Living Ring-Opening Homo- and Copolymerization of ε-Caprolactone and L- and D,L-Lactides by Dimethyl(salicylaldiminato)aluminum Compounds

The dimethylaluminum compounds {3-tBu-2-(O)C(6)H(3)CH=N-R) AIMe(2) [R = C(6)H(5) (1); 2,6-iPr(2)C(6)H(3) (2); C(6)F(5) (3)] were used as initiators in the ring-opening polymerization (ROP) of epsilon-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-epsilon-caprolactone) and poly(L-lactide-block-epsilon-caprolactone) copolymers. Random copolymers of e-caprolactone and L-lactide and Of E-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.