Determination of the Molecular Weights and the Structures of Rubber, Gutta-Percha and Balata. Communication No. 258 on Macromolecular Compounds. Communication No. 49 on Isoprene and Rubber

The method used to determine the constitutions of rubber, gutta-percha and balata is essentially the same as that used for organic substances of low molecular weights, i.e., the substance is dissolved in a solvent, and the size and character of the particles in solution are determined. For a long time the nature of colloidal solutions of these hydrocarbons was in dispute. Up to twenty years ago, it was commonly assumed that the molecules of these hydrocarbons are relatively small, and that their colloidal particles are formed by the assemblage of small molecules into micelles through the agency of secondary forces. It seemed to Pummerer, Nielsen and Gündel that in certain solvents, such as camphor and menthol, rubber is dissolved in a low-molecular state. Subsequently, however, this observation was proved to be incorrect. According to the opinion of Meyer and Mark, colloidal particles of rubber are composed of relatively long primary-valence chains, which contain from 75–150 isoprene residues. These chains are, in turn, assembled into micelles by “micellar forces.” The authors explain this in the following way: “The high viscosity of rubber solutions, e.g., in benzene, would lead one to conclude that very large, highly solvated micelles are present in these solvents.” At the time, this hypothesis seemed to explain quite satisfactorily the nature of rubber and its solutions, for the great tendency of these solutions to undergo certain changes on standing, which are manifest by an increase or decrease in viscosity, is readily comprehensible on this basis.