We report the highly isoselective ring-opening polymerization (ROP) of racemic β-butyrolactone (β-BL) using in situ-generated catalysts based on Y[N(SiHMe 2 ) 2 ] 3 (THF) 2 and salan-type pro-ligands. The catalyst system produces isotactic poly(3hydroxybutyrate) (PHB) with record productivity (TOF up to 32 000 h −1 ) and the highest isoselectivity (P m up to 0.89) in ROP of β-BL achieved to date. In contrast to bacterial PHB, the chemically synthesized PHB has beneficial material properties, such as increased melt processing window attributed to a lowered melting temperature (T m ≈ 140 °C) and drastically reduced brittleness. The produced PHB showed an elongation at break of 392%, thus demonstrating promising polyolefin-like thermomechanical material properties.

Poly(3-hydroxybutyrate) (PHB) is a material produced naturally by bacteria but is also chemically accessible via ring-opening polymerization (ROP) of β-butyrolactone (β-BL). In ROP, catalyst design plays a key role in the production of PHB with different stereomicrostructures, i.e., syndiotactic, isotactic, or atactic PHB. In this work, we demonstrate a simple procedure for generating the catalysts in situ by conveniently combining a suitable yttrium precursor with the respective salan pro-ligand. This approach circumvents the elaborate isolation of the catalyst and enables the high-throughput screening of a library of yttrium salan catalysts for the ROP of β-BL. Electronic and steric influences of the ligand framework on stereoselectivity and activity of the catalyst as well as limitations could be determined, and structure–property relationships were established. Depending on the substitution pattern, these in situ-generated catalysts produced syndiotactic-enriched, isotactic-enriched, or atactic PHB with high activity.

Utilizing renewable feedstocks for the synthesis of biobased and preferrable biodegradable polyesters as substitute for fossile-based polymers remains one of the major challenges towards a sustainable polymer economy. One such...