Chemosynthetic P4HB: A Ten-Year Journey from a “Non-Polymerizable” Monomer to a High-Performance Biomaterial

Abstract

Aliphatic polyesters consisting of hydrolytically and/or enzymatically degradable ester bonds in each repeating unit possess diverse thermomechanical properties and desired biodegradability and biocompatibility, thus, finding broad applications in biomedical fields. Among them, poly(4-hydroxybutyrate) (P4HB) is a biomaterial receiving particular attention, due to its proper thermal transition temperatures (T_g ∼ – 50 °C, T_m ∼ 60 °C) relative to the environment of living systems, excellent mechanical properties (high toughness and extensibility when molar mass is sufficiently high), and facile degradability in aqueous media where living systems function. The production of P4HB has long relied on biological fermentation, where it is stored in fermented cells and extracted at the end of the fermentation. However, the high production cost of the fermentation process, associated with its slow reaction kinetics and presently limited production volume, hinders broader implementations of P4HB. In addition, biological routes typically produce P4HB with poor control over the polymer molar mass and dispersity, and postfermentation treatment is employed to offer various molar mass P4HB formulations. Considering that chemical catalysis generally offers faster reaction kinetics, more rapid catalyst tuning, a higher degree of control, and better scalability, it would be desirable to develop a chemocatalytic route to access P4HB more rapidly, at scale, and on-demand for tailorable chain lengths and architectures. In this context, developing the effective and efficient chemocatalytic synthesis of P4HB through ring-opening polymerization (ROP) of γ-butyrolactone (γBL), which is bioderived and available at scale, is of great interest and significance.