摘要:

AbstractThe effects of zinc oxide, of zinc oxide and stearic acid, and of zinc oxide, stearic acid, and 2‐mercaptobenzothiazole on the products of interaction of sulfur with the diisoprene, 2,6‐dimethylocta‐2,6‐diene at 140°C. have been investigated in detail. Zinc oxide alone produces little change in the composition of the complex product mixture, but in the presence of stearic acid, and more so when the thiazole is also present, significant changes are produced in the distribution of combined sulfur which reflect more efficient use of the sulfur in crosslinking reactions, and which can be related rationally to important effects exerted by these additives on the sulfur‐vulcanization of natural rubber. It has recently been advanced that sulfur‐olefin interaction proceeds by a polar mechanism in which the dominant feature is the additive reactivity of persulfenium ionic species (T a+) towards double bonds. Evidence is now presented that the chemical and technological effects of soluble zinc salts and of thiazole accelerators stem from their action in enhancing the role of reactions promoted by the complementary persulfenyl anionic species (T b−) which involve the displacement of hydrogen from, and the addition of sulfur to, carbon atoms adjacent to double bonds. Essentially similar mechanistic considerations appear to apply to systems accelerated by amines and by metal dithiocarbam

ISSN:0021-8995    

DOI:10.1002/app.1959.070010301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractThe dynamic tensile modulus and energy loss have been measured for nylon 66 monofilaments at 9 and 60°C. over a wide humidity range in forced longitudinal vibration experiments. The frequency range covered was about 3 to 30 cycles/sec. (radian frequency 20 to 200 sec.−1). The results show dispersion of mechanical properties with change in humidity at both temperatures. At 60°C. a well‐defined maximum in the energy loss was observed, similar to that obtained previously at 35°C., but occurring at a somewhat lower water content. If a maximum in the energy loss exists at 9°C. (it is not well‐defined), it occurs very near 100% R.H. A time‐humidity superposition procedure is discussed by means of which the individual curves of modulus against frequency for the various humidities can be combined into a single “master curve” of modulus against reduced frequency. The order of magnitude of the activation energy for the dissipation mechanism has been estimated at 6

ISSN:0021-8995    

DOI:10.1002/app.1959.070010302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractA study was made of the dilute solution properties and the molecular weight distribution of a polyurethane polymer prepared from polypropylene glycol 2025 and toluene‐2,4‐diisocyanate by a bulk polymerization under anhydrous conditions at 60°C. Such conditions were chosen to minimize possible side reactions which could produce branching. The polymer, which had a weight‐average molecular weight of 36,500, was separated into fourteen fractions by fractional precipitation from a benzene solution with isooctane as precipitant. The fractions were characterized by light scattering measurements on methanol solutions and by dilute solution viscosities in methanol, benzene, and a theta‐solvent. The molecular weight distribution of the unfractionated polymer and the relations between molecular weight and intrinsic viscosity in the various solvents were determined. Polymer configurations and interaction parameters are d

ISSN:0021-8995    

DOI:10.1002/app.1959.070010303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractLatex thickening—the process of increasing the viscosity of a polymer emulsion by addition of a water‐soluble polymer —has been studied by rheological measurements and by the examination of other colloidal properties. For the systems studied, which represent a range of polymers in both the dispersion and solution phases, the flow curves were represented over a wide range of shear rate by the equation,S=K(τ − τ0)2, whereSis shear stress, τ is shear rate, andKand τ0are constants, of which the latter is considered to be a yield stress. Aside from the generality of the mathematical function, the behavior of various latex‐thickener pairs is extremely specific to the pair involved. Additional data on latex creaming and on the influence of the thickener and latex concentrations confirms the specificity. The available data indicate that latex thickening is not simply an enhancement of the viscosity of the aqueous phase by the thickener, but that in addition to this the ability of the thickener to flocculate or deflocculate the latex is an important part of the mechanism of thickening. These colloidal interactions change, often precipitously, with minor changes in the polymers, the latex emulsifier, and the concentrations of t

ISSN:0021-8995    

DOI:10.1002/app.1959.070010304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractCopolymers of styrene‐methyl methacrylate were irradiated in vacuo with γ‐rays; viscosity changes and gas yields (moles gas per mole methyl methacrylate in copolymer) for H2, CO, CO2, CH4, HCOOCH3, and CH3OH were examined at doses of 1.0 Mrep to 10.0 Mrep. It was found that styrene molecules protect the copolymer from degrading while decreasing the gas yields up to a styrene concentration of about 0.5 mole fraction; above this concentration, these radiation effects are independent of composition. When styrene–methyl acrylate copolymers were irradiated, styrene offered protection aganist gelation but simultaneously increased the gas yields (gases liberated were identical with those from the first s

ISSN:0021-8995    

DOI:10.1002/app.1959.070010305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractSome features of the molecular weight distributions found by experiment for low pressure polyethylenes are examined; an analytical interpretation of them is suggested which is in agreement with the polymerization mechanism resulting from kinetic investigations of Natta and co‐workers. Such interpretation is based on the consideration of the distribution of the individual times of growth (or of the “lifetimes”) of the single macromolecules. It is assumed that (a) these lifetimes tend to be distributed according to the Gauss formula, such as a series of events tending to be distributed at random about a mean; and (b) the growth of any single macromolecule proceeds at a rate which can be considered as the rate of a chain reaction. Possible deviations from such simplified scheme are taken into account. A distribution formula of a generalized Lansing‐Kraemer type is deduced, giving an explanation of all the observed features of the molecular weight distr

ISSN:0021-8995    

DOI:10.1002/app.1959.070010306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractThe reactivity of hydrofluorocarbon polymers toward organic amines increases, generally, with increasing fluorine content and with increasing basicity of the amine. The position of fluorine in the molecule with respect to hydrogen strongly affects the electrophylic character of the hydrogen atom. A discussion of the effects of neighboring groups on this reactivity is presented.

ISSN:0021-8995    

DOI:10.1002/app.1959.070010307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractA study has been made of the effect of fine structure on the decrystallization process which results from the ball‐milling of cellulose. The rate of decrystallization is sensitive to the type of fine structure and is accelerated by the presence of moisture. The extent of chain degradation was greater in air atmosphere than in carbon dioxide, suggesting that mechanically induced free radical degradation occurs along with other chain‐breaking processes. A study of the density and moisture regain of the samples after various times of milling showed that a linear relation between regain and density held over the entire range studied. The relation was the same for native and regenerated cellulose. The process of recrystallization of the ball‐milled samples was studied under various conditions and compared to the hydrolytically induced recrystallization of rayons. The type of lattice which develops on recrystallization was found to depend on the original lattice, the extent of ball‐milling and the conditions of recrystallization. A highly ball‐milled sample could be made to recrystallize as cellulose I, II, or IV depending on the c

ISSN:0021-8995    

DOI:10.1002/app.1959.070010308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractThe kinetics of the emulsion polymerization of methyl methacrylate have been examined in the light of recent advances in theory. It has been found that, if allowance is made for the decrease in the termination rate, the kinetics of the reaction can be predicted up to the point where all monomer is absorbed by growing monomer‐polymer particles. In order to do this it must be assumed that the efficiency of initiation is low and is a function of the size and number of growing particles in the latex. A possible explanation for these observations is discusse

ISSN:0021-8995    

DOI:10.1002/app.1959.070010309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractMolecular weight distributions of homopolymer and graft polymer obtained from the gamma and photoinitiated polymerization of methyl methacrylate with natural rubber latex have been determined. Broad distributions were found with peaks of low and high molecular weight polymer. The distributions were insufficiently defined to make definite assignments to the speeds of the reactions involved but were not inconsistent with the mechanism proposed in an earlier paper from kinetic considerations. Details are given of the column fractionation apparatus employed.

ISSN:0021-8995    

DOI:10.1002/app.1959.070010310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY