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

Abstract

The dimethylaluminum compounds {3-tBu-2-(O)C6H3CH═N−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.