Computional Study of Metathesis Degradation of Rubber, 2. Distribution of Cyclic Oligomers via Intramolecular Metathesis Degradation of Natural Rubber

The results of molecular modeling of the ring distributions for the intramolecular metathesis degradation of natural rubber (NR) at HF/6–31G(d) level of theory showed that in the ring‐ring equilibrium participate cyclic oligomers containing from two to four isoprene units with all‐trans cyclic isoprene trimer being the main product. The formation of trans,trans,trans‐1,5,9‐trimethyl‐1,5,9‐cyclododecatriene from larger rings is thermodynamically favored. According to the calculations, the ring‐ring equilibrium for the intramolecular metathesis degradation of cis‐polybutadiene (cis‐PB) is completely shifted towards the all‐trans cyclic butadiene trimer. These results are in reasonable agreement with recent experimental data.