bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemistry of the silylamines. II. The condensation of silylamines with silanediols
Authors: Pike Ronald M.
Published: April 2003

The condensation of mono‐ and difunctional silylamines with (C6H5)2Si(OH)2, (C2H5)2Si(OH)2, HO[Si(C6H5)2O]2H, HO[Si(CH3)2O]3H, and a 1530 mol. wt. hydroxy endblocked dimethylsilicone fluid was investigated. The structure of the reacting species, the addition of acid catalyst, temperature, and solvent were shown to have a marked effect on the reaction rate. The rate of reaction of silylamines toward a given silanediol decreased in the order

The information obtained from the condensation of hexamethyltrisiloxane‐1,5‐diol and N,N‐diethylaminotrimethylsilane demonstrated that self‐condensation of the silanediol did not occur to any extent under the reaction conditions employed. This condensation reaction offers a unique approach to the synthesis of silicone polymers and copolymers allows control of the location of crosslinking sites in the silicone polymer chain, and affords a method for the preparation of silicone block copolymers.
The autoorientation mechanism of crystallization
Authors: Schuur G.
Published: April 2003

Attempts have been made to explain a few details of the sometimes misunderstood autoorientation mechanism of crystallization. The autoorientation mechanism is not a model for a particular type of spherulite, but one of the fundamental factors which influence the structure of substances with linear molecules or linear aggregates of molecules or atoms. It is possible to explain on this basis why spherulitic structures are formed or not formed, depending on circumstances. Another argument for autoorientation is that under certain conditions the molecules in adjacent regions are perpendicular to each other. From that point of view the structure of “herringbone” spherulites and ringed spherulities is pertinent to autoorientation. These structures have been investigated and models for these spherulites are proposed. Herringbone spherulites are easily reproducible in gutta‐percha. The ringed spherulites have a rhythmic layer structure. The molecules in adjacent layers are perpendicular to the radius and perpendicular to each other. They grow probably by a process of twinning at regular intervals. The visibility of the rings, especially when the rings are out of focus in unpolarized light, is caused by Becke lines. Clear evidence for the layer structure is the fact that borderlines between adjacent spherulites sometimes follow a zigzag path. The structure of the center of spherulites is also in agreement with autoorientation. Popoff's double leaves in gutta‐percha spherulites are formed if regions at both sides of the sheaflike structure, in the center of spherulites, crystallize in a different manner from that of the sheaf itself. Spherulites formed at low temperatures usually have only an apparent fibrosity, whereas spherulites formed at high temperatures can consist of real needle‐shaped crystals, sometimes separated by less crystalline interstitial material. These and other aspects of the crystallization of polyolefins and other polymers are shown to be in general agreement with the conception of autoorientation.
Fracture processes in polymeric materials. II. The tensile strength of polystyrene
Authors: Berry J. P.
Published: April 2003

The Griffith treatment of brittle fracture predicts that the tensile strength of a material should vary inversely as the square root of the length of a crack or flaw which it contains, the proportionality constant being a function of the surface energy. This relation has been verified experimentally for a series of polystyrene samples which contained deliberately introduced cracks. The value of the surface energy obtained from the results is 1.7 × 106 ergs/cm.2. This is much larger than would be predicted from the molecular constitution, and also higher than the value found from similar experiments on poly(methylmethacrylate). Deviation from the theoretical relationship occurs at small crack sizes, an effect which is attributed to the tendency of the polymer to craze. The effective size of the crazing cracks is estimated to be ∼0.04 in. Because of its higher surface energy, polystyrene is intrinsically stronger than poly(methyl methacrylate). However, the effective flaw size of poly(methyl methacrylate) is only ∼0.002 in., and the tensile strength of conventional samples of this polymer is higher than that of similar samples of polystyrene. These results indicate the importance of two factors which determine the strength of glassy polymers: (1) the surface energy, and (2) the effective flaw size. It is believed that a viscous flow process which occurs during fracture makes a large contribution to the surface energy, but the factors which govern the effective flaw size are, at present, little understood.
The specification of biaxial orientation of polymer films
Authors: Stein Richard S.
Published: April 2003

It is shown that at least four functions are necessary to generally specify the state of orientation of a single phase of a biaxially oriented film. Relationships among these functions under particular constraints are discussed and are described in terms of three dimensional figures in “orientation space.” Only certain combinations of values of these functions are permitted. The physical properties of a film may be specified in terms of these functions.
Solubility of gases in polyethylene
Authors: Michaels Alan S. , Bixler Harris J.
Published: April 2003

The solubility constants for thirteen permanent gases were measured within the temperature range 5–55°C. in a linear and a branched polyethylene, hydrogenated polybutadiene, and natural rubber. Equilibrium and time lag solubility determinations were made, the latter being indirectly obtained as the ratio of the permeability to the diffusion constants. Within experimental precision, equilibrium and time lag measurements were in agreement. The solubility of each gas in polyethylene was found to be proportional to the volume fraction of amorphous material when the polymer was treated as a simple, two‐phase mixture of crystalline and amorphous polymer, each with a characteristic specific volume. Even the small helium molecule exhibited no detectible solubility in the crystallites according to this model. Therefore, a solubility constant in completely amorphous polyethylene could be determined for each gas which, with the density of an arbitrary sample, would enable calculation of the solubility of each gas in that particular sample. A correlation of the solubility constants in completely amorphous polyethylene was obtained from a thermodynamic model of the disolution process. Comparison of this correlation with a similar one for normal hydrocarbon liquids emphasized the analogy between the amorphous phase in polyethylene and these low molecular weight substances. The solubility constants in natural rubber, a completely amorphous polymer under the experimental conditions, were approximately 50% higher than those in amorphous polyethylene. Higher intermolecular forces due to the unsaturation in natural rubber may account for this result. The apparent heats of solution of all gases in branched polyethylene were approximately 1.0 kcal./g. mole more positive than those in linear polyethylene. This behavior was shown quantitatively, by comparison with dilatometric data, to be simply the result of crystalline melt‐out in branched polyethylene. In linear polyethylene the experimental solubility data yielded essentially true heats of solution, since negligible crystalline melt‐out occurred between 5 and 55°C. These were correlated quite satisfactorily by further application of the thermodynamic model for the dissolution process. Available evidence, therefore, indicates that the crystallites in polyethylene are impenetrable, and are randomly distributed on a macroscopic scale with respect to the diffusion and dissolution processes. The amorphous phase behaves as a homogeneous liquid whose thermodynamic properties are independent of the mode of polymer preparation, thermal history of the sample, and level of crystallinity.
Thermal conductivity studies of polymers
Authors: Kline Donald E.
Published: April 2003

A study of the thermal conductivity of some amorphous and partially crystalline polymers as a function of temperature (0–100°C.) is described. Experiments have been carried out, with the use of a thermal conductivity cell with cylindrical geometry, on polyethylene, polytetrafluoroethylene, polystyrene, polyhexamethylene adipamide, and polymerized epoxy resin. Results indicate that the conductivity of amorphous polymers increases with temperature and that the conductivity is significantly higher in crystalline regions than in the amorphous regions. Data concerning the change of thermal conductivity of polymerized epoxy with the addition of powdered aluminum filler are given. The results presented in the paper are discussed and compared with those reported by other investigators.
Internal friction in stereoregular polymethyl methacrylate
Authors: Gall W. G. , McCrum N. G.
Published: April 2003

New stereospecific polymerization systems for methyl methacrylate are reported. The temperature dependence of the internal friction of the stereoregular forms of polymethyl methacrylate (PMMA) has been determined at frequencies of ca. 1 cycle/sec. Isotactic PMMA does not exhibit a side chain relaxation and its main chain relaxation is 66°C. lower than that of conventional PMMA. Syndiotactic PMMA exhibits exactly the same relaxations as conventional PMMA. Since the density and infrared absorption spectra of syndiotactic and conventional PMMA are also comparable and differ from the isotactic form, it is concluded that conventional radical‐initiated polymer is not truly atactic but has considerable syndiotactic character.
Disiloxane benzimidazole polymers
Authors: Mulvaney J. E. , Marvel C. S.
Published: April 2003

Two disiloxane benzimidazole polymers are described. These materials show increased solubility and lower softening points than the previously described fully aromatic benzimidazole polymers. The synthesis of the required disiloxane monomers is given.
The chemical composition of carbohydrates of wood cells
Authors: Perilä Olavi
Published: April 2003

Wood cell fractions were quantitatively prepared from pine wood and holocellulose, from spruce holocellulose, and from birch holocellulose. The vertical tracheids were separated from ray cells of pine wood by micromanipulation under a microscope. The total hydrolysate of the tracheids contains more mannose and less xylose than the hydrolysate of the ray cells. The vertical tracheids and ray cells were fractionated from pine holocellulose by being first passed through a 40 mesh laboratory screen and then through a 180 mesh screen. The tracheids amounted to 97.8% and the ray cells 1.8% by weight of the holocellulose. The total hydrolysate of the tracheids was found to be richer in mannose and poorer in xylose than the hydrolysate of the ray cells. Both cell fractions were found to contain nearly equal amounts, about 20%, of hemicellulose soluble in an alkaline borate solution (17.5% NaOH + 4% H3BO3). Mannose was the predominant (nearly 70% of neutral monosaccharides) monosaccharide in the hydrolysate of the hemicellulose of the tracheids; xylose (nearly 50%), in the hydrolysate of the hemicellulose of the ray cells. The latter contained more glucose, arabinose, and galactose than the tracheids. The spruce holocellulose was found to contain 98.9% vertical tracheids and 1.1% ray cells by weight in microscopical fractionation. The total hydrolysate of the tracheids prepared via screening of holocellulose was found to be richer in mannose and glucose and poorer in xylose and arabinose than the hydrolysate of the ray cells. The hemicellulose amounted to 17.8% of the tracheids and to 30.3y0 of the ray cells. The total hydrolysate of the hemicellulose of the tracheids was found to be richer in mannose and poorer in xylose, arabinose, and galactose than the hydrolysate of the hemicellulose of the ray cells. Mannose was the predominant (50% of neutral monosaccharides) monosaccharide in the hydrolysate of the hemicellulose of the tracheids and xylose (50%) in the hydrolysate of the hemicellulose of the ray cells. The prosenchyma and parenchyma cells were fractionated from birch holo‐cellulose by scretmirig. The vessels have been separated from the fibers by manual fractionation of the prosenchyma cell fraction under a microscope. The holocellulose was found to contain 86.1% fibers, 9.3% vessels and 4.6% parenchyma cells, by weight. The ratio of xylose/glucose in the total hydrolysates of the fibers and of the vessels was about 0.6: 1.0, but xylose was the predominant (77% of neutral monosaccharides) mono‐saccharide in the total hydrolysate of the parenchyma cells. The hemicellulose was 21.5% of the prosenchyma cells and 39% of the parenchyma cells. The hydrolysate of the hemicellulose of the prosenchyma cells was found to be richer in mannose and poorer in xglose than the hydrolysate of the hemicellulose of the parenchyma cells. The former was found to contain xylose 86% of neutral monosaccharide; the latter 93%.
Preparation and characterization of sodium cellulosates
Authors: Schwenker Robert F. , Kinoshita Tetsuo , Beurling Karin , Pacsu Eugene
Published: April 2003

A method of preparing sodium cellulosates by an exchange reaction between cellulose and sodium alkoxide in alcohol medium is proposed. Anhydrous systems of sodium methoxide in methanol and sodium n‐butoxide in n‐butanol were used to treat cotton and viscose rayon celluloses to form sodium alcoholates of cellulose. It is shown that alcohols used as extraction solvents in the purification of the reaction products must be of low acidity, such as branched chain alcohols, since straight chain alcohols of relatively high acidity are shown to cause destruction of the sodio derivatives. The distribution of sodium in the products was found indirectly by methylating the sodio derivatives in pure methyl iodide and determining the distribution of methoxyl groups by paper chromatographic techniques. It was indicated that the sodium substituent was distributed in the various sodium cellulosates in a somewhat random arrangement. Glucose, mono‐O‐methyl glucose, di‐O‐methyl glucose, and tri‐O‐methyl glucose constituted the distribution products. The mono‐O‐methyl glucose fractions were further separated, to disclose the presence of the 2,3, and 6 isomers. The degree of substitution (DS) found for the sodium cellulosates ranged from 0.52 to 1.72.
Preparation, characterization, and properties of a deoxycellulose
Authors: Carter Mary E.
Published: April 2003

It has been shown that reduction of a cyanoethyl cellulose gives a deoxy cellulose. The deoxy cellulose averaged one deoxy group per anhydroglucose in one third of the monomer units in the polymer chain. This was determined by elemental analysis and acetyl content. Further study showed that the 2‐deoxy‐β‐anhydroglucopyranose was the predominant deoxy sugar. Weight loss upon acid hydrolysis, alkaline degradation, and periodate oxidation studies were made. The behavior of the cellulose toward cellulosic solvents indicates the presence of a few crosslinks.
The application of nuclear magnetic resonance to structural studies of carbohydrates in aqueous solution
Authors: Lenz Robert W. , Heeschen Jerry P.
Published: April 2003

High‐resolution nuclear magnetic resonance spectroscopy was applied to the study of the structure of carbohydrates in deuterium oxide solution. The structural problems considered were the configuration of anomeric protons, the conformation of pyranoside rings, the preferred ring form, the existence and form of complexes, and the mutarotation of carbohydrates in solution. A modification of the Karplus equation was applied to the calculation of the dihedral angles between the C1 and C2 carbon–hydrogen bonds for a number of carbohydrates. A harmonic oscillation of ±15° about the equilibrium dihedral angle was assumed in these calculations. The preferred conformations of several carbohydrates were deduced from the dihedral angles, and an analysis of the diamagnetic susceptibility anisotropy was applied to the predicted conformations in two cases. Observed and calculated shielding differences were determined for each of the ring protons in β‐glucose and β‐mannose. The good agreement obtained from this treatment appears to support the proposed distorted chair and half‐chair conformations for β‐glucose and β‐mannose respectively. Conclusions reached from consideration of NMR spectra were applied to discussions of the stability and structure of several borate complexes and of the preferred ring size of xylose in solution.
Highly stereospecific catalytic systems for the polymerization of α‐olefins to isotactic polymers
Authors: Natta G. , Pasquon I. , Zambelli A. , Gatti G.
Published: April 2003

The highly stereospecific catalytic systems for the polymerization of α‐olefins have been compared. These are obtained starting either from the α, γ, or δ modifications of violet TiCl3 with or without AlCl3 present in solid solution, and from aluminum diethyl monohalides, or from metalloorganic products obtained by reacting two molecules of aluminum monoalkyl dihalide with one molecule of particular electron donor compounds. The catalytic systems considered polymerize propylene, giving rise to crude polymers containing 90 to 100% isotatic propylene (nonextractable in boiling n‐heptane) for a wide range of polymerization temperatures. By fractionation of crude polymers prepared with the use of these catalytic systems, highly isotactic polypropylenes, having a melting temperature up to 177°C., have been separated. The results, correlated with those obtained in x‐ray determinations of the structure of the modification of TiCl3 used, demonstrate that the stereospecificity of all the catalytic systems examined is independent of the particular type of violet modification (α, γ, or δ), whether or not these contain aluminum as AlCl3 in solid solution. This proves that the single active centers are substantially of the same type; a variation in their number causes only a variation of the overall polymerization rate.
Changes in orientation of crystallites during stretching and relaxation of polyethylene films
Authors: Aggarwal Sundar L. , Tilley George P. , Sweeting Orville J.
Published: April 2003

A microbeam camera has been used in x‐ray diffraction studies of the changes which occur in orientation of crystallites in polyethylene film when the film is stretched and later relaxed. The collimator of the microbeam camera, 100 μ in diameter, allows one to follow the orientation changes very closely in the necked‐down region of a stretched sample. The stretching of polyethylene proceeds by alignment of the a‐axes of the crystallites perpendicular to the stretching direction with the planes containing b‐ and c‐axes perpendicular to the a‐axis but randomly oriented, followed by a gradual change to a state in which the c‐axes become more nearly aligned in the stretching direction although perfect alignment is not achieved. On relaxation, either the orientation of the c‐axis parallel to the original stretching direction becomes less perfect, or folding of the oriented crystallites about the b‐axis takes place. In the latter case the preferred crystallographic directions parallel to the stretching direction have indices such as [u0w]. These orientation changes during stretching and relaxation of the stretched samples suggest that crystallites in polyethylene films consist of parallel arrangements of platelets containing b‐ and c‐axes. The distinction between directions in the reciprocal lattice and the crystal lattice is clarified. A number of x‐ray diffraction patterns and charts of dimensional changes illustrate the paper.
Méthodes de synthèse de polymères greffés et de polymères à blocs
Authors: Smets Georges
Published: April 2003

Trois méthodes synthétiques principales de préparation de polymères greffés et séquencés ont été discutées. Dans la première méthode, basée sur des réactions de transfert de chaîne sur polymère, on envisage l'influence de la nature de l'initiateur (Bz2O2, azobisisobutyronitrile, et le peroxyde de di‐tert‐butyle) et des radieaux primaires, de même que l'influence de la présence de sites réactionnels dans le polymère. Dans la seconde méthode, ou l'initiation est réalisée par activation, on considère plus spécialement l'utilisation de radicaux piégés à la préparation de polymères séquencés; certains résultats nouveaux sont discutés et interprêtés. Finalement dans le cas de la méthode par initiation chimique, on a étudié la cinétique du greffage en utilisant des polymères contenant des groupes peroxy‐tert‐butyliques, soit comme groupes peresters latéraux, soit comme groupes peroxydiques terminaux. Les efficacités relatives des macroradicaux par rapport aux radicaux habituels ont été évaluées et comparées entr'elles; elles sont également fonction de la nature de monomère. Les autres méthodes de préparation de polymères greffés et séquencés ne sont que brièvement mentionnées.
Polymerisation et copolymérisation cationiques de l'indéne
Authors: Sigwalt P.
Published: April 2003

En général on considère que des monomères éthyléniques substitués en 1,2, tels que l'indène et la coumarone, ne peuvent pas donner de polymères de très haut poids moléculaire. On a obtenu les plus hauts poids moleculaires moyens par la polymerisation cationique de lindirne et leur valeur etait de quelques milliers. Une etude systematique des differents facteurs influenqant la polymbrisation cationique de lindbne nous a permis de prkparer des hauts polymbres dont la viscositt? intrinsirque peut re aussi blevee que 2 ou 4 pour des polyindhes ou polycoumarones. Laccroissement des poids mole‐ culaires de polymkres obtenus en utilisant des catalyseurs de Friedel‐Crafts a conduit & une classification de ces catalyseurs qui est analogue ii celle connue pour la polymerisation de lisobuthne. La viscosite intrinshque des polymirres croit regulibrement lorsque la temperature de polymerisation dhcroit La roncentration en monomere doit re limitee en vue dobtenir de hauts poids molkculaires, parce que la reaction est trirs rapide et exothermique, et parce clue la constante diklectrique du milieu est abaissee par la presence du monomere. La nature du solvant est trks importante: les halogenures dalcoyles qui sont de bons solvnnts pour le polymh‐e la temperature de polj mhrisation, et qui ont une constante diklectrique suffisamnient Clevee, donnent des polymkres avec les poids moleculaires les plus élevées. La copolymerisation dindhne avec la coumarone et une serie de monombres vinyliques fut egalement etudide. En general, les viscosites intrinsitques des copolymirres sont infhrieures & celles des honiopolymirres correspondants. Les plus hauts poids mol6culaires sont obtenus avec des comonomeres qui polymerisent aisCment avec des initiateurs cationiques (coumarone, ryrlopentadihe, a‐methyl‐ styrene, p‐m6thoxvstyrkne, isobuthe).
Polymerization inhibition by aromatic compounds
Authors: Bagdasar'Ian Kh. S. , Sinitsina Z. A.
Published: April 2003

A quantiative study of chain transfer and inhibition reactions makes it possible to determine the ratios kx/Kp where Kp and kx are the rate coefficients for propagation and for chain tranfer, respectively. Since the absolute values of the constants Kp are known for a number of monomers it is possible to determine the absolute values of the constants kx. We have investigated the inhibiting action of some types of aromatic compounds in the polymerization of vinyl acetate, methyl acrylate, acrylonitrile, and methyl methacrylate. In the polymerization of vinyl acetate the inhibiting effect of the aromatic hydrocarbons increases in the order: toluene, diphenyl, naphthalene, phenanthrene, anthracene. The logarithm of kx is linearly related to the logarithm of the methyl affinity. The inhibiting effect increases on incorporating substituents, both electrondonating and electron‐accepting, in the benzene ring. There is no relation, however, between the value of kx and Hammet's σ‐constant. An outstanding position is assumed by nitrobenzene, for which kx is higher by 3–4 orders of magnitude than that of the other substituted benzenes. The incorporation of substitutents in the meta and para positions of the benzene ring follows the Hammet rule, the electron‐donating substituents causing a decrease in the kx values. Similar relations are observed in the polymerization of methyl acrylate, but the absolute values of kx are lower by 3–4 orders of magnitude than in the polymerization of vinyl acetate. Because of this, under the experimental conditions the interaction of the polymethyl acrylate radical with molecules of the transier agent was not revealed (kx < 0.21 1./mole‐sec. at 50°) in the case of many of the substances investigated, for instance of all mono‐substituted benzenes except nitrobenzene. A comparison of the kx values for polyvinyl acetate, polymethyl acrylate, polymethyl methacrylate, and acrylonitrile radicals permits a number of conclusions to be made concerning the influence of the polar factor on radical reactions. The data obtained lead to definite conclusions as to the inhibiting mechanism of aromatic compounds. The primary act is the addition of the polymer radical to the aromatic ring with the formation of a nonreactive radical. In the case of nitro compounds, the polymer radical reacts with the nitro group, probably by transferring to it a β‐hydrogen atom. It has been found that in the polymerization of vinyl acetate in the presence of the inhibitors in question each molecule of the latter terminates two kinetic chains; regeneration of the chains does not take place, and the polymer molecules form as the result of disproportionation between the polymer radical and the radical formed during interaction of the former with the inhibitor molecule.
The mechanism of formation of stereoregular polymers
Authors: Mihail R. , Herscovici J.
Published: April 2003

At present various polymerization reactions are known which yield approximately identical types of eutactic polymers. This has been confirmed experimentally for a sufficient number of monomers (α‐olefins, conjugated diolefins, vinyl esters, alkylene oxides, etc.) to lead to the conclusion that stereoregularity is based on a single or a few general acts. The mechanisms proposed for the formation of stereoregular polymers, i.e., radical, through alkyltitanium compounds (Nenitescu), semiconductor surface (Topchiev), or ionic (Natta, Furukawa), do not give a sufficiently general solution to the problem. Whereas some authors do not take into account the ionic character of some types of polymerization reactions and the possibility of free rotation of the macroradical around the CC axis, others neglect the fact that radical reactions are known which leading to the formation of stereoregular units. Particularly useful is a generalization of the remarks concerning the steric control of unsymmetric induction (Cram). Stereospecific polymerization, or, to be more exact, the act or elementary acts leading to stereo‐regularity of the molecules formed, should proceed just in the same manner as other stereospecific reactions. The authors of the present report attempted to find common elements between the different reaction mechanism leading to the formation of eutactic polymers.
Rate of polymerization of a single particle in emulsion polymerization
Authors: Ryšáanek A. , Hloušek M.
Published: April 2003

The rate of polymerization for a single particle in emulsion polymerization in the region of constant reaction velocities has previously been expressed in the form of an equation which can be modified to the form:

where K = k2[M]/NA, and vpol (1) is the rate of polymerization of single particle (mole/sec.); n is the concentration of all particles in emulsion (mole/l.); v′i is the rate of incorporation of radical initiator into particles; [X] is active inhibitor concentration about the growing radical (mole/l.); k3 is the kinetic inhibitor chain scission constant (l./molesec.); k2 is the kinetic chain propagation constant (l./mole‐sec.); [M] is the active monomer concentration about the growing radical (mole/l.); and NA is Avogadro's number. With the aid of this equation one may experimentally determine the dependence of the rate of polymerization of a single particle upon the total number and upon the rate of initiation. For a given monomer K and k3[X] are constants and the expression 1/vpol(1) depends only upon the value of n/v′i. Extrapolating graphically the dependence of 1/vpol(1) upon n/v′i we obtain an intercept on the ordinate axis, the value of which is the reciprocal of the maximum rate of polymerization for a single particle in the given system. Maintaining v′i constant, from a series of experiments in which the number of particles is varied we obtain the dependence of the polymerization rate upon the particle number. In another series of experiments with constant particle number and changing rate of initiation (for instance, by varying the initiator concentration) we obtain the dependence of the rate of polymerization of a single particle upon 1/v′i. Changing both parameters simultaneously we obtain the dependence of the rate for a single particle upon the value of n/v′i. These relations were confirmed in experiments on the polymerization of vinyl acetate, styrene, and chloroprene.
Study of macroradical reactivity by an electron paramagnetic resonance method
Authors: Bresler S. E. , Kazbekov E. N. , Saminskiĭ E. M.
Published: April 2003

The formation of macroradicals in the mechanical degradation of polymers gives the means for the direct kinetic determination of macroradical reactivity (reaction of the macroradicals with each other and with various low molecular substances). The free radical concentration was determined by means of EPR spectroscopy. With the aid of this method a study was made of the characteristic reactions such as removal of a hydrogen atom, addition, etc.
Synthesis and polymerization of polyacrylic esters
Authors: Kefeli T. Ya. , Korolev G. V. , Filippovskaya Yu. M.
Published: April 2003

The method of telomerization has been employed in the synthesis of the telomer homologs of polyacrylate esters with successively increasing degrees of polymerization (n) and of telomers differing in the nature of the polyester chain. Compounds have been synthesized of the general formula
magnified image
where R and R1are alkyl or aryl radicals and n = 2, 4, 8, and 20. With changes in (n) from 2 to 20 the structural viscosity of the polyacrylate esters increased from 150 to 8000 centistokes (at 20°), the specific gravity from 1.213 to 1.308, and nD20 from 1.515 to 1.5479. The presence of double bonds in the molecules of the polyacrylate esters synthesixed made it possible to carry out their polymerization (hardening) in the presence of radical chain initiators with the formation of glassy or elastic, insoluble, nonmelting polymers of sufficient thermal stability and endowed with a number of valuable properties so as to be of considerable practical potentiality. The changes in physical properties of the reaction system (gelation, gradual increase in density and finally the formation of a glass structure) in the course of the polymerization beginning from the very early stages (the gelation point is reached at 5–10% conversion) are responsible for a number of specificities in the kinetics of the hardening of polyacrylate esters. Owing to this we undertook a detailed investigation of the polymerization kinetics under widely varying conditions. Polymerization in bulk takes place autocatalytically, since with increasing degree of structuration in the course of polymerization the rate of diffusion of free radical diminished, leading to a decrease in rate of chain termination. The rate of reaction begins to diminish markedly only at large extents of polymerization. A study has been made of the effect of diluting the reaction mixture with an inert solvent, of the initiation rate, nature of the initiating agent, temperature, chemical structure of the initial polyacrylate ester, as well as of the addition of inhibiting agents on the polymerization kinetics. The results obtained have been discussed from the standpoint of the capacity of the system for structuration under the various conditions of reaction. The heats of hardening of the polyacrylate esters with successively increasing distance between their values have been discussed with respect to the reaction mechanism.
Preparation of new types of linear polymers by the polyrecombination reaction
Authors: Korshak V. V. , Sosin S. L. , Alekseeva V. P.
Published: April 2003

In an extension of previously reported studies of the use of the polyrecombination reaction to synthesize high molecular weight compounds, it has been shown for the first time that this method yields linear polymers without any significant formation of threedimensional structures. Such polymers may be synthesized from compounds containing a methylene group in the α‐position to the benzene ring, carboxyalkyl or carboxyphenyl groups. On treatment of diphenylmethane with tert‐butyl peroxide, a linear polymer of molecular weight 10,000‐900,000 (depending on the quantity of peroxide used) was obtained. Linear polymers in the form of benzene‐soluble powders were also obtained from benzyl benzoate (molecular weight 400,000), methyl phenylacetate, etc. The composition and structure of the polymers obtained were confirmed by chemical analysis and infrared spectroscopy. The relation between the molecular weight of the polymer and the amount of peroxide consumed in the reaction was also established. If groups capable of serving as branching centers in the polymer (e.g., methyl groups in ditolylmethane) are present in the starting compounds, three‐dimensional products are formed along with the linear polymers.
Polymeric organotin compounds
Authors: Shostakovskiĭ M. F. , Kalinina S. P. , Kotrelev V. N. , Kochkin D. A. , Kuznetsova G. I. , Laine L. V. , Borisova A. I. , Borisenko V. V.
Published: April 2003

Organotin monomers and polymers are becoming of increasing importance. Of especial theoretical and practical interest are polymers of organotin materials. In the present report results are described of studies carried out in the Laboratory of Vinyl Compounds of the Institute of Organic Chemistry of the Academy of Sciences, USSR and in the Plastics Institute of the State Committee on Chemistry of the Council of Ministers, USSR. The syntheses of a number of organotin polymers are reported, in particular, of the organotin polymethyl methacrylates from trialkyl (or aryl) stannyl methacrylates R3SnOCO(CH3)CH2 and dialkyl (or aryl) stannylene dimethacrylates R2Sn[OCOC(CH3)CH2]2 and copolymers based on these. The high molecular compounds obtained by polymerization of the organotin esters are a new class of vinyl polymers with the structure:
magnified image
Organotin esters copolymerize with various unsaturated monomers such as methyl methacrylate, styrene, acrylonitrile, cyclopentadiene, etc. The copolymers are mechanically strong, transparent materials. They represent considerable barriers to the passage of x‐rays. The organotin esters R3SnOCOC(CH3)CH2 and R2Sn[OCOC(CH3)CH2]2 containing the alkyl radicals amyl, hexyl and higher groups polymerize at room temperature in the absence of catalysts to form soft and elastic polymeric materials. In the report a number of properties of another class of organotin polymers, namely, dialkyl (or aryl) stannones (R2SnO)n are discussed. It is suggested that they are high molecular compounds. Their x‐ray diagrams and the results of other physicochemical analyses are examined. A study of their Debye x‐ray diagrams showed that they have a regularly oriented structure. They are highly reactive and are sources for the preparation of new organotin compounds. Some of their physicochemical properties are described.
On the mechanism of ionic polymerization
Authors: Veselý K.
Published: April 2003

This lecture is devoted mainly to individual elementary reactions, especially those of chain growth taking place on a pair of ions, and termination in ionic polymerization. Two mechanisms of chain growth are possible and are known to occur: first, a gradual chain growth taking place at the ion pair (as is known in the case of “living” polymers), second, chain growth taking place at free ions. The velocity of chain growth is controlled by a number of factors amongst which may be cited the following (a) The type of the chemical bond in the monomer which undergoes cleavage during polymerization. In this respect the author correlates results of kinetic measurements (partly his own and partly other authors' data) relating to the bonds >CC< (in isobutylene, styrene), >CO (in formaldehyde), and (in octamethylcyclotetrasiloxane, OTS). (b) The size and type of ions forming the ion‐pair. Here different anions are compared for their effects on the cationic polymerization of isobutylene and, similarly, different cations are compared for their effects on the anionic polymerization of OTS. (c) The ability of monomer to form complexes with the ion‐pair at which growth occurs. During the anionic polymerization of OTS the free orbital of the Si atom of the monomer is directly engaged in the dissociation of the terminal ion‐pair . The role of the aromatic nucleus in the polymerization of styrene falls within the same category. More detailed data on the dissociation of ion pairs have been obtained by the study of electrical conductivities of catalyst‐cocatalyst systems on the one hand and of systems involving monomer on the other. The study of electrical conductivities in the presence of a monomer was carried out in the anionic polymerization of OTS which is characterized by relatively low rates of polymerization. Here it was possible to prove the active part played by the monomer in the dissociation of the ion‐pair at which chain growth takes place. The termination reaction on the other hand is also influenced by a number of factors. Among the most important factors is the acidity (or basicity) of the growing ion which decides whether the actual step is one of transfer or termination. By way of an example one may draw the attention to the difference in behaviour of water on the polymerization of the CC bond on one hand, that of the CO bond on the other. The reactivity of the very strong cations (of anions ) is sufficient for even relatively strong bases (or acids) to add irreversibly. As an example one may show the action of various bases in the cationic polymerization of isobutylene and that of acids in the anionic polymerization of OTS. In conclusion, absolute rates of the individual elementary reactions and the new possibilities opened by the study of electrical conductivities of monomer‐containing systems are discussed.
The mechanism of polymerization of ε‐aminocaprolactam catalyzed by phosphoric acid
Authors: Geleji F. , Szafner A. , Holly Z. , Szollar L.
Published: April 2003

The polymerization of caprolactam in the presence of water has been studied by several authors. In the papers of Wiloth, Hermans, and Mathes, the attention was essentially devoted to the temporary production of aminocaproic acid, which polymerizes progressively by a condensation mechanism. It was demonstrated that the catalyst (water, aminocaproic acid, hexamethylenediamine adipate) assures the polymerizability of the system at the condensation temperature. In order to verify the data of the literature concerning some resistance towards oxygen when prepared in the presence of phosphoric acid, we have used in our studies some phosphoric acid as a catalyst for the polymerization of caprolactam. However, we have found that the oxidation of caprolactam was lower in the presence of an acid than in its absence. It was shown that the higher sensitivity was due to the formation of free radicals by interaction of phosphoric acid with caprolactam, which reacts rapidly with oxygen. The oxidation is slowed down more effectively by inhibitors of polymerization, which react more easily with free radicals than the oxygen. We follow our studies on the basis of these data. It is known from the literature that phosphoric acid is a very effective polymerization catalyst as well in the presence of water as in that of anhydrous medium. Considering that phosphoric acid exerts during the polymerization not only a catalytic effect but, first of all, a chain‐breaking process, we have used optimal quantities of phosphoric acid which lead to the best end products. The best adapted molecular weights are obtained in the presence of 1/100–1/200 mole phosphoric acid for 1 mole caprolactam. With such quantities of phosphoric acid in the presence or in the absence of water, the polymerization proceeds rapidly. The rate of polymerization is inversely proportional to the square root of the catalyst concentration. By decreasing the amount of catalyst to 1/400 or 1/200 mole per mole of caprolactam, the water content which is present besides the catalyst becomes more important and different rates of polymerization are observed in function of the phosphoric acid concentration. At the polymerization temperature, the phosphoric acid tends to dehydrate into pyrophosphoric acid; this transformation enhances the production of the most reactive free radicals. These free radicals increase the rate of ring opening of caprolactam more strongly than in the presence of water. In agreement with our opinion, phosphoric acid catalyzes not only the ring opening, but increases also the chain propagation reaction.
The effect of aging of polychloroprene on its crystallization
Authors: Kössler I. , Švob L.
Published: April 2003

Samples of polychloroprene (Svitpren K) were submitted to aging in air at elevated temperatures (65, 80, 90 and 100°C.). The kinetics of the crystallization process were then followed on the samples. The degree of crystallization was determined by x‐ray diffraction. The maximum degree of crystallization was 34% with a fresh sample. With increasing degree of aging, this value decreases markedly even though the rate of crystallization does not change appreciably. The activation energy E of the chemical reaction was found from curves giving the dependence of the limiting degree of crystallization on the period of heating the sample at various temperatures to be E = 8.5 kcal./mole. This value was close to that determined directly from the splitting off of HCl, E = 9.2 kcal./mole. Thus the splitting off of HCl is the main factor in decreasing the limiting value of the crystallization. This process does not have any effect on the rate of crystallization since the segments on which the splitting off of HCl occurred do not decrease the mutual mobility of the chains. They cannot, however, participate in the formation of crystallites. We attribute the small lowering of this rate of crystallization to crosslinking of the polymer molecules but which has in the first phase of the aging only a secondary effect on the process of crystallization. The crystallization isotherms of all the samples thus satisfy the Avrami relation with a value of the constant n = 2. The rate of nucleation is large in comparison with the rate of growth of centers. Secondary crystallization was not observed.
The stereoregulating effects of aldehydes on the free radical polymerization of vinyl chloride
Authors: Rosen Irving , Burleigh P. H. , Gillespie J. F.
Published: April 2003

The discovery has been made that when vinyl chloride is polymerized in certain aldehydes, a highly crystalline polyvinyl chloride is obtained. In butyraldehyde, low yields of a range of low molecular weight polymers are produced. Elemental analyses showed that they may be characterized by the formula:
magnified image
where n = 6‐26. Support for this structure and molecular weight range was obtained from infrared and x‐ray examinations of the polymers. The polymers are highly crystalline, as demonstrated by the x‐ray and infrared results, and appear to have a syndiotactic structure. Variation of the polymerization temperature produced no measurable effect on the polymer stereoregularity. The ability of substituted aliphatic aldehydes to produce stereoregular PVC has shown a dependence on the electronegativity of the substituent in the aldehyde. Aliphatic aldehydes with an electron‐releasing α‐methyl group appear to give a more highly crystalline PVC. Aliphatic aldehydes with electron‐withdrawing chlorine and oxygen atoms gives less crystalline PVC than do the corresponding α‐methyl aldehydes. The dependence of the results upon polar effects suggests that the stereoregulating mechanism of the aldehydes involves association between the aldehyde, as a donor molecule, and the free propagating species, as the acceptor radical.
The viscoelastic behavior of oriented polyvinyl alcohol fibers at large strains
Authors: Laible Roy C. , Morgan Henry M.
Published: April 2003

The viscoelastic spectra of oriented polyvinyl alcohol fibers have been determined at large strains (2, 5, and 8%). Stress relaxation data were obtained from constant strain rate experiments conducted at testing speeds from 20 to 2,000,000 %/min. and have been used to calculate viscoelastic parameters, E, E0 and tan δ. The heights of the relaxation spectra were found to increase with increasing rate of test, up to the maximum strain rates possible before critical velocity failure occurs.
Über die polymerisationsgradverteilung bei der polykondensation. Ein versuch zur deutung der tungschen gleichung
Authors: Sippel A. , Heim E.
Published: April 2003

In 1956 L. H. Tung has given a quite empirical and formal mathematical relationaship, by which—appropriate plotting of data provided—it is possible to represent the distribution of DP values, as obtained by a completed polymerization (polycondensation or polyaddition), by means of a straight line. In the course of the present publication it is shown that the authors—starting from a quite different problem—have found a relationship that proves (after an insignificant simplification and by suitable interchange of symbols) to be identical with Tung's equation. According to some special ideas about the chemism, the method of deducing this equation enables the authors to interpret Tung's equations in terms of kinetics. The basic equations obtained are

These show that the reaction rate is merely proporional to the number N of monomers and to the time t. The chain lengths of the macromolecules are suggested to be only an appropriate measure for the time elapsed from the beginning of their formation. Interpreting Tung's equation kinetically it is possible to get information about the distribution of DP values that is to be expected at a given temperature. With regard to theoretical considerations one expects the integral number 2 to be used for the exponent b in the modified equation originally given by Tung:

This value is related to the fact that the chain growth takes place in two directions because of the bifunctionality of the monomers. Therefore, the termination of the reaction will also take place in two steps. The correctness of these suggestions is confirmed by the fact that (for all known fractionations of polycondensation products) the exponent b proves to be nearly 2. Using the value b = 2 the whole chain lengths distribution of normal polycondensation products can be easily calculated by means of one single number or weight‐average value of the DP as determined with an unfractionated sample.