bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cooperative processes in the polycondensation of biopolymers
Authors: Vol'Kenshteĭn M. V. 
Published: April 2003

AbstractThe main features of the polycondensation of biopolymers—nucleic acids and proteins—can be summarized in the following. The reactions are accomplished with the participation of enzymes and take place on some kind of template. Many facts show that the template for deoxyribonucleic acid (DNA) is a nucleoproteinic complex containing DNA; and for protein, a complex containing DNA and RNA (ribonucleic acid). The polycondensation process on a template is a cooperative phenomenon essentially determined by the near‐neighbor interactions of monomers linked by hydrogen bonds to the polymer chains acting as the template. From this a simple model and a statistical theory of the reduplication synthesis of DNA have been developed. The reaction has been shown to start at a certain critical concentration of the monomers in solution, the process being characterized by a specific thermodynamic phase transition.The following factors have been taken into account: the hydrogen bond energy, the energy of nucleotide polycondensation liberated in a sequence of coupled reactions, the influence of the solvent (water) and the flexibility of the free polymer chain. The calculations are based on the Ising method used in the theory of ferromagnetism. The transition during the reduplication synthesis is the sharper the greater the length of the template chain. The same treatment can be applied to the statistical‐thermodynamics analysis of protein biosynthesis in the form of α‐helices (after Pauling and Corey). Polycondensation of amino acids also proceeds by a cooperative mechanism. In this case not only the hydrogen bonds between the amino acids and the template have to be taken into account, but also the intramolecular hydrogen bonds of the resultant α‐helix. Also in the case of amino acid polycondensation on a template a sharp transition takes place at a definite monomer concentration (or at a definite temperature). The kinetics of polycondensation of biopolymers can be treated analogously if we take into account the cooperative character of the process. The corresponding differential equations are nonlinear, but their approximate solution makes it possible to characterize the main features of the process. The above simple models can be generalized to include the successive biosynthesis of nucleic acids and proteins as a united process. The same conceptions may be employed in the theory of heterogeneous catalysis.
The effect of chemical structure on the ability of unsaturated organometallic compounds to undergo polymerization
Authors: Koton M. M. , Kiseleva T. M. , Florinskiĭ F. S. 
Published: April 2003

AbstractThe synthesis of metal‐containing polymers is of considerable theoretical and practical interest (organotin rubbers, etc.). We investigated the polymerization and copolymerization capacities of various allyl and vinyl derivatives of tin and lead, of tin, lead and mercury methacrylates and of a number of metal‐containing styrenes. The allyl derivatives of tin and lead and the vinyl derivatives of tin do not polymerize under conditions of radical polymerization and have an inhibiting effect on polymerization of vinyl monomers (styrene, methyl methacrylate). The inhibiting effect increases with the number of allyl and vinyl groups in the organometal molecule, the allyl compounds of tin being more effective than the corresponding vinyl derivatives. The inhibiting action on the polymerization of vinyl monomers of the compounds decreases in the order: tetraallyltin > tetravinyltin > allyltrimethyltin > diallyldiphenyltin > allyltriphenyltin > vinyltriphenyltin > vinyltrimethyltin. Another relation is found in the case of organometallic compounds where the vinyl group is bound to the metal atom through a polar group or benzene ring. The acrylates and methacrylates of aryl and alkyl derivatives of tin, lead and mercury easily polymerize and copolymerize with vinyl monomers. New compounds also are the metal‐containing styrenes. We synthesized for the first time, under the conditions of a Leebrick‐Ramsden reaction, mercury‐ and lead‐containing styrenes. We investigated for the first time the polymerization and copolymerization as well as some properties of the following metallated styrenes: p‐phenylmercurostyrene, p‐styrenetriphenyllead, p‐styrenetriphenyltin. The compounds polymerize easily and copolymerize with vinyl monomers under conditions of radical reaction. A study of the reaction kinetics showed that the metallated styrenes polymerize at greater rates than unsubstituted styrene. The thermal stability of the metal‐containing styrenes decreases in the order: Sn > Pb > Hg. In studies on the polymerization of p‐vinylphenylmercury disproportionation was found to take place, leading to the formation of the symmetric divinyl derivative of diphenylmercury (I) and of diphenylmercury (II). Specially synthesized p‐vinylphenyl phenylmercury (I) was found to polymerize easily with the formation of an insoluble three‐dimensional polymer, not melting up to 250° and decomposing above this temperature with the liberation of metallic mercury. The polymer of (I) evidently has the structure
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The investigation shows that there is a considerable difference in the polymerization capacity of unsaturated organometal compounds and in the properties of the polymers and copolymers formed, depending upon the nature of the bond between the vinyl group and the metal atom.
Interfacial polycondensation of the hydrochlorides of dicarboxylic acids and diamines in the process of fiber formation
Authors: Mikhaĭlov N. V. , Maĭboroda V. I. , Nikolaeva S. S. 
Published: April 2003

AbstractThe method of interfacial polycondensation based on Schotten‐Baumann reaction is a new direction in the chemistry of high molecular compounds. The low temperatures and pressures at which this reaction takes place open up enormous potentialities for the synthesis of new polymers and the formatmionof articles from them directly in t.he course of the reaction.Experiments were launched on the use of the intcrfacial polycondensation reaction for the formation of fibers and films directly during the polycondensation process. The monomer pairs used for the reaction were: sebacoyl chloride‐hexamethylenediamine, adipoyl chloride‐hexamethylenediamine, and terephthaloyl chloride‐hexamethylene‐ diamine. Polycondensation takes place differently in the fiber‐forming process from un‐ der stationary conditions and under conditions of mixing of the monomers. Fibers were spun in an upward flow of the solutions of the two monomers. The schematic and pa‐ rameters of the polycondensation reaction and fiber production are described. Experi‐ mental data were obtained on the yields and molecular weights of the polymers with re‐ spect to the monomer concentration and characteristics of the flow in the interfacial polycondensat.ion reaction in the process of fiber formation. These data were compared with the results from stationary conditions. Considerable difference has been shown to exist bet.ween the two modes of reaction, both in regard to the yield and to the specific viscosity of the polymers obtained. A tentative explanation of t,hese phenomena has been given. It was shown that, various additions play an important part in the interfacial polycondensation reaction. Cellulose derivatives, etc. were employed as the addition agents. A method was developed for spinning fibers in the process of polycondensation and the properties of the filaments formed have been investigated. Fibers of specific vis‐ cosity 1.23 have been obtained with a yield of 87y0. The fibers are capable of stretching to fourfold length and are typically hollow tubes in cross section. They are of crystal‐ line structure with strongly expressed fibrillarity, as was shown with the aid of an elec‐ tronic microscope.
Heterogeneous polycondensation
Authors: Akutin M. S. , Rodivilova L. A. 
Published: April 2003

AbstractA study was made of the influence of various factors (time, concentration of the solutions, reagent ratios, nature of the solvent, stirring rate, etc.) upon the physical and physicomechanical properties of polyamides obtained from the chlorides of aliphatic and aromatic dicarboxylic acids. The polyamides were synthesized by means of heterogeneous polycondensation (at the interfacial boundar). The possibility of synthesizing polyamides containing heteroatoms (sulfur, phosphorus, etc.) in the polymer main chain has been investigated.
Synthesis of polyureas by the method of interfacial polycondensation
Authors: Alexandru L. , Dascălu L. 
Published: April 2003

AbstractThe interfacial polycondensation method is one of the main achievements recently made in the chemistry of high molecular compounds. Its theoretical importance and the expected practical results aroused considerable interest in the method. By its means polyamides, polyesters and polyurethanes have been synthesized. The present report is devoted to a presentation of the results of an investigation into the interfacial synthesis of polyureas. The synthesis was carried out starting from the diamines and phosgene:
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In this particular case the diamine used was hexamethylenediamine. The reagents were brought in contract in the form of their solutions, namely in aqueous alkali in the case of the amine and in various organic solvents in the case of phosgene. The effect of the solubility of the phosgene solvent in the hexamethylenediamine solvent (water) on the yield and reduced viscosity of the polyureides was investigated. It was found that with increase in solubility both the yield and the viscosity decreased. The influence of the molar ratio of the reagents, of excess NaOH, of the solution concentration, of the duration of reaction, of the temperature, on the degree of polymerization and reduced viscosity of the polymers was also studied. A decrease of the temperature flavors growth of molecular weight. For temperatures between 10°C. and −10°C. the viscosity varies within the limits 0.08 to 0.7.
Some observations on the application of generalized copolymerization equations to several systems involving highly polar monomers
Authors: Ham George E. 
Published: April 2003

AbstractA generalized theory of copolymerization, including the significant effects of monomer units at any distance from the growing chain ending on the competitive addition of monomers has been recently published. The equations presented at that time are extended to cover various specific copolymerizations involving as one of the reactants a highly polar monomer such as maleic anhydride. Use of these expanded equations led to much improved correlation between experimental data and theoretical predictions. Pertinent reactivity ratios weighing the contributions of units nearby and at considerable distances from the growing chain endings were calculated from the data for the copolymer systems: styrene–maleic anhydride, methyl methacrylate–fumaronitrile, vinyl chloride–maleic anhydride, vinyl acetate–maleic anhydride, and isopropenyl acetate–maleic anhydride.
Graft copolymerization with perester side groups
Authors: Smets G. , Poot A. , Duncan G. L. 
Published: April 2003

AbstractThe kinetics of the graft copolymerization of styrene onto methyl acrylate (MA) and methyl methacrylate copolymers (MMA) containing tert‐butyl perester groups have been studied. The synthesis of these perester copolymers was carried out in two steps: (1) copolymerization of acrylyl chloride with methyl (meth)acrylate, and (2) reaction of the acrylyl chloride copolymer with tert‐butyl hydroperoxide. Further, these perester copolymers were usually treated with diazomethane in order to methylate any carboxylic group which might be present. The graft copolymers were separated from both hompolymers by progressive precipitation on addition of methanol to the chloroform solution of the copolymers. The stability of these perester copolymers has been considered and found to depend on whether there are acid groups in the copolymer. The first‐order rate constants and the activation energy of decomposition in the absence of acid groups have been evaluated. These values depend on the molar composition of the copolymer; an induced decomposition of peresters is favored by a high perester content, which is responsible for a decrease in Ea (26.8 instead of 29.6 kcal./mole). In the presence of free carboxylic groups, some of the perester groups decompose very rapidly, the energy of activation of their decomposition being only 15 instead of 25.6 kcal./mole for the slow step. The degree of conversion attained during the rapid step is a function of the stereochemical structure of the copolymer, and the rate of decomposition is much higher than that produced by the addition of external acid. With the MA perester the rate of grafting is proportional to the square root of the perester concentration while it is first order with respect to the monomer concentration. These dependences were found to hold also for the overall rate of polymerization (from the total weight increase) as well as for the grafting rate (from the isolated graft copolymer and its styrene content). The styrene content of the graft copolymer increases with monomer concentration (e.g., 53.8 and 75.3 for monomer concentrations of 2.6 and 6.1 moles/l., respectively). At low monomer concentration, grafting is greatly favored over homopolymerization; it is also enhanced by the viscosity of the solution. With the MMA perester also, the grafting rate obeys the square root law for the perester concentration and the first‐order dependence on monomer. However, the rate of grafting is practically independent of the styrene concentration over a large range. The relative importance of grafting over homopolymerization is in this case much less than with MA‐TBP, except at high dilution. Different interpretations are suggested in order to explain the very high and sometimes very low values of Rg/Rh, the ratio of the rate of grafting to the rate of hompolymerization. The different behaviors of the MA and MMA peresters are discussed.
Present status of the rubber elasticity theory
Authors: Ciferri A. 
Published: April 2003

AbstractThe development of the rubber elasticity theory is reviewed. Particular emphasis is given to the recent generalization of the elastic equation of state to the case where the chains display changes in internal energy with change in conformation and to the correlation between the elastic behavior of a crosslinked amorphous polymer and its dilute solution properties. Experimental results on the tension–temperature coefficient and on the stress–strain isotherm for polymer networks, which demonstrate the correctness of the generalized elastic equation of state, are surveyed.
Radiation‐induced ionic polymerization of isoprene
Authors: Tabata Yoneho , Shimozawa Ryosuke , Sobue Hiroshi 
Published: April 2003

AbstractThe γ‐ray‐induced polymerization of isoprene was investigated in the temperature range of ‐78° to 40°C. The following variables were studied: the dependence of polymerization rate on temperature; the effects of DPPH and pyridine on the polymerization at various temperatures; the dependence of the polymerization rate on dose rate at ‐78° and 20°C.; and the structure of the polyisoprenes obtained at various temperatures. the following results were obtained: (1) Although the Arrhenius plot of the polymerization rate did not yield a linear relation, the total polymerization rate was successfully separated into radical and ionic contributions. (2) The polymerization rate was proportional to the square root of dose rate at 20°C., whereas it was proportional to the first power of the dose rate at ‐78°C. (3) The structure of polyisoprene prepared at ‐78°C. is closely similar to that of cationically polymerized polyisoprene. The partially ionic mechanism of the radiation‐induced polymerization of isoprene was elucidated in this investigation. It was concluded that a cationic mechanism is operative at low temperatures whereas a radical mechanism predominates at higher temperatures.
Molecular weight distribution changes during the thermal breakdown of poly‐α‐methylstyrene
Authors: Cowie J. M. G. , Bywater S. 
Published: April 2003

AbstractThe changes in the molecular weight distribution accompanying the thermal depolymerization of poly‐α‐methylstyrene have been investigated. The original polymer, produced by anionic catalysis, had a narrow distribution of molecular weights, which facilitated measurement of the changes. The depolymerization when carried out in a thin polymer film at 226 and 236° caused extensive randomization of molecular weights at low conversions. In contrast, a similar depolymerization carried out in Decalin solution at 232° produced polymer maintaining the original sharp distribution. It is concluded that the kinetic chain length of the depolymerization reaction is much smaller than the molecular chain length in solid film reactions, but much greater than the molecular chain length in solution, under the experimental conditions used.
Sorption and diffusion in crystalline elastomers. Part II. Permeation of isomeric hydrocarbons in stretched rubber
Authors: Barrie J. A. , Platt B. 
Published: April 2003

AbstractThe permeabilities and diffusion coefficients of propane, n‐butane, and isobutane in stretched peroxide‐cured natural rubber have been measured at simple elongations of 0 to 400% in the temperature range 30 to 50°C. To minimize the effect of penetrant on the degree of crystallinity, only regions of low penetrant concentration were chosen. At elongations not sufficient to induce crystallization the permeability did not alter significantly on stretching. At higher elongations the permeability decreased with increasing crystallization. Over a long period of time and at a given temperature the permeability of a crystalline membrane decreased slowly toward an equilibrium value. No such behavior was observed with noncrystalline membranes either stretched or unstretched. Part of the decrease is accounted for by a corresponding slow increase with time in the degree of crystallinity and the remainder is attributed to a partial reorientation or redistribution of the crystallites as the system tends toward an equilibrium state. The data are analyzed in terms of a model in which the crystalline rubber is presented as a rectangular array of small cylindrical crystallites impermeable to penetrant and embedded in an amorphous matrix. To a first approximation the dependence of the permeability on crystallinity and temperature is represented satisfactorily by expressions based on the model. The data indicate that the crystallites may impose slight restrictions on the segmental mobilities in the amorphous regions, but the effect is not pronounced. Some differences between steady and transient state diffusion coefficients are explained in terms of “dead volume” which is present in the steady state of flow to a greater extent than in the transient state.
Crystallization of copolymers of ethylene glycol and diethylene glycol terephthalate
Authors: Golike R. C. , Cobbs W. H. 
Published: April 2003

AbstractRates of crystallization of polyethylene terephthalate and copolymers of ethylene glycol and diethylene glycol terephthalate were measured in the temperature range of 110 to 240°C.; this is the region of temperature in which the crystallization takes place at a measurable rate. It was found that the rate is defined by a modified Avrami type of equation over the entire temperature range of crystallization. Molecular motion, which limits crystallization at lower temperatures, was found to be a relaxation mechanism rather than simple viscous flow; to account for this, a modification of the Avrami type of equation was made. Data on copolymers of ethylene glycol and diethylene glycol terephthalate have shown that introduction of the longer chain yields a more flexible structure; hence at lower temperatures, where molecular motion is rate‐determining, the rate is increased. At higher temperatures introduction of the copolymer decreases the crystallization rate in the manner one would expect from the depression of the crystalline melting point.
The decomposition of benzoyl peroxide in polystyrene. II
Authors: Haas Howard C. 
Published: April 2003

AbstractPolystyrene films containing benzoyl peroxide were heated in air at 73 and 90°C. and the products of decomposition were investigated. The products are benzoic acid, phenyl benzoate, polystyrene benzoate, and carbon dioxide. The same products, in very similar quantities, are formed at both 73 and 90°C., suggesting that diffusion of radicals out of the polymer cage is not an important occurrence either above or below the apparent second‐order transition temperature of polystyrene. The change in the temperature dependence of peroxide decomposition rate above 80°C. seems to be associated with a greater ease of reaction of benzoyloxy radicals with the walls of the polymer cage above the glass temperature. Considerably more ester formation and less carbon dioxide evolution are observed in this decomposition than when benzoyl peroxide is decomposed in benzene or toluene. Attack by benzoyloxy radical occurs on both the ring and backbone of polystyrene, the backbone attack seeming to take place predominantly on the secondary carbon atoms of the backbone.
Some aspects of the crosslinking and degradation of gelatin molecules in aqueous solution irradiated by 60Co γ‐rays
Authors: Tomoda Yoshitada , Tsuda Minoru 
Published: April 2003

AbstractWhen an aqueous gelatin solution was irradiated by γ‐rays from a Co60 source, crosslinking occurred if nitrogen gas was passed through the solution, while degradation occurred with irradiation in an oxygen atmosphere. Empirical equations for the changes of the viscosity and the number of inter‐ or intramolecular crosslinks were obtained in each case and the phenomena were explained on the basis of an assumed reaction mechanism. The general equation for crosslinking is [η] = [η]Oekar, where [η] represents intrinsic viscosity of the solution and r is the γ‐radiation dose. The number of inter‐molecular cross links [R‐R]inter is given by [R‐R]inter = N0 (1 ‐ e‐kr), and the number of intramolecular cross links by [R‐R]intra = N0(kr + e‐kr ‐ 1), where N0 is the initial number of gelatin molecules. In the case of degradation, the variation at intrinsic viscosity and the number of intermolecular cross links with radiation dose is given by the equations: [η] = [η]0[N0/(N0 + k′r)]a and [R—R]inter = −k′r.
Evaluation of the terpolymer composition equation
Authors: Kahn Donald J. , Horowitz Hugh H. 
Published: April 2003

AbstractThe equations describing the relationships between polymer composition and feed composition in a three‐monomer polymerization have been experimentally verified at high monomer conversions for the first time. In this paper, a three‐component system involving vinyl acetate‐octyl fumarate‐N‐vinyl pyrrolidone was analyzed. The six reactivity ratios, or relative reaction rate constants, were either taken from previous literature or determined from two‐component systems. The differential terpolymerization equations could be integrated analytically in special cases, owing to the negligibility of some of the terms, but a more precise technique was to integrate numerically with a digital computer. Two feed compositions were polymerized to various levels of fumarate conversion covering the entire range. The extent of conversion was determined polarographically. Average terpolymer compositions, determined by elemental analysis, checked with values predicted by the mathematical model well within experimental error. The calculations also showed that the instantaneous terpolymer composition can vary considerably during a batch polymerization and give rise to a spectrum of polymer properties.