Natural Rubber Solutions Research Articles

Chlorination of Natural Rubber Solutions by Means of Phenyl Iododichloride

Abstract The loss of unsaturation attending the chlorination of carbon tetrachloride solutions of unmasticated pale crepe and deproteinized rubbers by means of phenyl iododichloride was followed by quantitative ozonization of the chlorinated products, ranging in chlorine contents from 2.3 to 73.6 per cent. It is concluded from such studies that the reaction proceeds mainly by the additive reaction of the chlorine radicals produced by the thermal decomposition of phenyl iododichloride. The hydrogen chloride found in the preparation of these chlorinated products was determined. It has a value below 1 per cent up to about 15 per cent chlorine content and thereafter it increases. However, this value generally does not exceed 4 per cent. This indicates the occurrence of only a slight amount of substitutive reaction by chlorine. Cyclization also takes place, probably following an additive reaction of the chlorine radicals. The main difference between the deproteinized rubber and pale crepe rubber reactions is confined to the very early stages, wherein the nonrubber components have a directive influence in bringing about a slightly earlier onset of cyclization. It is also concluded that atmospheric oxygen has a negligible effect on the reaction.

The Mechanism of the Action of Aromatic Thiols on Rubber Solutions

Abstract 1. The effect of aromatic thiols on the kinetics of the change in viscosity of natural-rubber solutions on heating was studied. 2. Aromatic thiols accelerate the oxidation of rubber. 3. In the process of heating rubber solutions, thiols are oxidized to the corresponding disulfides. The rate of oxidation of the rubber depends on the rate of oxidation of the thiol. 4. The mechanism of the action of thiols is explained by the presence of an accompanying reaction, whereby oxidation of the thiol induces oxidation of the rubber.

Molecular Weight and Polydispersivity of Rubber by Diffusion Measurements

Abstract The study of diffusion in solutions of natural rubber (light crepe) by Lamm's method showed that even with a concentration of 0.1 per cent the normalized experimental diffusion curves diverge from the ideal Gaussian curve (Figure 1), in that they are characterized by a marked asymmetry and an excess of the maximal ordinate. It follows from an analysis of the experimental curves by the method of moments (up to moments of the fourth order) that they belong to Type IV Pearson curves, that is, to asymmetrical distribution curves with asymptotic branches. The determination of the perturbation multiplier enables us to calculate the course of the experimental curves with a fair degree of accuracy. The physical cause of asymmetry of the diffusion curves is the difference in the rate of diffusion to both sides of the interface (of the polymer into the solvent and back) due to a marked intermolecular interaction in the solution of the polymer at a given concentration. With a decrease of the concentration or of the molecular weight of the dissolved substance, the asymmetry of the diffusion curves becomes less pronounced. However, this asymmetry does not preclude the computation of the average diffusion coefficient D from the standard deviation of the curve. It can, indeed, be shown that the probable error does not exceed 1 per cent. The average value found for natural rubber in carbon tetrachloride is D20°=0.71×10−7 sq. cm. per sec.

Molecular Weight and Polydispersity of Rubber by Diffusion Measurements

THE study of diffusion in solutions of natural rubber (light crepe) by Lamm's1 method showed that even with a concentration of 0·1 per cent the normalized experimental diffusion curves diverge from the ideal Gaussian curve (Fig. 1), being characterized by a marked asymmetry and an excess of the maximal ordinate. It follows from an analysis of the experimental curves by the method of moments (up to moments of the fourth order) that they belong to Type IV Pearson curves, that is, to asymmetrical distribution curves with asymptotic branches. The determination of the perturbation multiplier enables us to calculate the course of the experimental curves with a fair degree of accuracy. The physical cause of asymmetry of the diffusion curves is the difference in the rate of diffusion to both sides of the interface (of the polymer into the solvent and back) due to a marked intermolecular interaction in the solution of the polymer at a given concentration. With a decrease of the concentration or of the molecular weight of the dissolved substance, the asymmetry of the diffusion curves becomes less pronounced. However, this asymmetry does not preclude the computation of the average diffusion coefficient D from the standard deviation of the curve. It can indeed be shown that the probable error does not exceed 1 per cent. The average value found for natural rubber in carbon tetrachloride is D20° = 0·71 × 10â7 cm.2/sec.

Reactions of Iodine, Iodine Chloride and Thiocyanogen with the Hydrocarbons of Natural Rubber and Synthetic Rubber

Abstract The reactions of iodine, iodine chloride and thiocyanogen with solutions of natural rubber and of synthetic sodium-butadiene rubber were studied. The experimental results show that the chemical properties of these two hydrocarbons are in general similar, although there are also certain differences which can be explained by the peculiarities of their structures. The products of the reactions of iodine chloride and of thiocyanogen with natural rubber and sodium-butadiene rubber were isolated, and their compositions and some of their properties are described.

The Structure of Synthetic Types of Rubber. Polychloroprenes

Abstract Ozonization is one of the most successful and most exact methods for determining the structure of rubber. It was this method which was first used by Harries and his numerous collaborators for determining the structures of various types of natural and synthetic rubbers. By ozonizing solutions of natural rubber, Harries obtained ozonides, the decomposition of which yielded levulinic acid and levulinic aldehyde. This was proof that the combination of isoprene residues in the rubber molecule is in the 1,4-1,4 position, and it also showed the nature of the base molecules of rubber and the manner in which they are united in chain formation. On the other hand, these investigations did not give any decisive evidence as to whether the rubber molecule is an open chain or has a ring structure. At the beginning of his investigations in this field, Harries assigned to the hydrocarbon which is the fundamental constituent of the rubber molecule the following formula: