bluuebunny/crossref_metadata_2025 huggingface dataset:
The stiffness modulus of polyethylene as a function of temperature and structure
Authors: Reding F. P.
Published: April 2003

The stiffness moduli of polyethylenes covering a wide range of degrees of branching and molecular weights have been investigated from −150°C. up to the melting points. Qualitatively, the stiffness temperature curves can be broken into three regions. The first of these is the very low temperature region which extends from −150 up to about −50°C. In this temperature region, all of the polymers have the same stiffness at a given temperature, although they do not have the same density. The second region extends from about −50° up to the melting region. In this region, it is generally true that the stiffness is a function of the density alone. This is the case even though the temperatures at which polymers have equal densities are different. There are exceptions, however. It has been found that extremely high molecular weight polymers have higher stiffness than would be expected from their densities. Presumably, this arises directly from the very high molecular weight. It has further been found that highly crystalline polyethylenes increase in density upon annealing, but show little increase in stiffness or degree of crystallinity as measured by x‐rays. This may well arise from the removal of small voids or flaws on i Annealing, the removal of which would increase density but not affect stiffness or crystallinity. The third region of the stiffness‐temperature curves is the melting region. As expected, the stiffness curves reflect the higher melting points of the more linear resins. The stiffness curves also qualitatively indicate the randomness of branching. Polymers which are nonrandomly branched suffer a more gradual decrease of stiffness with temperature, reflecting a broader melting range than the more randomlybranched polymers. This effect probably arises from a broader distribution of crystallite sizes in the nonrandomly branched polymers. Unlike any other crystalline polymer which has been examined, the stiffness‐temperature curves for polyethylene do not exhibit evidence of a sharp glass transition temperature. Rather, polethylene appears to undergo a gradual “thawing” from about −50°C. up to within a few degrees of the melting point.
The rupture process in carbon‐loaded rubbers: An electron‐microscopic investigation
Authors: Andrews E. H. , Walsh A.
Published: April 2003

A study has been made of the disposition of carbon‐black particles in the tear and fracture surfaces of various filled rubbers by replica electron microscopy. The surfaces are characterized by two parameters, viz., the proportion of the surface area occupied by filler, and the proportion occupied by particles extracted from the rubber by the gelatine first‐stage replica. Values obtained for the former quantity indicate that the rupture path departs strongly from a random plane through the material. The second quantity is a measure of filler‐to‐rubber adhesion, which is found to depend upon the nature of the filler‐rubber interface and is related to the energy required to produce rupture. Simple physical mechanisms are proposed to explain the observed influence of filler upon rupture propagation.
A comparative molecular weight study with particular reference to black wattle tannins
Authors: Evelyn S. R. , Cooper D. R. , Van Berge P. C.
Published: April 2003

Details are given of a further modification to the Ray ebulliometer which permits easy interchange of the Cottrell pump tube. The stability of the apparatus with different pump tubes and pumping conditions was also examined. Molecular weights obtained with the use of two ebulliometers and three solvent systems are compared. The validity of the recently developed ultracentrifuge methods for determining physical properties of molecules with molecular weights in the range 300 to 10,000 was checked by using a pure compound of known molecular weight. Agreement was obtained also between the data obtained by the Klainer and Kegeles method and separate sedimentation and diffusion data. The molecular weight of an ethyl acetate extract of black wattle tannin was determined by the ebulliometric and these ultracentrifuge methods. The ultracentrifuge value for the whole extract decreased with time due to sedimentation of high molecular weight impurities. The final ultracentrifuge weight‐average molecular weight (1175) is in good agreement with the number‐average value for the tannin polyphenols (922) obtained by ebulliometry. The difference between the values confirms the known heterogeneity of the polyphenols.
An excluded volume effect in light scattering
Authors: Hyde A. J. , Ryan J. H. , Wall F. T. , Schatzki T. F.
Published: April 2003

An expression for the intensity of light scattered by an isolated linear polymer chain with excluded volume has been evaluated for conditions corresponding to those met in experiment. The expression proves to be an excellent approximation to light scattering results for a very high molecular weight polystyrene fraction, thus providing an explanation for what appeared to be an anomalously large polydispersity when the data were treated according to the usual random flight model. Coil sizes were calculated and compared with the values obtained from the data by other methods.
Ionic grafting
Authors: Kockelbergh G. , Smets G.
Published: April 2003

Cationic polymerization of isobutene has been carried out in carbon disulfide solution in the presence of AlBr3 and chloromethylpolystyrene at −60°C. in order to obtain graft copolymers. The separation of the graft copolymers from the reaction mixtures in benzene solution was based on a standardized precipitation technique involving use successively of butanone and methanol as precipitating agents. By this method, fractions with an intermediate solubility have been isolated and purified twice. The differences of solubility of their products are discussed. Their isobutene content and intrinsic viscosities have been determined. The degree of grafting of these products is usually low (5–18%).
Inhibition in the polymerization of N‐carboxyglycine anhydride
Authors: Moos Gilbert E. , Budelman Hilda , Chen Pai‐Fun
Published: April 2003

The conversion of N‐carboxyglycine anhydride in dioxane to polyglycine has been completely inhibited with as little as 0.2 mole‐%, based on monomer, of acetyl chloride, thionyl chloride, 2,2′‐dichloro‐N‐methyldiethylamine hydrochloride, and AlCl3. Phenyl isocyanate and acetic anhydride also show strong inhibition. Myleran, and especially its 1,9‐relative, 1,9‐dimethylsulfonyloxynonane, show similar action at slightly higher concentrations. The most active inhibitors have in common a strong tendency to react with initiators such as water, alcohols, or amines.
Degradation of addition polymers by ultrasonic waves. VI. Effect of frequency
Authors: Mostafa M. A. K.
Published: April 2003

The effect of frequency (megacycle range) on the degradation of addition polymers (polystyrene) is studied. Results give evidence of occurrence of resonance. Optimum frequency for degradation is found to be 1 Mcycle/sec. Cavitation is suppressed at 2 Mcycle/sec. or more, or by irradiation in vacuo. Results show that degradation can be produced by ultrasonic waves in the absence of cavitation.
A mechanism of degradation of long chain molecules by ultrasonic waves
Authors: Mostafa M. A. K.
Published: April 2003

An alternative mechanism by which long chain molecules can be degraded by ultrasonic waves is discussed. Only the fundamental mode of vibration of macromolecules is treated mathematically. It is found that the kinetic energy of oscillation is sufficient to break a CC bond in the absence of cavitation.
Copolymerization of vinyl acetate–vinyl n‐butyl ether
Authors: Tichy Jerome R.
Published: April 2003

Data on the yields and composition of copolymers of vinyl acetate and vinyl n‐butyl ether formed at 170°C. are recorded. The yield of the copolymer is directly proportional to the amount of vinyl acetate in the monomer mixture. A copolymer which is relatively stable at elevated temperatures can be prepared by using a monomer mixture containing about 0.2 M of vinyl acetate. Above this limit of vinyl acetate, the copolymers are less heat stable. The change in composition of these copolymers has been interpreted as a chain degradation process.
The rheology of aqueous solutions of amylose and amylopectin with reference to molecular configuration and intermolecular association
Authors: Storey Bayard Thayer , Merrill Edward Wilson
Published: April 2003

Mathematical expressions relating shear stress, shear rate and time of shear for aqueous solutions of amylose and amylopectin, respectively, are developed from models based on the concept of the single‐point network association link, similar to that of C. F. Goodeve. The model for amylose solutions is as follows. (a) Molecules are joined by association links in a loose network in solutions at rest; (b) the network, though resisting shear, is disrupted by shear; (c) the linear amylose molecules of helical, rod‐like configuration becomes parallel‐oriented under shear, this orientation being less favorable for reformation of the links. The shear stress on the solution at constant shear rate is predicted to decrease with time, the ultimate relation between shear stress and shear rate being pseudoplastic. For solutions of amylopectin, the following model is suggested. (a) Network association links exist between the highly‐branched, roughly spherical molecules in solutions at rest; (b) disruption of these links occurs under shear, but since the molecules are spherical, orientation unfavorable to reformation of links cannot occur; (c) it is assumed that the rates of destruction and reformation are about equal, but that as shear rates increase, the number of links existing at any time decreases. Thus, the shear stress‐shear rate relation is predicted to be pseudoplastic but independent of time of shear. These conclusions and the mathematical expressions derived from the models are supported by experimental data obtained with a coaxial‐eylinder viscometer so designed that shear stress is recorded versus time of shear over a wide range of shear rates. Temperature was closely controlled at 49°C. to avoid gelation.
Ultrafein filters as osmotic membranes
Authors: Vaughan M. F.
Published: April 2003

The use of ultrafein filters as osmotic membranes has been investigated in various solvents. It has been found that, at 30°C., measurements can be made in benzene, toluene, ethanol, water, and, with difficulty, methyl ethyl ketone, but not in chloroform or dimethylformamide. In benzene it has been found that all grades of the membranes are more selective than the corresponding ultracella filters and that, with the allerfeinst grade, molecular weights of the order of 2000 can be determined. With solutions of pentaerythritol tetrastearate (M.W. 1200), tristearin (M.W. 891), and sucrose octaacetate (M.W. 679), the osmotic pressures developed were less than the theoretical values. The ratios of observed to theoretical osmotic pressure decreased with molecular weight, and these ratios appear to be examples of the reflection coefficients predicted by Staverman.
The initiator efficiency of 2, 2′‐azobisisobutyronitrile in the polymerization of styrene and methyl methacrylate, and dicumyl peroxide as a polymerization initiator
Authors: van Hook J. P. , Tobolsky A. V.
Published: April 2003

The polymerization of styrene with 2,2′‐azobisisobutyronitrile (Azo I) as initiator has been studied at eight temperatures from 30° to 85°C. and methyl methacrylate at six temperatures from 30° to 67°C. With the use of the expression for the thermal rate of decomposition of Azo I given in a previous paper, the maximum scavenger efficiencies of styrene and methyl methacrylate have been calculated to be 60 and 80%, respectively. The efficiency is shown to be almost independent of initiator concentration except in styrene at very low concentrations of Azo I, where f, increases rapidly. If the true efficiency in methyl methacrylate is the same as in styrene, then the ratio of termination by disproportionation to overall termination is equal to about 0.3 for methyl methacrylate. The dicumyl peroxide‐initiated polymerization of styrene and methyl methacrylate has been studied from 60° to 100°C. The rate laws expressing the decomposition of initiator are: (for methyl methacrylate) kdf′ = 1.26 × 1016 exp { −36.4 kcal./RT} and (for styrene) kdf′ = 1.00 × 1016 exp { −36.4 kcal./RT}. Evidence is given to suggest that the initiator efficiency of DCP in styrene and methyl methacrylate is equal to unity.
Kinetic studies of α‐olefin polymerization
Authors: Natta G.
Published: April 2003

The kinetics of chain growth and chain transfer processes in the stereospecific polymerization of propylene, using catalytic systems such as TiCl3Al(C2H5)3 and TiCl3AlCl(C2H5)2, has been examined. The number of active centers present on the catalyst surface has been determined radiochemically by kinetic and adsorption measurements, using aluminum labeled with C14. The mean life of macromolecules was determined by radiochemical determination of terminal groups, and the relationships between intrinsic viscosity and number‐average molecular weight were found. Kinetic research into ethylene‐propylene copolymerization enableld us to determine the different reactivity ratios of the monomers.
Polymerization of methacrylonitrile with lithium in ammonia
Authors: Overberger C. G. , Pearce Eli M. , Mayes N.
Published: April 2003

The molecular weight of polymethacrylonitrile obtained in the system lithiumammonia‐methacrylonitrile at −75° increased with decreasing concentrations of lithium and increasing concentrations of methacrylonitrile, and in addition was found to be proportional to [methacrylonitrile]/[lithium]. On the basis of this and additional evidence, a one‐electron transfer from lithium to methacrylonitrile to give an anion radical is postulated. In addition, the structure of the colored polymer obtained is discussed on the basis of the infrared spectra.
High polymers obtained using organometallic complexes containing lithium and titanium
Authors: Kocheshkov K. A. , Kargin V. A. , Paljev O. A. , Talalajeva T. V. , Sogolova T. I.
Published: April 2003

High polymers with a regular chain structure have been produced by polymerization of ethylene with complexes containing crystalline organolithium compounds and titanium tetrachloride in organic solvents. For this purpose RLi compounds have been prepared, R being methyl, ethyl, butryl, dodeeyl, tolyl, mesityl, naphthyl, benzyl, and other aliphatic and aromatic groups. The investigation of the polymerization has led to the elucidation of the influence of the nature of the organic radical bound with lithium on the properties of polythene formed. Thermomechanical data, infrared and X‐ray spectra, as well as viscometric molecular weight determination, have shown all specimens of polyethylene to be highly crystalline and of a regular chain structure. The polymers obtained have mechanical properties characteristic of polyethylenes of this type but with elongations that strongly differ in polymers produced using organolithium complexes with different radicals at the lithium. With some specimen, elongation has been found to reach extremely high values. Some suggestions have been made as to the causes of influence of different organic radicals in RLi on the properties of polymers.
On the question of applying chromium oxide and molybdenum oxide catalysts to obtain crystalline poly‐α‐olefins
Authors: Topchiev A. V. , Krentsel B. A. , Perelman A. I. , Miesserov K. G.
Published: April 2003

This article gives experimental data concerning the dependence of polymerization efficiency of chromium oxide catalyst upon the methods of preparation and reports on the character of the polymerization efficiency. The polyethylene and polypropylene obtained in this process of polymerization is characterized by high quality. Besides chromium oxide catalyst, molybdenum oxide catalyst with added lithium hydride was studied.
Polyethers. V. New catalysts for the preparation of isotactic polypropylene oxide
Authors: Osgan Mahesh , Price Charles C.
Published: April 2003

An exploration of a number of metal halides and metal alkoxides has revealed that a considerable number of these compounds are useful catalysts for conversion of propylene oxide to high molecular weight isotactic polymer. All contain metal ions capable of acting as Lewis acids. Mixtures of metal alkoxide and halide seem to be superior catalysts.
Trapped radicals in heterogeneous vinyl polymerization
Authors: Bamford C. H. , Jenkins A. D. , Symons M. C. R. , Townsend M. G.
Published: April 2003

The existence of trapped radicals in polymers prepared heterogeneously from vinyl monomers was first deduced from kinetic observations and subsequently confirmed by electron resonance spectroscopy. We have used this latter technique to determine the concentration of trapped polyacrylonitrile radicals obtained as a function of the experimental variables including the degree of swelling of the polymer, the rate of photo‐initiation and the temperature of polymerization. In the bulk polymerization of acrylonitrile at 25°C. the fraction of radicals which become trapped is approximately 12% for a conversion of 17%. The concentration of trapped radicals obtained in the presence of N,N‐dimethylformamide increases for low concentrations of the swelling agent, passes through a maximum, and subsequently decreases to zero. Qualitatively similar behavior is obtained if the swelling of the polymer is increased by the incorporation of methyl acrylate as commonomer. Addition of a swelling agent to the active photopolymer leads to destruction of the radicals. An increase in the concentration of trapped radicals with increasing light intensity (for a given conversion) is observed initially; at very high intensities the concentration decreases to zero. There is a marked decrease in the concentration of radical as the temperatur of polymerization increase; it is doubtful if trapping occurs significantly at 60°C. There observations are discussed in terms of previous kinetic studies and shown to be in general accord with the occlusion theory of heterogeneous polymerization. The effect of oxygen on the electron‐resonance absorption is characterized by a rapid initial decrease followed by a slow decay. The results are tentatively interpreted in terms of the formation of peroxy and/or HO2 radicals. It is surprising that the absorption line obtained with polyacrylonitrile radicals does not show the fine structure which would be expected to arise from interaction of the unpaired electrons with hydrogen and nitrogen nuclei. A possible reason for this is discussed.
Heterophase radiation polymerization of isobutene and methyl methacrylate
Authors: Worrall R. , Pinnar S. H.
Published: April 2003

The rate of the ionic polymerization of isobutene, induced at low temperatures by high energy radiation, is considerably increased when the reaction is carried out in the presence of certain inorganic compounds, notably metal oxides, of high surface area. The acceleration is not accompanied by a corresponding increase in the molecular weight of the polymer. The rate of polymerization of methyl methacrylate when exposed at room temperature to electrons at high intensity is increased by the presence of polyethylene powder. A consideration of the mechanisms of acceleration under heterogeneous conditions leads us to believe that the increase in rate in the first case is due to an increase in the rate of initiation and in the second case to a decrease in the bimolecular termination rate constant.
Some observaions on the effect of the physical nature of the separating phase on the rate of heterogeneous polymerization
Authors: Palit Santi R. , Guha Tilak
Published: April 2003

Study of the polymerization of methyl methacrylate and acrylonitrile in aqueous solution in a redox‐initiated system consisting in Na2S2O4–K2S2O8 reveals the fact that the initial rate of polymerization increases with increase in concentration of the catalyst or activator, and this is followed by a fall in rate with a further increase in concentration of either of the two, and finally the rate is found to increase again with higher concentration of the catalyst or activator. This peculiarity in the kinetics of the above heterogeneous polymerization seems to be connected with the physical state of the separating phase. In the region where the rate is increasing with increasing catalyst concentration, the insoluble phase is in the form of a fine sol. In the region where the rate falls with increased catalyst or activator concentration, the separating phase is in the form of a coarser, less stable sol (milky sol or latex). In the region where the rate again increases, the insoluble phase is in the form of a coarse precipitate or coagulum. The D.P. is observed to run more or less parallel with the rate. The above observations may have bearing on the kinetics of the emulsion polymerization and “explosive” polymerization.
The kinetics of block and graft copolymerization of acrylonitrile
Authors: Bamford C. H. , Jenkins A. D. , White E. F. T.
Published: April 2003

The polymerization of a monomer in the presence of a preformed polymer with suitable structural features gives rise to block or graft copolymers, which, in favorable circumstances, may be isolated as well‐characterized materials. For preparing block copolymers a primary polymer with amine endgroups can be used as a macromolecular transfer agent. Graft copolymers may be prepared by using a primary polymer with terminal double bonds which copolymerize with the second monomer. We have studied the kinetics of block and graft copolymerization based on these methods with particular references to the systems in which the second monomer is acrylonitrile. All transfer agents reduce the rate of heterogeneous polymerization of acrylonitrile since the reduction in molecular weight leads to a diminution in the mean degree of occlusion of the propagating radicals and a consequent increase in the effective termination coefficient. We have found the effect of macromolecular transfer agents on the rate to be greater than that of simple amines. This behavior is attributed to the fact that the radicals produced by transfer are attached to primary polymer chains which are present in solution; as propagation proceeds the growing radicals remain in solution until a comparatively late stage in their growth on account of the solubilizing action of the primary polymer chains. The termination coefficient for these radicals is therefore relatively high and the rate of polymerization correspondingly low. The solubilization of polymer radicals in graft polymerization is less marked than in block copolymerization; this is shown to be consistant with the mechanism of solubilization suggested.
Intermolecular forces and chain flexibility in linear polymers
Authors: Allen Geoffrey , Gee Geoffrey , Lanceley H. A. , Mangaraj D.
Published: April 2003

Intermolecular forces in a fluid can be measured by the internal pressure, obtained most directly from the coefficient (∂P/∂T)v. Results are reported for a fluid polyisobutene over the temperature range −20.9°C. to +38.9°C. (Pi = 76 to 71.7 cal./cc.). Flexibility is assessed by comparing the activation volume for viscous flow (ΔV) with the molar volume (Vm). ΔV is obtained from measurements of the pressure coefficient of viscosity and for polyisobutene of Vm = 500 is ca. 100 cc./mole at low tmperatures. Above 20°C., ΔV begins to fall sharply; this is ascribed to the onset of flexibility, permitting segmental flow.
Sur certaince propriétes des polymères greffés en solution
Authors: Danon J. , Jobard M. , Lautout M. , Magat M. , Michel M. , Riou M. , Wippler C.
Published: April 2003

Afin d'établir des régles générales de solubilité des copolymères greffés, nous proposons une ébauche de théorie et nous essayons de dégager, à partir de nos résultats et des données bibliographiques existantes, une base expérimentale pour une théorie plus perfectionnée. Les deux cas limités suivants sont envisagés:

(a) Les polymeères sont parfaitement miscibles; (b) les deux polymères sont complètement incompatibles.

Dans le cas (a), le coefficient de solubilité des copolymères greffés est une moyenne arithmétique de ceux des homopolyméres correspondants. Dans le cas (b), il est impossible d'attribuer au copolymère greffé un coefficient de solubilité et dans certaines conditions, les copolymères de taux de greffage intermédiaire devraient ětre insolubles. La séparation des copolymères greffés PVC–PAN, PVC–PMMA, PVC–PAN et PI–PS des homopolymères est étudiée et les résultats discutés à la lumière de la théorie cidessus. Dans le cas du copolymère greffé PI–PS, bien que les deux polymères constituants soient incompatibles, l'écart entre les coefficients de solubilité est suffisamment petit pour que son comportement se rapproche du cas (a) et il est possible d'évaluer le taux de greffage à partit des limites de précipitation. Les résultats expérimentaux de différents auteurs, relatifs à la solubilité des copolymères greffé sont également discutés.
Entanglement and other steric effects in crosslinked polymers
Authors: Blanchard A. F. , Wootton P. M.
Published: April 2003

It is well known that the modulus and equilibrium swellling of long‐chain polymers are both related to degree of crosslinking. Modulus theory normally assumes that chain segments are completely free at all points except the junctions of chains (crosslinks). In practice, however, there are trapped entanglements and other steric restrictions on the freedom of chains in highly crosslinked polymers. In addition, real polymers may not conform entirely with the Gaussian distributions assumed by elasticity theory. The present paper discusses these effects, including a steric effect whose contribution to modulus is dependent on chain flexibility and on linkage concentration. Similar but smaller modifications appear necessary in the case of equilibrium swelling in solvent. The molecular weight of the polymer is taken into account by an adaption of Flory's theory, and a simple correction is proposed to take account of entanglements. The relation between modulus and equilibrium swelling is considered for natural rubber when vulcanized by peroxides or by sulfur, and an assessment is made of the relative effects of steric hindrance on modulus and equilibrium swelling. This is converted to an absolute estimate of steric effects by calculations based on Moore and Watson's chemical determinatios of crosslinking. The equations derived have a convenient form in which there is a parameter ω to take account of steric effects. The contribution which this makes to the modlulus is not constant because it is determined by the magnitude of ω relative to the molecular weight Mc between crosslinks. The reciprocal of ω is taken to be a measure of chain flexibility. By measurements of modulus and equilibrium swelling over a wide range of crosslinking a measure of the molecular flexibility can be obtained, together with an estimate of the solubility parameter μ for the polymer and solvent. For peroxide cures it is found thatd that μ is roughly constant when toluene is the solvent, but for sulfor vulcanizates this appears to be true only at low states of cure. The evidence suggests that μ changes from 0.42 to 0.45 when a high proportion of sulfur is combined with the rubber. Therefore peroxide cures should be used for comparing the chain flexibility of polymers. For sulfur vulcanizates these changes in μ make swollen modulus the most reliable methode of measuring crosslinking. It is estimated that eight atoms of sulfur are combined for every crosslink that is formed in the early stages of vulcanization. The work described should assist studies of curative agents and of the difference between polymers.
The orientation of polyethylene
Authors: Stein R. S.
Published: April 2003

The orientation of the crystals and the amorphouse regions of polyethylene occurring during stretching has been studied using the combined techniques of x‐ray diffraction, infrared dichroism, and birefringence. The state of orientation is expressed in terms of the position of a point on a triangular “orientation diagram.” It is found that the a and b crystallographic axes orient differently. The degree of crystalline orientation is greater at a given elongation for a sample oflower degree of crystallinity than higher. An appreciable amount of amorphous orientation occurs, and appears greater in the more crystalline samples. Orientation oflarger crystalline aggregates has been studied using the light scattering technique and is found to parrallel that of the crystallites. A model consistent with these various types of experimental studies is proposed.
Strain‐induced crystallization in polyethylene terephthalate
Authors: Thompson A. B.
Published: April 2003

Although crystallization under stress occurs in nearly all synthetic fiber making, giving fine fibrillar fiber structures, it has been relatively little studied; and the literature, centered mainly round coarser spherulitic crystallization, does not take us very far in understanding it. However, a simple experiment shows that it is very important. If a filament of amorphous polyethylene terephthalate is stretched over a hot plate between two roller moving at different speeds, stretching can take place either without crystalization at low tension, or with considerable crystallization at high tension, at the same temperature and speed, simply according to the method of starting the machine. A model visco‐elastic theory based on Maxwell's equation is, therefore, developed to describe this behaviour using the simplest possible assumptions. Further experiments then show that this simple and partly empirical theory fits the observed behaviour of polyethylene terephthalate reasonably well, and the simple assumptions made, therefore, seem to give a first approximation to the course of strain induced crystallization. They correspond with the idea of exremely rapid crystallization from a nucleus to a small structural unit, the density of nucleation being dependent on the stress. Parallel work on the streching of spherulitic structures is then mentioned, and it is finally suggested that stress induction and rapid growth to a small structural unit may be common to both spherulitic crystallization under internal stresses, and fibrillar crystallization under an externally applied stress.
The relation between birefringence and draw ratio of man‐made fibers
Authors: de Vries H.
Published: April 2003

In the course of our investigations into the relation between draw ratio (i.e., the permanent extension ratio imparted during manufacture) and birefringence of man‐made fibers, we found that the relation published by Kordes et al. for Perlon (nylon 6) has equivalents for several different fibers that may be considered as special cases of one general empirical relation. This empirical relation, expressed in differential form, reads

where Δn = specific birefringence of the fiber, In λ = the natural logarithm of the permanent extension ratio, reckoned from the isotropic state, and m and p are constants. The constant m can assume positive or negative values, according to the sign of the birefringence of the fiber. The values found for p appear also to be characteristic of the polymer. It also appears that the experimental results can be described within experimental error by taking for p multiples of 1/2. This opens the possibility for a comparatively simple way of plotting the results. Thus, apart from the value p = −1/2 corresponding to Kordes' relation, for p the following values, which are multiples of 1/2, viz., −1, −1/2, +1/2, +1, have been found by us (e.g., respectively for nylon 66, polyethylene, polyethylene terephthalate, viscose rayon). These seem to be preferred values of p. So far no case has been found of the values p = 0 and p > ±1. As yet there is no theory forthcoming to explain the empirical relation in its general form nor the apparent rule of preference for the above‐mentioned values of p.
γ‐Irradiation of rubber and styrene. Graft polymer formation
Authors: Turner D. T.
Published: April 2003

Styrene, styrene mixed with rubber, and rubber alone have been exposed to γ‐radiation from Co‐60. The G value for polymerization‐initiating radicals formed from rubber in the mixture, G(i.r) = 0.26, has been calculated from corresponding values obtained by estimation of the number of polystyrene molecules formed in styrene and in the mixture. A G (radical) value for rubber when irradiated alone, G(r), has been assessed from a G (crosslinking) value, G(X), which was determined under closely similar experimental conditions, as G(r) = 2G(X) ∼ 6. The large discrepancy between G(r) and G(i.r.) cannot be explained satisfactorily on the supposition that radicals formed from rubber have a low efficiency in initiating the polymerization of styrene. Therefore, it is argued that the G(r) value itself is lower in the mixture. Evidence for this argument is provided by the lower rate of gelling in the mixture. this protection of rubber by energy transfer to styrene is an important example since in only one previous case has experimental evidence been provided to exclude an alternative radical mechanism. By polymerization in the presence of crosslinked rubber, uncombined polystyrene could be readily partioned into the sol fraction by equilibration of the gross polymer in benzene. About 15% of the polystyrene was free. Hexachloroethane was chosen as an example of an additive with a high G (radical) value. As would be expected, it increases the rate of polymerization but does not lead to a correspondingly large amount of free polystyrene (about 23%). Graft polymer formation from styrene and methyl methacrylate is compared and attention is drawn to the importance of the formation and subsequent reactions of initially nonpolymeric radicals in determining the proportion of free plastomer.
Solution studies of some polyethylene samples
Authors: Raman N. K. , Hermans J. J.
Published: April 2003

From studies on light‐scattering, viscometry, and osmometry in solutions of nonfractionated polyethylenes, it is concluded that none of the samples investigated shows an excessively broad molecular weight distribution. This conclusion is supported by the results obtained fro fractionated samples. The results of osmometry for two fractions confirm the [η]–Mn relation suggested by Trementozzi.
Molecular motion in polyamides
Authors: Slichter W. P.
Published: April 2003

It is well known that aliphatic polyamides with even numbers of methylene groups between amide groups melt at higher temperatures than those with odd numbers of methylene groups. Crystallographic studies in the past have sought to relate the packing of the amide groups to the variations in melting point, but these studies have been made almost exclusively at room temperature. In the present study, series of polyamide fibers were examined by x‐ray diffraction over a wide range of temperatures. In the even‐numbered polyamides, the triclinic structure occurring at room temperature shifts to a more symmetrical structure in which the chains assume hexagonal packing. This latter packing occurs in the odd‐numbered polymers at room temperature. The polar groups in the latter occur in layers which are normal to the chain axes. The layers of polar groups in the even‐numbered polyamides are tilted with respect to the chain axes at room temperature, and remain tilted at high temperatures even though the lateral chain packing becomes the same as the lower‐melting (odd‐numbered) members of the series. The spacing between polar groups along the chain decreases with increasing temperature, but the decrease is relatively less in the even‐numbered than in the odd‐numbered polymers, and is less in the more polar than in the more paraffinic compounds. These changes are ascribed to torsional and rotational motions of chain segments in the crystallites. Proton magnetic resonance studies demonstrate the onset of motion of the hydrocarbon segments and compare qualitatively the constraints to chain motion among isomeric members of the series. Some implications regarding the melting process are discussed.
Mechanism of hydrogen ion catalysis in esterification. II. Studies on the kinetics of polyesterification reactions between dibasic acids and glycols
Authors: Au‐Chin Tang , Kuo‐Sui Yao
Published: April 2003

On the basis of our experimental data and a detailed kinetic analysis, the following mechanism of hydrogen ion catalysis is proposed for polyesterification as well as for the simple esterification reactions:
magnified image
The kinetic equation in terms of [COOH] (= C) is

where C0 = [COOH] and r = [COOH]/[OH] at the time t = 0. All of our data on the polyesterification of succinic acid or adipic acid with ethylene glycol at various molar ratios and at different temperatures, in the presence or absence of a foreign acid, support the above equation. For the special case of r = 1 and in the absenc of a foreign acid, ([H+] = K[COOH]1/2), and polyesterification is hence shown to be a reaction of an order of 2.5. The data of Dostal and Raff, Flory, Davies, and Rafikov and Korshak, have been re‐examined and found to conform to the 2.5‐order relationship over the range of 0 to 92% polyesterification.
The second virial coefficient of polymer solutions
Authors: Koyama Ryuzo
Published: April 2003

A theoretical calculation of the temperature dependence of the second virial coefficient of polymer solution is carried out, assuming the Lennard‐Jones potential, φ(S) = φ0[(S0/S)12 − 2(S0/S)6], between two molecular segments of chain polymer molecules in the solution. The result gives a good explanation for the experimental relation between the second virial coefficient, A2 and the temperature, T: A2 = a + (b/T), where b > 0 for good solvents and b < 0 for poor solvents. According to this calculation, the theta point, θ, at which the second virial coefficient vanishes is given by the relation, φ0/kθ = 0.292., and the temperature gradient of A2 at this point is determined by another molecular parameter, SM, where M0 represents the molecular weight of the segment. The theoretical value of the second virial coefficient agrees well with the experimental data of Krigbaum and Flory for polyisobutylene in benzene near the theta point, and it gives a value of about S0 = 10 A. for the dimension of a segment consisting of seven monomer units in the solution. Another method for calculation of the molecular parameters, which employs the experimental data of the second virial coefficient is described. Application of this method to the light scattering data of Outer, Carr, and Zimm, permits calculation of the molecular paramenters of polystyrene in several solvents.
Extraction fractionation of polyvinyl acetate and of polyvinyl alcohol
Authors: Beresniewicz A.
Published: April 2003

Methods for rapid fractionation of polyvinyl acetate and of polyvinyl alcohol are described. By a slightly modified Fuchs' extraction technique, polyvinyl acetate can be fractionated into relatively homogeneous fractions. The ratio of osmotically determined M̄n of the nonfractionated sample to that calculated from fractionation data is 1.19. Extraction fractionation of polyvinyl alcohol is complicated by the crystallinity of this polymer. The molecular weight distribution of polyvinyl alcohol can be determined, however, in relatively short time, by first reacetylating the polymer and then fractionating the obtained polyvinyl acetate.
Thermal decomposition of poly(vinyl chloride)
Authors: Stromberg Robert R. , Straus Sidney , Achhammer Bernard G.
Published: April 2003

Poly(vinyl chloride), polymerized with the use of γ‐radiation, benzoyl peroxide, and 2,2′‐azobis(isobutyroitrile) as initiators, was thermally decomposed in vacuo. The gaseous decomposition products as analyzed by mass spectrometry consist primarily of hydrogen chloride for decomposition temperatures below approximately 300°C. At temperatures approximating 400°C., various hYdrocarbons are evolved along with the hydrogen chloride. Energetic considerations are discussed and the activition energy is determined. A free radical mechanism for the dehydrochlorination reaction that appears consistent with the reaction rate data for a three‐halves‐order reaction is postulated.
Fractionation of polymers by precipitation chromatography—microtechnique and theory
Authors: Caplan S. R.
Published: April 2003

A microcolumn for fractionation by precipitation chromatography is described. It operates in conjunction with a continuous paper‐strip fraction collector, and has been used successfully to fractionate milligram quantities of polysarcosine dimethylamide. Polymer which can either be labelled or dyed may be determined directly on the strip by scanning methods. A semi‐empirical theoretical consideration of the column has resulted in the followimg molecular weight vs. volume relationship (for the case of a single constant volume solvent‐precipitant mixing chamber):

where T2 is the temperature at the, bottom of the column, G is the volume of the mixing chamber, and τ and (σ+τ) may be identified with the Flory temperatures of solvent and precipitant, respectively. This has been found to be a close fit to published data for the fractionation of polystyrene. A comparison of exponential and constant solvent gradients shows that the former are advantageous for very broad distributions, the latter for narrow.
Emulsionspolymerisation des styrols mit radikalbildung in der Ölphase
Authors: Edelhauser H. , Breitenbach J. W.
Published: April 2003

Bei der Emulsionspolymerisation des Styrols wurde durch Anwendung von öllöslichen Startern bzw. durch rein thermische Polymerisation die Bildung der Radikale aus der Wasserphase in das Monomere verlegt. Hierbei ergab sich eine beträchtliche Erhöhung der Polymerisationsgeschwindigkeit gegenüber der Polymerisation in homogener Phase, die nur durch die Isolierung einzelner wachsender Ketten in Latexpartikeln bedingt sein kann. Dass trotz paarweiser Erzeugung der Radikale in der Öphase Latexpartikel entstehen, die nur eine wachsende Kette enthalten, wird auf eine verhältnismässig rasch verlaufende Diffusion der primär gebildeten niedrigmolekularen Radikale aus der Öphase in die Wasserphase zurüchgeführt, von wo sie dann einzeln in Mizellen bzw. Latexpartikel eintreten könuen. Der Einfluss einer solchen intermicellaren Diffusion niedrigmolekularer Radikale—womit die Isolierung in Mizellen bzw. Latexpartikeln nur mehr für makromolekulare Radikale vollständig wäre—auf die Abbruchsgeschwindigkeit in der Emulsionspolymerisation bei Kettenübertragung wird diskutiert. Für die thermische Styrolpolymerisation ist ein Diradikalmechanismus auf Grund der Unter suchungsergebnisse unwahrscheinlich.
The effect of inorganic electrolytes on the denaturation of arachin with urea and guanidinium salts
Authors: Naismith W. E. F. , Williams R. K.
Published: April 2003

The effect of a number of electrolytes on the denaturation of arachin with urea and guanidinium chloride has been examined by ultracentrifuge and viscosity techniques. With urea, all the sodium salts studied retarded the denaturation. With guanidinium chloride, however, it appeared that a salt accelerated or retarded the denaturation depending upon whether the guanidinium salt with the anion of the salt in question denatured arachin more rapidly or more slowly than guanidinium. chloride. The effect of some other guanidinium salts on the sedimentation of arachin is also briefly reported.
Phase equilibria in ternary systems containing a solvent a linear polymer, and a crosslinked polymer
Authors: Sakurada Ichiro , Nakajima Akio , Aoki Hirosi
Published: April 2003

The equilibrium compositions of gels obtained by swelling crosslinked poly(vinyl acetate) of each of the following solutions, at various concentrations, were determined: linear low‐polymeric poly(vinyl acetate) in ethyl acetate, linear low‐polymeric poly‐(methyl acrylate) in ethyl acetate, linear low‐polymeric polystyrene in benzene. From these data, the interaction parameters χij for pairs of the components were deduced and compared with each other and with comparable constants from the literature.
Polymer and group interactions. VII. Lactonization of polyethyl α‐chloroacrylate
Authors: Smets G. , Flore P.
Published: April 2003

Polyethyl α‐chloroacrylate (PCA) has been condensed in the presence of aluminum chloride and aromatic hydrocarbons; the molar ratio AICl3/PCA was usually higher than unity. Although the halogen content decreases with a higher degree of conversion, no aromatic hydrocarbons are incorporated into the polymer. The reaction proceeds through a nucleophilic substitution mechanism with intramolecular lactonization; the polymer composition has been calculated from the halogen content and the conductometric titration of free acid and lactone rings after opening. The degrees of polymerization of the reaction products were determined by the osmotic method in order to evaluate the importance of the chain degradation during the condensation. In spite of the high condensation temperature and the high degree of conversion, the degrees of polymerization are about 40–50% of that of the initial PCA. While the limited viscosity numbers vary only slightly, the Huggins‐Schulz k′ constant values decrease regularly with an increasing degree of lactonization.
Fractionation of polyethylene
Authors: Henry Patrick M.
Published: April 2003

A procedure and apparatus are described for the large scale (50‐gram) fractionation of high‐density polyethylene by Desreaux's fractional extraction technique. Two samples of Ziegler polyethylene were fractionated by this technique and the intrinsic viscosity in decalin at 135°C. and molecular weight by light scattering were measured on the fractions. The relationship [η] = 4.6 × 10−4 M̄w0.73 was found to hold for molecular weights between 25,000 and 640,000. The samples differed in polydispersity, one having a broad distribution and the other a rather narrow distribution. Evidence for the sharpness of the fractions obtained by the new technique was provided by refractionating of one fraction and the resolation of two fractions which were combined and refractionated.
Radiochemical studies of free‐radical vinyl polymerizations. Part I. The nature of the initiation and termination processes in methyl methacrylate and styrene polymerizations using C14‐labeled initiators
Authors: Ayrey G. , Moore C. G.
Published: April 2003

C14‐Labeled initiators, viz., di‐(ar‐C14)‐benzoyl peroxide, di‐(carboxyl‐C14)‐benzoyl peroxide, and C14‐azobisisobutyronitrile (AZBN), have been used to initiate the polymerization of methyl methaerylate at 60°C. in benzene. Determination of the rates of polymerization, and the molecular weights (M̄n) and C14‐contents of the resultant polymers permits the following conclusions to be made. (1) Rates of initiation by benzoyl peroxide and AZBN are given by the equations, Ri = 5.15 × 10−6 [Bz2O2] mole l.−1 sec.−1 and Ri = 1.17 × 10−5[AZBN] mole l.−1 sec.−1, respectively. (2) The initiator efficiency, f, for AZBN is 0.50; f for benzoyl peroxide cannot be evaluated in the absence of a reliable kd value for this compound in the present system. (3) Initiation is solely by addition of initiator radicals, R·, to the monomer; in the case of benzoyl peroxide, 43% of the radicals R· are phenyl and 57% are benzoyloxy under the reaction conditions used. (4) The average number of C14‐initiator fragments per polymer molecule, n, is 1.27, indicating that bimolecular termination of polymethyl methacrylate radicals is 57.5% by disproportionation and 42.5% by combination.