bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereospecific polymerization of 2‐substituted 1,3‐butadienes. II. Stereospecific polymers of 2‐n‐propyl‐1,3‐butadiene
Authors: Marconi W. , Mazzei A. , Cucinella S. , Cesari M. , Pauluzzi E. 
Published: April 2003

AbstractThe stereospecific polymerization of 2‐n‐propyl‐1,3‐butadiene with aluminum alkyls or aluminum hydride and different transition metal salts was investigated. The behavior of this monomer with respect to the various catalysts employed is similar to that of isoprene. With the AlEt3–TiCl4 and AlHCl2·(C2H5)2O–TiCl4 systems, rubbery polymers are obtained whose infrared spectra are consistent with the 1,4‐cis structure. With the AlEt3–Ti(i‐C3H7O)4 catalyst, a low molecular weight polymer with a prevailing 3,4 structure is obtained. The AlEt3–VCl3 system gives a crystalline product melting at 42°C. The identity period has been determined, and two possible chain conformations are proposed.
Kinetics of polymerization of butadiene, isoprene, and styrene with alkyllithiums. Part III. Rate of propagation
Authors: Hsieh Henry L. 
Published: April 2003

AbstractInitial propagation rates Rp for butadiene, isoprene, and styrene were obtained by using sec‐BuLi as the initiator. With this alkyllithium, initiation was so very rapid that propagation alone was easily studied. In the case of diene monomers at [RLi] > 10−2M and for styrene, Rp = kp [RLi]1/2[M]. Here no unreacted BuLi is present to associate with polymer‐Li. However, polymer‐Li association can occur to temporarily inactivate the propagating anion. A mechanism was proposed and the kinetic equations were derived. When [RLi] was 10−4 to 10−2M, Rp = kp[RLi]1/3[M] for both dienes, but not for styrene. Some propagation rate constants were calculated. The order of rate of propagation for three monomers was styrene > isoprene > butadiene.
Microstructures of polydienes prepared from alkyllithium
Authors: Hsieh Henry L. 
Published: April 2003

AbstractThe stereochemistry of polymerization of isoprene and butadiene by means of alkyllithium initiators was examined. The stereochemistry of polybutadiene and polyisoprene responded to the same variables in anionic polymerization. Microstructure of both polymers is sensitive to initiator level, solvent type, and polymerization temperature, but is independent of monomer concentration, conversion and initiator structure. The heat activation energy leading to 1,2 addition is greater than that leading to trans‐1,4 addition (1200 cal./mole). The exact pictorial sequence leading to stereospecific polymerization of dienes by means of alkyllithium is still not clear. However, it seems to involve the orientation of the incoming monomer units by association and passage through a transition complex in which all bonds are largely covalent in character and within which polymerization occurs.
Polymerization of butadiene by n‐butyllithium‐titanium tetrachloride (tetraiodide) catalysts
Authors: Lehr Marvin H. , Moyer Patricia H. 
Published: April 2003

AbstractThe structure of polybutadiene obtained with a n‐BuLi–TiX4 (X = Cl, I) catalyst depends on the Li/Ti ratio. At Li/Ti < 2.5 the result is similar to that with (i‐Bu)3Al–TiX4, predominantly, cis‐1,4‐polybutadiene. On the other hand, in the range Li/Ti = 3–4, the chloride catalyst produces largely 1,2‐polybutadiene, and at Li/Ti = 3 it is unaffected by ether in contrast to other ratios investigated. At Li/Ti ≥ 5 in both halide systems, the structure is essentially a mixture of isomers characteristic of the n‐BuLi catalyst alone.
Polyacrylonitrile prepared in ethylene carbonate solution. III. Molecular parameters
Authors: Peebles L. H. 
Published: April 2003

AbstractThe intrinsic viscosity–molecular weight equation for polyacrylonitrile polymerized in ethylene carbonate by an azo catalyst is [η] = 6.98 × 10−4 M̄w0.645 ± 0.036 dl./g. at 25°C. in DMF. The flexibility of the chain is found to be between that of poly(vinyl acetate) and a polycarbonate. The intrinsic viscosity decreases as the temperature is increased. This is shown to be due to two processes which occur simultaneously: A decrease in the polymer radius and an increase in the polymer–solvent interaction. The decrease in the radius overrides the increased solvent attraction. Comparison of the data with those of Fujisaki and Kobayashi suggests that polymers prepared by the aqueous redox and the homogeneous azo polymerization processes are different.
On the ultrastructure of cellulose microfibrils
Authors: Ohad I. , Mejzler D. 
Published: April 2003

AbstractStatistical formulae based on generally accepted models for cellulose microfibril structure were developed to calculate the mean length of microfibril segments which do not contain molecular chain‐ends, i.e., “continuous segments.” The calculated length of such “continuous segments” for microfibrils of 2–3 mμ cross section, containing molecules of a degree of polymerization from 2 × 103 to 6 × 103, is in the range of 300–1500 A. The relationship between “continuous segments” and crystalline and amorphous regions of cellulose microfibrils is discussed.
Anionic polymerization of butadiene and styrene
Authors: Johnson A. F. , Worsfold D. J. 
Published: April 2003

AbstractA kinetic study has been made of the polymerization of butadiene and styrene in an aliphatic hydrocarbon solvent with the use of butyllithium as an initiator. It is shown that the anomalous behavior in the initiation reaction exhibited by isoprene under these conditions is also found for these two monomers. These monomers give a sigmoidal rate curve in the initiation reaction in cyclohexane solution, and the reaction appears to be auto‐catalytic. The propagation reactions were studied also, and the results compared with the rather discordant sets of data published by other authors.
Crystallization and dissolution temperatures of polyacrylonitrile
Authors: Chiang R. , Rhodes J. H. , Holland V. F. 
Published: April 2003

AbstractThe dissolution temperature of the crystalline platelets of polyacrylonitrile in propylene carbonate bears a linear relationship with the crystallization temperature Tc. The step heights ζ of the crystalline platelets measured by electron microscopy increase with increase in crystallization temperature, in accordance with the current theory of high polymer crystallization in dilute solution. The step heights were found to be 100, 130, and 150 A. for Tc of 95, 116, and 125°C., respectively. By extrapolating the experimental values of Ts to the value at ζ = ∞, a characteristic constant (Tm)∞ is obtained. The (Tm)∞ was 175°C. for the sample studied in propylene carbonate. The interfacial free energy, σe, calculated from the melting point and the step height is of the order of 1950 cal./mole of emerging chain repeat unit, or 45 ergs/cm.2 as compared to 1900 cal./mole or 70 ergs/cm.2 for polyethylene. It appears that the surface free energies of various organic polymers are remarkably similar. Although the degree of crystalline perfection of polyacrylonitrile is inferior to that of organic crystals with three‐dimensional order, polyacrylonitrile displays a crystallization behavior similar to other semicrystalline polymers; this conclusion is supported by the linear relationship between Ts and Tc, the variation of the step height with the crystallization temperature, and the sigmoid relationship of the fractional change in specific volume as a function of time during crystallization.
Studies in cyclocopolymerization. Relative rates of addition in the free radical‐initiated copolymerization of 1,4‐dienes and substituted olefins
Authors: Barton John M. , Butler George B. , Chapin Earl C. 
Published: April 2003

AbstractA general copolymer composition equation is developed for the cyclocopolymerization of 1,4‐dienes (M1) and monoolefins (M2). The general equation relates copolymer composition to monomer feed composition in terms of five reactivity ratio parameters. When cyclization is very rapid relative to other chain propagation steps the general equation simplifies to the form: n = (1 + r1x)(1 + rcx)/[rcx + (r2/x) + 2], where n = [m1]/[m2] in the copolymer, x = [M1][M2] in the monomer feed, and r1, r2, and rc are reactivity ratios for the chain propagation steps of diene, monoolefin, and cyclized radicals, respectively. The theory is applied to the free radical initiated copolymerization of (A) divinyl ether/maleic anhydride, (B) 1,4‐pentadiene/maleic anhydride, (C) divinyl ether/N‐phenylmaleimide, (D), divinyl ether/acrylonitrile; and (E) 1,4‐pentadiene/acrylonitrile. Systems A, B, and C form alternating copolymers of composition n = 0.5. For system D, r1 = 0.024, r2 = 0.938, rc = 0.017. For system E, r1 ⋍ rc ⋍ O, r2 = 1.13.
Copolymerization of 4‐cyclopentene‐1,3‐dione with styrene
Authors: Winston Anthony , Hamb F. Lynn 
Published: April 2003

AbstractThe copolymerization of 4‐cyclopentene‐1,3‐dione (D) with styrene (S) is reported. The copolymers were prepared by heating sealed tubes containing the monomer feeds and azobisisobutyronitrile. The copolymers exhibited infrared bands for the phenyl and β‐diketone groups, indicating that copolymerization had occurred. The copolymers were completely insoluble in all solvents. Some swelling was observed in tetrahydrofuran, nitrobenzene, and aqueous sodium hydroxide. From the compositions of the copolymers, as determined from the carbon and hydrogen analyses, it was found that the copolymers were about 40 mole‐% styrene over an appreciable range of feed compositions (0.1–0.6 mole fraction styrene). The results at styrene feeds <0.5 were in general agreement with the equation: d[D]/d[S] = 1 1/2 + (kDD/2kDCK[S]). This equation was derived on the basis of monomer complex (C) participating in the propagation and a penultimate effect preventing the occurrence of a sequence of three dione units.
Differential thermal analysis of the cocrystal peak in linear–high pressure polyethylene blends
Authors: Clampitt Bert H. 
Published: April 2003

AbstractA DTA study of over 60 linear–high pressure polyethylene blends is reported. From this study a preliminary phase diagram for this type of system is derived; however, the main emphasis is on the nature of the cocrystal peak. The results appear to indicate that there are two classes of cocrystals in linear–high pressure polyethylene blends with the linear component being responsible for the division of the blends into two groups. The property of the linear component which is responsible for this division is related to the crystallite size of the pure linear crystal. While the division of the blends into two groups is primarily dependent on the linear component, the magnitude of the cocrystal peak height is dependent on the high pressure polyethylene component. Low melt index and low branching of the high pressure polyethylene favor large cocrystal formation. Indeed, resins containing 30 methyls per 1000 carbons do not possess a cocrystal peak.
Sound velocity in polyethylene at ultrasonic frequencies
Authors: Levene A. , Pullen W. J. , Roberts J. 
Published: April 2003

AbstractAn ultrasonic interferometer was used to measure the sound velocity at 1.45 Mcycle/sec. and 20°C. in small disk samples of polyethylene. A plot of sound velocity versus density does not conclusively show that the relationship is linear or cubic. The velocities were converted to dynamic Young's moduli by using Poisson's ratios given by Schuyer. Comparison of these results with the lower frequency moduli of Davidse, Waterman, and Westerdijk indicates that the test conditions may well be close to those pertaining when the viscoelastic effects have been more or less eliminated.
Rate of densification of gel during coagulation of viscose
Authors: Gupta Maharaj K. , Marker Leon , Wellisch Eric , Sweeting Orville J. 
Published: April 2003

AbstractWe have developed a simple method which permits measurement of the rate of densification of the gel forming during the coagulation of viscose and in effect experimentally separates the coagulation process from the regeneration process. The method is based on changes in density of a drop of viscose as it passes through a column of a salt solution. In devising the experimental program, three assumptions have been made: (1) Stokes' law is assumed to be valid for the movement of a drop of viscose through a column of a salt solution; (2) the volumes of sodium cellulose xanthate and water are assumed additive in viscose, permitting the calculation of the density of anhydrous xanthate; (3) the mechanics of loss of water initially from a surface are assumed to be the same whether the area is planar or spherical, i.e., a drop of viscose initially dehydrates in the same manner as does a thin film. Using this experimental technique, we have studied the coagulation of viscose as a function of salt index, ripening temperature, type of salt, and concentration of salt.
Stereospecific polymerization of 1,3‐butadiene. II. Kinetic studies
Authors: Mazzei A. , Araldi M. , Marconi W. , De Maldé M. 
Published: April 2003

AbstractThe kinetics of the polymerization of butadiene with catalysts prepared from some aluminum hydride derivatives, AlI3, and TiCl4 was investigated. It was found that the reaction rate is first‐order with respect to monomer and catalyst concentration when the catalyst is prepared in the presence of monomer. In such a case the polymerization takes place in a homogeneous medium. When the catalyst is prepared in the absence of monomer, the reaction takes place in an heterogeneous medium and the rate is still first order with respect to monomer concentration, while the dependence on the catalyst concentration is no longer linear. The activation energy of the entire process is about 8500 cal./mole. In addition, a comparison is made of the polymerization rate of catalysts obtained from AlI3, TiCl4, and various aluminum hydride derivatives.
Heat and entropy of fusion of isotactic polypropylene
Authors: Krigbaum W. R. , Uematsu Ichitaro 
Published: April 2003

AbstractHeats and entropies of fusion of polymers are customarily evaluated through melting point depression measurements with the assumption that the observed and thermodynamic melting points are nearly identical. However, it has recently become evident that the crystal surface free energy is not negligible, so that apparent melting points measured dilatometrically or calorimetrically are low by perhaps 5–15°C. the status of the accumulated body of thermodynamic data is rendered still more uncertain by the possibility that the surface free energy may vary in a systematic manner with diluent concentration. To investigate this question, dilatometric data were obtained by two procedures for tetralin solutions of isotactic polypropylene. The first set of measurements was performed upon samples which had been slowly cooled from the melt, while in the second procedure the apparent melting point was measured as a function of the isothermal crystallization temperature. Extrapolation of the latter data gave tM° = 186 ± 2°C., a value of 12°C. higher than the apparent melting temperature observed according to the first procedure; however, the heats of fusion obtained by the two methods agreed to within the experimental error. A possible explanation for this behavior may be offered by the observations that both the parameter β of Hoffman and Weeks, and the ratio of the temperature of maximum crystallization rate to the melting temperature, are independent of diluent concentration over the range investigated. This suggests that the addition of diluent does not affect the distribution of fold lengths. If this behavior proves to be general, dilatometric heats of fusion will be reinstated as valid thermodynamic data for polymers.
Investigation of comonomer distribution in ethylene copolymers with thermal methods
Authors: Bombaugh Karl J. , Clampitt Bert H. 
Published: April 2003

AbstractThis paper is an extension of an earlier work in which thermal pyrolysis gas chromatography and differential thermal analysis were combined to elucidate comonomer distribution in ethylene–acrylate copolymers. In this work consideration is given to the thermal degradation products of ethylene–acrylate and ethylene–vinyl acetate copolymers. The influence of cracking temperature is considered in terms of the utility of the data. The DTA measurements are primarily concerned with the crystallization of the ethylene chains between the branch points. Indeed, a linear relationship between DTA crystallinity and branching is indicated.
Preparation and hyperfiltration properties of a polyacrylate–cellophane membrane
Authors: Baldwin W. H. , Holcomb D. L. , Johnson J. S. 
Published: April 2003

AbstractPreparation of a carboxylic ion‐exchange membrane by grafting poly(acrylic acid) onto cellophane is described. This membrane filters appreciable fractions of dissolved salt from solutions 1M and less in NaCl; flow rates through the membrane at 2500 psi are 0.5 cm./hr. and higher. Comparison is made of salt rejection properties and flow rates with a film of cellulose acetate in which rejection does not depend on fixed ionizable groups. Rejections of salts having ions of different charges are presented. Experimental apparatus for hyperfiltration is described.
Mechanisms of thermal degradation of phenolic condensation polymers. II. Thermal stability and degradation schemes of epoxy resins
Authors: Lee Lieng‐Huang 
Published: April 2003

AbstractThe thermal degradation of uncured and cured epoxy resins was studied. By the use of the thermogravimetric analysis, the thermal stability of the cured epoxy resins, D.E.N. 438 and D.E.R. 331 resins, was compared with those of polycarbonate and polyphenylene sulfide. The resins, including novolac resin and D.E.R. 669 resins, were pyrolyzed, and their volatiles were determined with a mass spectrometer. The experimental results showed that the phenolic compounds were the major volatile products. Thus, the data do not support the degradation scheme proposed by Neiman and co‐workers. Several degradation schemes for epoxides are proposed based on the principles of the cleavage of simple ethers and the products obtained from the pyrolysis study.
Diffusion‐controlled termination in free radical polymerizations
Authors: Burkhart R. D. 
Published: April 2003

AbstractThe theory of Kuhn and Kuhn for the diffusion of polymer chain ends has been applied to the termination mechanism for free radical polymerizations, proposed by Benson and North. By using the dimensions for a Gaussian chain, an expression for this diffusion‐controlled termination rate constant in terms of solvent viscosity, polymer chain flexibility, and chain length has been derived. The theory predicts that the termination rate constant is inversely proportional to solvent viscosity for flexible polymer chains and independent of solvent viscosity for very stiff polymer chains. Several previously reported effects of solvent viscosity on the termination rate constant may be explained with the present theory. The effect of polymer chain length on the termination rate constant depends upon the range of chain lengths considered and upon the relative chain stiffness. The necessity of taking into account the frequency distribution of radicals which exists during polymerization is discussed. Calculated values of the termination rate constant have been carried out with the use of values for the various parameters which are believed to be typical of vinyl polymers in solution. These calculated values are in general agreement with those which are usually obtained experimentally.
Elastic, strength, and viscous properties of polymer (polyethylene and polystyrene) melts
Authors: Vinogradov G. V. , Belkin I. M. 
Published: April 2003

AbstractA description is given of a rotational elastoviscometer with a very rigid dynamometer designed for the investigation of the rheological properties of polymer melts and concentrated polymer solutions by the constant deformation rate method. Alkathene‐2 and polystyrene were studied over a wide range of temperatures. The deformation dependences of the shear stress obtained for these polymers became non‐monotonic with rising deformation rates. This was characteristic of the reversible destruction of the polymer structure which increased with growing rates of shear. The maximum on the shear stress vs. deformation curve enabled the ultimate shear strength to be determined as a specific point on this curve. The ultimate shear strengths were reached at a deformations of several hundred per cent, while steady flow conditions were attained at deformations of several thousand per cent. With rising deformation rates, the time for attaining the ultimate strength decreased, as did, to some extent, the time of attainment of steady flow conditions. The deformation corresponding to the ultimate strength increased slightly, and the deformation corresponding to the attainment of steady flow conditions increased greatly with growing deformation rates. The activation energies of steady flow and of the passage through the ultimate strength were close in value. The dependence of the modulus of highly elastic deformation in a polymer of intact structure on the deformation rate is expressed by a function of saturation. The saturation corresponds to the deformation rates at which viscous flow cannot develop without breakdown of the melt structure (without passage through the ultimate strength).
Ziegler polymerization of olefins. V. Site removal and site activation by electron donors
Authors: Boor J. 
Published: April 2003

AbstractElectron donors having different structures have been incorporated into the Ziegler catalyst, ZnEt2 + γ‐Alx Tiy Clz‐160, in order to understand the site removal and the site activation processes. Donors which were studied in the present work include: azulenes, unsaturated compounds, aromatics, substituted pyridines and quinolines, cyclopentadienyl compounds of V, Cr, Ni, and Co, (C6H6)2Cr, and PF3. Their effect on the polymerization of propylene was determined. It was found that the site removal and the site activation processes could be brought about by many different donors. Variations were noted among the donor types. This finding shows that a variety of isolated sites with different abilities to coordinate and orient the α‐olefin are found on the crystal surface of the titanium chloride cocatalyst.
Polyquinoxalines. II.
Authors: Stille J. K. , Williamson J. R. , Arnold F. E. 
Published: April 2003

AbstractFive new high molecular weight polyquinoxalines have been prepared by the reactions of combinations of two tetramines, 3,3′‐diaminobenzidine (II) and 3,3′,4,4′‐tetraminodiphenyl ether (IV), with the three bisglyoxals, 1,4‐phenylenediglyoxal (I), 1,3‐phenylenediglyoxal (VI), and 4,4′‐oxydiphenylenediglyoxal (IX). Solution and melt polymerization techniques afford intermediate molecular weight polymers which can be converted to high molecular weight samples (ηinh > 1.0) by heating at 375°C. under reduced pressure. All the polyquinoxalines have excellent thermal stability both in nitrogen and in air. Of these polymers, poly[2,2′‐(4,4′‐oxydiphenylene)‐6,6′‐oxydiquinoxaline] (XI) has the highest solubility in hexamethylphosphoramide (HMP), and films can be cast from intermediate molecular weight (ηinh = 0.3–0.7) polymer solutions in HMP. Tough, insoluble films can be obtained by heating the cast films in nitrogen or under reduced pressure to 350–400°C.
Copolymerization of methyl methacrylate with unsaturated esters of granular starch
Authors: Brockway C. E. 
Published: April 2003

AbstractMethyl methacrylate readily copolymerizes with methacrylate ester groups present at a degree of substitution of about 0.1 in granular starch. This is shown by (1) over 50% grafting efficiency by initiation with azoisobutyronitrile; (2) higher grafting efficiency with than without the methacrylate groups when initiation is by peroxide; (3) crosslinked structure of the copolymers obtained; (4) crosslinks which persist in the PMMA recovered after acid hydrolysis to remove starch. By the same set of criteria, maleate half‐ester groups in granular starch copolymerize with methyl methacrylate hardly at all.