bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of polar and nonpolar solvents on the viscosity and the molecular weight of polymer solutions
Authors: Kalpagam V. , Rao M. Ramakrishna 
Published: April 2003

AbstractLight‐scattering studies of well fractionated samples of poly(vinyl acetate) were carried out in four solvents, viz., acetonitrile, ethyl formate, methyl isobutyl ketone, and dioxane, in order to investigate the effect of the polar and nonpolar nature of the solvents on the molecular weight and the viscosity of the samples studied. The molecular weights thus obtained are found to be in good agreement in all the solvents except dioxane, in which the values are twice as high. This twofold increase in dioxane has been explained in terms of secondary bonding. The relation between [η] and Mw are established for the systems poly(vinyl acetate)–ethyl formate, poly(vinyl acetate)–acetonitrile, and poly(vinyl acetate)–methyl isobutyl ketone. The root‐mean‐square radii and the second virial coefficients are also determined.
Thermodynamics of crystalline linear high polymers. II. The influence of copolymer units on the thermodynamic properties of polyethylene
Authors: Wunderlich Bernhard , Poland Douglas 
Published: April 2003

AbstractCO and CHCH3 copolymers with polyethylene have been investigated by means of DTA and X‐ray methods. The reproducibility of DTA was investigated for monomeric and polymeric standard compounds and found usable for maximum melting point determinations. The maximum melting point is discussed for copolymers, and an equation is given which corrects the influence of chain folding. CO was found to be a crystallizable defect unit, while CHCH3 causes a noncrystallizable amorphous defect.
Homogeneous anionic polymerization. III. Molecular weight of polyisoprene initiated by butyllithium
Authors: Morton Maurice , Bostick E. E. , Clarke R. G. 
Published: April 2003

AbstractA study has been carried out on the molecular weights and their distribution for polyisoprene prepared with butyl lithium as initiator in n‐hexane and tetrahydrofuran solvents. A stoichiometry of one chain per initiator molecule was found to apply. As in the case of styrene, the initiation reaction in the hydrocarbon solvent was relatively slow compared to propagation, thus leading to a broadening of the molecular weight distribution. However, narrow distributions were obtained by using a preinitiation technique, whereby all chains had an opportunity of growing simultaneously. In the THF solvent, the molecular weight distribution waa somewhat broader (M̄v/M̄n, ∽ 1.3) presumably due to a slow competitive chain termination reaction between the growing anionic chains and the solvent, a t room temperature.
Rheology of polytetrafluoroethylene
Authors: Tobolsky A. V. , Katz D. , Takahashi M. 
Published: April 2003

AbstractThe rheology of polytetrafluoroethylene above its melting point was studied by the technique of stress relaxation. The temperature shift for the maximum relaxation time at various temperatures fits the WLF equation, if the value of Tg is taken to be 110°C. Degradation of the polymer becomes appreciable above 380°C. Master stress relaxation curves were constructed from the data between 336 and 380°C. The continuous distribution of relaxation times was obtained, and also the discrete distribution of relaxation times by procedure X. The contribution of the maximum relaxation time to the total flow viscosity indicates that the molecular weight distribution of the sample used was narrow.
Termination of the anionic polymerization of acrylonitrile at low catalyst concentrations
Authors: Ottolenghi Ariel , Zilkha Albert 
Published: April 2003

AbstractThe homogeneous anionic polymerization of acrylonitrile in dimethylformamide with n‐butyllithium was studied. Two different termination reactions were found to exist depending on catalyst concentration. At high catalyst concentrations termination was bimolecular by chain transfer to monomer, while at relatively low catalyst concentrations termination was monomolecular, by an inner cyclization reaction of the growing chain end. The existence of chain transfer only at high catalyst concentrations suggests the possibility of free catalyst molecules participating in the transfer reaction. At intermediate catalyst concentrations, both monomolecular and bimolecular terminations were found to occur side by side, and DP = Kp[M]/(Ktr[C][M] + Kt). Study of the dependence of molecular weight on per cent conversion at low catalyst concentrations showed that, up to about 30% conversion, there is a linear relationship between molecular weight and concentration of monomer consumed which is independent of temperature and monomer. After this degree of conversion, molecular weight stopped to increase and remained constant due to monomolecular termination. All over the wide range of catalyst concentrations investigated, the catalyst efficiency in initiating polymerization was found to be low. In the lowest range where there is a linear dependence of molecular weight on per cent conversion it was also found that the molecular weights are proportional to [M]/[C], which is a property of “living” systems.
Crystalline order in nylon 66
Authors: Starkweather Howard W. , Whitney John F. , Johnson Donald R. 
Published: April 2003

AbstractThe x‐ray diffraction patterns of nylon 66 at small and large angles have been correlated with the densities of samples prepared in various ways. Quenching from the melt to 0°C. produces structures which are less than 40% crystalline, as determined by density and have structures similar to nematic liquid crystals. More dense specimens have a triclinic structure and appear to contain lamellae 50–100 A. thick which consist of outer amorphous layers and a central portion which is about 80% crystalline. Thermodynamic and spectroscopic evidence indicates that the disorder on melting consists of rotations about the bonds connecting CH2groups.
Diffusion constants of a maltosaccharide series
Authors: Bourne M. C. , Chichester C. O. , Sterling C. 
Published: April 2003

AbstractA series of maltosaccharides, from glucose through maltohexaose, was prepared from starch labeled with 14C. Self and integral diffusion coefficients were measured in dilute and in concentrated solvents. The coefficients were related more or less rectilinearly with the logarithm of degree of polymerization, presumably because of molecule asymmetry. A greater diminution in the coefficient occurred in 20% sucrose than in 20% corn syrup of approximately equal molarity but considerably greater viscosity.
Polymer NMR spectroscopy. IX. Polyacrylamide and polymethacrylamide in aqueous solution
Authors: Bovey F. A. , Tiers G. V. D. 
Published: April 2003

AbstractThe NMR spectrum of polyacrylamide in aqueous solution exhibits a doublet resonance in the amide proton region, in contrast to the broad singlet shown by most smallmolecule amides. This is attributed to the relatively slow reorientation rate of the polymer segments, permitting effective coupling of the electric quadrupole moment of the N14 nucleus to the motions of the molecular framework. This, in turn, narrows the amide resonance to such a degree that the two protons can be discriminated. By observation of the collapse of this doublet, the rate of rotation of the amide groups can be measured; at pH 4.5 this rotation requires an activation energy of 10.5 ± 1 kcal. and is more rapid than proton exchange between the amide group and water. Rotation is not catalyzed by acid or base, where as exchange is catalyzed by both and becomes more rapid than rotation at high and low pH. The two amide protons exchange at equal rates; if intramolecular hydrogen bonding of amide groups is present, it has no apparent retarding effect on proton exchange. These results are discussed in terms of possible protonated intermediates.
Crystal structure of a new form of polyoxymethylene
Authors: Carazzolo Gianalvise , Mammi Mario 
Published: April 2003

AbstractA new crystalline form of polyoxymethylene is described with an orthorhombic unit cell, space group P212121, and lattice constants a = 4.77 A., b = 7.65 A., c = 3.56 A. The chains are helicoidal with the axis of the helix parallel to c. The period of identity of 3.56 A. comprises two monomeric units and one turn of the helix. The lattice of orthorhombic polyoxymethylene is made up of isomorphous helicoidal chains.
Fracture processes in polymeric materials. IV. Dependence of the fracture surface energy on temperature and molecular structure
Authors: Berry J. P. 
Published: April 2003

AbstractThe study of the influence of flaw size on the tensile strength of poly(methyl methacrylate) samples has been extended over the temperature range −190°C. to 50°C. The fracture surface energy increases with decreasing temperature, while the inherent flaw size of uncracked samples passes through a minimum at about −20°C. The fracture surface energy and inherent flaw size of a copolymer of methyl methacrylate and 10 mole‐% of ethylene glycol dimethacrylate have been obtained at room temperature, by a similar method. These results are examined in the light of the hypothesis already put forward concerning the factors which govern the strength and fracture properties of glassy polymers.
Light‐scattering studies on sugar beet arabans
Authors: Tomimatsu Yoshio , Palmer K. J. 
Published: April 2003

AbstractThe discrepancy in the light‐scattering molecular weight of sugar beet araban in two solvent systems, 2M NaCl and 1% (v/v) DMF, is explained as being due to a charge effect in the latter solvent. The previously reported explanation of a multicomponent effect in 1% (v/v) DMF, based on the assumption that araban is uncharged, is shown to be incorrect by equilibrium dialysis experiments. Titration and sodium analysis indicate a total charge of about 20 per araban molecule, while the limiting slope of the Debye plot of light‐scattering data in low ionic strength solvent indicate an effective charge of 10. Attempts to explain the observed curvature in the Debye plot for araban in low ionic strength buffer on the basis of the Stigter‐Hill method was unsatisfactory, probably due to the inadequacy of the solid sphere‐diffuse double layer model for araban and/or the inapplicability of the Stigter‐Hill virial expansion method at high ratios of macromolecule to salt in low ionic strength solvent. Molecular weight measurements on araban acetate prepared for purification purposes indicate considerable degradation during deacetylation but not during acetylation. This suggests that araban in situ has a molecular weight considerably greater than that observed for the purified araban.
Crystal structure studies on the polymorphic forms of nylons 6 and 8 and other even nylons
Authors: Vogelsong Donald C. 
Published: April 2003

AbstractPolymorphism present in the even nylons has been accounted for in terms of parallel and antiparallel packing of the polyamide chains. Hydrogen bonding appears to play the most important part in governing chain packing. For example, in the antiparallel structure (alternate chains running in opposite directions), complete hydrogen bonding is possible for fully extended planar zigzag nylon chains. In the parallel structure (all chains running in the same direction) complete hydrogen bonding is not possible for the fully extended nylon chains. Hence, the nylon chains twist to satisfy this requirement. This has been shown by interpretation of the x‐ray diffraction pattern of γ‐phase nylon 6. Between nylons 6 and 8 there appears to be a transition between the thermodynamic stabilities of the polymorphic chain packings. Antiparallel chain packing appears to be the common form of nylons 4 and 6. Parallel chain packing appears to be the common form of nylons 8 and 10. Apparently, when sufficient flexibility is given to the even nylon chains by the addition of methylene groups, the twisted chain structure is favored.
Photolytic degradation of poly(methyl methacrylate)
Authors: Fox Robert B. , Isaacs Lawrence G. , Stokes Suzanne 
Published: April 2003

AbstractThin films of poly(methyl methacrylate) (PMMA) at about 25°C. irradiated with a medium‐pressure mercury lamp undergo random scission with a quantum yield of 0.039 and 0.017 scissions/quantum absorbed in vacuum and in air, respectively. Crosslinking in air was not observed. Quantum yields for scission were independent of intensity. Volatile products included methyl formate, methyl methacrylate, and methanol in quantum yields of 0.14, 0.20, and 0.48 molecules per quantum absorbed, respectively. During irradiation in either vacuum or air, the ultraviolet absorption of PMMA increases with a band at 285 mμ, attributed to carbonyl groups in the polymer itself. A mechanism for the photodegradation of PMMA is suggested.
Interfacial polycondensation. XIII. Viscosity–molecular weight relationship and some molecular characteristics of 6‐10 polyamide
Authors: Morgan Paul W. , Kwolek Stephanie L. 
Published: April 2003

AbstractNumber‐average molecular weights were estimated by determination of endgroups on 6‐10 polyamide samples prepared by stirred and unstirred interfacial polycondensation procedures under varying conditions. Polymers made by melt and interfacial polycondensation methods obeyed the same dilute solution viscosity relationships. However, polymers from interfacial polycondensation reactions deviated in molecular weight distribution from that found for polymers prepared by the melt method. The deviation, which presents the appearance of broader than random distribution, is believed to result to a considerable degree from the presence of an unusually large low molecular weight fraction rather than a continuous distortion of the distribution curve. The interfacially prepared polyamides having the highest viscosity numbers, obtained by adjusting the concentration ratios of the two reactants, showed the least deviation from random distributions. Evidence was found for branching and even network formation in 6‐10 polyamide prepared by interfacial polycondensation as the concentration of the diacid chloride phase was increased. Branching probably occurred through acylation of amide links along the polymer chain to yield imide groups. These groups were cleaved to amide groups in the molten polymer or upon solution in sulfuric acid. Melt‐prepared, unfractionated 6‐10 polyamide followed the relationship [η] = 1.35 × 10−4 M̄n0.96, and a κ′ factor of 0.43 was found in the equation relating solution viscosity to concentration, ηnp/c = [η] + κ′[η]2c, for dilute solution determinations in m‐cresol at 25°C.
Crystallite orientation in regenerated cellulose filaments. I. Measurement of orientation by x‐ray methods
Authors: Ellis K. C. , Warwicker J. O. 
Published: April 2003

AbstractThe theory of the fiber diagram has been considered, and it has been shown that Polanyi's theory can be rewritten in terms of the reciprocal lattice and Ewald's construction. By the use of this theory the opacity at a point of an x‐ray diffraction photograph of a fiber has been related to the density of reciprocal lattice points at a point in reciprocal space. The effect of imperfections in the experimental arrangement on the azimuthal intensity distribution in a fiber diagram has been considered and an arrangement has been described with which the distribution of orientation of the crystallites can be obtained from the azimuthal intensity distribution after the application of only two simple conversion factors.
Inhibition kinetics of polymerization of styrene. III. Investigations on the effect of substituted trinitrobenzenes
Authors: Tüdös Ferenc , Kende Imre , Azori Mária 
Published: April 2003

AbstractIn the present paper the effects of substituted derivatives, namely the NH2, OCH3, CH3, Cl, and CO2C2H5 derivatives of s‐trinitrobenzene are described on the initiated polymerization of styrene. The investigations were extended to the determination of the relative reactivity k5/k2 of the inhibitor as well as of the value of stoichiometric coefficient. It was shown by the values of k5/k2 that the Hammett equation can be considered valid within a factor of two. Corresponding to the electron‐donating properties of the employed substituents, the values of the stoichiometric coefficient in crease from 2.7 to 3.8. This fact as well as other data from literature lead to a mechanism by which these values, which are unexpected in the case of molecular inhibitors, can be interpreted.
Cyclopolymerization. I. Structure of polyacrylic anhydride
Authors: Mercier J. , Smets G. 
Published: April 2003

AbstractThe structure of the cyclopolymers of acrylic anhydride has been examined by infrared spectrometry (cyclized units) and by chemical analysis (bromometry for vinyl unsaturation). The infrared analysis was based on the study of the two carbonyl absorption bands at about 1750 and 1810 cm.−1; two types of cyclized hexaatomic anhydrides, different in their stereochemical structure, have been shown to be present. By comparison with the meso and racemic varieties of α,α′‐dimethyl glutaric anhydride, the syndiotactic structure (racemic) has been assigned to the polyanhydride obtained at 35°C. in cyclohexanone. By heating, or in the presence of traces of acid this variety isomerizes into the isotactic form (meso). Pentaatomic cyclized units are formed only by polymerization at high temperatures, e.g., 115°C. (bands at 1780 and 1860 cm.−1). On the other hand, residual unsaturation has always been found on the basis of the vinyl absorption band at 1625 cm.−1; its intensity increases with an increase of monomer concentration during polymerization. The chemical analysis of the cyclopolymers by bromometry makes it possible to evaluate quantitatively the ratio ke/kp of the rate constant of vinyl propagation to that of cyclization; at 35°C. this ratio is equal to 0.17. By analysis of the polymers obtained at 25, 45, and 70°C. it has been demonstrated that the cyclization reaction is enhanced by an increase of temperature; the difference between the activation energies of propagation and cyclization is equal to 2.4 kcal.
Structure of the normal crystal form of polyoxymethylene
Authors: Carazzolo Gian Alvisé 
Published: April 2003

AbstractThe structure of hexagonal polyoxymethylene has been re‐examined by means of x‐rays. The parameters of the elementary cell, the space groups, and the model of the spiral chain previously described in the literature for this polymer have been discussed. A new elementary cell and a new type of helical chain with a higher periodicity have been proposed. The condition of isomorphism for chains belonging to the same lattice, which had already been found in the case of orthorhombic POM, has also been found valid for hexagonal POM.
Mécanisme réactionnel de la polymérisation alcaline des lactames
Authors: Sekiguchi Hikaru 
Published: April 2003

AbstractAs a consequence of objections raised to our interpretation concerning the reaction mechanism of the alkaline polymerization of lactams, we have re‐examined and justified our anionic “lactamolytic” mechanism. The criticism of our opponent is invalidated by mechanisms of analogous reactions, such as the reactions of organometallic compounds and hydrolysis of esters and amides. The opposing mechanism is criticized from a theoretical point of view and disproved by experimental facts which plainly justify our interpretation. The growth mechanism through imide, which consists of a nucleophilic attack of the polarized carbonyl group by the lactam anion, followed by neutralization of the resulting carbinolate ion and opening of the penultimate ring, is thus unequivocally confirmed.
The infrared spectrum of crystalline polysaccharides. IX. The near infrared spectrum of cellulose
Authors: Bassett K. H. , Liang C. Y. , Marchessault R. H. 
Published: April 2003

AbstractThe near infrared region of the spectra of cellulose from about 4000 to 8000 cm.−1 was investigated and assignments made to the absorption bands in this region. Assignments were made on the basis of combinations and overtones of fundamental frequencies and were checked where possible by various chemical and physical sample modifications. The dichroism of all absorption bands in this region was very slight.
Preparation and properties of some poly‐α‐methylstyrenes
Authors: Burge David E. , Bruss Douglas B. 
Published: April 2003

AbstractThe preparation of 20–40 g. quantities of sharply defined fractions of poly‐α‐methylstyrene, for use as standards in the correlation of molecular weight methods, is described. The procedure involves a moderately careful synthesis and fractionation. Differences in the light‐scattering second virial coefficient appear to be indicative of differences in the stereoregularity of the polymers prepared by different initiators. The intrinsic viscosities of all of the polymers studied are expressed by a Mark‐Houwink equation that is the same in all cases.
Electron exchange polymers. XIX. Copolymerization behavior of vinylhydroquinone dibenzoate
Authors: Kamogawa Hiroyoshi , Cassidy Harold G. 
Published: April 2003

AbstractThe copolymerization behavior of vinylhydroquinone dibenzoate monomer (VHDB), in solution under free radical initiator conditions, with styrene, α‐methylstyrene, 4‐vinylpyridine, methyl methacrylate, and methyl acrylate, to less than 10% conversion, showed good copolymerizabilities with these conventional monomers. Rates of polymerization are greater in VHDB‐rich monomer compositions in spite of the bulky character of the benzoyl group. Q‐e values (Alfrey and Price) are given. The resonance term (Q1) for VHDB is near unity, which seems to indicate that the resonance effect in stabilizing the radical is almost as large as that of styrene The polarity term, e1, is assigned a positive value for VHDB. Ultraviolet absorption spectra of the copolymers imply neighboring group interactions in the copolymer chains—interactions implied by the observed Q‐e values, and implied in earlier work by electrometric titration behavior.
Phthalocyanine‐crosslinked polyvinylphthalic acid
Authors: Winslow Eugene C. , Gershman Nancy E. 
Published: April 2003

AbstractCopper phthalocyanine‐crosslinked poly‐4‐vinylphthalic acid was prepared with the expectation that some increased thermal stability could be achieved with these thermally stable linkages. Thermal decomposition in air occurs at about 310°C. The crosslinked polymer proved to be less stable than the starting material, poly(4‐vinylphthalic acid). Analysis shows that an average of one copper phthalocyanine crosslink is formed for every twelve 4‐vinylphthalic acid segmers in the poly(4‐vinylphthalic acid) chain. A new compound, 4‐vinylphthalic anhydride, was produced in this investigation.
Polymeric derivatives of 3,3‐bis(aminomethyl)‐oxetane and of exoxysuccinyl chloride
Authors: Campbell Tod W. , McDonald Richard N. 
Published: April 2003

AbstractTwo monomers, bis(aminomethyl)oxetane (I) and epoxysuccinyl chloride (II)
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have been prepared and converted to condensation polymers, structurally similar to the epoxides. Both monomers were stable and easy to handle. The polymers crosslinked to insoluble, infusible products.