Living Ring-Opening homo- and co-Polymerization of ε-Caprolactone, L- and D,L-Lactides by Dimethyl(salicylaldiminato)Aluminum Compounds

The dimethylaluminum compounds {3-tBu-2-(O)C6H3CHdN-R}AlMe2 [R=C6H5 (1); 2,6- iPr2C6H3 (2); C6F5 (3)] were used as initiators in the ring-opening polymerization (ROP) of ε-caprolactone, L-lactide, and D,L-lactide. Compound 3, in combination with 1 equiv of methanol, exhibited a living behavior in the ROP of the cyclic esters. Such a feature allowed the preparation of poly(D,L-lactide-block- ε-caprolactone) and poly(L-lactide-block-ε-caprolactone) copolymers. Random copolymers of ε-caprolactone and L-lactide and of ε-caprolactone and D,L-lactide were also synthesized by compound 3. NMR and DSC characterization confirmed a highly random structure of these copolymers, even in the absence of transesterification reactions. All the materials, characterized by GPC, showed high molecular weight and narrow molecular weight distributions.