bluuebunny/crossref_metadata_2025 huggingface dataset:
The butyllithium‐initiated polymerization of 1,3‐butadiene
Authors: Kuntz Irving , Gerber Arthur
Published: April 2003

The structure of polybutadiene prepared by butyllithium initation in n‐heptane has been studied by four infrared procedures. A typical polymer prepared by n‐butyllithium at 30° gave values of 48–58% trans‐1,4‐ and 33–45% cis‐1,4‐, and 7–10% 1,2‐addition, depending on the particular analytical technique used. Iso‐ or n‐butyllithium gave polybutadienes with the same structure. Polymer stereochemistry is independent of monomer and initiator concentration and extent of polymerization conversion. Polybutadiene prepared in experiments from 4 to 80° showed the same structure. Polymerization in the presence of small amounts of ethers yields 1,2‐addition as the major structural unit. These results contrast with the reported behavior of isoprene in similar polymerizations where increasing alkyllithium concentration and reaction temperature increase the amount of 3,4‐addition and decrease the amount of cis‐1,4‐structure. Possible reaction routes for these transformations are discussed.
A theory of the thermodynamic behavior of nonelectrolyte solutions. III. The osmotic pressure of polymer solutions
Authors: Maron Samuel H. , Nakajima Nobuyuki
Published: April 2003

Data on the osmotic pressures of both dilute and concentrated polystyrene and polyisobutylene solutions in various solvents have been examined in terms of Maron's theory. It is shown that for each polymer‐solvent system at a given temperature the behavior over the entire concentration range studied can be characterized by a single interaction parameter μ, whose dependence on volume fraction v2 of polymer is given by

where μ° and σ° are constants. For two systems, where data are available, this linear relationship has been found to hold from v2 = 0 up to v2 = 0.90. With this relationship for μ, Maron's theory leads to functional plots for dilute solutions which are linear even in systems where the usual II/C vs. C plots are not straight lines. These plots yield the molecular weights from the intercepts and the quantities (μ° − σ°) from the slopes. However, the individual values of μ° and σ° cannot be obtained from dilute solution data. To arrive at these, data are required at concentrations higher than those customarily used for molecular weight determinations. The μ°'s show values which are frequently larger than 0.50 and which vary quite appreciably with change of solvent or temperature. Similarly the σ°'s are quite sensitive to these variables, and both positive and negative values have been observed for this quantity. On the other hand, the difference (μ° − σ°) is much less sensitive to these variables and consistently yields values of 0.50 or less. It is also shown that the parameter χ of the Flory‐Huggins theory does not measure explicitly the interactions in either dilute or concentrated solutions. Consequently, the dependence of χ on solution variables does not reflect directly the effect of such variables on the polymer‐solvent interactions in solution.
Transitions in ethylene polymers
Authors: Nielsen Lawrence E.
Published: April 2003

A study of polyethylenes and ethylene–vinyl acetate copolymers by dynamic mechanical mesurements gives new information on the transitions in polyethylene polymers. The melting points agree with the predictions of Flory's theory. The alpha transition is shown to be due to the melting of crystallites containing ethylene sequences of lengths near the average sequence lengths; this transition is related to the lengths of crystallites. The beta transition is not necessarily due to branch points, as a number of noncrystallizable groups produce beta transitions at the same temperature. The beta transition degenerates into the gamma transition if the crystallinity is destroyed.
Polymerization of dichlorophosphinic nitrides
Authors: Konecny Jan O. , Douglas Catherine M. , Gray Marilee Y.
Published: April 2003

Polymerization of the dichlorophosphinic nitride trimer, catalyzed by benzoic acid, ether, ethanol, or methanol, is first order in the trimer. With methanol and benzoic acid as catalysts, but not with ether, the first‐order rate constants increase linearly with catalyst concentration. Solution polymerization in benzene is somewhat slower than bulk polymerization.
A kinetic analysis for the free‐radical crosslinking of saturated polymers
Authors: Miller A. A.
Published: April 2003

A general expression for the crosslinking efficiency in saturated polymers by added free‐radical initiators is derived on the basis of a steady‐state kinetic treatment of the following reactions: (a) dissociation of initiator to form R· radicals; (b) transfer to produce P· polymer radicals; and (c) the three recombination reactions of P· and R· radicals, only one of which (P· + P·) produces a polymer crosslink. The instantaneous crosslinking efficiency (crosslinks formed per molecule of initiator decomposed) is given by: C = (k[I]1/2 + 1)−2, where [I] is the instantaneous concentration of initiator and k is constant for a given polymer–initiator system at constant temperature. Depending on the value of k[I]1/2 compared to unity, C may vary from zero to unity. An average value C̄ of C and therefore the crosslink concentration for any degree of decomposition of the initiator is given by an integrated form of the above expression. These kinetic expressions are confirmed by experimental results on the crosslinking of a polydimethylsiloxane polymer by benzoyl peroxide at 125°C. (previously reported work) and by dicumyl peroxide at 170°C. (present work). Both experiment and theory suggest that with polymers such as dimethylsiloxanes, which are more resistant to free‐radical attack, ionizing radiation may have unique advantages over conventional chemical initiators for the production of polymer radicals for crosslinking or graft polymerization.
Ultrasonic degradation of polymer molecules in solution: Some comments on recent papers
Authors: Ovenall Derick W.
Published: April 2003

Recent papers on the ultrasonic degradation of polymer molecules in solution are discussed. It is pointed out that the use of the Staudinger equation to derive weight‐average degrees of polymerization from the viscosities of benzene solutions of polystyrenes is a source of error, since these solutions have been found to obey the Houwink equation. Some measurements of degradation rates by the use of diphenyl picryl hydrazyl as a free radical scavenger are considered, and it is concluded that they can be fitted almost equally well by two different rate equations.
Tracer techniques for the determination of monomer reactivity ratios. I. A direct counting technique applied to the styrene–methacrylate copolymerization
Authors: Wiley Richard H. , Sale Edwin E.
Published: April 2003

A direct counting technique has been evaluated and used for the determination of monomer reactivity ratios. Windowless gas‐flow counting of polymer samples plated directly on planchets gave reproducible counting rates and nearly linear self‐absorption curves in the 8–25 mg./planchet range. Copolymer composition data obtained by radioactivity assay on a series of styrene C14/methyl methacrylate copolymers gave monomer reactivity ratios of r1 = 0.48, r2 = 0.46 at 60° and r1 = 0.60, r2 = 0.55 at 132°; these values are in good agreement with previously recorded values.
Tracer techniques for the determination of monomer reactivity ratios. II. Monomer reactivity ratios in copolymerizations with divinyl monomers
Authors: Wiley Richard H. , Sale Edwin E.
Published: April 2003

Monomer reactivity ratios have been determined for styrene (r1 = 0.35)–ethyleneglycol dimethacrylate (r2 = 0.65) and styrene (r1 = 0.65)‐m‐divinylbenzene (r2 = 0.60), a tracer technique being used to determine the copolymer composition. The data for these divinyl monomers give intersect plots with three different monomer ratios which determine the reactivity ratios. The usual two‐component copolymerization equation is modified by the use of 2M2 for the M2 term where M2 is the mole percent of the divinyl monomer in the charge. Similar data for p‐divinylbenzene do not locate a unique set of reactivity ratios. It is concluded that the copolymerization behavior of symmetrical divinyl monomers in which the vinyl groups do not interact can be evaluated through use of the two‐component copolymerization equation.
Pressure‐induced crystallization in polyethylene
Authors: Matsuoka Shiro
Published: April 2003

The 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

In 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

Cationic 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

The 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

A 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

Gelation 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

Monomer 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

Melting 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

Perfluoroalkyldiamidines 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

The 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

The 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

Polyvinylene 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

The 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

Free 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

Polyethylene 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

The 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

Dilatometers 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

Films 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

This 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.
On the mechanism of the polymerization of ε‐caprolactam. IV. Polymerization in the presence of water and either an amine or a carboxylic acid
Authors: Heikens D. , Hermans P. H. , Van Der Want G. M.
Published: April 2003

In continuation of previous kinetic work on the hydrolytic polymerization of εcaprolactam (CL) (Part I–III) in which evidence was obtained that all the predominant reactions are catalyzed by endgroups, special experiments were undertaken in order to study the specific role played by the NH2 and COOH endgroups. To that end kinetic runs at 221°C. were performed with Cl‐water systems (containing 5–7 mole‐% of water) in which the symmetry of the concentrations of NH2 and COOH groups was disturbed by the addition of about 1 mole‐% of either an amine or a carboxylic acid [hexamethylenediamine (HMD), adipic acid (ADA), and sebacic acid (SBA) were used]. The concentrations of unconverted lactam and of amino and carboxyl groups were determined as previously described; special techniques were worked out for the determination of the small concentrations of unconverted HMD, ADA, and SBA. The main observations are: (1) added HMD disappears much more rapidly from the reaction mixture than added ADA or SBA; (2) the dicarboxylic acids have considerable accelerating effect on the formation of endgroups. Only a general qualitative discussion of these results is given. The principal deductions may be summarized as follows. (a) The initial reaction of the polymerization process, the hydrolysis of CL, is found to be catalyzed by COOH groups. (b) The main contribution to the increase in chain length is furnished by the addition of CL to NH2 endgroups exclusively (aminolysis of the lactam molecule). (c) This addition reaction is catalyzed by COOH groups. (d) Probably, the polycondensation reaction of NH2 and COOH groups is also catalyzed by COOH groups.
Secondary crystallization of polymers
Authors: Rybnikář F.
Published: April 2003

The course of secondary crystallization in several polymers was investigated by the density balance method. At the end of primary crystallization it was possible to notice a stepwise increase of density with time, which cannot be fitted to the Avrami equation. The stepwise increase of density follow a further slow increase in density, which may be characterized by a linear dependence upon the logarithm of time. The onset of the secondary crystallization was in agreement with the value of two half‐times of primary crystallization, i.e., with the end of primary crystallization. It has been shown that the extent of secondary crystallization is related to the perfection of the structure formed in primary crystallization.
Investigation of the protective ultraviolet absorbers in a space environment. I. Rate of evaporation and vapor pressure studies
Authors: Schmitt Richard G. , Hirt Robert C.
Published: April 2003

Compounds which are effective in protecting materials from terrestial ultraviolet radiation may, in a high vacuum environment, suffer loss both by evaporation and by photochemical degradation from the shorter wavelength ultraviolet radiation. The rates of evaporation from a free surface in a high vacuum of the commercially available protective ultraviolet absorbers have been measured as a function of temperature. Vapor pressures of the solid absorbers were calculated from the rate of evaporation data. The equilibrium vapor pressures of the liquid absorbers were determined by a direct vapor spectrophotometric method. Absorbers containing more than one hydroxy group were found to be considerably less volatile than the monohydroxy compounds, probably because of intermolecular hydrogen bonding of the former.
The sorption, diffusion, and permeation of organic vapors in polyethylene
Authors: Rogers C. E. , Stannett V. , Szwarc M.
Published: April 2003

An investigation has been made of the sorption, diffusion, and permeation of several organic vapors in polyethylenes of different density over wide ranges of vapor activity and concentration. It was found that the equilibrium sorption isotherms, in terms of the solubility coefficient S, could be represented as exponential functions of the sorbed vapor concentration. The limits and physical significance of the relationship are briefly discussed in terms of the two parameters which characterize the sorption for a given solvent, polymer and temperature. The integral diffusion coefficients were estimated by three independent methods encompassing both the transient and the steady‐state of flow. The diffusion coefficients determined by the different methods generally agreed within experimental error, even though the rate of sorption—desorption indicated that some time‐dependent effects were present. These integral diffusion coefficients were found to be exponential functions of vapor activity. By combining the relation describing the dependence of the diffusion coefficient on vapor activity with the expression for the dependence of the solubility on concentration, it is shown that for an ideal vapor or, at least, low concentrations of sorbed vapor, the combined equation reduces to those equations previously reported in the literature describing the concentration dependence of the integral and differential diffusion constants. The observed trends of the permeability constant with vapor activity and concentration are then related to the activity and concentration dependence of the diffusion and solubility coefficients.
An investigation of lead tetraacetate, N‐bromosuccinimide, p‐toluenesulfonyl azide, benzenediazonium fluoborate, and saccharine–dimethylaniline as chain initiators
Authors: Dannley Ralph L. , Esayian Manuel
Published: April 2003

The thermal decomposition of several common materials in equimolar mixtures of styrene and methyl methacrylate has determined the initiator efficiency of the materials and permitted classification of the mechanisms as ionic or free radical. Both lead tetraacetate and p‐toluenesulfonyl azide are such weak catalysts for homolytic polymerization that careful work is required to differentiate catalyzed and blank runs. The proposed catalyst system, saccharine–dimethylaniline, is also homolytic in nature but is even less efficient (1% conversion in 1 hr. at 60°). Benzenediazonium fluoborate is a good initiator but is carbonium ion in nature. The active species is not proved but may be the phenyl carbonium ion. N‐Bromosuccinimide is an inhibitor not only for the monomer mixture but also for the homopolymerization of styrene. It is a catalyst however for the homopolymerization of methyl methacrylate. Apparently styryl free radicals are efficiently scavenged by N‐bromosuccinimide or its fragments to terminate the radical chain. The principal products are probably the brominated materials.
Thermal degradation of plastics. I. The kinetics of polymer chain degradation
Authors: Friedman Henry L.
Published: April 2003

Kinetic equations were derived for polymer chain degradation. The usual type of initiation‐depropagation‐termination mechanism was postulated. Chain transfer was ignored. Random and terminal initiation were considered as well as unimolecular, bimolecular, and no‐termination (complete unzipping). It was assumed that a steady state of radicals was achieved, and that monomer product rapidly diffused out of the polymer bulk as soon as it formed. Only average molecular weights were considered. Polymer and radical molecule concentrations were employed in the kinetic equations, while in all the previous work, polymer and radical molecule numbers were used. The same kinetic equations resulted for unimolecular termination and complete unzipping for both treatments, but for bimolecular termination, the results were different. Where the use of number units predicted that the rate of loss of polymer weight should be half‐order in polymer weight, concentration units gave a first‐order relationship. The equations that were derived in this work were found to be similar to those that were previously derived in treatments where number units were employed together with the assumption of exponential molecular weight distribution. A comparison of the various treatments showed that the similarities were not necessarily due to the use of the distribution assumption, but may have been a consequence of the forms of the basic kinetic equations that were utilized in the earlier work.
Dielectric properties of polypeptide solutions. V. Molecular association of the α‐helix in solution
Authors: Wada Akiyoshi
Published: April 2003

A device to study the molecular association of the α‐helix from the two sets of information in the dielectric dispersion curve; that is, specific polarization P2° and critical frequency v0, is proposed. The P2° is plotted against log v0 for each solution of associated helix. Comparing these plots with that of the perfect helix, the process of association is considered. The model in which side‐by‐side random orientation and head‐to‐tail types are superposed is suggested as the most probable association of the PBLG α‐helix in the dioxane—dimethylformamide mixed solvent.
Evaluation of surface treatment of glass fiber in fabric‐reinforced plastics
Authors: Ito Katsuhiko
Published: April 2003

The use of electron diffraction and adhesive strength tests as a method of direct evaluation of the effects of surface treatment of glass fiber on mechanical properties of fabric‐reinforced plastics is proposed. Glass plates, similar in quality to the glass fiber used in fabric‐reinforced plastics and surface‐treated with Volan and silane finishing compounds, are used as test specimens in these tests in order to eliminate complicated factors due to glass cloth reinforcement. The results obtained from tests of adhesive strength of lap joints are closely correlated with the improvement of mechanical properties fabric‐reinforced plastics by surface treatments of glass fiber; however, the molecular orientation of surface‐finishing compounds on glass plates, as determined from the electron diffraction pattern, has no such close relationship. In 18‐8 stainless steel plate surface‐treated by the procedures (chosen as the test specimen for comparing the effect of surface treatments on other materials) no such improvement due to surface treatment was noted.
Triethylaluminum—titanium tetrachloride catalysts for preparation of crystalline polystyrene
Authors: Kern R. J. , Hurst H. G. , Richard W. R.
Published: April 2003

The reaction between Et3Al and TiCl4 is discussed, with emphasis on the effect of temperature, concentration, stoichiometry, and order of component addition on the ability of products to catalyze the isotactic polymerization of styrene. A well‐defined peak in relative catalyst activity becomes apparent when the interaction of these variables is followed by measuring the average oxidation state of titanium. Experimentally, the polymerization is first‐order with respect to styrene and titanium, although efficiency of Ti use is small. The mode of polymerization is characterized by a lower activation energy for active site generation and a higher activation energy for termination than is typical of free‐radical polymerization. A convenient procedure for laboratory preparation of isotactic polystyrene employing the Et3Al/TiCl4 catalyst is given.
The flow of gases through high polymer films in equilibrium with sorbed vapors
Authors: Pilar Frank L.
Published: April 2003

A new apparatus is described for the measurement of the permeability constants of polymer—vapor film systems to atmospheric gases. The permeability constants of regenerated cellulose to oxygen, nitrogen, and carbon dioxide were found to increase rapidly and nonlinearly with increasing relative humidity. The permeability constants of polyethylene to oxygen and nitrogen were found to increase in a like manner with increasing relative pressures of n‐hexane and carbon tetrachloride. In the case of the polyethylene—organic vapor and gas systems the activation energy for the permeation process appears to be independent of sorbed vapor concentration. Furthermore, it was found that the permeability constants of the polymer—vapor films increased linearly with sorbed vapor concentration. A theory based on an analogy with electrical conductivity is proposed to explain the form of this relationship. The theory appears to give good quantitative agreement for the polyethylene—hexane—oxygen system, but further experimental data are needed to establish the generality of the theory.
A new method for measuring the degree of crosslinking in elastomers
Authors: Cluff E. F. , Gladding E. K. , Pariser R.
Published: April 2003

A rapid method for determining the degree of crosslinking in elastomers is described which involves measuring equilibrium compression modulus at very small deformations on solvent‐swollen samples. The elastomer used was a polyether urethane vulcanized by an accelerated sulfur recipe. The degree of crosslinking as measured by the compression method agreed with that measured by the extension method within 1–3%. Both methods agreed reasonably well with the theoretical values calculated from the sulfur level, polymer molecular weight, and crosslink structure.
Equilibrium polymerization of α‐methylstyrene. Part I. Initiation by means of sodium naphthalene and sodium diphenylacetylene at 0°C.
Authors: Tobolsky A. V. , Rembaum A. , Eisenberg A.
Published: April 2003

The equilibrium polymerization of α‐methylstyrene at 0°C. has been investigated, sodium naphthalene and sodium diphenylacetylene being used as initiators. With both initiators, the extrapolated equilibrium monomer concentration has been found to be equal to 0.89 mole/kg. This value remained unchanged when the sodium counterion accompanying the initiator was replaced by cesium. When sodium naphthalene is used for the polymerization, the initiator step consists of an equilibrium electron transfer reaction, where the equilibrium constant has a high value. In the sodium diphenylacetylene system, the initiation consists of an equilibrium step involving bond formation between the monomer and initiator, and the equilibrium constant has a sufficiently low value to be determined practically. Spectroscopic evidence for the presence of an initiator fragment in the polymer chain has been presented. The general equilibrium theory of polymerization has been applied to the present system and equations have been derived correlating degree of polymerization with the initial monomer and initiator concentration as well as with the equilibrium constants. Good agreement has been obtained between the theoretical calculations and experimental results.
Polymerization of allyl acetate
Authors: Litt Morton , Eirich F. R.
Published: April 2003

The kinetics of polymerization of allyl acetate with benzoyl peroxide at 65, 80, and 90°C. has been investigated, and was found to parallel normal vinyl kinetics. The reaction which alters the normal picture is the early production, by chain transfer, of a stable allylic radical which generally terminates rather than initiates new chains (degradative chain transfer). A kinetic scheme has been developed including: (1) normal initiation, (2) normal propagation, (3) allylic chain transfer, (4) induced decomposition of the peroxide by allylic and growing radicals, (5) initiation of new chains by the allyl radical, and (6) homo‐ and cross‐termination of the allylic and growing radicals. The equations developed were shown to fit the data quite well at all temperatures.
γ‐Radiation‐induced homopolymerization of diethyl fumarate
Authors: Wiley Richard H. , Parish D. J.
Published: April 2003

Homopolymerization of diethyl fumarate at 1.57 × 105−3.75 × 105 rep/hr. from a 1000‐c. cobalt‐60 source at temperatures from −56 to 22°C. has given brittle, solid polymers which are soluble in most organic solvents but insoluble in petroleum ether. These polymers have intrinsic viscosities of 0.123–0.178 in benzene and ebullioscopic molecular weights in toluene of 7500–9300. The viscosity constant K is 2.97 × 10−4−3.21 × 10−4 for an assumed value of a equals; 0.7. Inhibition by diphenylamine and decreased rate of reaction at low temperature indicate a radical initiation process.