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

Abstract

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.