Efficient Synthesis of α,ω-Divinyl-Functionalized Polyolefins

A facile one‐step olefin metathesis‐mediated ethenolysis reaction on polyolefins containing 1,4‐inserted butadiene units yields α,ω‐divinyl telechelic polymers. These reactions can be successfully performed with well‐defined thermally stable ruthenium catalysts to yield essentially complete metathesis of internal double bonds. The reaction progress is monitored by 1H NMR spectroscopy over time, by tracking the disappearance of the signal due to internal unsaturation of 1,4‐butadiene at ca. 5.5 ppm in toluene‐d8 solvent. The reaction conditions are optimized for ethylene pressure, temperature, catalyst loading, and reaction time. Catalyst loading of 45:1 1,4‐butadiene unsaturation to catalyst at 90 °C with 25 psi ethylene pressure is successful in removing internal unsaturation with no detectable isomerization side reactions. High‐temperature gel‐permeation chromatography (GPC) analysis of the depolymerized product correlates to the calculated molecular weight based on the number of internal double bonds observed in the 1H NMR analysis of the starting polyolefin. This method offers a single step, rapid, and clean route toward divinyl‐terminated telechelic polymers based on commodity materials in high yields. The olefin metathesis reaction of a polyolefin containing inserted 1,4‐butadiene using an indenylidene‐based ruthenium catalyst in the presence of ethylene gas yields the formation of an α,ω‐divinyl poly­olefin with undetectable isomerization side reactions and complete elimination of internal unsaturation.