Closed-loop recycling of lignin-based sustainable polymers with an all-hydrocarbon backbone

Abstract

Sustainable polymers from biomass with a nonhydrolytic backbone are highly desirable because they meet performance requirements. However, their inert nature hinders chemical recycling under mild conditions. In this work, we report a series of recyclable lignin-based sustainable polymers with an all-hydrocarbon backbone showing excellent thermal stability (decomposition temperature up to 380 °C) and tunable mechanical properties. These renewable polyolefins from lignin can be depolymerized back to pristine monomers with a quantitative (>90%) recovery rate under gentle heating (50 °C) by using a Grubbs II catalyst within several minutes. These polyolefins are prepared by the ring-opening metathesis polymerization (ROMP) of cyclooctene with a trans-dioxolane ketal installed at the 5,6-positions and lignin derivatives as pendants. The additional fused ring significantly reduces the ring-strain energy of the cyclooctene monomer to ∼5.0 kcal mol⁻¹, inducing the resulting polymer to be depolymerizable to establish a closed-loop life cycle.