A Biobased Approach to Mechanically Tunable Polyester

While holding great promise as sustainable and biodegradable, current biobased polyesters encounter significant difficulties in commercialization because of their brittleness and rigidity. This characteristic precludes their use in products required to be soft, elastic, or flexible. Recently we have developed a biobased approach to manufacturing a branched lactone, β-methyl-δ-valerolactone (MVL), and demonstrated its potential as the first scalable rubbery polyester. We designed an artificial metabolic pathway to MVL by extending the mevalonate pathway: introduction of fungal siderophore proteins to convert mevalonate into anhydromevalonolactone; and reduction of anhydromevalonolactone to MVL by enoate reductases. The total biosynthetic pathway produced 300 mg/L of MVL directly from glucose in shake flask experiments.  While directed evolution is ongoing to optimize the MVL pathway, as an alternative solution we developed a semisynthetic approach for the immediate commercial-scale production of MVL. In this approach we introduced the archaeal mevalonate pathway into production host E. coli and engineered the pathway to produce ~90 g/L mevalonate in a bioreactor. We then performed two simple chemical reactions, dehydration & hydrogenation, to produce MVL from mevalonate. The overall purification and reaction efficiency reached 90% . With the biobased MVL, we generated an amorphous rubbery polymer with a T_g at -51^oC, which can be used to prepare mechanically tunable polyesters for packaging, thermoplastic elastomers, agricultural mulch films, chewing gums and pressure sensitive adhesives.