bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies in some new initiator systems for vinyl polymerization. II. Ammonia–halogen system as the redox initiator
Authors: Pramanick Dinabandhu , Palit Santi R. 
Published: April 2003

AbstractThe ammonia–halogen redox system has proved a promising initiator for polymerizing a number of vinyl monomers in aqueous media. Chlorine and bromine are most efficient, whereas iodine fails to initiate polymerization, probably due to its inhibitive tendency. Endgroups are halogen and amine and total about 0.5 per chain. On the basis of results of endgroup analysis, a mechanism of initiation through halogen and amine radicals, mainly through hydrogen atoms, is suggested. Consistent with the proposed mechanism the endgroup profile changes significantly with changes in pH.
Mode of termination in the copolymerization of vinyl acetate–isobutyl methacrylate and methyl methacrylate–methyl acrylate at 60°C
Authors: Chaudhuri Ajit Kumar , Palit Santi R. 
Published: April 2003

AbstractThe mode of termination in the vinyl acetate–isobutyl methacrylate (VA–IBMA) and methyl methacrylate–methyl acrylate (MMA–MA) copolymerization systems has been investigated at 60°C. by using the dye‐interaction technique for functional endgroup estimation. The results show that pairs of poly(vinyl acetate) radicals interact almost exclusively through a disproportionation mechanism. In the homopolymerization of methyl methacrylate and methyl acrylate, about 1.16 and 1.22 carboxyl‐containing endgroups per polymer molecule have been estimated, which shows the predominance of disproportionation over combination in these termination reactions. In poly(isobutyl methacrylate) about 1.55 tagged initiator fragments per chain indicate that 29% of the total radicals terminate through the disproportionation mechanism. Cross termination in the (VA–IBMA) copolymerization system occurs almost entirely through combination for monomer feeds richer in isobutyl methacrylate content while for the MMA–MA system, combination is more important at intermediate monomer feed ratios. These results have been discussed in the light of different explanations for the reaction mechanism.
Heterogeneity parameters by light scattering for statistical copolymers incorporating long side‐chain comonomers
Authors: Jordan Edmund F. 
Published: April 2003

AbstractHeterogeneity parameters were obtained by light scattering for a series of statistical copolymers incorporating long side‐chain comonomers, by employing the method of Bushuk and Benoit. These copolymers were selected to exhibit varied compositional drift as required by copolymerization theory. The magnitude of the parameters found agreed qualitatively with the heterogeneity expected from the drift in composition with conversion. This was calculated using the treatment of Skeist, as modified by Kruse. However, values greater than the limit of unity were found in two instances for the heterogeneity index, Q/Qmax, which relates the compositional drift constant Q to the maximum value obtained for mixtures of homopolymers. These anomalies were attributed to the insensitivity of the method for heterogeneous copolymers having small differences in the refractive increaments of their respective homopolymers. The magnitude and sign of P, which reflects molecular weight effects on composition, was questionable because of experimental error. Both effects appear to be general deficiencies of the method, which limit its practical use. For solvents with high values of dn/dc (≈0.1), the observed weight‐average molecular weight approached the true value.
Polymerization of 2‐(chlorinated methyl)‐4‐methylene‐1,3‐dioxolanes
Authors: Dietrich Heinz J. 
Published: April 2003

AbstractThe polymerizations of the novel 2‐(chlorinated methyl)‐4‐methylene‐1,3‐dioxolanes derived from mono‐, di‐, and trichloroacetaldehyde were investigated. Poly‐2‐trichloromethyl‐4‐methylene‐1,3‐dioxolane was of particular interest because of its high hydrolytic stability and nonflammability. The monomers could be polymerized with cationic catalysts via the methylene functions without cleavage of the dioxolane rings. This selectivity was due to the acetal‐stabilizing negative substituents and to the use of Lewis acid complexes of low reactivity as catalysts. In contrast to previously reported poly‐4‐methylene‐1,3‐dioxolanes, the title polymers were high‐melting colorless solids of good to excellent fire resistance.
Polymers from 1,3‐dipole addition reactions: The nitrilimine dipole from acid hydrazide chlorides
Authors: Stille J. K. , Harris F. W. 
Published: April 2003

AbstractAn investigation of the suitability of the 1,3‐dipole addition reaction of bisnitrilimines, generated from the corresponding acid hydrazide chlorides, with diyne and dinitrile dipolarophiles was carried out. The reactions of iso‐ and terephthaloylphenylhydrazide chlorides and 4,4′‐oxydibenzoylphenylhydrazide chloride with the dipolarophiles m‐ and p‐diethynylbenzene, m‐divinylbenzene, and perfluoroglutaronitrile in the presence of triethylamine gave moderate molecular weight polymers containing pyrazole or triazole units along the polymer backbone. The polymers were soluble in such polar solvents as hexamethylphosphoramide and acids but had inherent viscosities only as high as 0.32. The thermogravimetric analyses of the finely powdered polypyrazoles showed breaks near 500°C. in air and in nitrogen atmospheres.
Fluorine magnetic resonance spectra and tacticities of poly(vinyl trifluoroacetate)
Authors: Fujii K. , Brownstein S. , Eastham A. M. 
Published: April 2003

AbstractFluorine magnetic resonance spectra of poly(vinyl trifluoroacetate) samples of different tacticities were investigated, along with those of model compounds. These polymers represent the first case where the line order in respect to stereostructure does not agree with that expected from the spectra of model compounds. More than four peaks were observed for signals from the trifluoromethyl groups of the polymers and the relative peak positions differed from those previously reported. The intensity ratios of the peaks were affected by the solvent employed. Therefore the spectra cannot be interpreted in terms of triad stereosequences. Seemingly longer stereosequences or other influences have to be considered to interpret the spectra.
Studies on the charge transfer complex and polymerization. XIV. Spontaneous copolymerization of 1‐methylcyclopropene and sulfur dioxide
Authors: Iwatsuki Shouji , Kokubo Takashi , Yamashita Yuya 
Published: April 2003

AbstractCopolymerization between 1‐methylcyclopropene (MCP) and sulfur dioxide (SO2) was studied. It took place spontaneously even at a low temperature, and was found to be consistent with polymerization by a “living” radical, as suggested by the increase of reduced viscosity with conversion and by the formation of block polymers in the presence of acrylates. The rate of copolymerization was proportional to [MCP]3 and [SO2]2, and the overall activation energy of copolymerization was about 15.1 kcal/mole. A tentative mechanism to explain the experimental results is discussed.
Synthesis and polymerization studies of several chloro and cyano epoxides
Authors: Wei Peter E. , Butler Peter E. 
Published: April 2003

AbstractThe polar epoxides, glycidonitrile, dimethyl glycidonitrile, tetracyanoethylene oxide, epicyanohydrin, 4,4,4‐trichlorobutylene‐1,2‐epoxide, and 1,1‐dichloro‐3,4‐epoxy‐1‐butene were prepared, characterized by their infrared and nuclear magnetic resonance spectra and their polymerizations studied. Epicyanophydrin was found to be an unpolymerizable dimer, and those epoxides with a cyano group attached directly to the epoxide ring could not be polymerized. The halogenated epoxides, 4,4,4‐trichlorobutylene‐1,2‐epoxide and its dehydrochlorination product, 1,1‐dichloro‐3,4‐epoxy‐1‐butene were polymerized to high polymers with a complex catalyst from aluminum alkyl, acetyl acetone, and water. The polymerization of these monomers gave low conversions and required large amounts of catalyst. Higher conversions were obtained by copolymerization with propylene oxide or terpolymerization with propylene oxide and allyl glycidyl ether. The polymerizability of the substituted epoxide in (where X is CH3, ClCH2, Cl3CCH2, and Cl2CCH) was found to follow the order: CH3 > ClCH2 > Cl3CCH2 > Cl2CCH. The polymers of 4,4,4‐trichlorobutylene‐1,2‐epoxide and its dehydrochlorination products were not vulcanizable through the chlorine functionality or the olefinic unsaturation of the type Cl2CCH. The presence of an active third monomer such as allyl glycidyl ether was necessary to facilitate vulcanization. Properties of such vulcanizates are reported.
Salt effects in the base‐catalyzed polymerization of unsaturated amide compounds. II. Polymerization of p‐vinylbenzamide and acrylamide
Authors: Asahara Tomohiko , Yoda Naoya 
Published: April 2003

AbstractIn the presence of a variety of inorganic salts, p‐vinylbenzamide underwent vinyl‐type polymerization by anionic initiators to form the polystyrene derivative, whereas in dimethyl sulfoxide as solvent the aromatic polyamide was always obtained through a proton‐transfer mechanism regardless of the presence of the salts.
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In the presence of of the salts, acrylamide is generally polymerized to the polyamide through a proton transfer reaction.
X‐ray degradation of penton and its potential use as a dosimeter for the 4–15 keV range
Authors: Mallon Barbara J. 
Published: April 2003

AbstractExposure of poly‐3,3‐(bischloromethyl)oxetane (Penton) to x‐rays produces a linear reduction of the molecular weight, heat of fusion, and melting point with increasing absorbed dose. Optical density measurements fit a smooth curve with absorbed dose. Exposures were made with 25, 50, and 100 cal/cm2 integrated incident energy at 50 peak kV with and without zinc and titanium‐aluminum filters. Because the molecular weight of Penton is relatively uniform from lot to lot, and because it is difficult to obtain spectral measurement in the 4–15 keV range to which Penton is particularly sensitive, it is believed that the data contained in this report can be used with an interative computer code to determine the spectrum and intensity of radiation in this region.
Macroreticular resins. III. Formation of macroreticular styrene–divinylbenzene copolymers
Authors: Kun Kenneth A. , Kunin Robert 
Published: April 2003

AbstractExperimental evidence is presented that describes the mechanism of formation of macroreticular styrene–divinylbenzene copolymers in which phase separation occurs during a suspension polymerization. The mode of formation of the macroreticular structure is described as a three‐stage process in which each droplet of the organic phase behaves as an individual in a bulk polymerization that results in a bead of copolymer. Macroreticular structure formation is described by changes in copolymer swelling ratios, infrared absorption spectra of vinyl groups pendent to the polymeric matrices, surface area, total porosity, and pore‐size distribution. The proposed mechanism of formation is also substantiated by electron micrographs of the copolymers during various stages of the copolymerization.
Wide line and pulsed NMR studies of carboxyl‐terminated polybutadiene polymers and binders
Authors: Tompa A. S. , Barefoot R. D. , Price E. 
Published: April 2003

AbstractNuclear magnetic resonance relaxation and line width studies were performed on two carboxyl‐terminated polybutadiene polymers and their corresponding binders at temperatures from −170 to 25°C. It was observed that the line widths of the binders increased as the functionality of the corresponding liquid polymers increased. In addition, glass transition temperatures and activation energies obtained from line width measurements were determined. From pulse measurements the magnitude of the relaxation time T1 and the temperature at which T1 is a minimum were determined for a polymer and its corresponding binder. These empirical quantities for the carboxyl‐terminated polybutadiene polymers were lower than those of the corresponding binders because of less restraints in the internal motions of the polymer chain.
Molecular weight distributions in polymerizing systems with different coexisting active centers
Authors: Bresler S. E. , Brussalimsky B. L. , Kulevskaya I. V. 
Published: April 2003

AbstractPolymerization of acrylonitrile initiated by organomagnesium compounds Bu2Mg or BuMgCl leads to almost monodisperse polymers. The molecular weight distribution (MWD) of these polymers is so narrow that it cannot be measured by means of the ultracentrifuge. It remains narrow till high conversions. On the other hand, initiation by complex Bu3Mg2I leads to polymers with a broad MWD. From kinetic measurements we know that this reaction is free of chain termination and chain transfer. Also the initiation of chains is practically immediate. The reason for broad MWD in this particular case is the coexistence of different growing centers of polymerization. The propagation constants for these centers are obviously different. If these different active centers can periodically undergo transition from one type into the other the MWD of resulting polymer chains will broaden. A very simple semiquantitative theory for this phenomenon was developed. It shows that the fewer exchanges between the coexisting centers that occur during the reaction time, the broader will be the MWD of the polymer chains. Hence it was concluded that the broadest MWD of products must be found at low conversions. With an increase of reaction time and conversion the MWD becomes more narrow. This peculiar prediction was corroborated by experiment.
Molecular structure of synthetic rubber. I. Light‐scattering properties of styrene–butadiene copolymers
Authors: Bahary William S. , Bsharah Lewis 
Published: April 2003

AbstractThe discrepancy between the values reported for the weight‐average molecular weight and molecular weight distribution of cold‐type styrene‐butadiene rubber is examined. The results obtained indicate that aggregation of the rubber due to hydrogen bonding or cluster formation is not a contributing factor to the high weight‐average molecular weights obtained. The very broad molecular weight distributions, the M̄w/M̄n of the order of 10–20, are attributable to the presence of a few per cent of very high molecular weight fraction microgel in samples polymerized to moderate conversions. This microgel has been removed to various degrees by several methods: (1) mastication, (2) treatment with CaSO4, (3) ultracentrifugation, and (4) ultrafiltration. The nature of this microgel is examined in terms of its light‐scattering property, intrinsic viscosity, and concentrated solution viscosity. The weight‐average molecular weight obtained by light scattering on these samples after removal of microgel are lower by as much as an order of magnitude. The operational definition of the weight‐average molecular weight, M̄′w, is therefore introduced, corresponding to the one obtained after removal of the microgel. It is suggested that the actual and the operational weight‐average molecular weights be used in conjunction in the characterization of these copolymers.
Novel bridged anthracene derivatives and polyesters and copolyesters therefrom
Authors: Klanderman B. H. , Faber J. W. H. 
Published: April 2003

Abstract9,10‐Bis(hydroxymethyl)triptycene, 9,10‐dihydro‐9,10‐bis(hydroxymethyl)‐9,10‐ethanoanthracene, 9,10‐dihydro‐9,10‐bis(hydroxymethyl)‐9,10‐(2,3‐bicyclo[2.2.1] heptano)‐anthracene, 9,10‐dihydro‐9,10‐bis(hydroxymethyl)‐N‐phenyl‐9,10‐ethanoanthracene‐11,12‐dicarboximide, and 9,10‐bis(carbethoxy)triptycene have been prepared and employed as modifying agents to improve the physical properties of polyesters such as poly(ethylene terephthalate). Especially noteworthy are the high glass transition temperatures (Tg) which can be obtained.
Studies on the polymerization of bifunctional monomers. XVI. Cyclopolymerization of o‐divinylbenzene with triphenylmethyl fluoroborate and presumption of the presence of the free growing cation in this system
Authors: Aso Chuji , Kunitake Toyoki , Matsuguma Yoshihiko , Imaizumi Yoji 
Published: April 2003

AbstractCyclopolymerization of o‐divinylbenzene was studied by using triphenylmethyl fluoroborate as initiator. The cyclization constant rc (ratio of the rate constant for intramolecular cyclization to that for intermolecular propagation) decreased with increase in polarity of the solvent. This solvent effect as well as the effect of catalysts reported previously could be accounted for by a revised model of the propagating species, where both the counter anion and the o‐vinyl group were coordinated to the carbonium ion. The difference in activation energy between intramolecular cyclization and intermolecular propagation was 6.2 kcal/mole. This value was close to that obtained previously with BF3·OEt2 catalyst but greater than those for anionic and radical polymerizations. When tetraalkylammonium flouroborates were added to the polymerization system in methylene chloride, rc and the molecular weight of the polymer decreased. These results were ascribed to the decrease in the amount of the free propagating cation by the common ion effect.
Electron‐transfer polymers. XXXIV. Redox polyurethanes from p‐benzoquinone‐2,5‐diols and diisocyanates
Authors: Wegner Gerhard , Nakabayashi Nobuo , Cassidy Harold G. 
Published: April 2003

AbstractIt is possible to prepare polyurethanes from p‐benzoquinone‐diols and diisocyanates by using dibutyltin diacetate catalyst at room temperature or below, since the benzoquinone group does not react with isocyanate under these conditions. This permits preparation of new redox polymers. In preparing the polyurethanes excess isocyanate groups must be destroyed at the end of the reaction time in order to prevent crosslinking during work‐up. These polymers are readily reduced by aqueous hydrosulfite. Good viscosity numbers are obtained; and, in general, upon reduction the viscosity increases over that of the oxidized form. There is no evidence of crosslinking. When oxidized and reduced forms of these polymers are mixed there is no evidence of charge transfer.
Polymerization of vinylcyclopropanes. III. Cationic polymerization of stereoisomers of 1‐halo‐2‐vinylcyclopropanes
Authors: Takahashi Takako 
Published: April 2003

AbstractVinylcyclopropane derivatives, 1‐chloro‐ and 1‐bromo‐2‐vinylcyclopropane, have respectively two stereoisomers, and radical polymerizations of both isomers gave 1,5‐type polymers. On the other hand, only the cis isomers gave a polymer which had mainly 1,2‐type structural units in cationic polymerizations with Lewis acids. The difference between the cationic polymerizabilities of the cis and trans isomers is interpreted in terms of steric conformation of monomers.
Statistical thermodynamics of polymer solutions. VI. Comblike branched molecules with branches placed randomly along the backbone
Authors: Casassa Edward F. , Tagami Yukiko 
Published: April 2003

AbstractThermodynamic interactions between arbitrarily branched flexible “comb” molecules (with branches of uniform length affixed to backbones of uniform length but with the number of branches on a molecule and their placement arbitrary) are treated by Zimm's perturbation method to obtain results valid to the double contact approximation. Thus, bimolecular cluster configurations with one and two intermolecular contacts, but not more, are correctly accounted for. This general result is applied to “random” combs (with the number of branches per comb uniform, but the placement random) and to “heterogeneous” combs (with both the number of branches on a molecule and their placement random). Results for the random combs are very similar to those reported earlier for “symmetrical” combs (with f uniform branches disposed at points along the backbone chain so as to subdivide it into f + 1 equal sections), but the second virial coefficient for the random model is slightly the larger when the number of branches per chain is small and the fraction of the molecule in the backbone is at least a few per cent. Since random combs are uniform in mass, the osmotic pressure and light‐scattering second virial coefficients are alike; but for a system of heterogeneous combs the virial coefficients differ from one another, and from the random comb result, when the mean number of branches f̄ per chain is small and they are of appreciable length in comparison to the backbone. This behavior reflects the heterogeneity in both molecular mass and dimensions existing under these circumstances. As f̄ increases and/or the mean fraction of segments in the chain backbone becomes large, coincidence with the random comb result is approached. The double‐contact second virial coefficients for both random and heterogeneous combs are obtained in closed analytical expression that are much more easily reduced to numerical results than the expression for symmetrical combs given earlier. These two models also correspond better than the symmetrical combs to materials actually obtainable.
Molecular weights and molecular weight distribution of polymers by equilibrium ultracentrifugation. Part II. Molecular weight distribution
Authors: Scholte Th. G. 
Published: April 2003

AbstractA method has been developed for determining the molecular weight distribution of a polymer sample from the sedimentation–diffusion equilibrium data for a solution under pseudo‐ideal conditions. From some theoretical examples it appears that the method works well and that the molecular weight distribution can be determined with a reasonable degree of resolution. From three polymer samples (polyethylene, polystyrene, and polycaprolactam) the molecular weight distribution was determined in this way. The average molecular weights, M̄n, M̄w, M̄z, and Mz+1, calculated from these distribution functions agree well with those calculated directly from the equilibrium data.
Flow birefringence and polydispersity
Authors: Daum U. 
Published: April 2003

AbstractFlow birefringence data for dilute solutions of various linear and branched polymers of different degrees of polydispersity are discussed. The polymers considered are polystyrene, polypropylene, and polyethylene. By making use of a well‐known stress‐optical relation, reduced elastic normal stresses, which can also be interpreted as coil expansions, are plotted against reduced shear stresses. As elastic normal stresses are rather sensitive to the shape of the molecular weight distribution at high molecular weight, a characteristic, p, related to the skewness of the distribution, is obtained. Experimental values of p are compared with theoretical ones based on special types of distribution functions. Attention is paid to the method of extrapolating experimental results to zero shear stress and concentration.
Crystallization kinetics of stretched natural rubber
Authors: Kim Hyo‐Gun , Mandelkern L. 
Published: April 2003

AbstractStudies of the crystallization kinetics of natural rubber networks held in simple extension are reported. In these experiments the length of the specimen was held constant, and the crystallization process was followed by the decay in stress that occurred. A wide range of extension ratios and crystallization temperatures was encompassed by these experiments. From an analysis of the shapes of the crystallization isotherms, it can be concluded that major changes take place in the nucleation and growth processes as the extension ratio is increased. This conclusion is in accord with reports in the literature of changes in the crystallite morphology with extension ratio. Analysis of the temperature coefficient of crystallization, by means of nucleation theory, indicates a substantial increase in apparent interfacial free energies with increased deformation. This latter observation is interpreted to indicate a departure from a correlated crystallization process to one where isolated crystallites are formed.