Metathesis degradation of natural rubber

Metathesis reaction of natural rubber was carried out using tungusten hexachloride and tetramethyl tin in chlorobenzene. The rubber had to be purified by several times precipitations before the reaction. Molecular weight decreased very much with the progress of reaction and with the increase of temperature. However, NMR studies indicated considerable decreases of carbon-carbon double bonds, which can not be explained by simple metathesis reaction. Some other reactions which consumed unsaturation have to be taken into account to elucidate the exact structure of resultant oligomers.