Computational Study of Metathesis Degradation of Rubber, 3. Distribution of Cyclic and Linear Oligomers via Intermolecular Degradation of cis‐Poly(butadiene)

The molecular modeling of the product distributions for the intermolecular metathesis degradation of cis‐poly(butadiene) (cis‐PB) in the presence of ethylene as chain‐transfer agent (CTA) at 298.15 K using the B3LYP/6‐31G (d, p) level of theory reveals that chain–ring and chain‐chain equilibria are shifted toward the formation of 1,5‐hexadiene. The amount of cyclic oligomers at equilibrium with linear molecules is negligible. The α,ω‐vinyl‐terminated butadiene oligomers–1,5‐hexadiene equilibrium constant depends on the cis/trans isomer ratio in linear butadiene molecules. While the concentration of 1,5‐hexadiene at equilibrium with cis‐butadiene oligomers is 86 mol‐%, this value for trans‐butadiene oligomers corresponds to 50 mol‐% of 1,5‐hexadiene. The results of calculations are in reasonable agreement with recent experimental data on the intermolecular metathesis of 1,4‐cis‐PB with ethylene using a well‐defined ruthenium alkylidene catalyst. The calculations predict that cis‐butene as a CTA is more efficient in the metathesis depolymerization of cis‐PB compared with ethylene.