Biosynthesis of High Toughness Poly(3‐Hydroxypropionate)‐Based Block Copolymers With Poly(D‐2‐Hydroxybutyrate) and Poly(D‐Lactate) Segments Using Evolved Monomer Sequence‐Regulating Polyester Synthase

Abstract

This study synthesized poly(3‐hydroxypropionate) [P(3HP)]‐containing polyhydroxyalkanoate (PHA) block copolymers, P(3HP)‐b‐P[2‐hydroxybutyrate (2HB)] and P(3HP)‐b‐P(D‐lactate) (PDLA), using Escherichia coli. The cells expressing an evolved sequence‐regulating PHA synthase, PhaCARNDFH, and propionyl‐CoA transferase were cultured with the supplementation of the corresponding monomer precursors in the medium. The block structure of P(3HP)‐b‐PDLA was confirmed by proton nuclear magnetic resonance analysis and solvent fractionation. The molecular weights of the polymers were in the range of 0.8–2.8 × 105. The solvent‐cast polymer films were subjected to isothermal treatment to promote phase separation and crystallization and were subsequently melt‐quenched to produce an amorphous phase. The melt‐quenched P(3HP)‐b‐P(2HB) film exhibited a high elongation at break (1153%), resulting in a toughness of 181 MJ/m3. The solvent‐cast film of P(3HP)‐b‐65 mol% PDLA exhibited partial elastic deformation, in which the P(3HP) phase functioned as a soft segment. The melt‐quenching of the polymer resulted in embrittlement presumably due to the high lactate fraction. Overall, the P(3HP)‐based block copolymers exhibited several mechanical properties depending on the higher‐order structure of the polymer and the properties of the P(2‐hydroxyalkanoate) segments. This study findings show that P(3HP)‐b‐P(2HB) and P(3HP)‐b‐PDLA can function excellently if their microstructures are properly controlled.