Computational study of metathesis degradation of rubber, 1 Distribution ofcyclic oligomers via intramolecular metathesis degradation of cis-polybutadiene

The results of the molecular modelling of the intramolecular metathesis deg radation of cis-polybutadiene (cis-PB) into cyclic oligomers at PM3 level o f theory showed that the chain-ring equilibrium is completely shifted towar ds the ail-trans cyclic isomers. The formation of cyclic products, containi ng from three to six butadiene units, from larger rings is thermodynamicall y favoured with cyclic butadiene tetramers and pentamers being the main pro ducts. These results are in reasonable agreement with most of the available experimental data. The discrepancy observed in some cases between found an d calculated ring distributions for the intramolecular metathesis degradati on of cis-PB suggests that the reaction is kinetically controlled under cer tain conditions.