Thin-Layer Chromatographic Method to Distinguish Natural Rubber and Synthetic Polyisoprene

Abstract With advent of increasing production of synthetic polyisoprene and subsequent use in commercial vulcanizates, there was an obvious need for a simple, reliable method to distinguish between natural rubber and synthetic polyisoprene, to be used in a research program of the Association. Present analytical methods, e.g., the Weber test, infra red spectroscopy etc., will only identify the polymers as cis-polyisoprene and will not differentiate between natural rubber and synthetic polyisoprene. Several methods have been published which depend on identification of a minor constituent of natural rubber not found in synthetic polyisoprene. Disadvantages of these methods are that they are time-consuming and present some uncertainty when dealing with rubber of unknown origin. Natural rubber contains about 1% w/w of extractable lipid materials consisting of phospholipids, sterols, tocopherols, tocotrienols, carotenes, squalene etc., whereas synthetic polyisoprene will contain only ingredients added during manufacture. A new approach to this problem is based on examination of a solvent extract of the rubber by thin-layer chromatography, in order to characterize and distinguish between the lipid components in natural rubber and additives in synthetic polyisoprene.