NMR-STUDIES OF IRREGULAR STRUCTURES IN POLYISOPRENE

In the reported experiments, irregular structures of synthetic polyisoprenes and natural rubber were studied by **1H and **1**3C NMR spectroscopy. In synthetic polyisoprene, only the (3,4) unit was observed besides the regular structure, but in natural rubber, it was not observed. The (3,4) unit content, which has an important effect upon the properties of the polymer, decreased as the molecular weight increased. In the **1H NMR spectrum of synthetic polyisoprene dissolved in CCl//4, the equals CH//2 proton signal of the (3,4) unit was separated into two peaks. The higher-field peak was assigned to a terminal (3,4) unit and the lower-field peak to an inner (3,4) unit. The terminal (3,4) unit content of the polymer suggested that there are branches in the polymer chain. The **1**3C NMR spectrum of hydrogenated isoprene oligomer indicated that the polymerization of isoprene propagated by the (4,1) addition and there is a considerable amount of the (3,4) unit at the chain end in the (4,3) structure.