bluuebunny/crossref_metadata_2025_split huggingface dataset:
Melt viscosity of polyethylene at zero shear
Authors: Tung L. H. 
Published: April 2003

AbstractMelt viscosities of polyethylene fractions were measured at low rates of shear in a cone‐and‐plate rotational viscometer and extrapolated to zero shear viscosity. More accurate molecular weight determinations could be made on these fractions since they were free from extra large molecules. Such molecules are known to be present in unfractionated polyethylenes, and they interfere with light‐scattering molecular weight determinations. The zero shear viscosity of both high‐density and low‐density polyethylene was found to obey the equation

where M̄w is the light‐scattering molecular weight. At 165°C. the zero shear viscosities of both types of polyethylene could be correlated by one single equation, but at higher temperatures and more branched low‐density polyethylene has a lower melt viscosity. The activation energy of flow was found to be 7.5 kcal./mole and 14.6 kcal./mole for high‐density and low‐density polyethylene, respectively. This difference activation energy is attributed to long‐chain branches in low‐density polyethylene rather than short‐chain branches. A discrepancy was observed between molecular weights of many high‐density polyethylene fractions determined by light‐scattering methods and the molecular weight of the same fractions calculated from inherent viscosity using a known intrinsic viscosity–molecular weight relationship. Examination of the data showed that the existence of a small amount of long‐chain branches in these high‐density polyethylene fractions was the probable explanation for this discrepancy.
Bulk polymerization of isoprene: Kinetic constants from the dead‐end theory
Authors: Gobran R. H. , Berenbaum M. B. , Tobolsky A. V. 
Published: April 2003

AbstractThe dead‐end radical polymerization theory of Tobolsky was applied to the bulk polymerization of isoprene. 2‐Azobisisobutyronitrile and benzoyl peroxide were used as initiators in the temperature range 60–90°C. Isoprene shows a dead‐end conversion under all the conditions we used. No Tromsdorff effect was observed in this system. The rate of decomposition of each initiator (kd)at different temperatures was obtained solely from the conversion‐time curve without further assumptions. The kd values thus obtained agree well with published data based on other methods. Knowing kd it was possible to compute (kp/k)f1/2, where kp is the specific rate of propagation, kt the specific rate of termination, and f the efficiency of the initiator. This allowed comparison of the efficiency of benzoyl peroxide with 2‐azobisisobutyronitrile as free‐radical initiators in the bulk polymerization of isoprene. kp/k values for the azo‐initiated polymerization were also obtained and were found to be much lower for isoprene in comparison to reported values for styrene or methyl methacrylate. The high values of kp/k found for isoprene explain the low conversions obtained when isoprene is polymerized in bulk. From reported values of kp it was possible to calculate kt. This is the first time where the specific rate of termination of isoprene is reported. The rate constant kt was found to be 1.34 × 108 liters/mole‐sec. and is independent of temperature in the range 60–90°C. High kt values account for the low molecular weights obtained during the bulk polymerization of isoprene. The theory was also used to predict the course of isoprene polymerization as a function of time using previously determined values of (kp/k)f1/2 and kd for the initiator used. The entire course of the conversion curves are well reproduced. The molecular weight distribution is also predicted as a function of conversion.
Viscosity–molecular weight relationship for polyvinyl acetate
Authors: Matsumoto Masakazu , Ohyanagi Yasuzi 
Published: April 2003

AbstractThe relationship between limiting viscosity number and molecular weight of PVAc was determined and compared with the results by several authors. Samples of lowconversion PVAc were used. The weight‐average molecular weights were determined by a light‐scattering method and the number‐average molecular weights by endgroup determinations and the osmotic pressure method. From those experiments, it was proved that the ratio M̄w/M̄n for low conversion PVAc is equal to 2, as expected by theory. The relationships obtained are the following: [η] = 1.02 × 10−2 Mw0.72 (in acetone); [η] = 1.07 × 10−2 Mw0.71 (in MEK); [η] = 3.14 × 10−2 Mw0.6 (in methanol); and [η] = 9.20 × 10−2Mw0.5 (in a ⊖ solvent)where [η] is expressed in milliliters per gram and a mixture of methyl isopropyl ketone (72.7 vol‐%)and n‐heptane (27.3 vol.‐%)was chosen as the ⊖ solvent. These relationships were converted to relationships for perfectly homogeneous fractions. The relationship in acetone, [η] = 1.08 × 10−2 M0.72, was compared with literature data after the latter were converted to data corresponding to perfectly homogeneous fractions in acetone at 30°C., and was found to be in good agreement. Mean‐square radii of gyration, 〈S2〉, and second virial coefficients, A2, of PVAc were also determined in the acetone and methyl ethyl ketone solutions and the results compared with literature values.
Idealized helical stereospecific polymerization
Authors: Ham George E. 
Published: April 2003

AbstractThis paper presents a mechanism for ascribing the observed stereoregular effects of certain polymerizations to helical stereospecific polymerization. The potential energy “sink” inherent in helical addition of monomer to a growing chain is taken as the controlling factor in such polymerizations. Two combinations, ∼mdmdmd− and ∼mlmlml− out of the eight possible random combinations of three units of two isomers, are presumed to be capable of sustained helical polymerization; the rest are not and are presumed unlikely to become fertile based on the disorder inherent in an atactic chain. With this assumption of idealized helical polymerization as a basis various conclusions may be drawn concerning isotactic‐atactic ratio, molecular weights of each portion, and degree of isotacticity of “isotactic” polymer.
High pressure polyethylene molecular dimensions as estimated from solution properties of whole polymers
Authors: Mendelson Robert A. 
Published: April 2003

AbstractSolution light scattering, osmotic pressure, and viscosity measurements at elevated temperatures in non‐ideal solvents were performed to characterize the M̄w's, M̄n's, mean‐square end‐to‐end distances, and second virial coefficients, of seventeen whole polymer samples of high pressure polyethylene (HPPE)and of five fractions of one of these whole polymers. The data were treated to eliminate the effects of excluded volume and of polydispersity on the molecular dimensions. As a measure of unperturbed chain extension, values of (〈R̄02〉wM̄w)1/2 and (〈R̄02〉w/〈R̄0f2〉)1/2 were calculated, where 〈R̄0f2〉 refers to a free rotational polymethylene chain. To estimate the extent of long‐chain branching, values of 〈R̄0f2〉 and [η]θ were calculated from literature equations for low pressure polyethylenes having molecular weights corresponding to those of the high pressure samples. This study confirms previous investigators' observations that HPPE polymers may have extremely broad molecular weight distributions. Considerably extended molecular configurations were observed in a number of instances. Clear evidence from the fractions studied indicates that branching increases with increasing molecular weight in a given polymer. It is considered that serious undercorrection occurs in 〈R̄02〉 for very broad distribution samples due to the distribution function used. This factor plus conflicting hydrodynamic theories do not permit quantitative evaluation of extent of branching; however, variation from essentially unbranched (long‐chain)to highly branched HPPE samples was observed.
Morphology of an acetal resin
Authors: Geil P. H. 
Published: April 2003

AbstractLamellae are basic structural elements of the acetal resin, polyoxymethylene. Lamellae, similar to those observed after precipitation of polymer single crystals from solution, are found both in the interior and on the surface of samples crystallized from the melt. Lamellae crystallized from the melt are organized into spherulites or hedrites. The latter are hexagonal structures, several microns thick, grown by slow crystallization of thin films. The thickness of the hedrite depends directly on the crystallization temperature and only indirectly on the thickness of the original film. New lamellae originate at screw dislocations on previously established lamellae at the centers of both spherulites and hedrites, as well as on the periphery of growing spherulites. A mechanism based on these observations is postulated for the crystallization of polyoxymethylene from the melt.
The effect of gamma radiation on the structure of pectin. An electrophoretic study
Authors: Skinner E. R. , Kertesz Z. I. 
Published: April 2003

AbstractCitrus pectin irradiated in the dry state with gamma‐radiation doses up to 2,056 Krad (2,056,000 rad) was studied by moving boundary electrophoresis in acetate buffer. The results showed that no extra components are produced upon irradiation and that there is no change in the mean mobility of the pectin boundary or in the mobility distribution about the mode. The heterogeneity constant, calculated from the rate of increase of standard deviation of the mobility curve, showed little change at doses up to 205 Krad, but at 528 and 2,056 Krad there was a large increase. The specific viscosity decreased with radiation dosage. These results indicate that the effect of radiation is to produce random hydrolytic fissure of the glycosydic linkages along the length of the pectin molecule. The increase in heterogeneity constant is explained on the basis of the fragments having slightly wider distribution in charge to mass ratio according to the location of the fissure in relation to the free carboxyl groups. The hydrolytic fissure results in a lower weight‐average molecular weight of which specific viscosity is a function. This process also results in a wider distribution of the charge to mass ratio, proportional to the heterogeneity constant. That the two measurements are related is shown by the fact that their product is approximately constant. The constancy of the mobility of the pectin boundary and the lack of any gross change in the electrophoretic properties precludes the occurence of changes such as deesterification which would alter the charge on the pectin molecule.
Infrared spectra of crystalline and stereoregular polymers. II. Carbon—hydrogen and carbon—deuterium stretching frequencies of polypropylene and deuterated polypropylenes
Authors: Liang C. Y. , Lytton M. R. , Boone C. J. 
Published: April 2003

AbstractThe polarized infrared spectra of polypropylene, poly(propylene‐1,1‐d2), poly(propylene‐2‐d), and poly(propylene‐3,3,3‐d3) in the carbon—hydrogen and carbon—deuterium stretching regions were observed and interpreted. The A and E components of each stretching mode were found to be at the same frequency. The polarization of both CH2 and CD2 symmetric stretching bands was observed to be weakly parallel. This observation would probably imply that the bisector of the HCH or DCD angle makes an angle somewhat less than 54° 44′ with the helical axis. The tertiary CH stretching frequency was found at about 2920 cm.—1. The two antisymmetric CH3 (or CD3) stretching frequencies were resolved in the polarized spectra of the polymers. From this infrared study, it is suspected that poly(propylene‐3,3,3‐d3) may have a different structure than the other polypropylenes used in this work.
The interaction of poly(vinyl pyrrolidone) with cosolutes
Authors: Eliassaf J. , Eriksson F. , Eirich F. R. 
Published: April 2003

AbstractThe interaction of poly(vinyl pyrrolidone) with a series of cosolutes has been studied by means of viscosity, solubility, dialysis, and electrophoresis methods. The cosolutes comprise a number of mono‐ and divalent acids and their salts, and most of the natural amino acids. It is found that appreciable interaction occurs with divalent acids and salts, with hydroxy acids, aromatic acids, and with amino acids which possess either aromatic or other ring structures. The interactions are probably related to a saltingout process, and a qualitative mechanism is suggested which accounts for the observed charge and specific effects in terms of dielectric attraction and repulsion between the cosolute anion and the pattern of polar and nonpolar sections of the PVP molecule.
Finite deformation and tensile strength of polystyrene and polyethylene solids
Authors: Hsiao C. C. 
Published: April 2003

AbstractFor samples of amorphous polystyrene and partial crystalline polyethylene, the fracture strengths for different degrees of uniaxial flow deformation are determined and are found to agree fairly well with theoretical predictions. For hard polymers, the effect of uniaxial deformation upon the tensile breaking stress of a simplified model solid is discussed. The fracture strength in any direction of this model material may be determined by obtaining the expectation of the strength components of a system of perfectly oriented model elements in that direction.
The non‐newtonian viscosity of polymers in relation to their molecular conformation
Authors: Passaglia Elio , Yang Jen Tsi , Wegemer Norman J. 
Published: April 2003

AbstractThe non‐Newtonian viscosities of polystyrene and polyisobutylene were measured in various solvents over a wide range of shearing stress, τ (up to the order of 104 dynes/cm.2). The shear dependence of the intrinsic viscosities, [η], is closely related to the molecular extension of the polymers. The non‐Newtonian behavior of a polymer is greatest in a “good” solvent and least at Flory's Θ temperature. The maximum percentagewise drop in the intrinsic viscosities at highest attainable shearing stress was found to increase with increasing root‐mean‐square end‐to‐end distance, 〈r2〉1/2, of the polymer chains in “good” solvents. By plotting [η]τ = ∞/[η] τ = 0 against 〈r2〉1/2 / 〈rof2〉1/2(where 〈rof2〉1/2 is the theoretical 〈r2〉1/2 assuming free rotation about the chemical bonds of the polymer chains), the shear dependence of the intrinsic viscosities appeared to be absent when 〈r2〉1/2 / 〈rof2〉1/2 was extrapolated to unity. Furthermore, polymer having different degrees of chain stiffness seemed to form a composite curve in the plot, where the stiffer chains exhibited the most drastic drop in the intrinsic viscosities. Additional support was given with the experimental results of polydimethylsiloxane and cellulose triacetate solutions.
Structural transformations in poly‐L‐proline
Authors: Sasisekharan V. 
Published: April 2003

AbstractThe structural transformations in poly‐L‐proline as revealed by x‐ray‐diffraction and optical‐activity studies are discussed. It is shown that the polymer can exist in many forms depending upon the solvent used and the way in which the precipitates were obtained. Only three forms were found to be important, and they are designated in this paper as I, IA, and II. The conditions under which these forms undergo interconversion are dealt with. The possible structures of the forms IA and I are also discussed.
The reaction of phosphorus trichloride and oxygen with polymers
Authors: Schroeder J. P. , Sopchak W. P. 
Published: April 2003

AbstractPhosphorus trichloride and oxygen react readily with polyethylene to introduce phosphonic dichloride (—POCl2) groups into the polymer (chlorophosphonation). Treatment of the resulting intermediate with water, alcohols, and amines yields polymeric alkylphosphonic acids, esters and amides, respectively. Derivatives containing as much as 16% phosphorus have been prepared. With increasing degree of phosphonation, polyethylene crystallinity is reduced, the acid and amide derivatives become stiffer, less extensible, and less soluble in nonpolar solvents, and internal plasticization is observed in the ester derivatives. No significant decrease in flammability is effected by phosphonation unless chlorine is introduced also. The ester and amide derivatives crosslink under mild conditions by an unknown mechanism, the acid derivative will crosslink on heating with litharge. The chlorophosphonation reaction is sensitive to inhibitors and no highly active catalyst was found. The rate appears to be governed by the rate at which oxygen dissolves in the mixture. Substitution of air or chlorine for oxygen, phenyldichlorophosphine or diphenylchlorophosphine for phosphorus trichloride results in introduction of phosphorus‐containing groups into polyethylene, also, but at reduced rates. In sharp contrast to polyethylene's apparent stability toward the phosphonation conditions, polystyrene, poly(methyl methacrylate), and polyisobutylene undergo a rapid decrease in molecular weight on treatment with phosphorus trichloride and oxygen. The fact that these four polymers exhibit the same relative behavior, i.e., polyethylene is stable whereas the other three polymers are unstable, in various free radical processes argues for a free radical mechanism in the chlorophosphonation reaction.
Novel types of chain reactions in polymer degradation
Authors: Grassie N. 
Published: April 2003

AbstractThe polymer chain environment in which polymer degradation reactions occur often confers to these reactions interesting new features which would not be predicted by direct comparison with the behavior of model compounds. In particular, reactions can involve rather novel types of chain mechanisms which may be radical or molecular processes. The nature of these reactions is illustrated by reference to the depolymerization of polymethacrylates, ester decomposition reactions in polyvinyl acetate, polyvinyl chloride, and polymethacrylates, and the coloration reaction which occurs in polyacrylonitrile and polymethacrylonitrile.
Intramolecular‐intermolecular polymerization of nonconjugated diolefins
Authors: Marvel C. S. 
Published: April 2003

AbstractThe literature dealing with the formation of cyclic recurring units in the polymerization of nonconjugated dienes by an intramolecular‐intermolecular polymerization mechanism is reviewed. Carbocyclic rings and heterocyclic rings containing oxygen, nitrogen, phosphorus, silicon, and tin are considered.
Polymérisation du formaldehyde amorcée par les radiations ionisantes
Authors: Chachaty Claude , Magat Michel , Minassian Leon Ter 
Published: April 2003

AbstractLa polymérisation du formaldéthyde par irradiation aux rayons γ et X a été étudiée dans une zone de température comprise entre −75° et −196° principalement par la méthode de l'analyse thermique. Les doses de rayonnement utilisées bien qu'inférieures en général á 2000 roentgens conduisent à des taux de conversion élevés. Aux températures les plus basses étudiées, la polymérisation prend une allure explosive soit au réchauffcment, soit au cours měme de l'irradiation selon la dose de rayonncment. Ce type de polymérisation a été interprété en fonction d'un échauffement interne dû à l'accumulation des chaînes croissantes. La théorie des explosions thermiques montre en effet qu'une augmentation de quelques degrès de la température interne par rapport ǎ la température extérieure au milieu réactionnel sufit à provoquer l'explosion. On a pu en déduire une énergic d'activation de réaction de l'ordre de 3 Kcal/mole. Aux températures supérieures, la polymérisation peut s'établir en régime thermique stationnaire car les chaînes s'amorcent et se terminent au cours même de l'irradiation.
Stereospecific polymerizations
Authors: Natta C. 
Published: April 2003

AbstractRecent results of investigations of stereospecific polymerizations are reported. Butadiene polymers very high in cis‐1,4 content have been obtained through polymerization in the presence of soluble catalysts prepared from compounds of group VIII metals, cobalt in particular, and from dialkylaluminum monohalides. The polymers thus obtained have higher melting temperatures and better elastomeric properties than those of cis‐1,4 polybutadienes of lower steric purity.Two types of butadiene polymers having 1,2 enchainment and isotactic or syndiotactic structure may be prepared in the presence of soluble catalytic systems prepared from trialkylaluminum and complexes of chromium or vanadium. A great number of nonhydrocarbon monomers have also been polymerized stereospecifically, in the presence of catalysts acting in homogeneous phase. Metallorganic compounds of magnesium act as stereospecific catalysts for the polymerization of 2‐vinylpyridine, with production of crystalline isotactic polymers. Crystalline isotactic polymers of acetaldehyde have been prepared by polymerization at low temperature with the use of metallorganic compounds such as alkylaluminum and alkylzinc as catalysts. Aldehydes higher than acetaldehyde have also been polymerized stereospecifically with catalysts that act usually with a cationic mechanism, such as aluminum bromide. The crystalline structure and the crystalline helical chain conformation of a great number of these polyaldehydes have been determined. A chemical mechanism for this polymerization, which makes clear the stereospecificity of the process even in the presence of soluble catalysts, has been proposed. Stereospecific catalysts have been prepared from compounds of amides with very electropositive metals. In the presence of TiCl3, these catalysts promote the stereospecific polymerization of propylene to isotactic polymer, whereas, as such, they furnish crystalline polymers of acrylates, methacrylates, and 2‐vinylpyridine. The nature of the terminal groups of the polymers establishes the fact that the polymerization occurs with an anionic mechanism. The mechanism of the stereospecific polymerization of α‐olefins is discussed, and further evidence is given confirming the previously hypothesized anionic coordinated mechanism. The factors determining stereospecificity are also discussed; it is concluded that when a group rich in electrons in addition to the polymerizable double bond is present in the monomer, stereospecific polymerization may take place in the presence of catalysts acting in homogeneous as well as heterogeneous phase. In these cases, stereospecificity must be ascribed to the coordination of the monomer to the catalyst, which results in a constant mode of presentation of the monomer to the growing chain, and to a constant type of opening, cis or trans, of the polymerizable double bond. For the polymerization of propenyl ethers to di‐isotactic polymers, we established that this opening is of the cis type.
Mécanisme réactionnel de la polymérisation anionique des lactames
Authors: Champetier Georges , Sekiguchi Hikaru 
Published: April 2003

AbstractComme suite à nos études sur la polymérisation catalytique (anionique) de l'α‐pyrrolidone, nous proposons une interprétation du mécanisme réactionnel de la polymérisation catalytique alcaline des lactames. En admettant trois sortes de réactions lactamolytiques entre les amides et l'anion lactame, et trois sortes de réactions aminolytiques entre les amides et l'amine terminale du polymère, suivant la nature des amides: amide cyclique (de la lactame), amide cyclique N‐carbonylée ou imide (du motif terminal de la macromolécule) et amide linéaire (du polymère) et en supposant une réactivité égale pour les deux amides non N‐carbonylées, et une réactivité notablement plus grande pour l'amide N‐carbonylée, il est possible de traiter mathématiquement la cinétique de la polymérisation et d'obtenir un bon accord avec les résultats expérimentaux. L'équilibre entre les amides cyclique et linéaire, ainsi que l'équilibre entre les chaînes, se trouvent bien expliqués par notre théorie. L'étude de la polymérisation en présence d'un initiateur tel que la N‐acyl‐lactame, conduit à penser que la concentration de l'amine et celle du groupement terminal lactame N‐carbonylée dominent l'équilibre entre les chaînes de longueurs différentes, ce qui justifie notre interprétation du mécanisme.