Aluminum Alkyl Complexes Bearing Salicylaldiminato Ligands: Versatile Initiators in the Ring-Opening Polymerization of Cyclic Esters

Abstract

Linear aliphatic polyesters are degradable thermoplastic polymers, which can be obtained by ring-opening polymerization (ROP) of cyclic esters through a coordination-insertion mechanism. Aluminum based organometallic complexes have a leading position as efficient catalysts for this polymerization process. Aluminumalkyl complexes bearing salicylaldiminato ligands, although less explored, have been shown to be efficient and versatile catalysts for the ROP of various cyclic esters. These species have the potential to function as active catalysts in the ROP because of their less coordinatively saturated nature with respect to analogous SALEN-type complexes. They have been used as efficient catalysts in the ROP of commercially available cyclic esters, such as ε-caprolactone, L-lactide, rac-lactide, and glycolide. Moreover, they resulted in efficient catalysts for the ROP of cyclic esters with large ring-size and for the ROP of functionalized lactide. Furthermore, they have been used in the co-and ter-polymerization of various cyclic esters affording well controlled polymerization and a plethora of microstructural architectures, ranging from random to block to multiblock.

Tuning the thermal properties of poly(ethylene)‐like poly(esters) by copolymerization of ε‐caprolactone with macrolactones, in the presence of a pyridylamidozinc(II) complex

“…To date, several metal‐based catalysts active in the ROP of macrolides have been reported, based on early transition metals (Y) and main group metals (Zn, Al, Ca, Mg) . In this regard, we have expanded the use of dimethyl(salicylaldiminato) aluminum compounds not only to the homo‐ and copolymerization of conventional small and medium‐sized cyclic esters but also to the ROP of an unsaturated macrolactone, the ω‐6‐hexadecenlactone (6HDL) . Both random and block copolymers were obtained by copolymerization of 6HDL with rac‐lactide and ε‐caprolactone (CL) .…”

Use of Metal Catalysts Bearing Schiff Base Macrocycles for the Ring Opening Polymerization (ROP) of Cyclic Esters

“…Screening of 1-5 (compared to 6-8) for the ROP of ε-caprolactone revealed how the pro-catalyst structure can influence the observed catalytic behaviour. The use of alkylaluminium complexes for the ROP of cyclic esters has recently been reviewed [17], as has the use of aluminium alkyl complexes bearing salicylaldiminato ligands [18].…”

Functionalizing PLGA and PLGA Derivatives for Drug Delivery and Tissue Regeneration Applications

“…[18,23] It is known that glycolide is preferably first inserted into the metaloxygen bond due to its higher reactivity compared to lactide. [24] Besides the effectiveness of Sn(Oct) 2 as a catalyst in ROP, safety concerns about its cytotoxicity has been arousing. Thus, in the biomedical field, recently developed less toxic alternatives as zinc salts or complexes, or even enzymes, should be considered.…”