bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of the crystal structure of cellulose I
Authors: Ellis K. C. , Warwicker J. O.
Published: April 2003

The possibility of formulating a structure of cellulose I without postulating a twofold screw axis in the structure has been investigated. Although structures of this type can be found for which the agreement between observed and calculated intensities is similar to that obtained by Meyer and Misch, none of them is completely satisfactory. In this analysis it is shown that the original interpretation of the x‐ray fiber diagram is uncertain because of the overlap of reflections and that a new approach is required that uses the envelope of diffraction spectra rather than the individual reflections.
Polyethylene unit cell variations with branching
Authors: Swan Paul R.
Published: April 2003

It is demonstrated by accurate x‐ray diffraction measurements that a variety of types of branches will affect the dimensions of the orthorhombic unit cell of polyethylene. In particular, the random placement of methyl branches on the molecular backbone by means of copolymerization of 12 mole‐% of propylene with ethylene will expand the a dimension of the unit cell by as much as 7%, and the b dimensions about 0.5%. In addition, alkyl branches up to five carbons in length, chlorine atoms, oxidation products, and probably crosslinks will also expand the cell dimensions. A qualitative explanation of the uniform, anisotropic expansion due to random inclusion of dilating centers is presented.
New methods for the synthesis of polyesters and their oligomers
Authors: Zil'berman E. N. , Kulikova A. E. , Teplyakov N. M.
Published: April 2003

Until recently the salts of iminoesters were prepared in general only from monofunctional nitriles and alcohols. In the papers published by us in 1959 we have shown that chlorides of imonium chlorides, produced by interaction between nitriles and hydrogen chloride in 1:2 molar ratios, will on reaction in the cold with equivalent amounts of primary alcohols give a high yield of imino ester hydrochlorides that in the presence of water will hydrolyze to the esters:
magnified image

An investigation into the mechanism of reaction between nitriles, hydrogen chloride and alcohols led to the synthesis of iminoesters using bifunctional reactants and thus to polyiminoester halohydrides and to the products of their hydrolysis, polyesters. The method developed differs from the conventional sysnthesis of polyesters in that it is based on a reaction heretofore not used for the synthesis of polymers. Moreover the reaction is carried out in the cold, whereas, ordinarily, elevated temperatures are used for obtaining polyesters. Depending upon the reactant ratio, from dinitriles, glycols, and hydrogen chloride new low molecular polyesters (M = 1000–1900) have been obtained with nitrile and alcohol terminal groups. First of all in the series of dinitriles and glycols containing aliphatic and aromatic radicals ω,ω′‐dioxyalkyl esters of dicarboxylic acids have been synthesized. Owing the selective reactivity of the nitrile groups from bisadiponitrile besides the diols the heretofore unknown ω‐oxyesters of δ‐cyanovaleric acid and glycol di(δ‐dicyanovalerates) have been obtained. The molecular weight of the polyesters was determined viscometrically and was calculated from the results of endgroup analysis. The results obtained in both cases coincided, which, in particular, indicates the practical absence of ring systems in the products.
A test of the validity of ferry's method of reduced variables in the case of certain dilute polymer solutions
Authors: Walters K.
Published: April 2003

Use is made of the relaxation spectrum to assess the validity of Ferry's method of reduced variables in the case of certain dilute polymer solutions. Both concentration and temperature changes are considered, and it is concluded that Ferry's theory can be expected to have serious limitations whenever the polymer concentration is low enough to allow a significant Newtonian element to enter into the relaxation spectrum.
Bonding in urethane elastomers
Authors: Weisfeld L. B. , Little J. R. , Wolstenholme W. E.
Published: April 2003

Ordinary modulus–temperature physical test data at low deformations for unswollen gum elastomers has been partitioned into contributions from primary and secondary interchain linkages. The analysis is based upon the supposition that primary or covalent bonds conform to the statistical theory of rubberlike elasticity, while secondary interchain bonding adheres to Arrhenius Law. This treatment was applied to peroxide‐cured millable elastomers, diamine‐cured polyester diisocyanates, and several thermoplastic polyureaurethanes. Information resulted on the primary crosslink density, cure agent efficiency, activation energy for secondary bonding, and the relative contributions of respective bonding phenomena at various temperatures. These considerations afford a better understanding of the relationships between structure, composition and mechanical properties in polyurethane elastomers. Mechanisms are proposed relating the type of crosslink to its effect on secondary bonding, and the geometry of the spine on deviations from kinetic elastic theory at high extensions.
Thermal degradation of polypropylene
Authors: Davis Thomas E. , Tobias Robert L. , Peterli Elizabeth B.
Published: April 2003

The molecular weight distributions of polypropylene samples subjected to various degrees of thermal degradation were experimentally determined and compared with those expected theoretically for random scission of the polymer chains. The comparison demonstrated that the chain breakage is predominately random and also indicates that current methods of determining molecular weight distributions are adequate for use in evaluating hypothesized degradation mechanisms. In terms of the free radical depolymerization theory, intermolecular transfer of the radical is the dominant process. A curve relating the degree of degradation to the intrinsic viscosity was obtained from calculations based upon a random degradation. With this curve, intrinsic viscosities measured as a function of degradation time could be used to obtain the time dependence of the degree of degradation. The observed degradation rates could not be described by a simple process in which the rate of bond rupture was proportional to the number of bonds present. Neither a similar process involving two bond types nor a dependence of the free radical diffusion rate upon the degree of degradation was by itself a satisfactory basis for interpreting the kinetics. The activation energy estimated for the polypropylene degradation at 250–300°C. was not significantly different from that determined by volatilization measurements at higher temperatures.
The effect of copolymerization on stereoregular polyvinyl chloride
Authors: Rosen Irving , Marshall W. E.
Published: April 2003

Copolymers of vinyl chloride and vinyl acetate were prepared by tributylboroncatalyzed polymerizations at −15 and −40°C. The Alfrey‐Price equations were used to calculate the monomer reactivity ratios to be expected in a free‐radical propagation at −40°C. The experimentally determined monomer reactivity ratios were in good agreement with the theoretical values and support the concept of free‐radical initiation by the tributylboron catalyst. Vinyl acetate interrupts the regular polymer sequences in polyvinyl chloride and interferes with the crystallizability of the polymer. The infrared D635/D692 absorbance ratio of the copolymers decreased approximately linearly with vinyl acetate content. The activation energy difference between syndio‐ and isotactic placements was calculated to be about 0.3 kcal./mole.
Viscosities of dilute solutions of polyvinyl acetate
Authors: Moore W. R. , Murphy M.
Published: April 2003

Viscosities of dilute solutions of six fractions of polyvinyl acetate covering the molecular weight range 40,000 to 340,000 have been obtained using acetone, chlorobenzene, chloroform, dioxane, methanol, and toluene as solvents at temperatures in the range 18–67°C. There is some evidence for association of polymer in methanol and toluene. Intrinsic viscosities and values of the Huggins constant k′ vary with solvent but the variation of k′ is not always that expected from considerations of solvent power. Where comparison is possible, values of the constant K and exponent a in the expression [η] = KMa are in reasonable agreement with other values. The variation of a with solvent is not always that to be expected from the variation of [η] with solvent. The variation with solvent of the swelling or expansion factor α in the expression [η] = K′M1/2α3 is similar to that of the exponent a. Values of K′ vary somewhat with solvent. Values of [η] for acetone, chlorobenzene, chloroform, and dioxane decrease with increasing temperature, the reverse being the case with methanol and toluene. The variation of k′ with temperature is the inverse of that of [η]. The exponent a increases with increasing temperature in all cases but that of toluene and values of K decrease. The swelling factor α increases with increase of temperature, and temperature coefficients of [η] seem to be primarily due to changes in the value of (r̄02/M), where r̄02 is the mean square unperturbed end‐to‐end distance of the chains.
Some polymers and copolymers of vinyldiphenylphosphine
Authors: Paisley David M. , Marvel C. S.
Published: April 2003

Vinyldiphenylphosphine has been homopolymerized with aluminumisobutyl/titanium tetrachloride catalysts and with boron fluoride etherate to give low molecular weight oily products. The same monomer has been copolymerized with ethylene and butadiene using Ziegler‐type catalysts and with styrene using azobisisobutyronitrile as the initiator. None of the polymers has a high molecular weight, as indicated by inherent viscosity determinations.
Calibration of light‐scattering instruments: A critical survey
Authors: Kratohvil J. P. , Deželić Gj. , Kerker M. , Matijević E.
Published: April 2003

A survey of the literature on the calibration of light scattering instruments has been made, including an extensive bibliography. The values of the Rayleigh ratio R90 and depolarization ρμ for benzene, toluene, carbon tetrachloride, and carbon disulfide and the excess turbidity of Cornell polystyrene and D.C./P.J.3 polystyrene (0.5% solutions in toluene) were tabulated for two wavelengths (4358 and 5461 A.). Examination of these results showed a larger variation in reported values than is generally assumed acceptable (only so‐called “high” values have been considered). No correlation was found with the various standards used for the original calibration. Some aspects of the most usual methods of calibration are discussed and arguments are considered which would favor those values of R90 (or excess turbidity) that are at the lower limits of the range reported (but still in the region of “high” values). The difficulty of using Einstein's equation in determining the exact values of R90 is pointed out.
Thermodynamics of polyisobutylene–n‐alkane systems
Authors: Delmas G. , Patterson D. , Somcynsky T.
Published: April 2003

The solubility parameter theory and the molecular theory of polymer solutions developed by Prigogine and his collaborators are used to treat two phenomena not predicted by better‐known theories: the negative (exothermic) heats of mixing occurring in some nonpolar polymer—solvent systems at room temperature, and the lower critical solution temperature (L.C.S.T.), recently found by Freeman and Rowlinson, above which immiscibility occurs. It is found that a negative heat of mixing and a L.C.S.T. must occur at high enough temperatures when there is a difference in chain length between polymer and solvent (and if the critical endpoint of the solution does not intervene). The results of the cell theory of Prigogine et al. are presented for mixtures of a long‐chain polymer with a series of homologous short‐chain solvents, the free energy and enthalpy parameters χ and κ being given by:

where rA is the number of segments in the solvent polymer, and A and B are constants. Heats of mixing have been obtained calorimetrically at room temperature for polyisobutylene with solvents in the n‐alkane series and with some others. The heats with the n‐alkanes are negative below C14, and are in good agreement with the theory which is also applied to the L.C.S.T. found by Freeman and Rowlinson for some of the same systems. Values of A and/or B obtained here compare with those found elsewhere from viscosity and swelling measurements and from the pure n‐paraffin equation of state.
Dilute solution properties of polyamides in formic acid. Part II. The influence of ionic strength
Authors: Saunders P. R.
Published: April 2003

The light scattering, differential refractive index and intrinsic viscosity of nylon 66 dissolved in formic acid—water—potassium chloride solution have been studied. In contrast to work reported previously on formic acid—water—sodium formate solution, the degree of ionization of the polymer has not been reduced by common counterions; rather, the polyelectrolyte effects have been swamped by means of excess potassium chloride. The values of weight‐average molecular weight deduced from all the light scattering measurements in both systems were identical, which removes any doubts concerning the influence of selective absorption around the nylon molecules. A theta solvent was obtained from the potassium chloride solution, and the value of intrinsic viscosity measured in this solvent was identical with that predicted from the results in sodium formate solution. It was shown that the differential refractive index of nylon in dilute solution depends markedly on its degree of ionization.
Estimation of diffusivities and solubilities from sorption studies
Authors: Lundberg J. L. , Wilk M. B. , Huyett Marilyn J.
Published: April 2003

Techniques and results are reported for the joint estimation of kinetic (diffusion) and equilibrium (solubility) properties of gas—polymer systems. Pressure decreasing with time is measured in a closed, isothermal system as gas diffuses radially into a cylindrical mass of polymer held in a sintered steel or glass container. Polyethylene and polystyrene with various gases have been studied at temperatures up to 227°C. and pressures to 650. Gas pressures are raised “incrementally” to minimize (and to study) the dependence of diffusivities on concentration and pressure and to improve solubility estimation. Data collection techniques have evolved from hand recording of time, temperature, and pressure to use of an automatic analog and digital recording system. Pressures are converted to moles by use of an empirical equation of state based on published P—V—T data. Fourier's equation for radial diffusion from a closed well‐mixed solution into an infinite cylinder and some approximations thereto serve as a frame of reference for analysis of the data. Least squares estimates of the diffusivity and solubility are obtained by a numerical iteration process on an electronic computer. Some of the effects of departures from applicability of Fourier's equation are overcome by extrapolating series of estimetes of diffusivities and solubilities obtained from systematically censoring the data.
A study of the crystalline structure of synthetic fibers by dark field electron microscopy
Authors: Scott R. G.
Published: April 2003

The crystalline structure of synthetic fiber has been studied by the combined techniques of electron diffraction and dark field electron microscopy. By peeling layers a few tenths of a micron thick from drawn fibers and preparing electron diffraction patterns from them one can resolve structural variations that take place through a fiber. Application of the same sample preparation technique on drawn linear polyethylene fibers combined with dark field electron microscopy can reveal crystalline structures that have an average size and distribution predicted from x‐ray diffraction and lightscattering studies.
Contribution à l'etude des proprietés thermodynamiques des solutions de copolymères
Authors: Lautout‐Magat Mme.
Published: April 2003

La méthode quasi‐chimique de Guggenheim est appliquée a l'étude des propriétés thermodynamiques des solutions de copolymeres. Dans le cas des exemples numériques traités cette méthode ne fournit pas une meilleure approximation que le calcul plus simple basé sur la moyenne des indices de solubilité des polymères constituants.
Solution properties of poly(N,N‐dimethylacrylamide)
Authors: Trossarelli L. , Meirone M.
Published: April 2003

In connection with the research on the influence of the substituents on the intrinsic configurational character of the polymers of the derivatives of acrylic acid as related to the solution properties, experiments have been made on poly(N,N‐substituted acrylamides). In the present paper the results obtained by light scattering and viscosity on the behavior in methanol at 25°C. and in water at 25 and 40°C. of unfractionated samples of poly(N,N‐dimethylacrylamide) with molecular weights ranging from 5 × 104 to 1.2 × 106 are reported. The intrinsic viscosity‐molecular weight relationships for the polymer dissolved in the three solvents are reported, as well as the viscometric constant Ki in ideal solution and the (ri2/M)1/2 ratio which characterize the polymer. By comparing the value of the (ri2/M)1/2 ratio for poly(N,N‐dimethylacrylamide) with those already reported for poly(methyl acrylate) and poly(acrylic acid) and other nonionic polymers, it is shown that the N(CH3)2 groups have practically no influence upon the configurational character of the polymer chain.
Preparation and properties of monodisperse branched polystyrene
Authors: Morton M. , Helminiak T. E. , Gadkary S. D. , Bueche F.
Published: April 2003

Model branched polymers have been prepared by the reaction of relatively monodisperse polystyryl lithium with silicon tetrachloride. The branched molecules have been carefully characterized by light scattering and osmotic pressure measurements. A study of the dilute solution properties of the branched molecules has confirmed the theoretical development of the branching coefficient, g′, by Zimm and Kilb. The second virial coefficient, A2, has been found to decrease with increased branching. In addition, the Huggins constant, k′, has been found to be a poor measure of branching in molecules.
Glass transitions in ethylene copolymers and vinyl homopolymers and copolymers
Authors: Reding F. P. , Faucher J. A. , Whitman R. D.
Published: April 2003

In ethylene copolymers isolatedCH2CHRCH2 groups undergo a glass transition at about −10 to −50°C., the exact temperature depending upon the nature of R. For any given copolymer the temperature of the transition remains reasonably constant over a broad composition range at high ethylene contents. At high comonomer content the transition rises with composition along the line drawn between the glasstransition temperature of polyethylene and that of the homopolymer of the comonomer in question. A second glass transition is also observed in ethylene copolymers at about −125°C. over the whole composition range. This transition corresponds to motion of CH2 sequences of three to five or more in the main chain. The temperature position of this transition is usually independent of the nature of the rest of the chain. The behavior of ethylene copolymers is quite different from that of normal vinyl copolymers, where only a single glass transition is observed for each composition and where the temperature position of the transition changes uniformly with composition along the line drawn between the glass transitions of the respective homopolymers. It is concluded that the motions involved in the glass transitions of the main chain CH2 sequences and of isolated CH2CHRCH2 groups in ethylene copolymers are localized, involving only a few carbon atoms. In the case of the normal vinyl copolymers, on the other hand, the motion at the transition appears to be a long‐range motion involving a great many chain carbon atoms and cooperative motion of the pendent groups. This change in the nature of the motion involved at the glass transition in going from high ethylene content copolymers to low ethylene content or vinyl copolymers appears to arise because of steric hindrance and/or restrictive dipolar forces between the pendent groups of the CH2CHRCH2 segments in those cases were they are not isolated from each other. Finally, it is concluded that all vinyl homopolymers would have glass transitions in the −10 to −50°C. range if steric hindrance between the side groups did not occur. It is shown that as the pendent group becomes less bulky or is further separated from the main chain by CH2groups the glass transition temperature decreases presumably towards the −10 to −50° range characteristic of the transition of isolated CH2CHRCH2 groups.
Determination of a number criterion of polymer heterogeneity
Authors: Sibiński Henryk
Published: April 2003

A critical survey of number criteria of heterogeneity of polymers based on differential distribution function and on measurements of different average molecular weights has been presented. Because of the difficulties connected with measurements of the number‐average molecular weight and the errors inherent in differentiation of the integral distribution function a number criterion of heterogeneity based on the latter is proposed. The area limited by the integral distribution curve and the straight line defining an absolutely homogenous polymer having the same weight‐average degree of polymerization as the polymer tested is defined as absolute heterogeneity. On the basis of the weight‐average degrees of polymerization calculated directly from the integral distribution curve it is proved that the value of proposed number criterion increases with the increase of the weight amount of fractions having different degree of polymerization from the average one of the tested polymer. This value also increases with the increase of the difference between the degree of polymerization of these fractions and the average degree of polymerization of the tested polymer. On the basis of Flory's equation the absolute heterogeneity of polymers having the most probable distribution has been determined. The ratio of absolute heterogeneity of the tested polymer to the absolute heterogeneity of polymer having the most probable distribution and the same average molecular weight as the tested polymer has been defined as relative heterogeneity. On the basis of Scott's theoretical fractionation data changes in heterogeneity occurring during the fraction have been revealed.
Etude cristallographique de la structure de films de polytétrafluoroéthylene greffés de styrègne. Destruction du copolymère greffé par un traitement thermique
Authors: Sella Claude , Chapiro Adolphe , Matsumoto Akira
Published: April 2003

On a étudié les variations de la cristallinité et des paramètres cristallographiques du polytétrafluoroéthylène (PTFE) qui se produisent lors du greffage du styrène dans la masse de ce polymère. On a constaté que les paramètres de la maille cristalline du PTFE restent pratiquement inchangés lorsqu'on greffe du styrène dans la masse du polymère et ceci měme pour des taux de greffage élevés. Au cours d'un tel greffage le taux de cristallinité du PTFE diminue progressivement et tend vers zéro pour les taux de greffage élevés. Ce comportement est différent de celui observé antérieurement dans le cas du polyéthylène (C. Sella, J. Polymer Sci., 48, 207 (1960)). Il démontre qu'au cours du greffage sur le PTFE le styrène ne pénètre pas dans les zones cristallines du polymère mais que l'importance de celles‐ci est progressivement réduite au cours de la réaction. Des clichés de la surface des films greffés, pris au microscope électronique ont mis en évidence une structure hétérogène de celle‐ci. Des échantillons de PTFE fortement greffés ont été soumis à un traitement thermique dans le but d'essayer de recristalliser le polymère. Dans ces conditions, on a observé à 300° une destruction rapide du copolymère greffé, celui‐ci étant scindé en deux phases constituées respectivement par le PTFE initial et par du polystyrène pur. La cinétique de ce processus a été brièvement examinée en mesurant les pertes de poids des films greffés en fonction du temps de chauffage.
Morphology and crystal growth rate of polyethylene crystalline complexes
Authors: Holland V. F. , Lindenmeyer P. H.
Published: April 2003

An investigation of the morphology of crystallization of fractionated linear polyethylene has shown that single crystal platelets may be obtained from dilute xylene solutions only in a limited region of temperature. The variation of this temperature region with molecular weight is greater than would be expected from the theoretical variation in equilibrium melting temperature. Uniformity of the crystallization conditions was sufficient to permit the measurement of size and thickness of the crystals as a function of both time and temperature. It was shown that the change in platelet thickness with temperature cannot be accounted from by the kinetics of nucleation with the assumption that the thickness is essentially equal to the critical nucleus dimension. The crystal growth rate data show that growth occurs by a nucleation process but the data are not compatible with the assumption that nucleation occurs through the formation of a homogeneous monomolecular layer on the growth surface. Evidence is presented to show that crystallization habit is dependent not only on the degree of supercooling but is also a function of some other factor that acts as a resistance or impedance to crystallization.
The effect of phenols on the polymerization of styrene
Authors: Godsay M. P. , Harpell G. A. , Russell K. E.
Published: April 2003

The effect of a variety of phenols on the rate and degree of polymerization of styrene has been studied. With 1‐naphthol it is found that polystyryl radicals abstract the phenolic hydrogen atom, since 1‐naphthol has a far greater effect on the rate and degree of polymerization than 1‐deuteroxynaphthalene. Many phenols do not significantly retard the polymerization of styrene and transfer constants ranging up to 7.7 × 10−3 have been estimated for them. Other phenols, such as 1‐naphthol, 4‐methoxyphenol and 2,6‐diisopropylphenol, significantly decrease the rate and degree of polymerization. Transfer constants for these retarders have been calculated, both from the rate data alone by means of the treatment of Jenkins and from molecular weight data. The estimated values depend on the assumptions made concerning the mode of disappearance of the retarder radicals produced in the transfer reaction. Most of the retarders investigated give transfer constants in the range 10−2 to 10−1 but catechol, tert‐butylcatechol, and pyrogallol give larger values. An increased rate of polymerization observed in mixtures of styrene and some phenols is probably due to a higher rate of production of radicals by the initiator, azobisisobutyronitrile.
Monomer reactivities in radiation‐induced graft copolymerization. Part II. Graft copolymerization to Teflon
Authors: Odian George , Acker Terese , Rossi Albert , Ratchik Elliot
Published: April 2003

The gamma radiation‐induced surface graft copolymerizations of styrene—acrylonitrile and styrene—methyl acrylate to Teflon were studied. It was observed that the compositions of the various grafted copolymers are richer in the more polar monomer than one would predict from the Lewis‐Mayo copolymer composition equation. These results were interpreted in terms of a preferential solvation of the relatively immobile growing graft polymer free radicals by the polar monomers.
Emulsion copolymerization of butadiene and styrene in the presence of carbon black
Authors: Medalia A. I. , Hagopian E. , Hall J. P.
Published: April 2003

Carbon blacks inhibit and retard free radical polymerization in bulk and solution. The mechanism of this is discussed in terms of the chemical groups present on the carbon surface. It is shown that the number of free radicals which react during the induction period (polymerization of styrene with AIBN) is much less than the number of quinone groups but of the same order of magnitude as the number of easily oxidizable groups. Inhibition by carbon black was also found in an emulsion polymerization system with cumene hydroperoxide as initiator (no reducing components). By use of highly active redox recipes, reasonable rates of polymerization were obtained at both 50°C. (sugar‐iron‐hydroperoxide recipe) and 5°C. (peroxide‐polyamine recipe), with as much as 40 parts of black per 100 parts of monomers. In these systems, the carbon black was charged as an aqueous dispersion stabilized with Daxad 11; the latices were stable and showed evidence of association between some of the carbon black and some of the latex particles. The coagulated rubber stocks, when compounded and cured, gave properties closely similar to those of dry mixed stocks.
Inhibition and retardation of the polymerization of ethyl methacrylate
Authors: Funt B. Lionel , Williams Fredrick D.
Published: April 2003

Combination of C14‐tagged or inactive benzoquinone with tagged or inactive azobisisobutyronitrile was used to study the kinetics of polymerization of ethyl methacrylate. The course of the reaction was followed by dilatometry, and the resultant polymers were assayed for C14 content by liquid scintillation techniques. Molecular weights were obtained by osmometry in order to determine the number of tagged fragments per polymer molecule. A transition from a retarded polymerization to one showing an inhibition period was found at a critical concentration of p‐benzoquinone. This transition was accompanied by a marked change in the C14 content of the polymers. The magnitude of chain transfer or copolymerization was directly estimated from the number of tagged fragments incorporated per polymer molecule. These indicated that no more than two molecules of p‐benzoquinone could copolymerize or that a limit could be set of one chain transfer step per kinetic chain. Hence, neither of these processes can be considered as highly significant in the mechanism. The formation of a transient adduct between primary radicals of initiation and benzoquinone is postulated, and the transition from retarded to inhibited polymerization in this system is discussed on this basis. These ideas were extended to a consideration of the role of primary radical capture and radical reactivity for other monomers, such as styrene and vinyl acetate.
Anionic copolymerization
Authors: O'driscoll Kenneth F.
Published: April 2003

Previous work with anionic copolymerizations held that the terminal carbanion played no role in determining which monomer was next added. Recent work by Graham et al. has demonstrated that this is untrue for monomers of extremely dissimilar polarities. In this paper the kinetics of copolymerization of dissimilar monomers has been developed. As a result it is shown that the ratio of monomers in the initial copolymer d[M1]/d[M2] is directly proportional to the square of the initial monomer ratio ([M1]/[M2])2 when the monomers are dissimilar. The earlier theory resulted in a first‐power proportionality for all cases. Log—log plots of the equation d[M1]/d[M2] = K([M1]/[M2])a show that a has a value of 2.0 for styrene—methyl methacrylate, 1.0 for styrene—isoprene and 1.3 for methyl methacrylate—methacrylonitrile. The conclusion is drawn that values of a of 1.0 and 2.0 represent extremes of behavior for monomers of very similar and very dissimilar polarites. As a corollary of this it is concluded that reactivity ratios for these systems where a is not 1.0 are of questionable theoretical significance.
Stereoregularity and optical anisotropy of polymers
Authors: Tsvetkov V. N.
Published: April 2003

The flow birefringence and the photoelastic effect in films have been used to study the molecular optical anisotropy of stereoisomers of polystyrene (PS), poly(p‐methyl styrene) (PMS), poly(methyl methacrylate) (PMMA), and poly‐(n‐butyl methacrylate) (PBMA). Considerable differences in the optical anisotropy are observed between the atactic and isotactic structures of the molecular chain. These differences change in value and sign for various polymers and in some cases cause a change of the sign of the birefringence. The observed effect is due to the difference between the character of the rotation of the side radicals of the macromolecule in the isotactic and atactic isomers. The molecular optical anisotropy is shown to be especially sensitive to side group rotation in those cases where the positive anisotropy of the principal molecular chain is to a considerable degree compensated by a negative anisotropy of similar absolute value in the side groups. In these cases the study of the molecular optical anisotropy may serve as a sensitive method for studying the stereoregularity. The strain birefringence observed in films of crystallizable polymers is a sum of the two effects: the orientation of chains in the amorphous phase and the orientation of the stereoblocks forming crystallites. These two processes can be differentiated owing to differences in their time dependences, and experimental study of these may serve as a sensitive method for revealing traces of a crystalline phase in a polymer.
Cyclopolymerization. II. Kinetics of polymerization of acrylic anhydride
Authors: Mercier J. , Smets G.
Published: April 2003

The kinetics of polymerization of acrylic anhydride has been studied at 34.6°C. in bulk and in solution in cyclohexanone and in dimethylformamide. The order of reaction with respect to the initiator concentration (azobisisobutyronitrile) varies from 0.67 to 1. The rate of reaction is high; it remains practically constant over a range of monomer concentration from 0.76 to 4.29 mole l.−1; at higher concentrations, it increases linearly with the molar concentration. The results have been interpreted on the basis of a progressive insolubilization of the polymer molecules on account of residual double bonds, and on the basis of the occlusion of growing chain radicals. The presence of trapped radicals was demonstrated by EPR measurements. Their concentration was evaluated by comparison with the spectrum of DPPH; it increases with the time, and with the polymerization temperature. After 8 hr. polymerization at 60°C. it is equal to 5 × 10−4 mole l.−1.
Copolymerization studies. II. Effect of high pressures on monomer reactivity ratios
Authors: Burkhart R. D. , Zutty N. L.
Published: April 2003

Studies of the effect of pressure on comonomer reactivity ratios in the styrene—acrylonitrile and methyl methacrylate—acrylonitrile systems show that the values of r1 and r2 increase in both cases and that the relative activation volumes (ΔV11‡ − ΔV12‡) are −9.8 and −9.5 cc./mole respectively, where acrylonitrile is monomer 2. The product r1r2 increases toward unity in both systems. A study of the effect of temperature on these reactivity ratios shows that (ΔH11‡ — ΔH12‡) is essentially zero for methyl methacrylate—acrylonitrile, but 500 cal./mole for styrene—acrylonitrile. Within the pressure range studied, it has been found that the e values for the two monomer pairs are dependent upon pressure, tending to become equal, the higher the pressure, while the Q values are relatively unaffected by pressures up to 1000 atm.
Permeation, solution, and diffusion of water in some high polymers
Authors: Yasuda H. , Stannett V.
Published: April 2003

The equilibrium sorption isotherms of water in polyethylene terephthalate, ethyl cellulose, and rubber hydrochloride have been measured at 25°C. by means of the quartz helix technique. The permeability constants and the diffusion constants have been measured on the same polymers and on polyethylene and polypropylene by the time‐lag technique of Barrer but with a modified apparatus. The solubility coefficients from the sorption measurements (values for polyethylene and polypropylene have been previously reported) are compared with those obtained as the quotient of the permeability and diffusion constants. In the case of polyethylene, polypropylene, and polyethylene terephthalate, excellent agreement between the two sets of values were obtained, but with rubber hydrochloride and ethyl cellulose the sorption values are much higher. These differences are interpreted in terms of clustering of water vapor in the film at higher relative humidities. The modified time‐lag technique showed concentration‐independent diffusion constant for all five polymers.
Modification of spectral and semiconducting properties of polyvinylidene chloride by ultraviolet light of specific wavelengths
Authors: Oster Gerald , Oster Gisela K. , Kryszewski Marian
Published: April 2003

Polyvinylidene chloride—polyvinyl chloride copolymer (saran) when irradiated with 254 mμ light produces a species which absorbs maximally at 285 mμ and has a tail in the spectrum which extends into the visible region. Irradiated samples show a further increase in absorption when heated at 100°C., while unirradiated samples are unaffected by such heating. Irradiation at 254 mμ results in crosslinking which is further increased on heating. On the other hand, heating destroys the Carr‐Price reaction exhibited by irradiated material. Heating also destroys the electron spin resonance signal of the irradiated material. Irradiated films are photoconducting, but this property is destroyed by heating. The compound produced irradiation at 254 mμ is destroyed by irradiation at 310 and 365 mμ, but the products are different in the two cases and depend on the presence of oxygen.
Stress relaxation phenomena: Multiple box distribution treatment of relaxation times
Authors: Chang Franklin S. C.
Published: April 2003

The box distribution of relaxation times was generalized for the interpretation of stress relaxation of viscoelastic material under small constant strain. The generalization consists of the use of a number of box distribution functions, each of which is characterized by three parameters; namely, modulus constant, Cj; largest relaxation time, τmj; and width of spectrum. The logarithms of Cj and τmj obtained by applying the multiple box distribution function to published stress relaxation data for polyisobutylene, polystyrene, and GR‐S vulcanizate are linear functions of the reciprocal of absolute temperature, 1/T. The log Cj versus 1/T curves divide into two groups. The group showing relatively small change with temperature is likely due to interchain forces, while the other group, increasing rapidly with decreasing temperature, can be attributed to intrachain forces. Each curve of the latter group consists of three distinct segments of straight line with the middle segment bracketing the glass transition temperature. Thus, the transition from rubbery to glassy state covers a temperature range which can be determined by stress relaxation. Other viscoelastic properties, such as viscosity, activation energy, and tensile stress—strain at various strain rates are discussed on the basis of multiple box distribution.
On the characterization of stereoregular polymers. IV. Application to polypropylene
Authors: Miller Robert L.
Published: April 2003

By viewing a stereoregular polymer as if it were a copolymer, one may obtain relationships between its physical properties and its molecular structure. In particular, melting points and maximum crystallinities were related to sequence propagation probabilities. Thus, in principle, the kinetic parameters for any semicrystalline polymer may be obtained. This information is generally unobtainable by other means. By use of the parameters thus evaluated for a series of polypropylene samples, melting curves were calculated. These represented experimentally determined ones as well as, or better than, existing theories of crystallization.
Time–humidity superposition in some crystalline polymers
Authors: Onogi Shigeharu , Sasaguri Kiichiro , Adachi Tomio , Ogihara Sadahide
Published: April 2003

In order to verify precisely the applicability and reasonableness of the time–humidity superposition method to hydrophilic crystalline polymers, stress relaxation measurements were carried out with films of polyvinyl alcohol and nylon 6 by means of a table model Instron Tensile Tester equipped with a special glass cell to control temperature and humidity. In the case of PVA, only the time–humidity superposition is applicable at humidities higher than that at which the transition begins. For nylon 6, on the other hand, time–temperature and time–humidity superposition apply very well in the transition region and fairly well at higher temperatures and humidities. The results obtained by both the superpositions coincide very well, showing the time–humidity superposition is as reasonable as the time–temperature one. The superposed results were also compared with other existing data, and the reasonableness of the time–humidity superposition was confirmed.
Dynamic mechanical studies of irradiated polypropylene
Authors: Sauer J. A. , Merrill L. J. , Woodward A. E.
Published: April 2003

The internal friction and the dynamic modulus of isotactic polypropylene samples subject to varying degrees of pile irradiation have been studied at low audio frequencies and over the temperature range from 100°K. to over 400°K. The radiation dosages used varied from 5.4 × 1017 to 14 × 1018 nvt. For irradiation doses up to about 3 × 1018 nvt, one observed change is a decrease in the temperature at which the final upswing in damping and drop in modulus occurs, presumably as a result of defects produced in the crystallites by the irradiation. As the irradiation dose increases above 3 × 1018 nvt, all evidence of crystallinity is lost, and the internal friction peak which occurs in the neighborhood of 300°K. and which is associated with the glass transition of the amorphous regions moves to higher temperatures as a result of the increasing chainstiffening effect due to crosslinking. The secondary loss peak at 250°K. attributed to the motion of a small number of segments in the amorphous regions is found to increase in magnitude with increasing dose. The results of density determinations made before and after irradiation and also after subsequent exposure of the irradiated samples to melting temperatures and of solvent extraction studies of the irradiated samples confirm the simultaneous occurrence of crosslinking and of crystalline degradation upon pile irradiation of polypropylene samples.
Microvoids in fibers as studied by small‐angle scattering of x‐rays
Authors: Statton W. O.
Published: April 2003

Commercial and experimental fibers show diffuse small‐angle x‐ray scattering which varies in amount and shape, depending upon how the fibers were produced and also upon what aftertreatments they have received. Evidence is given showing that the amount of scattering should be interpreted in terms of the void content or microporosity in the fiber. These voids are too small to be seen by the light microscope, but are found to be measurable in the 15–200 A. range by present techniques. The spinning method greatly affects a fiber's void content. Wet‐spinning and dry‐spinning of a polymer solution produces fibers with a high void content. Melt‐spinning produces yarns with relatively low void content. The cause of this difference is discussed. Voids are shaped by the spinning process in almost all cases. The fiber can be visualized as having longitudinal cracks, crevices, or ellipsoidal. voids in the as‐spun condition, even though no molecular alignment is observed. This shaping was found to arise from a combination of (1) a shearing action of the spinneret and (2) tension on the windup. The voids are further elongated as the fiber is drawn.
The polyelectrolytic nature of cellulose gels in alkali solutions
Authors: Pennings A. J. , Prins W.
Published: April 2003

The swelling of cellulose in alkali solutions has been the subject of numerous investigations in the past. However, there still exists a controversy as to whether the reaction with alkali yields a true alcoholate or an addition compound without ionization of the cellulose. This study presents experimental data on swelling pressures that develop when water‐swollen cellulose is exposed to alkali solutions while its volume is kept constant. The measurements are carried out on extensively extracted and conditioned regenerated cellulose gels with the use of a previously described gel osmometer. It is shown that these pressures can be quite well described using the simple Donnan equilibrium theory put forward originally by Neale in 1929. In this theory, the cellulose is considered as a weak polyacid. From the wet weights and the Na+ ion concentrations inside and outside the cellulose gel, we find the acidic ionization constant to be Ka = 0.52 × 10−14. From free swelling measurements and the corresponding alkali contents, the same value is found. It is shown that the value 1.84 × 10−14 given by Neale is in error, largely due to a nonpermissible approximation in his computations. In the polyelectrolyte model used, the maximum in the free swelling as well as the maximum in the swelling pressure derive directly from the ionization equilibrium. On the basis of ideal behavior, these maxima will occur at a degree of ionization of approximately 0.6, which in the case of our cellulose gels corresponds to a 13.5% NaOH solution outside the gel. Although at higher concentrations the ionization will proceed further, the effect on the unequal Na+ ion distribution becomes less pronounced, thus leading to a decrease in swelling and swelling pressure. In a critical appraisal of earlier work, it is pointed out that the concept of bound alkali and excess alkali in the cellulose gel is unnecessary. On thermodynamic ground, it is also shown that the determination of the bound alkali by pressing excess alkali out of the gel is unreliable. Although admittedly based upon an oversimplified model, the Donnan equilibrium theory provides an explanation for the most salient points in the swelling behavior of cellulose and has in the past been unjustifiably discarded by several authors.
Phenylene sulfide polymers. III. The synthesis of linear polyphenylene sulfide
Authors: Lenz Robert W. , Handlovits Carl E. , Smith Harry A.
Published: April 2003

Linear polyphenylene sulfide has been synthesized by the condensation polymerization of alkali metal salts of p‐halothiophenols. The monomers investigated included the lithium, sodium and potassium salts of p‐bromothiophenol and the sodium salts of p‐fluoro‐, p‐chloro‐, p‐bromo‐, and p‐iodothiophenol. The mass polymerizations of these monomers were carried out below the melting points of the salts and appear to involve a solid state reaction. Rate measurements were made on the polymerization of these monomers in pyridine and on a model of the propagation reaction. In both cases, the order of reactivities of the sodium salts was I > Br > F ∼ Cl, and in the polymerization reaction, the order of reactivities of the alkali metal salts of p‐bromothiophenol was K < Na < Li. Comparison of the rates of the polymerization and model reactions indicates that the reactivities of all functional groups were essentially identical for the iodo and bromo derivatives. However, this comparison indicated that for the chloro and fluoro derivatives, the polymer chain endgroups were more reactive than the monomers. This effect, termed preferential polymer formation, has been verified for the polymerization of sodium p‐fluorothiophenoxide by the determination of unreacted monomer after the polymerization. Complete control of side reactions which lead to chain termination has not as yet been achieved for these condensation polymerization. Linear polyphenylene sulfide is kinetically stable in air and nitrogen up to 400°C. In nitrogen, a residue forms, representing approximately 50% of the original weight of the polymer, which is kinetically stable up to 900°C.