Factors influencing the ring-opening polymerization of racemic β-butyrolactone using Cr^III(salphen)

The recently discovered ring-opening polymerization (ROP) of β-butyrolactone (β-BL) using Cr^III(salphen) as catalyst converts racemic β-BL to isotactic enriched poly(hydroxybutyrate) (PHB). These achiral complexes arrange themselves in a dimeric sandwich-like structure entrapping the growing polymer chain and the monomer. The polymerization mechanism discussed based on previous DFT calculations is supported by kinetic studies in here. Furthermore, the influence of different substitution patterns in salphen complexes on polymerization of β-BL was investigated. In addition, effects of different polymerization starters and additives on the broad molecular weight distribution of PHB have been investigated, which show the limitations of this catalysis.