Showing papers in "Transactions of The Faraday Society in 1942"

The course and mechanism of autoxidation reactions in olefinic and polyolefinic substances, including rubber

Abstract: The tendency of olefins to absorb molecular oxygen increases rapidly with increase in unsaturation. In monoolefins absorption is usually very slow unless it is actively promoted by irradiation, by the use of temperatures above room-temperature, or by chemical catalysts; in dienes and trienes it usually becomes considerable in diffused daylight; and in higher polyenes it tends to occur unpreventibly and excessively. The strong tendency towards oxidation shown by polyenes appears to be shared by unconjugated and conjugated substances alike, although the precise courses of reaction are probably somewhat different in the two cases. In the present paper attention is focussed mainly on monoolefinic and unconjugated polyolefinic substances.

Permeability in relation to viscosity and structure of rubber

Abstract: Some properties of flow of solutes in and through rubbers are outlined. These properties indicate that, due to fluctuations of thermal energy, activated zones exist in certain polymers, of which viscous flow and diffusion are a consequence. A simple statistics of activated zones has been given, and from it equations are obtained for ΣN, D, Ds, and η, denoting respectively the total number of activated zones in rubber, the diffusion constant of simple solutes in the polymer, the self-diffusion constant of rubber, and its viscosity. Functional relations are predicted between log Do, log ηo, or ΔS* (the entropy of activation) and the Arrhenius energy of activation for diffusion or viscous flow. The available data clearly demonstrate this relationship. They also indicate no discontinuity between rubbers and liquids as diffusion media.

The interaction between rubber and liquids. 1. A thermodynamical study of the system rubber-benzene

Abstract: Equations are developed relating the thermodynamic properties of a mixture of rubber + liquid with the vapor pressure of the liquid above the mixture Experimental methods are described for the determination of vapor pressure over the whole range of composition of the mixture By the use of four different methods, it was possible to measure relative vapor pressure lowerings Apo/po° from 2×10−6 to 0997 Complete vapor pressure data are given for rubber-benzene mixtures at 25° C, together with the calculated Gibbs' free energies of dilution and solution Temperature coefficient measurements at a number of concentrations are employed to calculate heats of dilution, and these are interpplated by a modified form of an equation due to Langmuir In this way the heats of dilution and solution are also obtained over the whole range of composition Combining the heat and free energy data gives the entropies of dilution and solution The entropy of dilution is approximately twice the heat of dilution over

The interaction between rubber and liquids. III. The swelling of vulcanised rubber in various liquids

Abstract: The entropy of swelling of vulcanized rubber is estimated, and assumed independent of the nature of the swelling liquid. The heat of swelling is related to the cohesive energy of the liquid, and a value of 66 calories per cc. deduced for the cohesive energy density of rubber. The swelling power of a liquid can be calculated approximately if its cohesive energy and molecular volume are known. Substantial agreement with theory is found in most cases, although it is necessary to consider aliphatic and aromatic liquids separately. The anomalously high swelling power of acids and alcohols arises from their association.

Ionic and radical mechanisms in olefinic systems, with special reference to processes of double-bond displacement, vulcanisation and photo-gelling

Abstract: The α-methylenic reactions discussed in the preceding two papers recall a series of interesting observations by Baker and Nathan, which indicate that a p-methyl substituent attached to the benzene nucleus can permit electron release to the nucleus in a manner that appears only in lesser degree in higher alkyl groups, and may be absent in some (e.g., Buγ). Thus in p-methylbenzyl bromide, the suggested function of the methyl group (dotted arrows in (I) permits (see PDF for diagram) additional electron release at the C—Br bond, and so facilitates the anionization of the bromine. Baker and Nathan suggest that the electrons of the duplet constituting the C—H bond of the methyl group are less localized than those in a similarly placed C—C bond, and hence that a methyl group attached to the necessary conjugated unsaturated system is capable of electron-release by a mechanism similar to the tautomeric effect:

The kinetics of high elasticity in synthetic polymers

Abstract: The simple Mark-Kuhn theory of high elasticity of rubber has been extended, on the basis of the work of Alexandrov and Lazurkin, to cover the elastic properties of other polymers. The chief principle invoked is that high elasticity is developed only when rotation of the main C—C chain in the polymer is comparatively free. The effect of molecular structure, plasticizer and cross-links on elastic properties has been indicated, and also a connection with other observed physical properties, such as volume expansion, dielectric dispersion and specific heat.

The influence of chemical structure on the imbibition of liquids by rubber. I

Abstract: Studies of the swelling of rubber which had been carried out up to 1924 were reviewed by one of the authors in an earlier publication. A review of subsequent studies is to be found in a paper by Scott, who himself has contributed some data on the subject. These prior studies were not, however, concerned primarily to secure systematic information on the influence of the chemical structure of liquids on their imbibition by rubber, and they involved only a relatively small number of liquids, except for the study by Lee, in which the behavior of raw rubber in sixty-nine liquids was observed only qualitatively. Further, a good many of the earlier observers used material of unknown history and composition, such as “black rubber tubing”, and often assuming the swelling to reach a maximum in twenty-four hours. In the present study the course of the swelling of rubber, both raw and vulcanized, has been followed, quantitatively, at intervals over long periods, and a very large number of liquids have been e...

The interaction between rubber and liquids. II. The thermodynamical basis of the swelling and solution of rubber

Abstract: It has been the purpose of this paper to show that the general phenomena of solubility and swelling of rubber could be understood on the basis of the detailed results found experimentally for the rubber-benzene system. Using no arbitrary constants which cannot be related to experiment, temperature coefficients of solubility of the right order of magnitude are calculated. It is clear that the qualitative agreement of this treatment with the meagre experimental data at present available must not be taken as evidence of the accuracy in detail of the equations employed for the heat and entropy of solution. This paper is based on work carried out under the programme of fundamental research on rubber undertaken by the Board of the British Rubber Producers' Research Association.