ISSN:0022-3832    

DOI:10.1002/pol.1959.1203512801

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractMany articles have been written attempting to explain the degradation processes which take place when polyvinyl chloride is aged. Everyone agrees that hydrogen chloride is evolved, color develops, and the polymer eventually becomes stiff and insoluble as a result of crosslinking. Early workers believed that hydrogen chloride catalyzed the decomposition and that the role of stabilizers was to react with it to render it ineffective. More recent work has shown that hydrogen chloride is not a catalyst for the decomposition in the absence of oxygen and that the function of stabilizers may be quite different from that earlier assumed. In this paper an attempt is made to weigh the results of many workers and to explain the observable changes brought about during degradation by a consistent free radical mechanism. Under milling conditions, temperatures are attained at which even saturated hydrocarbons will oxidize; hence it is not unreasonable to assume the presence of free radicals in polyvinyl chloride. Free radicals may also result from the ejection of a chlorine atom from a polymer chain. At room temperatures chlorine atoms may be formed as the result of the absorption of light energy. Once radicals are produced, degradation in the presence of oxygen may take many routes. A few of these are discussed. Many stabilizers are believed to act by disrupting radical chain processes.

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203512802

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractStyrene, styrene mixed with rubber, and rubber alone have been exposed to γ‐radiation from Co‐60. TheGvalue for polymerization‐initiating radicals formed from rubber in the mixture,G(i.r) = 0.26, has been calculated from corresponding values obtained by estimation of the number of polystyrene molecules formed in styrene and in the mixture. AG(radical) value for rubber when irradiated alone,G(r), has been assessed from aG(crosslinking) value,G(X), which was determined under closely similar experimental conditions, asG(r) = 2G(X) ∼ 6. The large discrepancy betweenG(r) andG(i.r.) cannot be explained satisfactorily on the supposition that radicals formed from rubber have a low efficiency in initiating the polymerization of styrene. Therefore, it is argued that theG(r) value itself is lower in the mixture. Evidence for this argument is provided by the lower rate of gelling in the mixture. this protection of rubber by energy transfer to styrene is an important example since in only one previous case has experimental evidence been provided to exclude an alternative radical mechanism. By polymerization in the presence of crosslinked rubber, uncombined polystyrene could be readily partioned into the sol fraction by equilibration of the gross polymer in benzene. About 15% of the polystyrene was free. Hexachloroethane was chosen as an example of an additive with a highG(radical) value. As would be expected, it increases the rate of polymerization but does not lead to a correspondingly large amount of free polystyrene (about 23%). Graft polymer formation from styrene and methyl methacrylate is compared and attention is drawn to the importance of the formation and subsequent reactions of initially nonpolymeric radicals in determining the proportion of free p

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203512803

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractLow levels of periodate oxidation increased the dispersibility of cornstarch in water at 98°C. Above the 10% level of oxidation, cornstarch became more resistant, and longer heating times were generally required to form stable solutions. Light‐scattering, sedimentation, and viscosity measurements showed that the average particle weight in solutions of periodate‐oxidized starches generally decreased with increased level of oxidation and time of heating. Introduction of dialdehyde groups into the anhydroglucose residues of the starch molecules thus made the structure labile toward degradation on heating in water. The experimental results showed, however, that an aggregation reaction also occurred in solutions of oxidized starches. This reaction was most evident at 10% oxidation level, but it was found to occur simultaneously with degradation over a range of oxidation levels. Aggregation probably results from the reaction of aldehyde groups of one molecule with hydroxyl groups of neighboring molecules. The observation that aggregation could be prevented by additon of glucose was explained by competition of hydroxyl groups of glucose with hydroxyl groups of starch in their reaction with aldehyde groups. The angular dependence of the light‐scattering measurements indicated that formation of dumbbell‐shaped particles by crosslinking of near‐spherical particles was probably quite important to the aggregation reaction. Preliminary investigation of periodate‐oxidized waxy maize starch showed that this starch had a much lower average molecular weight in solution than ordinary cornstarch at a comparable level of oxidation. This value may result from the contribution of amylose to the aggregation of ordina

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203512804

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractThe influence of nearest‐neighbor interaction on the potentiometric behavior of polyampholyte is discussed. It is shown how this effect superposes itself on the normal random electrostatic interactions between segments of the chain. Only interactions between oppositely charged nearest neighbors are considered. Other specific interactions, such as ion binding and nearest‐neighbor interaction between like charges, are neglected as being of interest only in special cases. A simplified model is treated in which one of the groups is present in large excess while the other exists only in singlemembered sequences in the chain. It is shown that positive‐negative nearest‐neighbor interaction always has the effect of increasing the strength of the group, an acidic group becoming a stronger acid, a basic group, a stronger base. The effect is most pronounced for groups which are already strong, and, in this case, the titration (proton binding) curve of the polyampholyte is considerably changed; on the other hand, if both groups are weak, the titration curve is hardly affected, even when the interaction is strong. In this case, however, the pH dependence of the degree of ionization of the group present in minority shows peculiarities. The isoelectric point of polyampholytes can be considerably affected by (+ −) nearest‐neighbor interaction, that of molecules containing an excess of basic groups being raised by the interaction, and that of polyampholyte containing an excess of acidic groups being lowered. These shifts are again far more pronounced when the groups involved are strong. It is shown how use can be made of these predictions to analyze and understand the behavior in practical cases. The data for two types of synthetic and one naturally occurring polyampholyte are interpreted in this way, and satisfactory results

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203512805

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractFrom studies on light‐scattering, viscometry, and osmometry in solutions of nonfractionated polyethylenes, it is concluded that none of the samples investigated shows an excessively broad molecular weight distribution. This conclusion is supported by the results obtained fro fractionated samples. The results of osmometry for two fractions confirm the [η]–Mnrelation suggested by Trement

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203512806

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractIt is well known that aliphatic polyamides with even numbers of methylene groups between amide groups melt at higher temperatures than those with odd numbers of methylene groups. Crystallographic studies in the past have sought to relate the packing of the amide groups to the variations in melting point, but these studies have been made almost exclusively at room temperature. In the present study, series of polyamide fibers were examined by x‐ray diffraction over a wide range of temperatures. In the even‐numbered polyamides, the triclinic structure occurring at room temperature shifts to a more symmetrical structure in which the chains assume hexagonal packing. This latter packing occurs in the odd‐numbered polymers at room temperature. The polar groups in the latter occur in layers which are normal to the chain axes. The layers of polar groups in the even‐numbered polyamides are tilted with respect to the chain axes at room temperature, and remain tilted at high temperatures even though the lateral chain packing becomes the same as the lower‐melting (odd‐numbered) members of the series. The spacing between polar groups along the chain decreases with increasing temperature, but the decrease is relatively less in the even‐numbered than in the odd‐numbered polymers, and is less in the more polar than in the more paraffinic compounds. These changes are ascribed to torsional and rotational motions of chain segments in the crystallites. Proton magnetic resonance studies demonstrate the onset of motion of the hydrocarbon segments and compare qualitatively the constraints to chain motion among isomeric members of the series. Some implications regarding the melting proces

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203512807

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractChanges in the accessibility of the fine structure of cellulose as a result of mild acid action on standard cellulose, cellulose mercerized with and without the application of tension, viscose rayon, and cuprammonium rayon have been studied with respect to changes in DP, fiber density, fiber crystallinity, moisture regain, oxidative susceptibility, and equilibrium adsorption of Chrysophenine G, Chlorazol Sky Blue FF, and Procion Brilliant Red 2Bs. Results indicate that the mild acid action on all the cellulosic fibers studied, appears to proceed in three different stages. In the initial stages the acid action is rapid and results in a sudden decrease in DP, moisture region, oxidative susceptibility, and adsorption of dyes with a simultaneous increase in fiber crystallinity and fiber density. The subsequent acid action is slower than that in the initial stages during which the extent of lowering in the values of fiber characteristis is much less, and during the final stages of acid action there is a tendency for the leveling‐off of all the fiber characteristics. The extent of reduction in the values of the fiber properties and the stages during hydrolysis at which the changes take place in different cellulosic fibers depend mainly on the rate of removal of hydrolyzable fraction and the extent of crystallization of cellulose chains taking place during the acid actio

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203512808

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractBy crosslinking natural rubber in benzene, networks are prepared in which the degree of coiling is higher than normal (“supercoiled” networks). On heating, these networsk are converted to normal ones with the same number of crosslinks but a lower degree of equilibrium swelling. The results of the swelling experiments are in quantitative agreement with theoretical predictions. Results of strees relaxation experiments at elevated temperatures support the conclusion reached on the basis of swelling. It follows that great caution is needed when calculating changes in the density of the crosslinks from changes in stress alone as is sometimes done in kinetic stud

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203512809

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractSome experiments are described which show that the polymerization of ϵ‐caprolactam (CL) can be accomplished by heating the lactam under anhydrous conditions in the presence of hydrogen chloride or of salts of strong acids and ammonia or amines at temperatures of 220–260°C. To study this type of polymerization more closely, two series of kinetic experiments with the sytem CL–HCl hae been performed (254°C.; initial molar ratios of HCl to CL, 0.025 and 0.0125). The progress of the reaction, characterized by the degree of conversion (determined by extraction of the unconverted lactam with water), is compared with the polymerization of CL initiated by corresponding amounts of water or of ϵ‐aminocaproic acid. The products obtained have been characterized by endgroup titration values and intrinsic viscosity. Some additional data have been obtained by chromatography and IR investigations. The titrations show that the molecules bear an amino group at one end of the chain; the nature of the other endgroup is still obscure. Reaction constants calculated for an uncatalyzed additon of CL to amino groups prove to be of about the same magnitude as those of the water‐initiated polymerization without additional HCl. At the same time some kinetic experiments with the system CLH2OHCl are presented. Both systems have some striking features in common. The catalytic effect of the HCl present in this system can be attributed to the rapid formation of amino groups in the very first moments of the reaction, thus leading to an enhanced rate of polymerization by addition of C

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203512810

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY