Rubbers and their Characteristics: Real and Ideal*

Abstract

Chemical Structure of Rubbers NATURAL rubber, extracted from latex by coagulation with acid, and afterwards washed and rolled, appears on the market as crepe or smoked sheet. Raw rubber, as these materials are called, is essentially a hydrocarbon (C₅H₈)n having the chemical structure shown in Fig. 1. It is a polymer of isoprene, the isoprene units being joined together in the form of a long chain. The actual length of the molecular chain, or molecular weight, of rubber has been the subject of much discussion, estimates obtained by different methods having ranged from about 1,000 to about 500,000; and it is only within the last few years that the question has been settled. The reliable measurements of Dr. G. Gee show that the mean molecular weight of a typical raw rubber is about 350,000, corresponding to a chain of about five thousand isoprene units.