bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on Ziegler‐Natta catalysts. Part IV. Chemical nature of the active site
Authors: Rodriguez L. A. M. , van Looy H. M. 
Published: April 2003

AbstractThe determination of the number of sites active in the polymerization of ethylene on the surface of α‐TiCl3–Al(CH3)3 dry catalysts leads to the conclusion that this number is small in comparison to the total surface of the catalyst. Qualitatively this conclusion is also reached by two other independent methods. Infrared spectra of the catalyst before and after polymerization do not show a change in the type of bonds present in the surface. Electron microscopy proves that no active sites are formed on the basal plane of the α‐TiCl3 which constitutes 95% of the total surface. The results strongly favor the lateral faces of α‐TiCl3 as the preferred location of active centers. The lateral faces contain chlorine vacancies and incompletely coordinated titanium atoms. This must then be the essential conditions for the formation of active centers. The propagation of the polymer chain has been repeatedly shown to follow an insertion mechanism. The active site, therefore, necessarily contains a metal–carbon bond. The study of catalysts derived from TiCl3CH3 leads to the conclusion that a TiC bond on titanium of incomplete coordination is the active species in these cases. The alkylation of surface titanium atoms was proven to be an intermediate step in the catalyst formation from TiCl3 and AlR3. Survival of titanium–alkyl bonds on the lateral faces, where titanium atoms are incompletely coordinated explains best, in the light of our data, the activity of Ziegler‐Natta catalysts. Coordination of aluminum alkyl compounds in or around the active center probably complicates the structure of the active centers.
New high‐temperature polymers. II. Ordered aromatic copolyamides containing fused and multiple ring systems
Authors: Dobinson Frank , Preston J. 
Published: April 2003

AbstractSymmetrical diamines, containing preformed carbonamide linkages, were prepared by reacting nitrobenzoyl chlorides with aromatic diamines and reducing the dinitro intermediates. The diamines were polymerized with aromatic diacid chlorides to give wholly aromatic ordered copolyamides of exceptionally high thermal stability. Ordered diamines were prepared containing only phenylene units as the aromatic portion, and others containing phenylene and naphthylene or biphenylene groups. Low‐temperature solution polymerization of these diamines with isophthaloyl chloride, 4,4′‐bibenzoyl chloride, or 2,6‐naphthalenedicarbonyl chloride, gave thirteen ordered copolyamides, each containing a naphthylene and/or biphenylene group in its repeating unit. Differential thermal analyses and thermogravimetric analyses showed these polymers to have melting points or decomposition temperatures of from 420 to over 500°C. Films of one of the polymers had a breakdown voltage of 3000 v./mil at 180°C. Fibers of the same composition had tenacities of up to 8 g/den.; a 5.5 g/den. sample retained 85% of its tenacity after 17 hr. at 300°C. and 21% after 9 days.
Correlation of cationic copolymerization parameters of cyclic ethers, formals, and esters
Authors: Yamashita Yuya , Tsuda Tetsuo , Okada Masahiko , Iwatsuki Shouji 
Published: April 2003

AbstractCarefully determined cationic copolymerization parameters of cyclic ethers, formals, and esters are collected. Relative reactivity correlates with basicity and free energy. Further correlations of the copolymerization parameters for styrene, the effect of promoters, and the known mechanism of hydrolysis permitted a decision between the carbonium ion (including acylium ion) or the oxonium ion as the active intermediate of the propagation. Structural features which promote depropagation are identified. Equations describing these possibilities were derived and briefly discussed. Catalyst and solvent effects limited the correlation possibilities.
Flow rates of polymer solutions through porous disks as a function of solute. II. Thickness and structure of adsorbed polymer films
Authors: Rowland Fred W. , Eirich Frederick R. 
Published: April 2003

AbstractThe thickness of films of poly(methyl methacrylate) (PMMA), poly(vinyl acetate) (PVAc), and polystyrene (PS) adsorbed on Pyrex glass was studied by measuring the flow rates of polymer solutions and the corresponding pure solvents through sintered filter disks. Adsorption isotherms were in agreement with those reported by other workers and showed saturation adsorption equivalent to 2–8 condensed monolayers of monomer units. Film thicknesses were of the order of magnitude of the free coil diameters in solution and were directly proportional to the intrinsic viscosity of the polymer, except for PS in benzene where the thicknesses leveled off as molecular weight increased. It was concluded that polymers adsorb from solution in monolayers of compressed or interpenetrating coils; that below some critical molecular weight which varies with polymer and solvent, a much larger fraction of the segments lies directly in the interface; that adsorbed films may consist of a dense layer immediately adjacent to the surface and a deep layer of loops extending into the solvent; and that it is the segment—solvent interaction rather than the segment—surface interaction which dominates the conformation of the adsorbed chain.
Crystalline polymers of bis(β‐chloroethyl) vinylphosphonate
Authors: Marktscheffel Fritz , Turbak A. F. , Wilchinsky Z. W. 
Published: April 2003

AbstractThe polymerization of bis(β‐chloroethyl) vinylphosphonate to a crystalline solid was carried out with a Ziegler‐Natta catalyst. A confirmation of the crystalline nature of the polymers was carried out by x‐ray diffraction. The polymers would not melt even at temperatures up to 620°C., but instead began to char. However, they were soluble in dimethylformamide and acrylonitrile.
Rates of copolymerization of acrylonitrile and ethylenesulfonic acid
Authors: Alfrey Turner , Pfeifer Charles R. 
Published: April 2003

AbstractUse was made of differential absorption in the near‐infrared region to follow the rates of copolymerization of acrylonitrile (AN, M1) with ethylenesulfonic acid (ESA, M2) in aqueous zinc chloride solution. The concentrations of the monomers were followed separately and simultaneously. It was found experimentally that the ratios d log [M1]/dt and d log [M2]/dt were each constant. This was interpreted to mean that the product of the reactivity ratios of the two monomers (r1,r2) is unity and that the ratio of termination rate constants is equal to the propagation reactivity ratio. It was found that d log [M1]/d log [M2] = r1 = 4.52. This value is in fair agreement with polymer composition data obtained independently. In the Q—e system the equality r1r2 = 1 is equivalent to the monomers having equal e values. Thus, in the AN—ESA system, P1/P2 = k11/k21 = k12/k22 = k1T/k2T, where P1 is the resonance constant of polymer radicals ending in units of M1; and k11, k12, and k1T are the rate constants involving the reaction of this radical with M1, M2, and T (terminating agent), respectively. A gel effect was not observed even at M1 conversions as high as 88%.
Thermal volatilization analysis: A new method for the characterization of polymers and the study of polymer degradation
Authors: McNeill I. C. 
Published: April 2003

AbstractIn a continuously evacuated system in which volatile products are passing from a heated sample to the cold surface of a trap some distance away, a small pressure will develop which varies with the rate of volatilization of the sample. If this pressure (measured by Pirani gage) is recorded as the sample temperature is increased in a linear manner, a TVA thermogram showing one or more peaks is obtained. TVA thermograms for a number of polymers and copolymers are presented and briefly discussed. The technique has some advantages over TGA for characterizing polymers or studying qualitative aspects of polymer degradation.
Polymerization in the crystalline state. IX. Relation between the velocity of radiation‐induced in‐source polymerization and post‐polymerization
Authors: Morawetz Herbert 
Published: April 2003

AbstractA general relation is derived between the polymerization velocities to be expected for crystalline monomers during irradiation at a polymerization temperature and the post‐polymerization observed in samples irradiated at very low temperatures and subsequently warmed outside the irradiation source. For acrylamide, the experimental data are in satisfactory agreement with the theoretical relationship. The possible reasons for a deviation from this relationship are discussed.
Polymers derived from fluoroketones. I. Preparation of fluoroalkyl acrylates and methacrylates
Authors: Pittman A. G. , Sharp D. L. , Lundin R. E. 
Published: April 2003

AbstractThe preparation and physical properties of some perhaloalkyl acrylate and methacrylate esters are discussed. In the synthetic route to the perhaloalkyl esters, acryloyl or methacryloyl chloride is made to react with a metal fluoride—perhaloketone adduct. A side reaction which accompanies esterification is the formation of acryloyl or methacryloyl fluoride. Possible mechanisms for the formation of acyl fluoride and ester are considered. Evidence is presented which suggests that acyl fluoride formation may occur by a breakdown of the fluoroalkyl esters through an intramolecular fluorine shift.
Studies on addition polymerization in mixed solvent system. Part I. Chain transfer of water in polymerization of methyl methacrylate
Authors: Bhattacharyya Bhupati Ranjan , Nandi Umasankar 
Published: April 2003

AbstractThe role of water as a chain‐transfer agent in addition polymerization of methyl methacrylate and acrylamide in a mixed solvent system was studied. Water does not have any transfer with the growing polymer radical. The degree of polymerization is found to increase with increasing water concentration. This is probably due to a reduced termination rate resulting from coiling of the polymer chain in the presence of a nonsolvent like water.
Mechanism of ozone attack on α‐methyl glucoside and cellulosic materials
Authors: Katai Andrew A. , Schuerch Conrad 
Published: April 2003

AbstractOzone attack on cellulose and related substances was investigated and appears to involve a twofold mechanism. One is a free‐radical chain mechanism involving oxygen in the propagating step. This slow reaction is highly indiscriminate, showing very little, if any, specificity as to the site of attack and resulting in the formation of peroxide, carbonyl, carboxyl, and presumably lactone groups. In the presence of oxygen, kinetic chain lengths of over 100 were measured, but in nitrogen atmosphere the total oxidation of substrate was equivalent to the amount of ozone consumed. The second process appears to be an electrophilic attack which liberates the anomeric carbon of glycosides via an ozone‐catalyzed hydrolysis of glycosidic linkages. This reaction, analogous to a nitronium or chloronium ion‐ or proton‐catalyzed hydrolysis, is postulated since chain degradation of polysaccharides is equally severe in the presence or absence of oxygen, and occurs in buffered solutions or suspensions even in the neutral pH range, and because the main product of ozone attack on α‐methyl glucoside is glucose. Brightness improvement in cellulose involves an electrophilic attack on double bonds and therefore is a direct function of the quantity of ozone used, like chain degradation. It is therefore not surprising that we have found no method of enhancing the specificity of ozone attack on the colored material relative to chain degradation. Because of the topochemical and diffusion‐controlled character of the reaction on cellulose, the use of a different temperature range will cause only a trivial difference in the relative rates of attack.
Effect of thiourea on the radical polymerization of vinyl monomers. Part II. Effect of diphenyl thiourea on the polymerization of methyl methacrylate with benzoyl peroxide as initiator
Authors: Minoura Yuji , Sugimura Takaaki 
Published: April 2003

AbstractThe polymerization of methyl methacrylate (MMA) initiated by benzoyl peroxide (BPO) in the presence of diphenyl thiourea (DPTU) has been studied. It was found that the BPO–DPTU catalyst system was not an effective accelerating system but showed a relatively strong retarding effect. With DPTU derivatives, the polymerization rate was found to decrease with the increase in the electron‐attracting forces of substituents attached to the phenyl groups of DPTU. In the polymerization of MMA initiated by AIBN, the addition of DPTU to the reaction systems affected neither the polymerization rate nor the degree of polymerization. From this fact, it might be concluded that DPTU itself serves as a radical scavenger. It seems most probable from the results of kinetic studies, iodometric titration, and from the effect of an oxidation product of DPTU (diphenyl formamidine disulfide) that the retardation effect observed is attributable to the action of the disulfide (DPFDS). By extending the Alfrey‐Price scheme for the copolymerization reactions to the chain‐transfer reactions, the Q and e values of DPFDS were determined. The apparent chain‐transfer constants for DPTU and its derivatives were calculated by means of rate measurements and were correlated with substituent constants. The mechanism of the polymerization is discussed on the basis of these results.
Effects of polysulfides on the polymerization of methyl methacrylate
Authors: Sugimura Takaaki , Ogata Yayoi , Minoura Yuji 
Published: April 2003

AbstractThe effect of organic sulfur compounds on the radical polymerization of methyl methacrylate initiated by azobisisobutyronitrile at 50°C. has been studied. The sulfur compounds used were benzene‐type polysulfides (C6H5CH2SnCH2C6H5; n = 0–4), benzyl mercaptan, and sulfur (S8). All sulfur compounds studied, except dibenzyl, dibenzyl monosulfide, and dibenzyl disulfide, were found to behave as retarders under these experimental conditions. Chain‐transfer constants of these compounds were determined from rate measurements and from the conventional method based on numberaverage degree of polymerization. Chain‐transfer constants of benzyl‐type polysulfides were less than those of mercaptan and sulfur and increased with increasing sulfur. The correlation of the reactivities of sulfur compounds as transfer agents and their molecular structures is discussed.
Ionic polymerization under an electric field. III. Cationic polymerizations of α‐methylstyrene and styrene
Authors: Sakurada Ichiro , Ise Norio , Tanaka Yoshinobu , Hayashi Yuzuru 
Published: April 2003

AbstractCationic polymerizations of α‐methylstyrene and styrene were carried out in an electric field with iodine as a catalyst and ethylene dichloride as the solvent. The effects of the field on the rate of polymerization and the degree of polymerization were studied. It was found that the field increased the rate of polymerization of α‐methylstyrene and, also slightly increased the degree of polymerization, whereas the field had no influence on these quantities in the case of styrene. The expressions for the rate of polymerization and the degree of polymerization, which were derived in a previous paper and refined in the present paper, show that these quantities are generally a function of the degree of dissociation of ion pairs at growing chain ends. For a comparatively large degree of dissociation, these expressions can account for the field effect as was observed on α‐methylstyrene, if one assumes that the degree of dissociation in the presence of an electric field is larger than that in its absence, and that the free‐ion propagation proceeds much faster than the ion‐pair propagation. For a small degree of dissociation, however, these expressions become practically independent of the degree of dissociation so that a possible increase due to the presence of an electric field gives rise to no observable effect on the polymerization. This situation may be interpreted as corresponding to the case of styrene. In other words, the polymerization of α‐methylstyrene has more free ionic character than that of styrene.
Copolymerization of styrene and methyl methacrylate. Reactivity ratios from conversion–composition data
Authors: Meyer Victor E. 
Published: April 2003

AbstractA method for the determination of reactivity ratios from conversion–composition data has been outlined. The conversion–composition changes during the copolymerization of styrene (M1) and methyl methacrylate (M2) have been studied at 60°C. By a method of graphical intersection, the integrated form of Skeist's equation has been used to determine the reactivity ratios (r1 = 0.54 ± 0.02 and r2 = 0.50 ± 0.06) in reasonably good agreement with values reported in the literature. The area of intersection was used as a measure of the precision of the data.
Solution Polymerization of Acrylonitrile Catalyzed by Sodium Triethylthioisopropoxyaluminate: A Polyacrylonitrile with High Structural Regularity
Authors: Chiang R. , Rhodes J. H. , Evans R. A. 
Published: April 2003

AbstractA new catalyst for the polymerization of acrylonitrile has been found by reacting sodium aluminum tetraethyl with a stoichiometric amount of oxygen, alcohols, or mercaptans, etc. The catalyst prepared by reacting NaAlEt4 with RSH remains active at temperatures as low as −78°C., polymerizing acrylonitrile into high molecular weight polymers with high conversions. At −78°C., the propagating chain remains active over a period of days, and the chain length increases with time or conversion. At high conversions the molecular weight of the polymer is directly proportional to the concentration of the monomer, the catalyst concentration being kept constant. The efficiency of the catalyst expressed as the ratio of the number of the polymer molecules produced to the number of the sulfur atoms used is in excess of 80%. The weight‐average molecular weight of the polymer measured by light scattering is roughly equal to the number‐average molecular weight determined by sulfur analysis assuming only onesulfur atom in each polymer molecule. Although the data given here are only qualitative in nature, it is nevertheless evident that this system bears great resemblances to anionic polymerizations resulting in “living polymers.” The polymer obtained with the NaAlEt3S(i‐Pr) catalyst at −78°C. differs from free‐radical polyacrylonitrile in exhibiting substantially lower solubility, higher melting point, and higher rate of crystallization than that for the free‐radical polymer. The polymer is also free from structural mpurities; it does not cause fluorescence in dilute solutions and has no absorption peak at 265 mμ; both these effects are produced by impurities in free‐radical polyacrylonitrile. It is concluded that the polymer reported here is more regular in structure than free‐radical polyacrylonitrile.
Mechanism of fracture in glassy polymers. II. Survey of crazing response during crack propagation in several polymers
Authors: Kambour Roger P. 
Published: April 2003

AbstractOf nine glassy polymers so far investigated, eight yield evidence that fracture propagation involves the formation and breaking of craze material. All eight produce fracture surfaces exhibiting interference colors to one extent or another and even the colorless areas cause low angle x‐ray scattering. Ranked in terms of decreasing ease of colored surface formation, these polymers are poly(methyl methacrylate), poly(ethyl methacrylate), polystyrene, acrylonitrile—styrene copolymer, poly‐α‐methylstyrene, poly(vinyl acetate), a polyhydroxy ether, and polycarbonate. Only rigid poly(vinyl chloride) has failed to show evidence of precrack craze formation.
Thermodynamics of crystalline linear high polymers. V. Extended‐chain copolymers of polyethylene
Authors: Arakawa Tamio , Wunderlich Bernhard 
Published: April 2003

AbstractEthylene—propylene and ethylene—butene‐1 copolymers with up to 1.7 side groups per 100 carbons have been crystallized at 227°C. and under 4100–4900 atm. pressure. The resulting crystalline polymers are at least partially of extended‐chain crystal morphology. Comparison with the same polymers crystallized at atmospheric pressure, which gives folded‐chain crystal morphology, revealed: (1) a density higher by 0.008–0.019 g./cm.3 depending on copolymer content; (2) a similar decrease of crystallinity with side group concentration; (3) a similar decrease of the beginning of melting from 125°C. for homopolymer to 65°C. for 1.7 side groups per 100 carbons; (4) a higher (138 ± 0.8°C.) experimental maximum melting point which, in contrast, is independent of copolymer content and seems to vary only with the fraction of low molecular weight material; (5) a decreasing amount of high‐melting crystals with increasing copolymer content (72–8%) and an increasing amount of low‐melting crystals (27–53%) with increasing copolymer content. In addition, superheating, which reached 5.5°C. for 50°C./min. heating rates, was detected. It was concluded that high‐pressure crystallization leads, at least for part of the crystals, to solid solution formation, while atmospheric pressure crystallization does not. Which mode of crystallization is achieved seems kinetically determined. Experimental techniques were dilatometry, DTA, and calorimetry.
Single crystals of amylose V complexes. II. Crystals with 71 helical configuration
Authors: Yamashita Yuhiko , Hirai Nishio 
Published: April 2003

AbstractIt has been shown that lamellar crystals of amylose V complexes with 71 helical configuration can be obtained by using complexing agents larger in cross section than n‐butanol. The electron diffraction studies indicated a new unit cell for the unheated lamellar crystals which are composed of molecules with 71 helical configuration and hold water molecules on the exterior of the helix. Furthermore, from a throughly dried specimen at 100°C. in vacuo we obtained a pattern which showed only three Debye rings. Its spacings were explained by a two‐dimensional hexagonal unit cell having a = b = 14.7 A. proposed by Zaslow. It was also found that when the crystals were dispersed in methanol at room temperature, their electron diffraction pattern was the same as that of the anhydrous amylose V complex of n‐butanol.
Intercrystalline links in polyethylene crystallized from the melt
Authors: Keith H. D. , Padden F. J. , Vadimsky R. G. 
Published: April 2003

AbstractIntercrystalline links in polyethylene have been revealed by crystallizing from the melt mixtures of fractionated polymer and the linear hydrocarbon n‐C32H66, the latter constituent being removed later by washing at room temperature in an organic solvent. These fibrous links measure up to 15,000 A. in length and are 30–300 A. in thickness. Molecular chains are oriented parallel to the lengths of the links, and apparently nucleate on tie molecules formed by the simultaneous crystallization of different parts of the same molecule on the surfaces of different, and often widely separated, crystals. The maximum length of the links found in a given polymer varies as the square root of molecular weight, and there are indications that molecules in the melt are much more extended than is predicted by conventional configurational statistics. The links are under tension and presumably exert a significant influence on physical properties.