bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ethylene–propylene copolymerization in the presence of catalysts prepared from vanadium triacetylacetonate
Authors: Natta Giulio , Mazzanti Giorgio , Valvassori Alberto , Sartori Guido , Fiumani Diego 
Published: April 2003

AbstractEthylene–propylene copolymerization in the presence of catalysts prepared from vanadium halides was described in our previous papers. Linear, high molecular weight, completely amorphous copolymers, having an ethylene molar content up to 80%, can also be von 0°C weitaus höhere Copolymerausbeuten als bei Raumtemperatur. Die höhere Bruttopolymerisationsgeschwindigkeit bei tiefen Temperaturen ist spezifisch für dieses besonder katalytische System und tritt bei Katalysatoren, die aus Vanadinchloriden dargestellt wurden, nicht auf. Bei −20°C ist die Zusammensetzung der Copolymeren von der Polymerisationsdauer, dem Molverhältnis Al(C2H5)2Cl/VAc3, der Katalysator‐konzentration oder der Gesamtkonzentration der Monomeren unabhängig. Das mittlere Molekulargewicht der Copolymeren nimmt mit steigendem Al(C2H5)2Cl/VAc3Verhältnis und steigender Katalysatorkonzentration ab, was für das Auftreten eines Ubertragungsprozesses zwischen den wachsenden Ketten und den im System vorhandenen organometallischen Verbindungen spricht. Bei konstantem Verhältnis zwischen den Monomerkonzentrationen und zwischen den Katalysatorkomponenten ist die Bruttopolymerisationsgeschwindigkeit in bezug auf die Katalysator‐ und Monomerkonzentrationen von erster Ordnung. Die Reaktivitätsverhältnisse der Monomeren, r(C2H4) = 15.0, r(C3H6) = 0.04, sind zwischen −20°C und +25°C von der Temperatur unabhängig. Das Produkt der beiden Werte (0,6) weist darauf hin, dass eine Abwechslung der Monomereinheiten in den Ketten wahrscheinlicher ist als eine statistische Verteilung, bei der das Produkt dieser Verhältnisse gleich 1 ist.
Kinetics of ethylene–propylene copolymerization
Authors: Natta G. , Mazzanti G. , Valvassori A. , Sartori G. , Barbagallo A. 
Published: April 2003

AbstractThe values of the reactivity ratios for ethylene–propylene and ethylene–1‐butene copolymerization, described in previous papers, and the distribution of monomer units in different length sequences are discussed. In this paper the kinetics of ethylene–propylene copolymerization in the presence of catalysts prepared from trialkylaluminum and vanadium tetrachloride is studied. Having adopted the conditions leading to the formation of catalysts having an activity independent of time, we were able to determine that the copolymerization rate is first order with respect to the catalyst concentration and to the sum of the concentrations of the two monomers. With the total concentration of the monomers constant, the copolymerization rate increases very rapidly as the ethylene concentration increases. The activation energies of the four chain growth reactions of the copolymerization proved to be practically equal.
Stereospecific polymerization of 2‐vinylpyridine
Authors: Natta G. , Mazzanti G. , Longi P. , Dall'Asta G. , Bernardini F. 
Published: April 2003

AbstractSome metalloorganic or metal amide compounds of very electropositive metals, such as lithium, sodium, beryllium, magnesium, and aluminum, cause the polymerization of 2‐vinylpyridine. Whereas the compounds of beryllium and of aluminum furnish slightly crystalline 2‐vinylpyridine polymers, by using magnesium derivatives it is possible to obtain polymers which are highly crystalline by x‐rays. The results obtained from the systematic study of the polymerization in the presence of amides or of metalloorganic compounds of magnesium are reported. In particular, it has been examined the influence of the monomer/catalyst molar ratio, of the temperature, of the polymerization time, and of the nature of the substituents bound to magnesium, on the course of the polymerization and on the properties of the obtained polymers. Examination by IR spectrography allowed us to conclude that at least a part of the macromolecules contain, as endgroup, the organic groups which were initially bound to the metal in the compounds used as catalyst. The stereospecificity of the process must be ascribed to the possibility of coordination of the catalyst to the monomer molecules entering the growing chain. In fact, the addition of organic Lewis bases to the system, causes the reduction or the disappearence of stereospecificity. The obtained results allowed us to conclude that the stereospecific polymerization of 2‐vinylpyridine takes place by an anionic coordinated mechanism. 4‐Vinylpyridine, in the presence of catalysts which are stereospecific for the polymerization of 2‐vinylpyridine, gives amorphous noncrystallizable polymers. That was ascribed by us to the fact that the nitrogen atom, in the case of 4‐vinylpyridine is too far from the vinyl double bond to form, with the catalyst, an addition complex able to give the same orientation to all the monomer molecules, at the very moment of the polymerization.
Isomorphism phenomena in macromolecules
Authors: Natta G. , Corradini P. , Sianesi D. , Morero D. 
Published: April 2003

AbstractThrough x‐ray and infrared examinations of stereoregular polymers and copolymers of vinylaromatic monomers, the occurrence of chain isomorphism phenomena, together with many cases of a new type of isomorphism between monomeric units, have been proved. Isomorphism of macromolecules, allowing true solid solutions, has been observed when melting and crystallizing mixtures of homopolymers (i.e., isotactic polystyrene) and of crystalline copolymers (i.e., styrene‐p‐methylstyrene) having the same identity period and differing very little in lattice constants. Isomorphism among monomeric units occurs in copolymerizing monomers that have a chemical nature and shape slightly different one from the other, e.g., styrene and o‐fluorostyrene. This allows the formation of crystallizable copolymers in the entire composition range. They show physical properties (lattice constants, melting temperatures, etc.) continuously varying between those of the pure homopolymers. The occurrence of isodimorphism phenomena has been observed in crystalline copolymers obtained from monomers the homopolymers of which have different crystalline structures (e.g., styrene‐p‐fluorostyrene), and also in copolymerizing styrene with monomers (e.g., p‐methyl, p‐chlorostyrene) giving only amorphous homopolymers. In the latter case, of course, the copolymers show crystallinity only in a limited composition range.
The influence of substituents on the properties of crystalline polyhydrocarbons. I. Methyl‐substituted arylpropene and arylbutene polymers
Authors: Price J. A. , Lytton M. R. , Rånby B. G. 
Published: April 2003

AbstractThe new alpha olefins 2‐allyl‐p‐xylene, 4‐allyl‐o‐xylene, 5‐allyl‐m‐xylene, 4‐(o‐tolyl)‐1‐butene and 4‐(p‐tolyl)‐1‐butene were prepared. These olefins, in addition to the known ortho, meta and para allyltoluenes, have polymerized, using aluminum alkyl titanium chloride catalyst, to crystalline polymers. Physical properties of these polymers, both as powder and molded sample, have been studied. Melt temperatures (Tm) and glass transition temperatures (Tg) have been determined using differential thermal analysis, dynamic modulus measurements, and dilatometric measurements; observations on the birefringent melting behavior were also noted. The effects of both olefin chain length and substitution of methyl groups in the ortho, meta, and para position, respectively, on the properties of these polymers have been interpreted according to present concepts. The results are in general agreement with corresponding data for isotactic methyl‐substituted polystyrenes. Substitution in the ortho position raises both transition temperatures considerably, while meta and para substitution cause only smaller effects.
Changes in potential during polymerization in redox systems
Authors: Turska E. , Wisniewski J. 
Published: April 2003

AbstractThe change in potential during emulsion polymerization in a system in which the oxidizing agent is soluble in the disperse phase and the reducing agent in the aqueous phase was studied. The process was also followed by means of an ultraviolet spectrophotometric method. The time‐potential curve was found to be linearly related to the curve depicting the change in monomer concerntration. The experimental data were subjected to mathematical treatment to determine the correlation coefficient and to derive a direct regression equation. In addition, systems containing reducing and oxidizing agents and monomer in a single phase were also studied, and the change in potential during polymerization was determined at various initial monomer concentrations. A relation was established between the results obtained and the polymerization process.
Emulsion polymerization of chloroprene
Authors: Hrabáak F. , Zachoval Ya. 
Published: April 2003

AbstractThe emulsion polymerization of chloroprene was investigated. Determinations were made of the effect of the emulsifier on the polymerization rate in the presence of varying initiators. It has been found that in the case of monomer‐soluble initiators, rosin soap (as compared with mersolate and hydrogenated rosin) has been found to be a strong inhibitor of polymerization. With the objective of ascertaining the optimum conditions of interaction between TETD and the polysulfide bonds of the chloroprene‐sulfur copolymer the rate of rupture of the bonds in relation to the pH of the latex was determined. Polymerization of chloroprene in the presence of various initiator systems of the peroxide‐tertiary amine type was investigated with the use of mersolate as emulsifier. During the course of the polymerization the viscosity of the polymer was determined with the aid of the Vistex method for determining gel formation. On adding 5 wt‐% of carbon tetrachloride in the presence of sodium N,N‐dimethylsulfanilate and benzoyl peroxide, a soluble polymer was obtained, the conversion reaching a value of 100%. Phenyl‐β‐naphthylamine is an inhibitor of peroxide‐induced polymerization but has no inhibiting effect when azobisisobutyronitrile is employed as initiator.
A study of emulsion polymerizations
Authors: Krishan T. , Margaritova M. 
Published: April 2003

AbstractA kinetic study of the polymerization of methyl methacrylate, vinylidene chloride, and chloroprene in aqueous emulsion has been studied over a wide range of concentrations of emulsifier and initiator. Potassium persulfate, hydrogen peroxide, sodium perborate, benzoyl peroxide, and azobisisobutyronitrile were used as initiators, and the sodium salts of the sulfonic acids of aliphatic hydrocarbons (SA emulsifier) and sodium laurate as emulsifiers. A soap titration method coupled with conductometric titration was employed to determine the number and size of the polymer particles formed at various stages of the polymerization process with respect to the concentration of the substances participating in the latter. The kinetic relations and the data on the particle number and size were discussed from the standpoint of existing views on the mechanism of emulsion polymerization. This led to the conclusion that the principle of discrete particles cannot be applied to polymer particles; i.e., they cannot be considered as microspaces where polymerization takes place independently of each other. The experimental findings indicate that the relations are determined by the overall volume of the emulsifier independently of whether it is in the form of micelles or is on the surface of the polymer particles.
Interchain exchange reactions in radical polymerization
Authors: Pyrkov L. M. , Frenkel S. Ya. 
Published: April 2003

AbstractInterchain exchange reactions with the formation of “hybrid” polymers take place in mixed solutions of two polymers or in solutions of polymers dissolved in “foreign” monomers, in the presence of free radical initiators. A number of methods, namely, turbidimetric titration, ultraviolet spectroscopy, refractometry, and pycnometry were used to identify and analyze the hybride polymers. A qualitative method for determining the “hybridity” of polymers was developed. This consisted in determining the optical and mechanical (relaxation) properties of polymer films obtained from various solvents (poor solvents for one and good solvents for the other type of block or branch of the hybrid polymer). For the quantitative investigation of systems containing the hybrid polymers a new method employing an ultracentrifuge has been developed. This is a modification of Meselson's method (equilibrium centrifugation in a concentration gradient) and consists in centrifuging a mixture of two homopolymers and their hybrid polymer in a mixture of two solvents of which the density has been so chosen that the homopolymers give the Boltzmann distribution at the bottom and at the meniscus of the cell. The hybrid polymer accumulates in a band in the central part. Theoretically the method allows one to determine simultaneously the molecular weight distribution of all three polymers and the composition of the “hybrid” polymer. The present experiments are important in throwing light on the secondary reactions taking place in radical homopolymerization and leading to unusual multimodal or “tailed” molecular weight distributions.
Polymerization and grafting processes on freshly formed surfaces
Authors: Kargin V. A. , Platé N. A. 
Published: April 2003

AbstractThe intensive mechanical dispersion of a number of solid crystalline and amorphous inorganic substances (metals, oxides, and salts) in vinyl monomers was used for polymerizing the latters under simple conditions. The reaction was induced by free radicals or active ions arising on the newly formed surface of the dispersing inorganic substances. Depending upon the nature of the active surface, such polymerization reactions may lead to grafting of the resultant polymer onto the solid surface of the dispersing substances.
Synthesis of cis and trans polymers of dienes on oxide catalysts and investigation of their structure and properties
Authors: Tinyakova E. N. , Dolgoplosk B. A. , Zhuravleva T. G. , Kovalevskaya R. N. , Kuren'Gina T. N. 
Published: April 2003

AbstractCrystalline 1,4‐trans polymers of butadiene and isoprene of regular structure are formed in polymerization of dienes in a chromia catalyst (chromium oxide on aluminum silicate). 1,4‐trans‐Polybutadiene with a specific gravity of 1.015 has crystalline modifications melting at 75 and 135°C. The 1,4‐trans‐polyisoprene resembles natural gutta‐percha. When α‐butylene undergoes polymerization on the same catalyst, a crystalline polymer is formed of specific weight 0,96 and melting point ca. 140°C. Any disturbance of the 1,4‐trans‐structure by copolymerization of butadiene or isoprene with other compounds leads to a loss of capacity for crystallization and to transition to the high elastic state. The butadiene‐isoprene copolymer contains about 55% butadiene links while preserving the 1,4‐trans structure of the chain and has a glass temperature of ca. −90°C., coinciding with the value calculated on the basis of a linear relation between the copolymer composition and the glass temperature. By copolymerization ethylene units could be incorporated in the trans‐polyisoprene chain to the extent of ca. 40 mole‐%. The polymer formed has a glass temperature of −76°C., as compared with −71°C., for 1,4‐polyisoprene. Polymerization of butadiene induced by the cobalt oxide‐diethyl‐aluminum halides proceeds at a high rate, even at 0°C. The polybutadiene formed contains predominantly links cis‐1,4 (about 85%) and only a small quantity (5–8%) of 1,2 links. Owing to the high content of 1,4 links the polymer has a glass temperature as low as −115°C. Unlike organometallic‐titanium tetrachloride systems, interaction between cobalt oxides and organoaluminum compounds in the temperature range 0–80°C. is not accompanied by formation of gaseous hydrocarbon products.
The synthesis and properties of crystalline polymers of the type of poly‐p‐xylenes and polyphenylene methyl derivatives
Authors: Vansheĭdt A. A. , Mel'Nikova E. P. , Krakovyak M. G. , Kukhareva L. V. , Gladkovskiĭ G. A. 
Published: April 2003

AbstractFor the purpose of obtaining polymeric hydrocarbons of enhanced thermostability, linear polymers of regular structure of the type (CH2ArCH2)n and (ArCH2)a with aromatic units in the chain were synthesized. Polymers of the first type were obtained by reaction of metallic sodium with the dichloromethyl derivatives of benzene, m,‐ and p‐xylenes, diphenylmethane, diphenyl and naphthalene in dioxane medium at 20–25°C. The m‐xylene derivative had a CH2Cl group in the m‐position and the others, dichlorides in the p‐ or p,p′‐positions. The polymers were precipitated from the solutions on forming and after removal of excess sodium with the aid of methanol and elimination of the low molecular impurities they appeared as colorless powders of the composition of hydrocarbons, at times containing chlorine. X‐ray analysis of the polymers revealed the presence of a crystalline structure the degree of which varied, depending upon the structure. The polymers differed greatly in solubility and melting points. Thus naphthalene and diphenyl derivatives, evidently being crosslinked three‐dimensional polymers, did not dissolve even in boilling α‐bromonaphthalene and decomposed above 300° and 550° without melting, while derivatives of other hydrocarbons dissolved in bromonaphthlene, melted, and probably were linear polymers of low molecular weight. The m‐xylene derivative was distinguished by low crystallinity, low melting point (130–135°C.) and easily dissolved in chloroform even in the cold. Diphenylmethane derivatives with a more clearly expressed crystallinity melted at 250–255°C. and began to dissolve in α‐bromonaphthaline only at 130°C. p‐Xylene derivatives, like poly‐p‐xylylene, were highly crystalline and melted at 350°, but began to dissolve in bromonaphthalene only at 235°. The molecular weight of the soluble polymers could be determined (according to Rast's method) only for the soluble m‐xylene derivative, which, depending upon the conditions of formation, varied from 1850 to 4000. Polymers of the second type were obtained by polycondensation of aromatic hydrocarbons with paraform and also with the dichloro‐, dioxy‐, and diacetoxymethyl derivatives of aromatic hydrocarbons in boiling glacial acetic acid containing sulfuric acid. In this way starting from p‐xylene and durene one could obtain high‐melting crystalline polymers with melting points above 250 and 320°, dissolving only in high boiling solvents. Condensation of durene with dichloromethyl derivatives of p‐ and m‐xylene as well as with p‐xylylene chloride led to the formation of high melting polymers of the type (ArCH2Ar′CH2)n containing two different aromatic units in the chain.
Cyclic polymerization and copolymerization of divinyl acetals
Authors: Matsoyan S. G. 
Published: April 2003

AbstractCyclic polymerization constitutes an intramolecular closure of isolated dienes into five‐ or six‐membered rings with concurrent intermolecular growth of the chain. We have synthesized for the first time divinyl acetals and have investigated their capacity for cyclic polymerization. A method had been developed for the synthesis of divinyl‐acetals through interaction of aldehydes with ethylene chlorodihydrin and the subsequent dehydrochlorination of β,β′‐dichlorodiethylacetals. The structure of the divinyl‐acetal monomers was proved, in particular, by hydrolysis and hydrogenation. It has been shown that, in the presence of initiators of radical polymerization, divinylacetals polymerize only by means of the cyclic mechanism, with the formation of acetal derivative of polyvinyl alcohol, i.e., polyvinylacetals. The name “polyvinylacetal” based on the name of the monomer should be changed to “polydivinylacetal”
magnified image
Where R = H, CH3, C3H7, iso‐C3H7, iso‐C4H9 and C6H5. Polyvinylacetals have been obtained with an extent of acetylation of 100%. Until recently the possibility of cyclic copolymerization was not known. We have investigated this reaction on the examples of the copolymerization of divinylacetals with vinyl and diene monomers:
magnified image
where R = H, CH3, and C3H7 and X = OCOCH3, CN, and C6H5.The possibility of cyclic cyclopolymerization has been demonstrated by copolymerization of divinylformal and divinylethanal. All polymers obtained by us are white powders or rubberlike thermoplasts, easily soluble in most organic solvents and possessing high adhesive properties. They do not add hydrogen or bromine, indicating the absence of double bonds. The structure of the polyvinylacetals obtained on cyclopolymerization of divinylacetals was demonstrated by means of hydrolysis. As was to be expectd, polyvinyl alcohol was formed, of which in turn the glycol structure was proved by its oxidation to oxalic acid. Hence two vinyl groups of the divinylacetals during intrainter molecular polymerization react by the “head to tail” mechanism to form polyvinylacetals with six‐membered cyclic structures.
Polymerization of vinylcarbazole in the presence of butyllithium and titanium tetrachloride
Authors: Solomon O. F. , Dimonie M. , Ambrozh K. , Tomesku M. 
Published: April 2003

AbstractThe polymerization of large cyclic vinyl compounds is of considerable interest in the interpretation of the mechanism of action of complex organometallic catalysts. Numerous vinyl compounds have been investigated up to now but no study has been made of compounds containing large rings. Studies on the isotactic polymerization of vinylcarbazole have brought to light very important facts permitting of a number of inferences as to the mechanism of isotactic polymerization. Despite the large molecular volume of vinylcarbazole and the steric hindrances that should be expected due to this, a study of the polymerization kinetics has revealed reaction rates similar to those observed in the polymerization of other monomers. The study of the polymerization of vinylcarbazole and of other monomers showed that the butyllithium‐titanium chloride catalyst belongs to the class of organometallic complexes that act either by a stepwise or ionic mechanism. The specific features of complex organometallic catalysts in the polymerization of vinylcarbazole are evidently associated with preliminary activation of the active centers during which activation of the monomer also takes place. The formation of polymers with an isotactic microstructure is due to one of the possible mechanism of the catalysis, namely, to nonstepwise action. In the polymerization of vinylcarbazole in the presence of organolithium compounds and titanium tetrachloride the microstructure of the resultant polymer and the rate of polymerization depend upon the formation of other than primary complex compounds. The microstructure of isotactic polyvinylcarbazole shows a particular shape of spherulites, depending upon the nature of the catalyst.