Abstract
Abstract Flash pyrolysis of polyisoprene at 500°C in nitrogen atmosphere leads to four isomeric dimers of isoprene: dipentene, diprene, and 1,4-, and 2,4-dimethyl-4-vinyl-cyclohexenes. From systematic studies of various synthetic polyisoprenes of different microstructures, the four cyclic dimers have been assigned to specific diads of 4,1-4,3 or 1,2 units; for instance, dipentene and 2,4-dimethyl 4-vinyl cyclohexene are respectively characteristic of 4,1-4,1 and 4,1-4,3 diads. It has been possible to draw some correlations between the nature and the amount of the thermal degradation products and the distribution of the different kinds of units along the polymeric chain; anionic polyisoprenes obtained in the presence of alkali earth metals behave as random copolymers of 4,1 and 4,3 units, but Ziegler-Natta polyisoprenes shew a definite tendency to alternate the same units.
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