bluuebunny/crossref_metadata_2025 huggingface dataset:
The scattering of light from thin polymer films. I. Experimental procedure
Authors: Stein R. S. , Keane John J.
Published: April 2003

The measurement of the scattering of light by solid polymers is a means for studying their structure. Films are the most convenient form for working with highly scattering polymers, which are subjected to such treatment as temperature variation, mechanical deformation, and orientation. In measuring scattering from films, it is necessary to correct the observed scattered intensity for (a) refraction at film interfaces, (b) reflection, and (c) secondary scattering. The necessary correction factors are described in this paper. The application of these correction factors is illustrated in the case of scattering by a polyethylene film.
Hydrogen peroxide as initiator in vinyl polymerization in homogeneous system. I. Kinetic studies
Authors: Nandi Uma Sankar , Palit Santi R.
Published: April 2003

The kinetic study of the polymerization of methyl methacrylate initiated by hydrogen peroxide in toluene, ethyl acetate, and methyl ethyl ketone as well as in bulk has been made. It has been established that the catalyst has no inhibition period and follows the square root relation. The initiation order is unimolecular with respect to the monomer in the fist two solvents and is half‐molecular with respect t o methyl ethyl ketone. The value of Δ (= κ/κp) for methyl methacrylate a t 60°C. a t various concentrations in the three solvents has been measured and found to remain sensibly constant and its value is 8.43. From bulk polymerization data the value of Δ at temperatures of 50, 60, 80, and 115°C. has been determined and they are 11.62, 8.43, 5.26, and 2.48, respectively. The temperature variation of Δ, and hence the corresponding energy of activation (Ep − 1/2Et), has also been measured and its value is found to be 5.71 kcals. The initiation constant under a variety of conditions has been determined by two independent methods (kinetic and DP) which have been found to yield values in fairly good agreement with each other, leading to a strong support to the usually assumed mechanism of polymerization. However, the initiation constant is found to change considerably with monomer concentration and change of solvent.
Viscosity, diffusion, and sedimentation of polyacrylonitrile solutions
Authors: Bisschops J.
Published: April 2003

Intrinsic viscosity measurements of polyacrylonitrile fractions in dimethyl formamide at 25°C. and molecular weight determinations by the sedimentation‐diffusion method led to the following relation :

equation image

The data are consistent with the model of a coiled chain, impenetrable to the solvent, in agreement with the theories of Flory and co‐workers. The influence of the concentration upon the sedimentation constant was interpreted by an extension of the concept of the equivalent hydrodynamic sphere to the range of small finite concentrations. The following relation was thus obtained:

equation image

K should be a universal constant and its value is about 1.6 for most flexible polymers.
Determination of molecular weight of polyvinylpyrrolidone. II
Authors: Levy Gabor B. , Frank H. P.
Published: April 2003

Additional polyvinylpyrrolidone samples of great homogeneity have been prepared, and their intrinsic viscosity and molecular weight (by light scattering) have been determined in water and chloroform. In view of the new results the previous data were reinterpreted particularly with respect to the shift in K (in [η] = KMα) with homogeneity. All data were evaluated by objective statistical techniques and revised intrinsicviscosity molecular weight equations are proposed.
Effect of loss of low molecular weight polymers on molecular weight averages
Authors: Valentine L.
Published: April 2003

The effect of loss of low molecular weight species on the number and weight average molecular weights of polymers has been calculated for the main molecular weight distributions found for synthetic linear polymers. The expressions derived indicate that such an effect is most likely to be important for polycondensations and vinyl polymerizations propagated by monoradicals and terminated by transfer or disproportionation. Number average degrees of polymerization are much more liable to be seriously in error due to this factor than are weight average degrees of polymerization.
On the measurement of polymerization rates by means of infrared absorption spectra
Authors: Slowinski Emil J. , Claver George C.
Published: April 2003

Measurements have been made of the rate of thermal polymerization of styrene by observation of the infrared absorption spectrum of polymerizing samples in infrared absorption cells at 100°C. No effect of cell thickness on polymerization rate was noted, and the rate obtained agrees well with previously published values. An infrared method for determination of residual styrene monomer in polystyrene is described, and its possible application to rate studies on systems at high per cent conversion is noted.
The spherulitic structure of crystalline polymers. Part I. Investigations with the polarizing microscope
Authors: Keller A.
Published: April 2003

An investigation on polymer spherulites is being described in three parts. Part I (the present paper) describes the various effects observed under the polarizing microscope. These are interpreted in terms of the concepts of crystal optics; the problem of the position of the molecules and that of the microscopic fine structures will form Parts II and III. The materials examined were: polyethylene terephthalate, polyhexamethylene sebacamide and adipamide, and polyethylene. It is confirmed that the growing spherulites are a crystalline part of the crystallizing melt, and their individuality is demonstrated. The spherulites are radiating fibrous structures and the various observed extinction effects were interpreted in terms of such fibrous units. These extinction effects varied with the different materials and also for a particular substance with conditions of crystallization. Apart from the usual Maltese crosses, zigzag and ringshaped extinction lines were observed between crossed Nicols. The zigzag lines were interpreted as resulting from the index ellipsoids lying along elongated helical paths, while the most plausible explanation of the rings is given by closely coiled or strongly twisted arrangements of the index ellipsoids. The possibility of the existence of helical structures in spherulites is discussed in the light of earlier work on spherulites of simple substances.
Effect of electric field on light scattering of solutions of polar chain polymers
Authors: Isihara Akira , Koyama Ryuzo , Yamada Nobuo , Nishioka Atsuo
Published: April 2003

The effect of strong uniform electric field on the statistical configuration and the light scattering of linear chain polymers in solutions is studied. The statistical configuration of linear chain molecules is affected by the mutual interactions between the dipoles attached to the segments of the molecules and the external electric field. The radial distribution function of molecular segments from arbitrary chosen segment and that around the center of gravity of the molecule are calculated. The distribution functions are not spherically symmetric, and show that the molecules are slightly stretched toward the applied electric field. Using the radial distribution function calculated, we calculated the angular distribution of the intensity of scattered light by the deformed chain molecules. The intensity of scattered light is dependent on the magnitude of the applied electric field and the relative orientation of the incident ray, scattered ray, and electric field. Several special cases are illustrated. The effect of electric field is most conspicuous when the incident ray is parallel to the electric field and the scattered angle is 180°. We observed the effect of electric field on the light scattering of polyvinyl chloride molecules in diethylene oxide at the field intensity of 3000 v./cm. and the concentration 1%.
The spherulitic structure of crystalline polymers. Part II. The problem of molecular orientation in polymer spherulites
Authors: Keller A.
Published: April 2003

The orientation of the crystallites in spherulites was investigated by using special microbeam x‐ray techniques. The materials studied were: polyhexamethylene adipamide and sebacamide, polyethylene, and polyethylene terephthalate. In all these substances the c axes (molecular chains) were perpendicular to the radii of the spherulites, with some deviation from strict perpendicularity in the case of polyethylene terephthalate. The particular orientation of the crystallites around their c axes was in full agreement with the observed sign of birefringence, in the positive and negative polyamide spherulites, in polyethylene (where the indirect deduction made in earlier works has also been confirmed), and in the negative spherulites of polyethylene terephthalate. In the positive polyethylene terephthalate spherulites, while a fit between x‐ray results and birefringence might still be possible, it is somewhat doubtful whether the sign of birefringence could be accounted for by the crystallite orientation alone. The possible arrangements of the crystallites is discussed and it is suggested that the picture of closely coiled helices with the molecules lying along the winding direction might offer the most satisfactory explanation.
Polymethyl methacrylate: Dilute solution properties by viscosity and light scattering
Authors: Chinai S. N. , Matlack J. D. , Resnick A. L. , Samuels R. J.
Published: April 2003

A polymethyl methacrylate polymer, prepared by the emulsion technique, was fractionated three times to obtain essentially homogeneous fractions. The intrinsic viscosities and weight average molecular weights were determined in an ideal solvent at 23°C. and in nonideal solvents at 25°C. The constants K and a in the conventional modified equation [η] = KMa were determined. The intrinsic viscosity in an ideal solvent was found to fit closely over the molecular range studied with the relation [η]θ = KM1/2. Light scattering measurements giving root‐mean‐square distance between ends of a polymer chain were carried out. It was shown that these results support both Kuhn's relation (r̄2)1/2 ≈︁ M0.50 and Flory's relation (r̄2)3/2 = M[η]/2.1 × 1021 in an ideal solvent. In a nonideal solvent only Flory's relation was found to be in agreement with the experimental results. The values of volume expansion factor α3 ratios A2M/(r̄2)3/2 and A2Mw/[η] in a nonideal solvent and the value of the ratio [η]/M1/2 in an ideal solvent showed that the polymer molecules were expanded beyond their random flight dimensions in a nonideal solvent.
Linear polyesters derived from vanillic acid
Authors: Bock Louis H. , Anderson James K.
Published: April 2003

Vanillic acid, which is potentially available from lignin, was converted to dibasic acids by etherifying the phenolic hydroxyl group with alkylene dihalides. The dibasic acids were esterified with ethylene glycol and condensed to linear polyesters. The polyesters were converted to fibers by melt spinning. The fibers could be stretched, preferably in a warm water bath, to give fibers with good tenacity and increased crystallinity as shown by birefringence measurements. The polyester obtained from ethylenedivanillic acid melted at 210°C. but softened and shrank at 80°C.
Polymer/solvent interactions in dilute solution
Authors: Rosen Bernard
Published: April 2003

Apparent specific volumes of two, previously well‐characterized, polystyrene fractions were determined at 25° in solvents offering an interesting display of polymer/solvent interactions. Adaptations of differential pycnometry techniques permitted a sensitive detection of the small density differences between solvents and solutions, allowing four significant figures in the apparent specific volumes at concentrations as low as 0.20%. The measurements unambiguously confirm the solvent and concentration dependencies. The solvent dependency at high dilutions also confirms the anomaly that the extremes in polymer/solvent interactions causing very good and very poor polymer solubility yield higher values for the partial specific volumes of polystyrene than obtained for the intermediate range of interactions. The concentration dependency permits indirect approximations of the functions, ΔH̄1 and ΔH̄2 vs. poIymer concentration. The deviations from athermal mixing are greater and more irregular than anticipated, and are shown frequently to complicate both experimental and theoretical studies of the properties of dilute solutions. The thermodynamic behavior of dilute solutions of polystyrene in butanone appears to be particularly complex.
Streaming birefringence behavior of dextrans produced by leuconostoc mesenteroides
Authors: Yang Jen Tsi , Foster Joseph F.
Published: April 2003

The results of a large number of streaming birefringence studies on dextran fractions, both native and degraded, produced by Leuconostoc mesenteroides are reported. The following solvents have been examined, all in admixture with varying proportions of glycerol (to enhance the solvent viscosity): water (with and without prior autoclaving), aqueous sodium hydroxide, formamide, and ethylenediamine. The results are surprisingly independent of the solvent used. Ethylenediamine–glycerol (equal parts by weight) was adopted for further investigation because of the high solvent viscosity. This solvent was found to yield a small birefringence with extinction angle near zero degrees, which, however, contributed no appreciable error except at polymer concentrations below 0.3%. Results were found to be substantially independent of polymer concentration and of temperature. Characteristically, the dependence of extinction angle on gradient was found to be much less than is to be expected for solutions of homogeneous, rigid molecules. It is concluded that this cannot be due to heterogeneity, at least in the case of certain well‐fractionated preparation, and must be attributed to flexibility of the polymer molecule. It is shown that extrapolation of the apparent rotary diffusion constants to zero gradient can be carried out in most cases with some confidence. The resulting values, which should characterize the rotary diffusion properties of the undistorted polymers, are shown to be quite reasonable in terms of the known intrinsic viscosity and molecular weight of the fractions. The reduced birefringence of the various fractions is shown to be rather rigorously proportional to their intrinsic viscosity. Further, the extinction angles are found to approach a lower limit, at high gradient, which is related also to the intrinsic viscosity through the empirical equation Xlim = 24/[η]1/4.
Ultrasonic studies of high polymers
Authors: Maeda Y.
Published: April 2003

The variations of elastic modulus and mechanical tan δ with temperature and frequency have been studied for polyvinyl chloride, natural rubber, Hycar OR‐15, GR‐S 65, and GR‐I using pulsed ultrasonic waves of 2.67 and 8.01 Mc. Tricresyl phosphate and dioctyl phthalate were used as plasticiziers for polyvinyl chloride. PVC‐plasticizer system, when the amount of plasticizer is large, shows the steep decrease in effective modulus and the peak of the value of tan δ within the range of measuring temperature from 10 to 90°C. The peak of tan δ shifts to lower temperature with an increase of the amount of plasticizer, and its value becomes smaller. Heat and enttropy of activation derived from the difference between the temperatures of peaks in two frequencies decrease with the amount of plasticizer. Within the range of measuring temperature from −60 to + 80°C., all rubbers used in this measurement show a sudden decrease of the modulus of elasticity and the peak of tan δ. The peaks become higher in the order of GR‐S, Hycar OR, natural rubber, and GR‐I, and heat and entropy of activation become smaller in this order. As a mechanism of viscoelasticity to explain the results of this measurement, we think of the break and remake of secondary bonds by thermal motion of segments and assume that shear modulus is proportional to the number of segments per cc. The changing of modulus of elasticity with temperature, the effect of plasticizer, and the relation between tan δ and heat, and entropy of activation can be understood on this assumption. The dielectric constants of the samples of PVC‐plasticizer systems used in this experiment are measured at the same frequency. As a result of comparison with those dielectric constants, it can be said that electrical tan δ shows the peak at 40–50°C. higher temperature than mechanical tan δ, and that heat and entropy of activation show considerable differences.
Effect of substituents upon melting points of linear polyesters
Authors: Doak Kenneth W. , Campbell Herbert N.
Published: April 2003

Melting points were determined for several series of linear polyesters containing substituents either in the acid or glycol unit. The number of substituents was progressively increased by preparing copolyesters containing both unsubstituted and substituted glycol or acid units. The following systems were studied: (1) Those with trimethylene and 2‐methyltrimethylene glycols show decreasing melting points as the number of methyl groups is increased, because they introduce tetrahedral asymmetry. If the structrual unit is relatively short, crystallinity is completely destroyed. (2) Those with trimethylene and 2,2‐dimethyltrimethylene glycols show eutectic type melting point curves, since the substituent groups do not introduce asymmetry. The completely substituted polyesters have new crystal structures which give sharp X‐ray patterns. Those from short acids (C2–4) have higher melting points than the unsubstituted polyesters, while the others have lower melting points. The polyesters with an odd number of chain atoms in the unit have higher melting points than the even ones. The ability to pack closely into the crystal lattice appears to be important, a view supported by melting points of certain polyesters of β,β‐dimethylgultaric acid. (3) Those with trimethylene and 2‐methylenetrimethylene glycols and sebacic acid give a eutectic type curve, because of the appearance of a new crystal structure. (4) Those with succinic and α‐methylsuccinic acids and decamethylene glycol give progressively decreased melting points, decreased breaks in heating curves, and an increasingly distorted lattice as the number of methyl groups is increased, because random “head‐to‐head” and “head‐to‐tail” polymerization makes the completely substituted polyester irregular. (5) The polyester of d‐α,β‐dimethoxysuccinic acid and tetramethylene glycol is highly crystalline because the substituent groups are oriented in a regular manner. The meso‐polyester did not crystallize because of more random orientation of substituents. Decamethylene d‐tartrate similarly melts higher than the meso‐tartrate.
A comparison of the dynamic properties of natural rubber and GR‐S
Authors: Zapas L. J. , Shufler S. L. , DeWitt T. W.
Published: April 2003

The dynamic moduli and loss factors have been determined for high molecular samples of GR‐S and natural rubber. Comparison of the two sets of data shows that the general characteristics of the two materials are quite similar. The main differences are that GR‐S shows a higher temperature for the apparent second order transition, and also a higher value for the modulus in the relatively level portion of the highly elastic region. The usual superposition procedures are used for correlating the data. Several indications that the equivalence of frequency and temperature may not be of universal applicability are noted. It is suggested that the higher elastic plateau modulus of GR‐S my, in conjunction with usual levels of vulcanization, lead to a modulus dispersiion with its attendant loss and thus be a contributing factor to the lower resilience and higher heat development characteristic of GR‐S.
Effects of salts on the viscosity of polyelectrolyte solutions
Authors: Conway B. E.
Published: April 2003

The viscosities of preparations of sodium polymethacrylate and polyvinyl‐n‐butylpyridinium bromide have been measured in water and salt solutions in the Couette viscometer down to very low concentrations and rates of shear. The dependence of reduced specific viscosity upon polymer concentration has been compared with that for DNA in water and salt solutions. It is concluded that there is a finite effect of salts upon the intrinsic viscosity of the synthetic polyelectrolytes in contrast to the result found with DNA. The viscosity behavior of solutions of intermediate concentration is very similar to the of DNA solutions. The shape of the reduced viscosity–concentration plots has been interpreted as arising from the combined effect of interaction and contraction of the molecules with increasing concentration.
Association effects in polymer solutions
Authors: Frisch H. L.
Published: April 2003

The equilibrium theory of polymer solutions capable of association into complexes is presented. The principal thermodynamic functions of such a solution are given; in particular the average molecular weight of such a solution determined by extrapolation of the reduced osmotic pressure is that of the unassociated polymer. It appears unlikely that data on the temperature variation of the second osmotic virial coefficient can give reliable estimates of the degree of association.
Polymer to metal adhesion. The system polyvinyl acetate–steel
Authors: Lasoski S. W. , Kraus Gerard
Published: April 2003

In the limit of small film thickness the effective tensile adhesion of polyvinyl acetate to steel is of the order of the tensile strength of the polymer. Furthermore, the dependence of the limiting tensile adhesion on temperature, rate of loading, molecular weight, molecular weight distribution, and plasticizer content is the same as that of the cohesional tensile strength suggesting that in thin adhesive films the mechanism of failure is in cohesion. At greater thicknesses, shear components derived from strains in the adhesive film initiate failure at progressively lower tensile loads, causing the effective tensile adhesion to be lowered. The above results are realized with clean, though at least partially oxidized metal surfaces and carefully purified polymer. Even minute traces of fatty acids as surface impurities are capable of reducing the adhesion to less than one‐half of the original value. In a particular example, 0.05 of a calculated monolayer of decanoic acid reduced the limiting effective tensile adhesion from 7000 to 3900 p.s.i. Inasmuch as the adsorbed impurity is soluble in the polymer, it can be desorbed on prolonged heating, and, provided the polymer film is thick enough, the original adhesive strength can be restored. In extremely thin films, some permanent loss in adhesion will result from the establishment of an adsorption equilibrium in which appreciable amounts of fatty acid are left on the surface. The effect of perfluorodecanoic acid on the adhesion of polyvinyl acetate to steel is almost exactly the same as that of decanoic acid. The adhesion of polyethylene to steel is likewise critically dependent on surface purity. The results of this research point to the need for extreme cleanliness in studies of adhesion, a fact which, though seemingly obvious, has all too often been overlooked in past investigations.
Styrene popcorn polymers
Authors: Miller Glenn H. , Perizzolo Arl F.
Published: April 2003

A study of the growth of butadiene popcorn polymer seeds in the presence of styrene monomer vapor at 60° has shown the growth to be logarithmic with time. The growth appears to be independent of the peroxide content of the seeds and can be retarded by the presence of various sulfur containing compound. Oxidation of the butadiene seeds grown in styrene by air exposure destroys their activity for continued growth.
The nature of tensile rupture
Authors: Gruntfest I. J.
Published: April 2003

The problem of tensile failure is discussed in terms of the conditions for mechanical stability. Data are not available for detailed examination of the usefulness of this approach. However, some measurements on plasticized polyvinyl chloride, cellulose acetate, and polymethyl methacrylate suggest that the arguments may have some validity. The toughness and brittleness of materials are also considered briefly in the same terms. Attention is called to the complications that may arises from the adiabatic character of the failure process.
Rates of termination in polymerizations initiated by benzoyl peroxide and by ammonium persulfate
Authors: Jarkovsky I. , Stannett V. , Szwarc M.
Published: April 2003

Polymerizations of styrene have been carried out in solution using as initiators benzoyl peroxide or ammonium persulfate. It has been shown that the ammonium persulfate initiated polymerizations proceed at a faster rate and produce polymers of higher molecular weight than those initiated by benzoyl peroxide, although all the conditions for polymerization remained identical in both cases. This behavior is explained in terms of a reduced rate of termination. It is suggested tentatively that the reduction in the rate of termination may be due to the mutual electrostatic repulsion of the chains caused by the presence of electrically charged end groups arising from initiation by the sulfate ion radical. Calculations are presented showing the essential conditions that have to be fulfilled to make the explanation tenable.
Vulcanization studies
Authors: Barton Bernard C.
Published: April 2003

Use has been made of the statistical theory of elasticity to calculate the number of crosslinks in vulcanizates that have been formulated and vulcanized in such a manner as to have the greatest number of crosslinks for the amount of sulfur present. These calculations suggest that the formation of up to 80% of the crosslinks are accompanied by the formation of a molecule of sulfide sulfur and that the crosslinks are largely, if not entirely, of the monosulfide type.
Mastication. Part III. Chemical verification of the mechanical degradation mechanism of cold mastication
Authors: Ayrey G. , Moore C. G. , Watson W. F.
Published: April 2003

The mechanism of cold mastication of natural and synthetic rubbers, as proposed by Kauzmann and Eyring, and by Pike and Watson, in volves the mechanical rupture of the polymer chain yielding polymer radicals which are stabilized by interaction with radical‐acceptor molecules to give the degraded polymer. This mechanism has been verified by a spectroscopic study of the cold mastication of natural rubber with 1,1‐diphenyl1‐2‐picryl hydrazyl and a radioisotopic tracer study of the cold mastication of GR‐S using [S35]‐labeled 1,1′‐dinaphthyl disulfide as the radical‐acceptor molecule. Correlation of the decrease in molecular weight of the polymer and the amount of radical acceptor in corporated during the cold mastication process agrees with prediction according to the mechanical degradation mechanism.
Ladder structures for representation of viscoelastic systems
Authors: Gross Bernhard , Fuoss Raymond M.
Published: April 2003

The theory of a finite continuous system representing the limiting case of a springdashpot ladder network is developed. The partial differential equation which describes this system has the form of the diffusion equation. A complete mathematical treatment is given. The result is shown to be practically identical with that of Rouse's theory. Formally it represents an extension of Blizard's treatment.
Inhibition of polymerization. II. Methyl acrylate
Authors: Kice John L.
Published: April 2003

The effect of nine inhibitors on the 2,2′‐azobisisobutyronitrile initiated polymerization of methyl acrylate in methyl propionate solution has been studied kinetically by a dilatometric method. The rate constants obtained are compared with those found for these same compounds in methyl methacrylate polymerization. The ratio of the reactivity of an inhibitor toward methyl acrylate and methyl methacrylate radicals is found to vary considerably from inhibitor to inhibitor; these variations in behavior seem readily interpretable in terms of polar and steric effects. Specifically, it is found that the three quinones—benzoquinone, 2,6‐dichloroquinone, and 2,5‐dichloroquinone—show a smaller increase in reactivity on going from methacrylate to acrylate than any of the other compounds studied. This is consistent with the presumably strongly “electron‐accepting” nature of the quinone ring. On the other hand, the tetrachloroquinone, chloranil, shows a much larger increase in reactivity on going from methacrylate to acrylate. Models indicate that this different behavior is due to the existence of considerable steric hindrance in the reaction of the bulky methacrylate radical with chloranil and not to any difference among these quinones as regards their mechanisms of reaction with methacrylate and acrylate radicals. With the other compounds which showed inhibitory activity—trinitrotoluene, furfurylidene malononitrile, dinitrobenzene, and sulfur—the relative magnitude of the increase in reactivity varies in a manner consistent with the differing polarities of these four compounds.
Improvement of bonding properties of polyethylene
Authors: Rossmann Kurt
Published: April 2003

If the surface of a polyethylene film is subjected to certain treatments, printing on the surface becomes possible, or, in other words, the bonding properties of the polyethylene film are improved. Two forms of treatment, involving the use of a Tesla coil discharge at atmospheric pressure and of a glow discharge at reduced pressure, have been developed. Through the use of a Beckman IR‐3 spectrophotometer, it has been found that the treatments cause formation of unsaturated (CC) bonds and carbonyl (CO) groups in the polyethylene molecule. The improved bonding properties may be due to oxidation of the plastic surface.
Ozone attack on rubber vulcanizates
Authors: Buckley D. J. , Robison S. B.
Published: April 2003

Cracking on the surface of vulcanizates exposed to ozone under strain has been studied quantitatively. Butyl rubber vulcanizates were used to allow ready variation of polymer unsaturation. A relaxed sample under tension when exposed to ozone undergoes a work change manifested by increased length and decreased stress as cracking occurs. The change in work is considered related to generation of new surface in the form of cracks. Cracking is found to be primarily a surface phenomenon and in this wise permeation of the ozone into the sample assumes an important role in this phenomenon since it defines the “depth of the surface.” Polymer structure as it affects permeation appears as important as chemical inertness in controlling ozone cracking. The amount of cracking judged by change of work measured in these experiments is related linearly to the time squared. The rate of cracking is related linearly to ozone concentration squared over the range 0.03–0.20 volume per cent in air. The rate and type of cracking is dependent on extension. The analysis of this relation is complicated by relaxation effects. The state of relaxation of a sample under tension has a profound effect on the rate of ozone cracking. This effect is discussed in terms of distribution of strain of the network chains. Although cracking requires a stored energy to produce new surface, the chemical action of ozone proceeds in the absence of strain. Whether the effects of polymer degradation under conditions of zero strain become large enough to be measurable depends on the rate of permeation of ozonized air into the specimen.

Vulcanization has an important bearing on ozone cracking in Butyl rubber. This is probably due to a significant decreases in the percentage of unreacted double bonds and also to a local densification of the network in the region of the double bond involved in a crosslink. Cracking is particularly sensitive to the onset of reversion. This sensitivity may arise because state of reversion may be a gradient, greatest on the surface and least at the center of the sample.
Determination of degree of crosslinking in natural rubber vulcanizates. Part II
Authors: Moore C. G. , Watson W. F.
Published: April 2003

Natural rubber vulcanizates have been prepared by a method permitting determinations by chemical analysis of the number of crosslinking introduced. The crosslinking agent was di‐tert‐butyl peroxide, and the peroxide and its decomposition products–tert‐butanol, acetone, methane, and ethane—were determined by infrared spectroscopic and manometric methods. tert‐Butanol and methane result from the abstraction of α‐methylenic hydrogen atoms from the rubber hydrocarbon by means of tert‐butoxy and methyl radicals, respectively. On the assumption that the resultant rubber hydrocarbon radicals undergo exclusive mutual combination a chemical evaluation of degree of crosslinking, 1/2 Mc, is given by ½(moles of tert‐butanol + moles of methane), where Mc is the average molecular weight between crosslinks. Physical values of 1/2 Mc for rubber of infinite initial molecular weight have been obtained by determining the volume fraction of swollen rubber, vr‐, in n‐decane, and by using the method described in Part I for correcting for the finite initial molecular weight of the rubber. A comparison of the physical and chemical values of 1/2 Mc indicates that the former is greater than the latter for all degrees of crosslinking, the major divergence being accounted for by an additive term which is pictorially visualized as due to entanglements.
The mechanism of chain initiation and chain transfer in the polymerization of vinylpyridine
Authors: Dannley Ralph L. , Schufle Joseph A. , Cohen Irwin , Chambers James R.
Published: April 2003

(1) Polymerization of 2‐vinylpyridine in p‐chlorotoluene solution produced a polymer which, when oxidized with potassium permanganate in dilute sulfuric acid, gave no chlorophthalic acid, but a 35.7% yield of p‐chlorobenzoic acid (based upon the halogen content of the polymer). Therefore, incorporation of the aromatic groups in the polymer, probably in the step of chain transfer, occurred by reaction with the side chain and not the nucleus of the p‐chlorotoluene. The absence of chlorophthalic acid was significant, for a similar oxidation of α‐(p‐methylbenzyl)pyridine gave a 3% yield of terephthalic acid as well as a 23% yield of 2‐(4‐carboxybenzoyl)pyridine. (2) Permanganate oxidation of this same polymer in 25% sulfuric acid gave a 27% yield of p‐chlorobenzoic acid. This represents the maximum yield of halobenzoic acid to be expected from a polyvinylpyridine containing trace quantities of halophenyl and pyridine nuclei separated by a chain of two or more carbon atoms. In contrast, similar oxidations in 25% sulfuric acid of α‐(p‐bromobenzyl)‐ and α‐(p‐chlorobenzyl)pyridine gave much smaller yields (16 and 14%, respectively) of the corresponding halobenzoic acids. In concentrated acid, the heterocyclic rings form stable salts and oxidation of the benzylpyridine type structure leads to preferential cleavage of the benzene nucleus. (3) Initiation of the polymerization of 2‐vinylpyridine with N‐nitroso‐p‐bromoacetanilide formed a polymer which, upon oxidation with potassium permanganate in 25% sulfuric acid, gave a 31% (average) yield of p‐bromobenzoic acid. Since this yield is that expected from a polymer in which pyridine and bromobenzene rings are separated by a chain of two or more carbon atoms, beta carbon atoms addition in chain initiation by a bromophenyl radical is substantiated. (4) Polymerization of 2‐vinylpyridine in bromobenzene solution provided a polymer which, upon oxidation with permanaganate in 25% sulfuric acid, gave only a 6% yield of bromobenzoic acid, corresponding to a bromobenzylpyridine structure in the polymer. Reasons are given why this data supports but does not prove the hypothesis that chain transfer consists of substitution in the bromobenzene nucleus by a polymer radical possessing a 2‐pyridylmethyl structure.
Raman spectra of monomeric and polymeric allyl diglycol carbonate
Authors: Jeppesen Myron A.
Published: April 2003

The Raman spectra of monomeric and polymeric allyl diglycol carbonate (CR‐39) have been photographed. A partial frequency assignment has been made on the basis of a comparison of the two spectra, depolarization measurements, and reference to published spectra of related compounds. The spectrum of the polymer indicated almost complete polymerization of the unsaturated aliphatic double bonds. A channelled comparison spectrum was used, and its advantages noted.
The melting range of semicrystalline polymers and copolymers
Authors: Dole Malcolm
Published: April 2003

An equation is derived for the weight‐average crystallite length of crystallizable sequences between noncrystallizing copolymer units. This expression is used to estimate the depression of the melting point due to the subdivision of the crystalline regions into small crystallites. An explanation is given for the failure of the value of the heat of fusion calculated from the equation relating the freezing point lowering to the mole fraction to agree with observed values.
Copolymerizations of vinyl silanes
Authors: Thompson B. R.
Published: April 2003

A brief experimental investigation was made of the copolymerization of twelve alkoxysilanes with monochlorostyrene, vinyl chloride, and acrylonitrile. These new monomers include vinyltrimethoxy‐, vinyltriethoxy‐, vinyltriisoproxy‐, vinylmethyldiethoxy‐, vinylethyldiethoxy‐, and vinylphenyldiethoxy‐silanes as well as allyl‐, propenyl‐, 2‐butenyl‐, Δ3‐cyclohexenyl‐, 6‐triethoxysilylbicyclo [2.2.1]heptane‐2, and α‐chlorovinyl‐triethoxysilanes. No copolymerization took place with monochlorostyrene. In the copolymerizations with vinyl chloride, and with acrylonitrile, the reactivity ratio r2 was assumed to be zero and the value of r1 determined.
Polyethyl methacrylate. II. Dilute solution properties by viscosity and light scattering
Authors: Chinai Suresh N. , Samuels Robert J.
Published: April 2003

A polyethyl methacrylate polymer, prepared by the emulsion technique, was fractionated three times to obtain ten fractions. The intrinsic viscosity‐molecular weight relations were established in an ideal and in a nonideal solvent at 23°C. Light scattering measurements giving polymer dimensions were compared with the viscosity theories advanced by Debye‐Bueche, Kirkwood‐Riseman, and Flory‐Fox. The calculated values of the effective bond length b for polymethyl methacrylate and polyethyl methacrylate show that polymethyl methacrylate chain has greater hindrance to rotation than the polyethyl methacrylate chain. The results are explained by consideration of the free volume occupied by the solvent molecules.
Light scattering and viscosity studies of polyvinyl acetate solutions
Authors: Varadaiah V. V.
Published: April 2003

A light scattering photoelectric photometer was built and calibrated by a narrow fraction of polystyrene for which the molecular weight was assigned by the viscosity method. The instrument was used to determine the molecular weights of polyvinyl acetate fractions. The light scattering molecular weights of the polyvinyl acetates, up to a value of 477,000, agreed with those obtained from viscosity data employing the Nakajima equation: [η] = 8.91 × 10−3 × P0.62, where [η] is the intrinsic viscosity in benzene and P is the degree of polymerization. k′ and μ values lie in the expected ranges. The rootmean‐square end‐to‐end distances of the polyvinyl acetate molecules determined by the dissymmetry method are found to be much smaller than those calculated by Fox‐Flory relation from viscosity data.
An independent measurement of the amorphous content of polymers
Authors: Miller R. G. J. , Willis H. A.
Published: April 2003

Attempts have been made, particularly by American workers, to exploit differences in crystalline and amorphous polymer spectra to determine crystalline/amorphous ratios. In most published work authors have been forced to rely on calibration by other methods, especially density. They have justified the use of the spectroscopic method principally on the grounds of speed in obtaining results. We propose a spectroscopic method, applicable to a number of polymers, which is entirely independent of other measurements. We are thus able to compare our results with those obtained by other methods and have in some cases been able to draw useful conclusions from apparent anomalies. Our method depends upon measurement of pure amorphous bands. We consider these to arise from the multiplicity of rotational isomers present in the amorphous phase. The pure amorphous spectrum of many polymers can be obtained, and by this means an absolute calibration of amorphous content is possible. Crystalline bands cannot be so calibrated; they are dangerous to use quantitatively, although superficially more attractive because of their sharpness. The application of the method to some common polymers including polythene, polyethylene terephthalate, and polytetrafluorethylene is described; the results are compared with values obtained by x‐ray and density methods.
Emulsion polymerization of chloroprene. II. Molecular weights
Authors: Morton Maurice , Piirma Irja
Published: April 2003

The molecular weights of emulsion polychloroprenes, prepared at four different temperatures in the presence and absence of a suitable mercaptan chain‐transfer agents, have been studied. The particular mercaptan used, a tertiary dodecyl type, was found to disappear at the relatively slow rate, which was first‐order up to high conversions. This permitted the preparation of polymer having a relatively uniform intrinsic viscosity up to high conversions. However, under certain conditions, the crosslinking reaction was found to give rise to the usual peaks in the viscosity–conversion curves. These curves differed from those of other dienes studied, in that the heights of the maxima depended not only on polymerization temperature but also on the mercaptan charge. This anomaly could be accounted for by the possibility of more than one mechanism of crosslinking. The above behavior made it impossible to obtain a quantitative measures of the crosslinking rate. However, observations of the postpolymerization changes experienced by this polymer lead to the conclusion that it has a high crosslinking rate.
A light scattering study of corn amylopectin and its beta‐amylase limit dextrin
Authors: Stacy Carl J. , Foster Joseph F.
Published: April 2003

The degree of dispersion of a corn amylopectin and its ß‐amylase limit dextrin was studied in 1 N alkali, anhydrous ethylenediamine, ethylenediamine hydrate, formamide, and water by means of measurements of the concentration and angular dependence of scattered light. It was found that the degree of dispersion in the first three solvents is essentially the same for both preparations. The molecular weight of the amylopectin and limit dextrin are 80 million and 29 million, respectively. This result is in agreement within experimental error with the ratio of molecular weights to be expected on the basis of the known degree of degradation by ß‐amylase, and supports the view that essentially molecular dispersions were obtained. The agreement further indicates that the molecular weight distributions of the amylopectin and limit dextrin are similar in form. With this assumption and the radii of gyration of the materials, 2090 and 1340 A., it is concluded that the simplest model consistent with the data is a spherically symmetrical distribution of segments with segment density decreasing with r.
Linear phenol‐formaldehyde polymers—condensation of p‐chlorophenol with formaldehyde
Authors: Burke W. J. , Craven W. E. , Rosenthal Alex , Ruetman S. H. , Stephens C. W. , Weatherbee Carl
Published: April 2003

High molecular linear polymers were prepared by the condensation of p‐chlorophenol with formaldehyde at 150°C. for 24 hours in a closed system with bis(2‐ethoxyethyl) ether as solvent and p‐toluenesulfonic acid as catalyst. The importance of reaction variables including temperature, time, solvent, catalyst, and concentration and ratio of reactants was studied. Polymers of this type were also prepared by the polymerization of 4‐chloro‐2‐hydroxymethylphenol and by the condensation of p‐chlorophenol with 2,6‐bis(hydroxymethyl)‐4‐chlorophenol. Data obtained on the polymers from the three independent routes indicated the presence of methylene bridges between the ortho position of the p‐chlorophenol residues. The polymers were soluble in N,N‐dimethyl formamide and reacted readily with acetic anhydride to form the corresponding acetylated derivatives.
Viscoelastic behavior of polyisobutylene under constant rates of elongation
Authors: Smith Thor L.
Published: April 2003

The use of stress‐strain curves to characterize the linear viscoelastic properties of rubberlike materials is discussed. Tensile stress‐strain curves for a high molecular polyisobutylene were measured at ten temperatures between −54 and 85°C. and at strain rates between 0.104 and 0.104 × 10−3 sec.−1. At a single temperature, the data superpose on a double logarithmic plot of stress divided by strain rate against strain divided by strain rate. By superposing data obtained at different temperatures, the temperature dependence of viscosity was obtained. All data for elongation up to 100% were combined to give a single reduced stress‐strain curve, which extends over ten decades of reduced time. From the reduced curve, the stress‐relaxation modulus was calculated and found to agree satisfactorily with published data.
Ermittlung der äusseren Abmessungen statistisch geknäuelter Fadenmoleküle durch Ausmessung makroskopischer Modelle
Authors: Hoops Irmgard , Kuhn Hans , Huber Walter , Eckert Lieselotte
Published: April 2003

Es wurden 362 Kreissegmentmodelle statistisch geknäuelter Fadenmoleküle hergestellt und daran die Parameter h (Abstand zwischen Fadenanfangs‐ und ‐endpunkt), R (Abstand zwischen Fadenanfangspunkt und demjenigen Fadenelement, das von allen den grössten Abstand vom Anfangspunkt besitzt), H1 (Maximalabmessung des Knäuels), H2 (grösste senkrecht zu H1 gemessene Querabmessung des Knäuels), H3 (grösste Abmessung des Knäuels senkrecht zu H1 und H2) gemessen. Die auf Grund dieser Messungen sich ergebenden Verteilungsfunktionen W(H1), W(H2), W(H3), die bisher ungenügend genau bekannt waren, werden angegeben. Zwischen den Mittelwerten der erwähnten Parameter werden die Beziehungen \documentclass{article}\pagestyle{empty}\begin{document}$\bar H_1 = 1,74\bar H_2 = 2,72\bar H_3 = 1,36\bar h;(\bar H_1^2)^{1/2} = 1,78(\bar H_2^2)^{1/2} = 2,77(\bar H_3^2)^{1/2} = 1,41\bar h = 1,30(\bar h^2)^{1/2}$\end{document} gefunden. Daraus folgt, dass dem Knäuel im Mittel ein Achsenverhältnis H1:H2:H3 = 2,72:1,56:1 zuzuschreiben ist. Es wird untersucht, wie häufig bei gegebenen Werten von H1 die verschiedenen Werte von H2, H3, h und R vorkommen, wieweit also Beziehungen zwischen diesen Parametern bestehen. Man findet, dass Konstellationen, in welchen das eine Ende von H1 (Verbindungsstrecke zwischen den beiden am weitesten auseinanderliegenden Fadenelementen) mit dem Fadenanfangs‐ oder ‐endpunkt zusammenfällt, relativ häufig vorkommen (bei Modellen mit 20 Vorzugselementen beispielsweise in 37% aller Fälle).
Some factors involved in the preparation of uniform particle size latexes
Authors: Vanderhoff J. W. , Vitkuske J. F. , Bradford E. B. , Alfrey T.
Published: April 2003

Some factors involved in the preparation of monodisperse polymer latexes by seeded emulsion polymerization are discussed. In this technique monomer and catalyst are added to a previously prepared latex; during the subsequent polymerization these seed particles grow to a larger size. A mathematical analysis has been developed relating the particle volume increase to particle size as a power function. Competitive particle growth has been determined experimentally by polymerizing monomer in a seed latex comprised of a mixture of two monodisperse latexes of different sizes. In these experiments the diameters of the smaller particles increase at a slightly greater rate than those of the larger ones. Therefore the final particle size distribution is narrower than that of the seed latex. In these growth experiments the concentration of emulsifier is also important. An illustrative example shows that excessive emulsifier initiates new particles and insufficient emulsifier causes coagulum.