Alternating copolymerization reaction of propylene oxide and CO: Variation of polymer stereoregularity and investigation into chain termination

The cobalt-catalyzed alternating copolymerization reaction of racemic propylene oxide and CO affords regioregular but atactic poly(hydroxybutyrates). The application of enantiomerically pure (R)- or (S)-propylene oxide results in the formation of isotactic, optically active and crystalline materials. In contrast to the perfect isotactic microstructures that are available via the microbial pathway, our approach allows to tailor the stereoregularity of the polymer products, and hence their melting points by application of mixtures of the epoxide enantiomers. Investigations into the polymer stereochemistry show that the epoxide units undergo a clean regioregular incorporation into the polymer chain with retention of configuration at the stereogenic carbon centers. MALDI-TOF and online ATR-IR experiments give insight into the mechanism of chain termination reactions.