Copolymerization of γ‐butyrolactone and β‐butyrolactone

The copolymerization of a 4‐membered β‐butyrolactone (βBL) and a thermodynamically stable 5‐membered γ‐butyrolactone (γBL) proceeds in the bulk state with BF3 · OEt2 as a catalyst at room temperature to give poly[(3‐hydroxybutyrate)‐co‐(4‐hydroxybutyrate)] (P(3HB‐co‐4HB)) whose structure is identical with that of a polyester formed by microorganisms. The copolymer structure was confirmed by 1H and 13C NMR spectroscopy. The monomer reactivity ratios were r(γBL) = 0.48 and r(βBL) = 0.58, respectively, and the unit composition of 4HB increases to 56% at high γBL to βBL ratio in the feed. End group analysis of the copolymer suggests the presence of a hydroxyl group and a carboxyl group at the ends of each polymer molecule. It was postulated that the monomers activated by BF3 react with the hydroxy group derived from the water contaminant in the monomers.