils thick was reduced to approximately 1 mil. The data indicate that the carbonyl groups are present in a relatively thin oxidized layer, estimated to be between 5 X 102 and 7 X 104 A. in depth. Carbonyl groups were also formed in films which were not in the discharge area but were exposed to the ozone produced by the discharge. The position of the carbonyl band in both types of oxidized film is consistent with either carboxylic acids or ketone. The relative amounts of the two were determined by soaking the films in ethanolic sodium hydroxide solution to convert the acid to carboxylate ion and measuring the decrease in intensity of the 1717‐cm.–1 band. In the sample which was exposed to the discharge, 60% of the carbonyl was carboxylic acid and 40% was ketone. In the sample exposed only to ozone, the proportion was 30% acid and 70% ketone. It is believed that the carbonyl groups in both cases are the result of attack of ozone on the carbon‐carbon double bonds of the polymer. Small amounts of oxalic acid and other low molecular weight acids were also produced in films exposed to the discharge, presumably due to oxidation of the surface by one or more of the unstable species of the corona.
On the mechanism of polymerization of ε‐caprolactam in the presence of water. III. Supplementary remarks on a previous paper. Introduction of volume correction
Authors: Heikens D. , Hermans P. H. 
Published: April 2003

AbstractThis paper is the third in this series and gives data and rate constants for the polymerization of ε‐caprolactam in the presence of water, corrected for volume changes during reaction at 221.8°C. The influence of the experimental uncertainties of the reaction velocities at small reaction times is discussed.