Abstract
Although poly[(R)-3-hydroxybutyrate)] [P(3HB)] is a microbial polyester that can be used as a sustainable and biodegradable plastic, its use has been limited because of poor material properties due to its stiff and brittle nature. To overcome this issue, it is critical to diversify the monomeric composition of P(3HB) polymers through the introduction of new repeating units that can improve material properties. In this study, a new 3HB-based copolymer was biosynthesized with 3-hydroxypivalate (3HPi) units containing signature dimethyl groups on the α-carbon. To biosynthesize poly[(R)3-hydroxybutyrate-co-3-hydroxypivalate] {P(3HB-co-3HPi)}, recombinant Escherichia coli LSBJ was cultured with glucose and 3-hydroxypivalic acid (3HPiA) as the carbon source and 3HPi precursor, respectively. This resulted in the successful synthesis of P(3HB-co-3HPi) copolymers with a 3HPi fraction in the range of 2–50 mol% by adjusting the precursor concentration to the microbial catalyst. Interestingly, the biosynthesized polymers exhibited an increasing molecular weight with increasing 3HPi fractions, up to 424 × 104 in weight average molecular weight. The thermal properties of P(3HB-co-3HPi) were similar to those of conventional 3HB-based copolymers, but the copolymers displayed extraordinary mechanical performance compared to other P3HB homo- and copolymers. P(3HB-co-32 mol% 3HPi) displayed an elongation at break of 1,919%, the highest value ever reported for bacterial polyesters. Given its high flexibility, P(3HB-co-3HPi) copolymers exhibited reversible deformation during tension testing, unlike other 3HB-based copolymers. Furthermore, P(3HB-co-3HPi) copolymers and monomeric 3HPiA were both biodegradable. This study has demonstrated that the incorporation of 3HPi monomers into 3HB-based copolymers results in superior mechanical properties and has introduced a promising new class of materials for use as sustainable and biodegradable plastics.