bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of the crystal structure of cellulose I
Authors: Ellis K. C. , Warwicker J. O. 
Published: April 2003

AbstractThe 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

AbstractIt 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

AbstractUntil 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 imageAn 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

AbstractUse 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

AbstractOrdinary 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

AbstractThe 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

AbstractCopolymers 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

AbstractViscosities 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

AbstractVinyldiphenylphosphine 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractTechniques 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

AbstractThe 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

AbstractLa 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

AbstractIn 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

AbstractModel 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

AbstractIn 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

AbstractA 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.