l-Lactide homopolymerization and l-lactide-ε-caprolactone block copolymerization by lanthanide tris(2,4,6-trimethylphenolate)s

The l-lactide (LLA) homopolymerization and copolymerization with ε-caprolactone (CL) in solution initiated by lanthanide tris(2,4,6-trimethylphenolate)s (Ln(OTMP)₃) are systematically investigated. The results indicate that La(OTMP)₃ is quite effective for the LLA polymerization. The ¹H NMR spectrum suggests the homopolymerization proceeds through an acyl-oxygen bond cleavage. Thermal analysis of homopolymers by DSC shows typical features of optically pure PLLA. The copolymerization of LLA with CL can only be achieved when CL is first polymerized followed by LLA. Feeding the two monomers simultaneously, however, only results in the formation of LLA homopolymers. The structure of the copolymers has been characterized by ¹H NMR and ¹³C NMR and the thermal behavior has also been evaluated. All these measurements demonstrate the pure diblock copolymer has been synthesized successfully.