Chemical upcycling of polybutadiene into size controlled α,ω-dienes and diesters via sequential hydrogenation and cross-metathesis

Plastic waste conversion into valuable chemicals is a promising alternative to landfill or incineration. In particular, the chemical upcycling of polybutadiene rubber (PBR) could provide a renewable route towards highly desirable α,ω-dienes with varying chain lengths, which can find ample industrial application. While previous research has shown that the treatment of polybutadiene with a consecutive hydrogenation and ethenolysis reaction can afford long-chain α,ω-dienes, achieving precise control over the product chain length remains an important bottleneck. In this work, it was discovered that undesired isomerization during the initial hydrogenation step compromises the product selectivity after ethenolysis, leading to a distribution of α,ω-dienes that covers the full range of chain lengths from C6 to C22. Based on this insight, we show that the suppression of isomerization affords a well-defined product distribution predominantly consisting of C4n+2-dienes (with n = 1-5). With tight control over both the hydrogenation degree and isomerization in the studied PBD samples, we demonstrate that rational modifications to the reaction conditions can steer the selectivity towards the desired chain lengths of the α,ω-diene products. In addition, these insights were expanded to cross-metathesis (CM), giving access to a diverse range of high-value bifunctional products.