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}AlMe 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 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.