Rubber-like Polymers / Polyisoprenes

The first record mentioning the use of rubber goes back to the 11^th century. Since this time, the Indians of Middle America use rubber balls in their ball games. From a chemical point of view rubber is a carbohydrate consisting of high molecular weight chains of 1,4 - polyisoprene residues in cis-configuration (caoutchouc). The main source is Hevea brasiliensis. Gutta-percha consists of 1,4 - polyisoprene residues in trans-configuration. Its molecular weight is far below that of rubber. The main source is Palaquium gutta. A similar substance, balata, is obtained from Mimosops balata.

Chicle (obtained from Achras sapota), finally, is a polymer containing both cis- and trans-bonds (in the ratio 1:2). It is the basic substance of bubble gum.

Altogether, more than 1800 plant polyisoprenes have been identified. Their cellular concentrations are usually small, and their molecular weights are relatively low.

Polyisoprenes occur in certain plant cells as small latex particles. They can be seen in the electron microscope as clearly defined, cytoplasmatic inclusions specific for the respective species.