Triacetic acid lactone conversion to methylene-δ-caprolactone: a renewable monomer for bio-based circular polymer synthesis

Abstract

To enable a circular and sustainable plastics economy, polymers must be derived from renewable carbon feedstocks and designed for chemical recyclability. Here, we report a multistep catalytic strategy for converting triacetic acid lactone (TAL), a biomass-derived platform chemical, into poly(α-methylene-δ-caprolactone) (PMCL), a more sustainable (bio-based and chemically recyclable) analogue of poly(methyl methacrylate) (PMMA). The process proceeds via the (i) quantitative hydrogenation of TAL to 4-hydroxy-6-methyltetrahydro-2-pyrone (HMTHP) catalyzed by Ru/C, (ii) HMTHP conversion to δ-caprolactone (dCL) over Pt/TiO₂ with 88% yield, (iii) Cs₂O/SiO₂ catalyzed vapor-phase aldol condensation of dCL with formaldehyde to methylene-δ-caprolactone (MCL) at 92% yield, and (iv) vinyl addition polymerization of MCL to PMCL. The resulting PMCL exhibits performance and recyclability advantages over its fossil-based linear analogue, PMMA. Overall, this work demonstrates the integration of selective catalytic biomass transformations with polymer synthesis to access recyclable vinyl polymers from a bio-based platform molecule.