Geoffrey Gee

Recent Advances in the Physics and Chemistry of Rubber. III. The Solubility and Swelling of Rubbers

Abstract In Parts I and II we have built up a picture of the molecular structure of a piece of rubber, which we have envisaged as a mass of interpenetrating chains, each of considerable length, but randomly kinked and in constant thermal motion, so that its shape is continually changing. Vulcanization restricts the possible motions of the mass by introducing permanent connections between pairs of chains at a series of irregularly spaced points. The purpose of Part III is to show how the picture can be extended to account for the behavior of such a system in contact with a liquid. If we imagine a liquid as a mass of more or less spherical molecules in constant thermal motion, it is clear that, when a liquid is brought into contact with a rubber, there is a tendency for molecules of liquid to diffuse into the rubber structure. Considering first the case of an unvulcanized rubber, we should expect the liquid to enter in increasing amounts, thereby separating the rubber chains and giving them very much greate...

The Interaction between Rubber and Liquids. VI. Swelling and Solubility in Mixed Liquids

Abstract The equations derived in the previous paper for the osmotic equilibrium between a ternary mixture of polymer + two liquids and a mixture of the two liquids are applied to the swelling of cross-linked polymers in mixed liquids and to the solubility of linear polymers in mixed liquids. A mixed liquid has solvent properties intermediate between those of its components only when these mix ideally. The larger the heat of mixing of the liquids, the greater is the solvent power of the mixture relative to those of the components. This conclusion forms the basis of an explanation of the enhanced swelling of rubbers in pairs of dissimilar liquids and of the fact that a mixture of two nonsolvents may be a solvent over a certain range of concentration. Experimental results are given for the swelling of vulcanized rubbers and the critical solubility limits of unvulcanized rubbers. It is shown that these can be explained qualitatively from the cohesive energy densities of the three components, and semiquantita...

Equilibrium Properties of High Polymer Solutions and Gels

Abstract The equilibrium between a polymer and a liquid is of fundamental importance in a number of problems of considerable practical as well as theoretical interest. As examples may be mentioned: (1) the choice of a solvent or plasticizer for a given polymer; (2) choice of a suitable polymer for use, e.g., as a gasket in contact with specified liquids; (3) the combined solvent or swelling action of a mixture of liquids; (4) the effect of mechanical deformation, e.g., compression, on the solvent resistance of a polymer; and (5) the separation of a polymer into fractions by the use of solvent-precipitant mixtures. It must be emphasized at the outset that in some of them other factors are involved, but these are not considered in the present paper. The basic assumption is made here that, given enough time, a system comprising polymer and liquid will reach a steady state, and that if two condensed phases are then present, they must be in true thermodynamic equilibrium. The disturbing influence of such time-...

Recent Advances in the Physics and Chemistry of Rubber. I. The Size and Shape of the Rubber Molecule

Abstract During the last decade, enormous strides have been made in the scientific study of rubber and related polymers. The main factors combining to make this possible have been the realization that the physical behavior of these materials depends on their long chain character, while their chemical properties are essentially those of a low molecular substance of similar structure. Contrary to earlier belief, neither the physics nor the chemistry of rubber involves any mysterious new forces or reactivities unknown among smaller molecules. Since such importance attaches to the size and shape of the rubber molecule, we begin by reviewing briefly the evidence on which our present theories are based. Methods of determining molecular weights may be divided into “counting” methods and “weighing” methods. The former include the determination of any of the “colligative” properties of a solution; the latter depends on the use of an ultracentrifuge.