Controlled bulk polymerization of l-lactide and lactones by dual activation with organo-catalytic systems

Abstract

The acid–base catalytic system based on N,N-dimethyl-4-aminopyridine (DMAP) and a protic acid that has already been revealed to be efficient for the ring-opening polymerization (ROP) of L-lactide in solution at room temperature was tested for the same polymerization in bulk at 100 °C. As observed in solution, the presence of the DMAP·HX (X = Cl, CH₃SO₃, CF₃SO₃) salt enhanced yields. Linear and star-like polylactides with 3 and 4 branches were prepared. Polylactides were thus easily prepared reaching high molar masses (up to 75 000 g mol⁻¹ for linear PLLA and 140 000 g mol⁻¹ for star-like PLLA) with good control in less than 1 h. In all cases, the appearance of transesterification reactions was shown to occur only at very high yield. The ROP of lactones (ε-caprolactone and δ-valerolactone) was also investigated with the same catalytic systems in bulk conditions. In contrast to lactide polymerization, only the DMAP/DMAP·HOTf allowed lactone polymerization with a slower rate. However, the control over the molar masses remained very good. Block copolymers were also synthesized.