摘要:

AbstractRate parameters for dielectric relaxation and the thermal properties of long‐chain molecular systems are shown to provide evidence for chain twisting at chain lengths shorter than previously suggested. Comparison of the temperatures of maximum absorption at 1 Hz for mechanical and dielectric relaxation suggests that the underlying motion is not the same for the two observed quanties. The evidence for relaxation in polyethylene is shown to be compatible with this suggestio

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080201

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractThe copolymer composition curve of the methyl methacrylate–styrene copolymer obtained by the copolymerization in the presence of ZnCl2has more alternating tendency than that of ordinary methyl methacrylate–styrene copolymer obtained by radical copolymerization. The fine structure of the copolymer was examined by NMR, and the mechanism of the propagation step of the copolymerization in the presence of ZnCl2, which was proposed in the first report of this series, was verif

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080202

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractCerium (IV) oxidations of model compounds for the hydroxylic functional groups of cellulose were conducted in 1.0Mperchloric acid. Glucose, the model selected for the reducing end group, was oxidized 360 times faster than Schardinger β‐dextrin, the model for anhydro‐D‐glucose repeating units. In the presence of a fourfold excess of glucose, stoichiometry indicated specific conversion to arabinose; the competitive oxidation of arabinose produced is insignificant. Specific C1–C2bond cleavage was also indicated for 2‐O‐methyl‐D‐glucose, galactose, 2‐O‐methyl‐D‐galactose, and cellobiose. Anhydro‐D‐glucose units were oxidized predominantly by C2–C3bond cleavage as shown by the identification of erythrose and glyoxal in hydrolyzates of cerium (IV) oxidized Schardinger β‐dextrin and cellulose. Kinetic studies showed that chelate complexes were involved in oxidations of glucose, methyl β‐D‐glucopyranoside, 1,5‐anhydro‐D‐glucitol, and Sahardinger β‐dextrin. The oxidations of glucose derivatives which differed with respect to substituents on C1and C2demonstrated the importance of the hemiacetal group and the presence of oxygen on C2. For example, the relative rates of oxidation at 15°C for methyl β‐D‐glucopyranoside, 1,5‐anhydro‐D‐glucitol, 2‐deoxy‐D‐glucose, glucose, and 2‐O‐methyl‐D‐glucose are 1:1:12:360:1860, respectively. The mechanism of glucose oxidation is thought to involve formation of a chelate complex, disproportionation of the complex to form a free radical at either C1or C2and further rapid oxidation to 4‐O‐formyl‐D‐arabinose which is hydrolyzed in the reaction medium. General implications of the experimental results

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080203

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractA convenient method is described for the preparation of isotactic and syndiotactic poly(trimethylsilyl methacrylates) by using the monomer trimethyl silyl methacrylate and butyllithium initiation in toluene and tetrahydrofuran, respectively. The structure of these polymers enables complete hydrolysis to the corresponding poly(methacrylic acids), which were characterized with respect to tacticity and molecular weight. The asymmetric induction in toluene produced 89% isotactic polymer, while that in tetrahydrofuran gave polymer<90% syndiotactic and heterotactic in terms of triads. A method of fractionation of the polyelectrolytes by gel‐permeation chromatography on a preparative scale was shown to be applicabl

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080204

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractThe transient torsion pendulum of arbitrary cross section is analyzed as a device for obtaining physical properties of a viscoelastic material. The damped sinusoidal motion yields a damping factor and frequency from which the complex modulus is computed. The particular cases of circular and rectangular cross section are considered with tables and approximations simplifying the practical application of the method.

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080205

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractIn a study aimed at process optimization of caprolactam polymerization, particular reference has been paid to the competing role of water in caprolactam hydrolysis and endgroup polycondensation. The dependence of the apparent equilibrium constant for polycondensation on water concentration indicated that there is a strong effect of the medium on the activities of the reacting species which can not be neglected in a kinetic study of the polycondensation reaction. The effect of a variation of the medium was taken into account by using a polycondensation rate constant which included a function of the water present at any given time. With the aid of analog computer curve‐fitting techniques, good agreement with second‐order kinetics was found. The validity of a second‐order mechanism was confirmed in a kinetic study of the chain amide linkage hydrolysis. The hydrolysis of caprolactam follows substantially different kinetics, where the generation of carboxyl groups reduces the activation energy of the reaction, which follows predominantly a third‐order me

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080206

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractThe system water–caprolactam–polymer at equilibrium is regarded as a solution consisting of two solvents (water and caprolactam) and one solute (polymer). The activities of water and caprolactam in equilibrium at 270°C in the range of 2–10 wt‐% total water content have been determined by vapor‐pressure measurements. Water shows large negative deviations from Raoult's law, as a consequence of the different size of water and polymer molecules. The partial molar free energies of mixing are compared with the expressions derived from the Flory‐Huggins theory of polymer solutions; the results are not conclusive, but seem to indicate a qualitative agreement with the theory. The increase in vapor pressure during polymerization in sealed systems and the water dependence of the polycondensation equilibrium are discussed and explained in terms of water acti

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080207

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractVinylcyclopropane was polymerized with a catalyst of diethylaluminum chloride and titanium trichloride and fractionated to yield isotactic, atactic, and stereoblock fractions, as shown by a combination of physical and chemical evidence. The atactic fraction contained a significant portion of product from 1,5‐polymerization as well as the usual 1,2‐polymerization, and this occurrence is explained by modifications in a mechanism for normal 1,2‐coordination polymerization such that abnormal alkylations occur during the propagation step in the coordination sphere of the catalyst surface. Addition of hydrogen bromide to the isotactic fraction yielded predominantly poly‐3‐bromo penten‐1 and in‐chain cyclohexane and vinylidene structures. A mechanism is proposed for these occurrences involving a hydride shift and various reactions of the initially generated carbonium ion with neighboring cyclopropyl rings. Addition of acetic acid yielded 25% addition and 25% cyclization and crosslinking. Hydrogen sulfide did not add to the cyclopropyl ring. Hydrogenation of the atactic fraction yielded poly‐3‐methylbutene‐1 quantitatively, demonstrating that the polymeric environment did not affect the direction of ring opening but that the state of crystallinity as compared to the isotactic polymer did affect the extent of reaction. In general, the cyclopropyl ring in a polymeric environment underwent its usual reactions but was subject to reactions with neighboring groups resulting from its fixation

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080208

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractMethacrylonitrile was polymerized by a number of ate‐complex catalysts. The catalysts used were NaAlR4, LiAlR4, LiZnR3, Li2ZnR4, RMg[AlR4], and Mg[AlR4]2. It was found that the ate‐complex catalysts in which one of the alkyls is replaced by a diphenylamino group are capable of producing polymers with higher degrees of crystallinity than those of polymers obtained by unmodified catalysts. It was shown that the diphenylamide linkage in these catalytic systems must play an important role in the steric control in the propagation steps of this type of polymerization, although the mechanism is not clear at present. The crystallinity index used in this research gave a linear relation againstImeasured by NMR, and can be used as a measure of the stereo‐regularity of the po

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080209

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractA kinetic study has been made of the polymerization of methyl methacrylate (MMA) initiated by a charge‐transfer complex of poly‐2‐vinylpyridine (electron donor) and liquid sulfur dioxide (acceptor) in the presence of carbon tetrachloride. It is concluded that the polymerization proceeds through free‐radical intermediates, as with the pyridine‐liquid sulfur dioxide complex system. The association constantsKof acceptor and polymer electron donors which range widely in their molecular weight were determined spectrophotometrically, and it has been found that bothKand overall rate of polymerizationRpof MMA decrease with increasing molecular weight of polymer donor; contrary to this, molecular weight of PMMA formed increases with increasing molecular weight of the polymer donor. Other kinetic behaviors was essentially the same as in the pyridine–liquid sulfur dioxide system, i.e.,Rpis proportional to the square root of the concentration of the complex and to the 3/2‐order of the monomer concentration;Rpis clearly sensitive to the carbon tetrachloride concentration at low concentration of carbon tetrachloride, but for a higher concentration it is practically independent of the carbon tetrachloride concentration. It has been deduced from a kinetic mechanism for the initiation that a primary radical may be produced from the reduction of carbon tetrachloride by an associated complex consisting of liquid sulfur dioxide–polymer donor

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080210

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY