bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymerization by oxidative coupling. III. Mechanistic type in the copper–amine catalyzed polymerization of 2,6‐dimethylphenol
Authors: Endres G. F. , Kwiatek Jack 
Published: April 2003

AbstractSince the oxidative polymerization of 2,6‐disubstituted phenols through copper–amine catalysis represents a novel polymerization reaction, particular interest attaches to the question of mechanistic type, i.e., stepwise or chain reaction. In the oxidation of 2,6‐dimethylphenol in the presence of copper(I) chloride in pyridine solvent, the dependence of the degree of polymerization on the extent of reaction corresponds to a stepwise reaction of the type where polymer growth occurs through reaction of polymer molecules with each other, as well as with the monomer. The reaction is thus formally analogous to a bifunctional polycondensation. The isolation of low intermediate polymers from the reaction mixture and the facile polymerization of these intermediates or the synthetic dimer or trimer in the absence of monomer supports this view. Comparison of the infrared spectra of the intermediates with the model compounds supports the poly(1,4‐phenylene ether) structure, and the absorbance in the hydroxyl region indicates one hydroxyl group per molecule. Partially oxidized reaction mixtures also yielded small amounts of the compound 4,4′‐dihydroxy‐3,5,3′,5′‐tetramethyldiphenyl, the precursor of the tetramethyldiphenoquinone formed as by‐product on complete oxidation. A study of the rates of oxygen absorption in the polymerization of the monomer, dimer, trimer, and intermediate polymer showed little dependence on the degree of polymerization from the dimer upward.
Condensation polymers from 3,9‐bis(7‐carbomethoxyheptyl)‐2,4,8,10‐tetraoxaspiro[5.5]undecane. II. Poly(amide‐acetals)
Authors: Pryde E. H. , Moore D. J. , Teeter H. M. , Cowan J. C. 
Published: April 2003

Abstract3,9‐Bis(7‐carbomethoxyheptyl)‐2,4,8,10‐tetraoxaspiro[5.5]undecane (the pentaerythritol acetal of methyl azelaaldehydate) was found to undergo condensation polymerization with diamines to give linear polymers, either alone or in conjunction with dimethyl azelate. These novel, linear poly(amide‐acetals) were susceptible to crosslinking by p‐toluenesulfonic acid and by various metal oxides and salts, such as zinc oxide, zinc acetate, litharge, and magnesium oxide. The crosslinked polymers were insoluble, infusible, transparent solids which were strongly adherent to glass.
Chain propagation constants in the cationic polymerization of styrene
Authors: Pepper D. C. , Reilly P. J. 
Published: April 2003

AbstractPerchloric acid initiates reproducible polymerization of styrene (unaffected by traces of water) in ethylene dichloride and mixtures with carbon tetrachloride over the temperature range 25–30°C. The rate of polymerization is accurately first order in monomer concentration, with a rate constant (k) proportional to the initial concentration of perchloric acid. The constant k/[HClO4]0 is identified with the rate constant for the propagation reaction (kp), since in these polymerizations there is no true termination step, and the initiation rate is believed to be so fast as not to be rate‐determining. Values of the rate constants, activation energies, and frequency factors are presented. Ep and log kp show linear relationships with the reciprocal of the dielectric constant (ε) of the solution in ethylene dichloride–carbon tetrachloride mixtures over the range ε = 5–10. In solution in ethyl chloride, and in ethylene dichloride mixtures with nitrobenzene and nitroethane, the rates are anomalously low.
Light‐scattering studies of crosslinking unsaturated polyesters with methyl acrylate
Authors: Gallacher Lawrence , Bettelheim Frederick A. 
Published: April 2003

AbstractThe Debye‐Bueche theory of light scattering of inhomogeneous solids was applied to a three‐dimensional crosslinking process. A series of unsaturated polyesters of an average degree of polymerization of 7.4 were prepared in which the double bond spacings were varied. These polyesters were crosslinked with methyl acrylate in 1 : 2, 1 : 3, and 1 : 4 polyester double bond: monomer ratios. The crosslinking process was followed up with measurements of the light‐scattering envelope beyond the gel point. Parameters corresponding to the extent of inhomogeneities and the mean square deviation of the local refractive index from the average were evaluated. The data were interpreted by proposing a gelation mechanism which can be separated into three phases by optical means.
Thermal x‐ray diffraction study of highly acetylated cotton cellulose
Authors: Conrad Carl M. , Creely Joseph J. 
Published: April 2003

AbstractCotton cellulose in the form of scoured yarn was acetylated at 15°C. in a mixture of isopropyl acetate and acetic anhydride in the presence of perchloric acid catalyst to various degrees from 1.1 to 2.9 acetyl groups per anhydroglucose unit. For comparative purposes some of the yarn was acetylated at 20°C. by a more conventional method with a 3:1 mixture of acetic acid and acetic anhydride, also with perchloric acid as catalyst. The products were studied by x‐ray diffraction, both at room temperature and, with the aid of a specially controlled diffractometer furnace, at elevated temperatures. Diffractograms of the products show that as acetylation proceeds, the crystal structure of native cellulose disappears progressively until at a substitution of 2.93 acetyls per anhydroglucose unit it is nearly all gone. Examination with the diffractometer furnace shows in an impressive way the acetyl content and temperature at which cellulose acetate first begins to crystallize, the progressive increase in crystallizable acetate as acetylation proceeds, the temperature range over which the crystal structure is stable, the temperature at which it melts, and finally the temperature at which the acetate eventually carbonizes.
The anionic polymerization of acrylonitrile
Authors: Cundall R. B. , Eley D. D. , Worrall J. 
Published: April 2003

AbstractThe polymerization of acrylonitrile initiated by diethyl sodiomalonate in dimethylformamide has been investigated. The degree of polymerization was found to be independent of the monomer conversion but was dependent on the extent of polymerization. The polymers produced were examined for functional groups by infrared spectroscopy. An anionic mechanism involving hydride ion transfer to monomer has been suggested. The kinetics of the reaction can be followed because of the slow initiation step and are found to be governed by the rate expression −d[M]/dt = k[M]2[C]. The decrease in DP with increasing conversion is due to degradation of the polyacrylonitrile by basic ions. The ratios of the rate constants for both the monomer and polymer transfer reactions to the rate constant for propagation have been determined. The coloration of the polymers appears independent of the degradation reaction.
Kinetics of the oxidation of cotton with hypochlorite in the pH range 5–10
Authors: Epstein Joseph A. , Lewin Menachem 
Published: April 2003

AbstractThe rate of consumption of oxygen by cotton and cottom cellulose from solutions of hypochlorite in the pH range 5–10 has been studied. Kinetic plots were obtained either by periodically titrating aliquots or by automatically recording the amount of alkali required to keep the pH constant. In the case of pure cotton cellulose the plots are linear, whereas in the case of cotton the plots consist of two parts, an initial, rapid oxidation of the impurities followed by a slower, linear oxidation of the cellulose. The dependence of the rate of oxidation on the pH may be expressed by:

which also accounts for the dependence of the rate on the initial concentration of oxidant. A mechanism is suggested in terms of the free‐radical OH and Cl2OOH.
Functional groups and degradation of cotton oxidized by hypochlorite
Authors: Lewin Menachem , Epstein Joseph A. 
Published: April 2003

AbstractFunctional groups and degradation of cotton oxidized by hypochlorite at several pH values in the range 5–10 were studied. The carboxyl group content of the oxidized cottons increases, while the aldehyde and ketone group contents decrease with increase in pH. Approximately 40% of the oxidant consumed is accounted for by the functional groups at all pH values. The ratio of carboxyl, aldehyde, and ketone groups formed per scission is 1–1.5:3:3.5 at the acidic pH range and 5:0.8:0.0 at pH 10. Oxygen consumption per scission is 26 atoms, out of which 10.4 atoms are accounted for by the functional groups. The rest of the oxygen is explained by oxidation of the soluble products of the short chain material in the fiber phase and by the functional groups of the short chains with D.P. up to 37. The degradation was found to be random at the whole pH range studied, as proved by the ratio of the number‐average and weight‐average molecular weights and by the linearity of the plot of log [η] vs. log (Oc + Oc0) where Oc is the oxygen consumed and Oco a constant. It is suggested that the degradation and oxidation reactions occur simultaneously and, at a given pH, with similar rates, so that all carbon atoms of an anhydroglucose unit in all chains of the amorphous phase will have a similar probability of being attacked.
Investigation of the mechanism of radiolysis of polymers containing quaternary atoms of carbon
Authors: Pravednikov A. N. , Teleshov E. N. , Shen‐Kan In , Medvedev S. S. 
Published: April 2003

AbstractThe initial act of interaction of radiation in a polymer, irrespective of its chemical structure, is abstraction of an electron with formation of a positive ion. Neutralization of this ion by the electron leads to the formation of an excited molecule which subsequently breaks up with formation of free radicals. The pattern of changes occurring in the structure of the polymer will evidently depend upon the stabilization mechanism of these radicals. The fact that up to now the process of crosslinking during the radiolysis of polymers containing quaternary carbon atoms (polyisobutylene, poly‐α‐methylstyrene) has not been observed as well as the available data concerning the pattern of temperature dependence of the destruction rate, make it possible to draw the conclusion that, in these polymers, due to steric hindrances, the radicals formed as a result of the abstraction of side groups or hydrogen atoms react with each other with the breaking of the backbone chain of the polymer molecule. A study of the radiolysis of copolymers of styrene with α‐methylstyrene in a swollen state showed that, in this case, because of the absence of steric hindrances, the interaction between the polymer radicals and radicals formed from the solvent results in the insertion of the solvent molecules into the polymer chains (demonstrated by a tracer technique); in this case the rate of degradation is decreased. Data obtained during the study of the radiolysis of the mixture of low molecular radioactive polyisobutylene with the conventional high molecular polyisobutylene show that interaction of radicals formed during the radiolysis of this polymer represents a kind of a disproportionation reaction accompanied by a transferal of the low molecular groups from one polymer radical to another.
Observations on the thermolytic decomposition of poly(tert‐butyl acrylate)
Authors: Schaefgen J. R. , Sarasohn I. M. 
Published: April 2003

AbstractThe thermolytic decomposition of crystalline and amorphous poly(tert‐butyl acrylate) was investigated. At elevated temperatures thin films of polymer were found to evolve isobutylene quantitatively. The weight loss curve has been analyzed, and a mechanism has been suggested involving a slow random decomposition of tert‐butyl ester groups followed by a faster decomposition of ester groups due to neighboring carboxyl groups. The rate and activation energy for isobutylene evolution in both sections of the weightloss curve are not very different for tactic and atactic polymer modifications.
Infrared study of the reaction of polyisoprene and polybutadiene with sulfur by use of deuterated polymers
Authors: Shipman J. J. , Golub M. A. 
Published: April 2003

AbstractAn infrared study of the sulfur vulcanization process was carried out with very high cis polymers of isoprene‐d8, isoprene‐3‐d1 and butadiene‐2,3‐d2 as well as the corresponding perprotio polymers. The use of deuterated polymers permitted more definitive interpretations of the spectral changes associated with vulcanization than those previously reported or were possible with the undeuterated polyisoprene or polybutadiene. It was concluded that the 10.4 μ band which develops in the spectrum of cis‐polyisoprene on extended reaction with sulfur at 140°C., and which has been the subject of some controversy, arises largely from a combination of saturated ring structures, such as cyclic sulfides, and conjugated double bonds, and to a minor extent from shifted double bonds. In addition to the processes leading to these various structures, crosslinking also occurs, but it apparently produces no important changes in the spectra of the polyisoprene vulcanizate other than that associated with a decrease in the original unsaturation. Polybutadiene, in contrast to polyisoprene, undergoes extensive cis—trans isomerization when extensively vulcanized with sulfur. Apparently, ring formation and concurrent production of conjugated double bonds also occur, but there is only a very slight amount of double‐bond shifting in polybutadiene.
Molecular weight of silk fibroin
Authors: Hyde A. J. , Wippler C. 
Published: April 2003

AbstractThe molecular weight of silk fibroin in several different solvent systems has been measured by light‐scattering techniques. The values obtained lie between 250,000 and 450,000, with a tendency to lie fairly close to 300,000. The difference between this value of the molecular weight and the values obtained by other workers is discussed.
Hydrodynamic studies on sodium carboxymethyl cellulose in aqueous solutions
Authors: Sitaramaiah G. , Goring D. A. I. 
Published: April 2003

AbstractSodium carboxymethyl cellulose was fractionated and the fractions characterized by light scattering, viscometry, and sedimentation and diffusion in 0.1M NaCl. Viscosity and sedimentation measurements were extended to lower ionic strengths by the isoionic dilution technique. Light‐scattering molecular weights were from 3 to 9 times higher than the values computed by the hydrodynamic equations of Svedberg or Mandelkern and Flory. It appeared that the light‐scattering method yielded anomalously high Mw values because of a small proportion of colloidal material persisting in solution in spite of the rigorous ultraclarification procedure adopted. Interpretation of the results was therefore based on the sedimentation‐diffusion molecular weights which ranged from 45,000 to 350,000. The exponents determined from the logarithmic dependence of [η] on MsD were 0.95 and 1.40, respectively, in 0.1M and 0.001M NaCl. This indicated an extended, non‐Gaussian configuration at low ionic strength due to expansion of the polyelectrolyte molecule. The corresponding exponents for the molecular weight dependence of s0 were 0.35 and 0.11 at 0.1M and 0.001M NaCl respectively. Tests of the Kirkwood‐Riseman and Debye‐Bueche theories were made by substituting the parameters [η], MsD and the frictional constant, F0 in cubic equations derived from the approximate relationships recently proposed by Marrinan and Hermans. In this way, the monomer frictional constant, ζ could be calculated from data for each fraction. From both theories values of ζ were considerably lower than an approximate figure of 4 × 10−9 g./sec. deduced from the diffusion coefficient of sucrose at 25°C. However, at low molecular weights in 0.1M NaCl and at all molecular weights in 0.001M NaCl, ζ approached most closely the expected value indicating that the theories hold best for a highly extended configuration.
Polymerization catalyzed by lithium and lithium alkyl
Authors: Spirin Yu. L. , Arest‐Yakubovich A. A. , Polyakov D. K. , Gantmakher A. R. , Medvedev S. S. 
Published: April 2003

AbstractIn previous kinetic investigations it was found that polymerization initiated by alkyllithium in hydrocarbon media is not a typical anionic process. The peculiarities of this type of polymerization have been explained by the participation of both carbanion and lithium components of an active center in the chain propagation. In connection with suggestions previously made, the effect of the solvents (toluene, triethylamine, ethyl ether, dioxane, and tetrahydrofuran) on the homo‐ and copolymerization of styrene, butadiene, and isoprene in the presence of ethyllithium was studied. It was found that in hydrocarbon media these monomers form mutually associated “living” polymers. Regarding the nature of monomers the degree of association increases as follows: styrene < isoprene < butadiene. The reactivity of these monomers increases in the same sequence. The solvation of the growing lithium chains or its association complexes with monomers gives rise to the possibility of chain propagation in hydrocarbon media by a two‐step mechanism. In electron‐donating solvents the total activation energy of polymerization decreases, and reaches a minimum in THF. The relative reactivity of the investigated monomers in chain propagation increases in the sequence: isoprene > butadiene > styrene.
Mechanism of alternating inter‐intramolecular propagation. I. Methacrylic anhydride
Authors: Gibbs William E. , Murray Joseph T. 
Published: April 2003

AbstractThe solution polymerization of methacrylic anhydride, a monomer which undergoes predominantly inter‐intramolecular propagation, shows kinetics similar to vinyl polymerization. The overall rate of polymerization is proportional to the square root of the initiator concentration and to the 3/2 power of the monomer concentration. The apparent, overall energy of activation was found to be 23.0 kcal./mole when azobisisobutyronitrile was used as the initiator. The value of Ep − Et/2 obtained is 8.0 kcal./mole. This compares with the value of Ep − Et/2 found for methacrylic acid in the same solvent (DMF) of 9.8 kcal./mole. Both values are in the range of values for other vinyl monomers. The polymer obtained from reactions carried out at monomer concentrations of 17% and lower were completely soluble, showed low amounts of residual unsaturation, and did not appear to be branching to a measureable extent. At higher monomer concentrations, gel was formed, and the polymers showed higher residual unsaturation levels. Poly(methacrylic anhydride) hydrolyzed to the polyacid did not show any enhancement in crystallinity over the polyacid prepared directly from methacrylic acid. Both show only low orders of crystalline content.
Study of polydispersity of cotton cellulose according to molecular weight
Authors: Usmanov Kh. U. , Sushkevitch T. I. 
Published: April 2003

AbstractA study has been made of the molecular heterogeneity of cotton fiber cellulose from fibers of different age. Analysis was carried out by the precipitation fractionation (10 to 12 fractions) and turbidity titration methods. The molecular weight distribution curves show that the cotton fiber in its early development period (grown 5 days) contains mainly low molecular weight cellulose and a small quantity of high molecular weight cellulose. Therefore, the sample is to some extent polydisperse. With continued fiber development (grown 10 to 20 days), the quantity of high molecular weight cellulose increases and the polydispersity increases also. Finally, in the late development period, the polydispersity of the sample decreases, and the fibers grown 50 days and more contain mainly homogeneous cellulose of high molecular weight. The distribution curve of the youngest fiber has only one maximum. As the fiber development proceeds, the number of maxima increases to three and reduces to one maximum again as growth is carried to maturity.
On the cutting mechanism of high polymers
Authors: Kobayashi Akira , Saito Katsumasa 
Published: April 2003

AbstractThe characteristics of the cutting phenomena in linear high polymers, such as polytetrafluoroethylene, polystyrene, and poly(methyl methacrylate) are described in order to make clear the cutting mechanism which is available to produce high quality and accurate parts. Thus, the types of chips, the deformation of the work material, and the critical rake angle defined by the authors are described. Several discussions on the thermal, the time (or cutting speed), and the frictional dependencies are also described. The chips are divided into two main categories the continuous (curl, flow, and shear type) and discontinuous (crack and tear type). These are influenced by the kinds and temperature of the work materials, the rake angle of a tool, and the depth of the cut and cutting speed. It was clarified by the discussions that the viscoelastic behavior of the work material was important during cutting of high polymers. Therefore, the Voight and Maxwell Model were introduced to explain the time dependencies. We could say that the types of cutting mechanism of high polymers are classified as, slip on the shear plane, crack at the tip of a tool, tear at the cutting edge accompanied by heavy strain, and some combinations of these. Cutting with the critical rake angle (that is a rake angle which makes the thrust force during cutting equal to zero), the work material was neither deformed upwards nor downwards, thus the highest accuracy was obtained. Furthermore, the work material must be equal to the frictional angle of the rake surface of the tool, and was decided upon by the frictional behavior of the chip on the rake surface.
Viscoelastic properties of branched whole polymers. II. Regularities in the solution viscosity, melt viscosity, and molecular weight
Authors: Peticolas Warner L. 
Published: April 2003

AbstractFor linear polymers there is generally an experimental relation between the melt viscosity η, intrinsic viscosity [η], and viscosity‐average molecular weight M̄v, which forms a one‐dimensional curve in the three‐dimensional space, η, [η], M̄v. Thus, from a knowledge of one of these quantities it is possible to obtain the other two. For randomly branched polymers, evidence is given in this paper to show that there exists a twodimensional surface in this same space so that any one of these three variables may be obtained from a determination of the other two. In such cases the viscosity‐average weight may be obtained from a measurement of both [η] and η. Such a relationship is shown to exist from the data of Charlesby on branched silicones as well as our own data on polyolefins.