bluuebunny/crossref_metadata_2025 huggingface dataset:
The study of the polydispersity of polymers by viscometry
Authors: Lundberg J. L. , Hellman M. Y. , Frisch H. L.
Published: April 2003

A viscometric polydispersity index may be calculated by forming the ratio of the viscosity‐average molecular weights of a polymer in a relatively good solvent and in a relatively poor solvent and subtracting 1. This index has been examined by measuring dilute solution viscosities of a polydisperse polystyrene and a polydisperse methyl methacrylate in a variety of solvents, calculating viscosity‐average molecular weights using Mark‐Staudinger‐Houwink equations, and forming the viscometric polydispersity indices. These are compared to Schulz parameters, weight‐average–number‐average molecular weight ratios minus 1, determined from osmotic pressure and light scattering. Viscometric polydispersity indices are more sensitive to polydispersities than expected when compared to Schulz parameters if account is taken of the differences in the powers of molecular weight in the various molecular weight sums. Viscometric polydispersity indices are examined for other polymers, including an almost monodisperse polystyrene. From these measurements it is concluded that the viscometric polydispersity index is valuable for characterizing the polydispersity of polydisperse linear polymers and rough fractions. The weight‐average–viscosity‐average polydispersity index is more sensitive than the viscometric polydispersity index and may be used to characterize relatively monodisperse linear polymers.
Equilibrium polymerization of selenium
Authors: Eisenberg Adi , Tobolsky Arthur V.
Published: April 2003

A theory of the ring‐chain equilibrium in liquid selenium is presented which is mathe‐matically identical to our theory for polymer equilibrium in liquid sulfur. The numerical treatment is based on: (a) the entropy and enthalpy of the propagation reaction (Sen* + Se8 ⇌ Sen+8*, the asterisk denoting a diradical) which were calculated from values of the Se8 concentrations in the liquid as given in the literature, and (b) the entropy and enthalpy of the initiation reaction (Se8 ⇌ Se8*) which were estimated by comparison to the sulfur values. The “transition” temperature for the appearance of polymer in the liquid state is calculated as 83°C. (134° below the melting point of selenium), and the chain length at the melting point is estimated as ca. 1300 Se8 units.
Local regularity of chain substances. II
Authors: Miyake Akira
Published: April 2003

The eigenvalue method of introducing a virtual boundary energy, examined in the previous article, is extended to take account of next nearest neighbor interactions. To discuss the stereospecific polymerization of the vinyl polymer, an energy −K is assumed for every two consecutive L‐configurations, besides the energy difference J between the H‐ and L‐configurations. To discuss the helix–random coil transformation in synthetic polypeptide chains, a hydrogen‐bonding energy −K is assumed between the first and the fourth monomers to every three successive L‐configurations, and three or more than three successive L‐configurations are regarded as making a helix part, a random coil region being formed otherwise. We can see that the more the value of J/K, the more rapid is the transformation.
A contribution to the study of random degradation of chain polymers
Authors: Mejzler D. , Schmorak J. , Lewis M.
Published: April 2003

A uniform rigorous mathematical treatment is presented for the random degradation of chain polymers, including the three fundamental initial states, viz., (a)a finite single chain (b)a number of chains of equal length, and (c)a number of chains of varying lengths. Limiting expressions are derived for the number fraction and weight fraction of chains of a given degree of polymerization, theoretically obtainable for a given degree of degradation in all three cases. The stochastic approach is employed for the derivation of the mathematical expression for the degree of degradation as function of time. It is assumed in the derivation that the probability P that a given bond still unbroken at the time t will break in the time interval between t and t + Δt is of the form P = φ(t)Δt, where φ(t)is not necessarily a constant. Instead of the well known formula α(t)= 1 − exp { − kt} an empirical formula α(t)= 1 − exp { − ktm} is proposed; this formula includes the former as' a special case (when φ(t)= const.), and is shown to better fit the experimental results obtained in studies on the degradation of cellulose and of polystyrene solutions.
On the characterization of stereoregular polymers. I. Theory
Authors: Miller Robert L. , Nielsen Lawrence E.
Published: April 2003

Through an extension of a generalized copolymer theory, a mathematical description of the chain structure of homopolymers (whether stereospecific or not)has been obtained, relating distributions of sequences, sequence lengths, and bonds formed to the kinetics of the propagation step in the polymerization reaction. Existence of stereoblock structures is accounted for by the model and chain structural details sensitive to directing influences (such as the so‐called “penultimate” monomer effect or the catalyst surface)are predicted. It has been shown that in the general case, knowledge of at least two independent parameters is required to characterize the chain structure. The tacticity definitions currently used have been shown to have simple mathematical expressions and to be equivalent and interchangeable.
A theory of the thermodynamic behavior of nonelectrolyte solutions. IV. Application to low molecular weight systems
Authors: Maron Samuel H. , Wang Mei‐Mei , Nakajima Nobuyuki
Published: April 2003

A study has been made to show that Maron's theory of the thermodynamic behavior of nonelectrolyte solutions is applicable to systems with low molecular weight solutes as well as polymers. In this connection were investigated three systems of varying degrees of complexity, namely: (1)carbon tetrachloride–cyclohexane, (2)acetone–chloroform, and (3)water–ethyl alcohol. The first of these systems yields a small positive interaction parameter μ which is essentially independent of volume fraction v2 but which decreases with temperature T. On the other hand, the system acetone–chloroform gives μ's which are large, negative, and strongly dependent on both T and v2. Similarly the system water–ethyl alcohol yields μ's which vary with both v2 and T, but in this case they are large and positive. The relations deduced for the μ's as a function of T and v2 reproduce very satisfactorily the available thermodynamic data for these systems. A discussion is also given of the significance of the observed interaction parameters.
Thermoelasticity of open systems
Authors: Oplatka A. , Michaeli I. , Katchalsky A.
Published: April 2003

The thermoelastic properties of contractile open systems, in equilibrium with an external bath containing permeating components, are related to those of the corresponding closed systems, in terms of two isothermal parameters, the change of the degree of swelling with elongation and the isometric enthalpy of dilution of the swollen contractile phase. The thermodynamic analysis is applied to evaluate the thermoelastic properties of the Flory‐Rehner model for swollen rubber, and experimental results from the literature are discussed.
Melt viscosity of polyethylene at zero shear
Authors: Tung L. H.
Published: April 2003

Melt 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

The 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

The 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

This 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

Solution 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

Lamellae 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

Citrus 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

The 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

The 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

For 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

The 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

The 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

Phosphorus 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

The 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

The 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

La 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

Recent 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

Comme 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.
Photopolymerization of acrylamide. I. Formation of the initiating redox system
Authors: Delzenne G. , Toppet S. , Smets G.
Published: April 2003

The photopolymerization of acrylamide in aqueous solution can be sensitized by various dye–reducing agent systems. The reaction is initiated by free radicals produced during the decomposition, in the presence of reducing agents, of hydrogen peroxide. This substance is formed during the reoxidation reaction by the oxygen present in the solution of the leuco derivative or the semiquinone which are produced in the photoreduction of the dyes. The formation of hydrogen peroxide during the photoreduction of dyes in the presence of oxygen has been demonstrated polarographically for the following systems: tetrabromofluorescein (eosin), 3,6‐diaminoacridine (acriflavin), 3,6‐bis(dimethylamino)acridine (acridine orange) as dyes and l(+)‐ascorbic acid or thiourea as reducing agents.
The structures and reversible polymerization of cyclic oligomers from poly(ethylene terephthalate)
Authors: Goodman I. , Nesbitt B. F.
Published: April 2003

Poly(ethylene terephthalate) prepared or fabricated by melt processes is shown to contain about 1.5% of extractable, oligomeric material composed mainly of cyclic ethylene terephthalates which exist, at high temperatures, in equilibrium with the molten polymer. An ester interchange‐elimination reaction is proposed as the main route of formation of these compounds. An additional minor component of the polymer, produced by side reactions, is the mixed cyclic bisterephthalate of ethylene and 3‐oxapentamethylene glycols. This compound, together with cyclic bis(3‐oxapentamethylene terephthalate) is also formed in the forced thermal depolymerisation of ethylene/3‐oxapentamethylene terephthalate copolymers.
Greffage sur polychlorure de vinyle par préozonisation
Authors: Landler Y. , Lebel P.
Published: April 2003

Une bréve discussion est faite au sujet du greffage de monomères polymérisant par un mécanisme radicalaire au départ d'un tronc polymérique préalablement ozonisé, sujet déjà décrit précédemment par de nombreux auteurs. Dans le présent travail, une étude détaillée a été faite dans le cas particulier du greffage sur le chlorure de polyvinyle. On considère séparément le comportement du chlorure de polyvinyle obtenu par polymérisation en suspension et soumis à l'action de l'ozone à l'état sec. Tout d'abord on a étudié la vitesse d'ozonisation en fonction de la durée du processus, ce qui a permis de préciser ce que l'on peut attendre de conditions variées d'ozonisation. Ensuite on a étudié la cinétique de décomposition thermique du chlorure de polyvinyle ozonisé à
diverses températures. Les variations de poids moléculaire du PVC ont été suivies en fonction des conditions d'ozonisation et des conditions de dégradations du polymère ozonisé, à savoir, sous vide en présence d'oxygètne, ou en présence d'un inhibiteur de radicaux libres. Le comportement du PVC à l'égard de l'ozone et le comportement thermique du polymère ozonisé ont montré que le polymère subit aisément l'ozonisation et que les groupes formés sont thermolabiles. L'ozonisation et la décomposition ultérieure des groupes peroxydiques ne sont pas accompagnées d'une dégradation considérable de la chaîne macromoléculaire. Le PVC est un substrat excellent pour le greffage par ozonisation préliminaire. Les vitesses de polymérisation de divers monomères éthylèniqiies en présence du PVC ozonisé comme initiateur ont été étudiées. Les résultats obtenus ont été examinés du point de vue de la réactivité relative des divers monomères. L'effet du milieu a également été étudié. De cette manière divers polymères greffés de composition très variable ont été obtenus. Ainsi certains copolymères qui ne peuvent être obtenus par simple copolymérisation radicalaire ont été préparés, par exemple, des copolymères de styrène et de chlorure de vinyle. En variant les conditions d'ozonisation et de décomposition des groupes peroxydiques fixés sur le polymère, une grande variété de produits de composition et structures diverses a pu être obtenue. Ce travail est limité à la synthèse de copolymères greffés à base de PVC. Une étude détaillée des diverses propriétés en fonction de ces facteurs, fera l'objet de publications ultérieures. Les auteurs remarquent qu'une modification des propriétés du PVC est causée par l'incorporation de groupes étrangers au moyen du greffage.
A kinetic study of the mild oxidation of wheat starch by sodium hypochlorite in the alkaline pH range
Authors: Schmorak J. , Mejzler D. , Lewin M.
Published: April 2003

(1) Some kinetic aspects of mild oxidation of wheat starch by sodium hypochlorite in the pH range 7.5–11.0 were studied. (2) No significant chlorate formation was observed at any time. From this and from other experimental evidence it is concluded that the reaction is most likely to be purely chemical in type and to proceed according to the overall scheme:

(3) The reaction appears to be of the first order with respect to starch. (4) The reaction appears to be of the first order with respect to hypochlorite at pH = 8.0. At pH = 9.0 and 10.0, the reaction velocity is still approximately proportional to the concentration of the oxidant present, but the course of the reaction appears to be more complicated. (5) The reaction rate decreases with increasing pH of the oxidizing medium. An approximate empirical equation is proposed adequately representing the interdependence of the first‐order constant and pH in the pH range 7.5–10.0. (6) The activation energy of the reaction is within the range of 21–23 kcal./mole, i.e., that obtained for many homogeneous, truly chemical reactions. (7) The fact that the reaction rate of a starch solution is about 50% higher than the corresponding rate for a starch suspension would seem to indicate that the number of sites available for oxidation in a granule is about two‐thirds of that available when that granule is dissolved. (8) The addition of neutral salts had an accelerating effect on the reaction rate. Under the experimental conditions of the present paper, this effect was negligible, but at much higher salt concentrations it would have to be taken into account.
The effect of C‐substitution of caprolactam on the ring‐opening polymerization reaction
Authors: Wolinski L. E. , Mighton H. R.
Published: April 2003

Caprolactam was modified with alkyl groups of various sizes and in different positions on the ring. The resulting substituted caprolactams were polymerized and the comparative degree of polymerization was used as a measure of the inhibiting effect of the substituting group. There was less inhibition on substitutions in 5‐ and 7‐positions than in the 4‐ and 6‐positions. The order of increasing inhibition of alkyl groups was methyl, ethyl, n‐propyl, isopropyl, cyclohexyl, tert‐butyl and gem‐dimethyl.
Isomorphous replacement in a copolyamide system
Authors: Levine M. , Temin S. C.
Published: April 2003

In a study of isomorphic behavior, it was found that the melting point—composition curve of the copolyamides prepared from caprolactam and p‐aminomethylcyclohexylcarboxylic acid was sigmoidal, indicating that the methylcyclohexyl group was interchangeable in the crystal lattice with aliphatic carbon atoms of ω‐aminocaproic acid. On the other hand, the benzyl group in the copolymers of caprolactam and p‐aminomethylbenzoic acid did not interchange as well, and only partial isomorphism occurred. The analogous meta derivatives, m‐aminomethylcyclohexylcarboxylic acid and m‐aminomethylbenzoic acid, did not fulfill the spatial requirements of caprolactam. Although V‐shaped melting point—composition curves resulted, the disturbance in the crystal network was more severe with the m‐phenyl derivative than with the m‐cyclohexyl derivative.
Radiation grafting of allylic monomers to solid polymeric substrates
Authors: Zimmerman J.
Published: April 2003

The kinetics of grafting of allylic monomers to a solid polymeric substrate are compared with those for normal vinyl monomers which have been treated in a previous paper. The particular case treated theoretically for both types of monomers (using well established basic principles) is the sequence where the polymer is soaked in a solution of the monomer, the excess monomer is removed from the surface, the polymer is then irradiated at −78°C. at a high dose rate, and the system subsequently allowed to condition at 25°C. under an oxygen free atmosphere. It was previously shown theoretically that with a normal vinyl monomer in a very viscous matrix, the conversion of monomer to polymer increases indefinitely with post‐irradiation time and that radiation dose and post‐irradiation time are interchangeable in the absence of inhibitors. It is shown here that under similar conditions with allylic monomers, the existence of degradative chain transfer to the monomer places a definite limit on the maximum conversion and makes this conversion quite dependent on dose. The theory for the case involving degradative chain transfer is applied to data on the grafting of itaconic acid to 66 nylon and values are deduced for the ratio of transfer to propagation constants and transfer to termination constants. Lower limits for the absolute values of these constants are also deduced. The ratio of propagation kp and termination kt rate constant in this very viscous medium is kp/2kt = 0.58.
The ionic polymerization of cyclic olefins using optically active gegen ions
Authors: Schmitt G. J. , Schuerch C.
Published: April 2003

The cyclic olefins 4, 5‐dihydro‐2‐methylfuran, indene, 1‐methylcylcopentene, and αhyphen;angelica lactone were polymerized using catalyst‐cocatalyst complexes of boron triflu‐oride with asymmetric Lewis bases. Various conditions of temperature and dielectric constant of the media were employed but in no case was optical activity observed in the polymers produced. The stereochemistry of the addition polymerization of cyclic olefins is discussed and it is proposed that a thermodynamically preferred trans‐trans addition may predominate over any asymmetric inductive effect to yield an internally compensated polymer. The anionic polymerization of 1‐cyanocyclopentene is also described.
Twisting of bundles of bacterial cellulose microfibrils
Authors: Colvin J. Ross
Published: April 2003

The majority of, but not all, bundles of bacterial cellulose microfibrils show a characteristic left‐handed twist which has a pitch of about 1 μ. The remainder show no apparent coiling. The twist must reflect an internal strain in the component microfibrils which may be due to a slight progressive molecular asymmetry in the way in which glucose residues are incorporated into the microfibril.
The scission step in hevea oxidation
Authors: Bevilacqua E. M. , English E. S.
Published: April 2003

Three recent attempts to formulate a reaction mechanism for scission during the oxidation of rubber have been evaluated with respect to their predictions concerning the formation of formic acid and the step at which scission occurs. Two do not account directly for formic acid as a principal product or for the failure of antioxidants to influence scission yield. The third, while consistent with available evidence, does not predict the observed product distribution as a necessary consequence of decomposition of the postulated intermediate.
Thermodynamics of crystalline linear high polymers. I. Comparison of the melting transitions of solution and melt‐crystallized polyethylene
Authors: Wunderlich Bernhard , Kashdan W. H.
Published: April 2003

Differential thermal analysis (DTA) of the melting range of annealed and solution‐crystallized low‐pressure polyethylene (Marlex 50) has been carried out and found to be comparable in precision with earlier calorimetric determinations. The melting range of the single‐crystalline material is shifted by 3.7°C. to lower temperature with respect to the melt‐annealed polyethylene. Heat of fusion estimates from the peak height and area of the DTA curves as well as density determinations gave a ratio of about 1.08 for the crystallinities of annealed and single‐crystalline polyethylene. The per cent crystallinity calculated from density for annealed polyethylene was found to be 90 ± 3, which is in good accord with calorimetric and x‐ray determinations.
Oxyluminescence from polypropylene
Authors: Ashby G. E.
Published: April 2003

Several polymers emit light when heated in the presence of oxygen. Experimental observations are made concerning the light from polypropylene. The portion of light detectable with a RCA‐5819 photomultiplier tube is blue‐violet in color. When polypropylene is at 180°C. the wavelengths of the light are between 3000 and 5150 A. The intensity of the light is determined by the temperature of the polymer, the concentration of oxygen in contact with the polymer surface, and the concentration and type of antioxidants present. For every photon of light emitted by polypropylene about 104 carbonyl groups are formed. The behavior of antioxidants in polypropylene, including concentration and synergistic effects, are illustrated by measurement of this light.
Fracture processes in polymeric materials. I. The surface energy of poly(methyl methacrylate)
Authors: Berry J. P.
Published: April 2003

The general aspects of the problem of fracture and strength are briefly reviewed. The discrepancy between the observed strength of materials and the theoretical value calculated from the molecular structure is usually ascribed to the presence of adventitious flaws present in all samples tested. The Griffith theory of brittle fracture gives the relation between the tensile strength T and the size of the flaw in the sample c as T = A(Eγ/c)1/2. The tensile strengths of samples of poly(methyl methacrylate) containing artificially induced cracks of known size were determined. The results could be represented over a wide range of experimental conditions by the form of the Griffith theory. The value of the specific surface energy obtained from the position of the theoretical curve was ∼3 × 105 ergs/cm.2. The value calculated from the molecular structure of the material is ∼450 ergs/cm.2. The discrepancy is attributed to the energy consumed in a viscous flow process in a thin layer of material at the fracture surface. As a result of this process it is believed that in the surface layer polymer molecules are oriented normally to the fracture plane. This mechanism accounts for the colors observed on the fracture surface and for their lability on exposure to solvents or heating. The Griffith theory postulates a strong dependence of tensile strength on surface energy. In poly(methyl methacrylate) the largest contribution to the surface energy appears to arise from a viscous flow process. Hence for polymers the strength may depend much more on the intermolecular (van der Waals) forces than on then ature of the intramolecular primary valence bonds.
Some physical properties of polyoxymethylene dimethyl ethers
Authors: Boyd Richard H.
Published: April 2003

The vapor pressures, liquid density (25°C.), and melting points of the lower members of a homologous series of compounds of simple linear structure have been measured. These are the polyoxymethylene dimethyl ethers, CH3O(CH2O)nCH3, where n = 2 to 5. The heats of vaporiziation derived from the vapor pressures are used in establishing the heat of vaporization of high molecular weight polyoxymethylene. The densities of these compounds allow the density of the high molecular weight liquid polymer (25°C.) to be determined. The values were used for calculating the cohesive energy density of liquid polymer at 104 cal./cc. at 25°C. The limiting heat of vaporization is used with other thermochemical data in the estimation of the lattice energy (heat of sublimation at 0°K.) of polymer; this estimate is 3.8 ± 0.4 kcal./mole of CH2O.
Transition metal catalysts. V. Methyltitanium trichloride
Authors: Karapinka George L. , Smith Joseph J. , Carrick Wayne L.
Published: April 2003

The reported preparation of methyltitanium trichloride has been refined to give a product free of aluminum compounds. The infrared spectrum of this material in the 2–15 μ region was recorded, and suggested assignments for the various vibrations are given. Aluminum‐free methyltitanium trichloride is not a catalyst for the low‐pressure polymerization of ethylene, but it forms an active catalyst in the presence of its lower valence, thermal decomposition products. Mixtures of methyltitanium trichloride with vanadium tetrachloride or vanadium oxytrichloride lead to reduction of the vanadium valence and are active polymerization catalysts. In these bimetallic cases, polymer growth seems to occur at the vanadium center.