Kinetics and mechanism of the ring opening polymerization of (R,S)-β-butyrolactone initiated with dibutylmagnesium

Ring opening polymerization (ROP) of (R,S)-β-butyrolactone (BL) using dibutylmagnesium (Bu₂Mg) as initiator was investigated both in bulk and in solution. The synthetic poly-3-hydroxybutyrates (P3HB) were characterized by ¹H NMR, ¹³C NMR, FT-IR and GPC. Effects of molar ratio of initiator to monomer, reaction temperature and time on the monomer conversion and the polymer molecular weight and its distribution were discussed. The kinetics of the solution polymerization of BL was examined and showed a first order both in monomer concentration and initiator concentration. The end groups analysis suggested that the monomer inserted into the growing chain proceeding through the coordination-insertion mechanism based on the acyl-oxygen bond scission rather than the alkyl-oxygen bond cleavage of the BL ring. Furthermore, a possible mechanism for the initiation and propagation procedures of P3HB synthesized from BL with Bu₂Mg was proposed.