Ring-openging Polymerisation Of E-caprolactone And L-lactide Catalyzed By B-ketiminato Aluminium Complexes

Aliphatic polyesters are currently receiving a growing scientific interest asbiodegradable and biocompatible materials. The ring-opening polymerisation (ROP) ofcyclic esters, such as ε-caprolactone (ε-CL) and lactide (LA), promoted by metal catalystsvia a coordination–insertion mechanism is an effective method for the synthesis ofbiodegradable and biocompatible materials, due to the advantages of well controlledmolecular weights and low polydispersity indices. Because some key physical propertiesand functions of these two polymers are complementary, their copolymers are of greatinterest and intriguing, and feature different advantages in comparison to the parenthomopolymers. Our aim is to obtain highly efficient aluminium catalysts not only for ε-CLpolymerization but also for L-LA polymerisation, to prepare well defined copolymers.As part of our investigation of β-ketiminato ligands in homogeneous polymerisationcatalysis, we were interested in preparing a new family of aluminium complexescontaining cyclic β-ketiminato ligands. Herein, we thus described the synthesis andcharacterization of some novel aluminium complexes containing cyclic β-ketiminatoligands of type Me2Al{O-[(ArN=CHC4H4(C6H4)]}(4a, Ar=2,6-iPr2C6H34b, Ar=C6H5;4c, Ar=C6F5). With2-propanol as an initiator, these well-defined complexes proved to behighly active towards ring-opening polymerisation of L-lactide and ε-caprolactone in acontrolled manner. Complex4a could polymerize ε-CL in a controlled manner with highefficiency. Based on the living characteristics, the preparation of welldefined blockcopolymers PCL-b-PLLA via sequential addition of monomers was performed by4aefficiency. Note that complex4c exhibited rather high catalytic activity for the ROP ofL-LA. The monomer conversion reached completion only in4h when the L-LA/Al molarratio was100at80°C. PLLA-b-PCL copolymers were thus easily produced by4c.In addition, we thus described the synthesis and characterization of some binuclearaluminium complexes containing salen ligands of type Me2Al{O-[(N=CHC4H4(C6H4)]})2R (4d, R=-CH2CH2-;4e, R=-C6H10-;4f, R=-CH2C(CH3)2CH2-)。With2-propanol as an initiator, these well-defined complexes proved to be highly active towards ring-opening polymerisation of L-lactide and ε-caprolactone. Among them,4fexhibited rather high catalytic activity for the ROP of L-LA. The monomer conversionreached completion only in1h when the L-LA/Al molar ratio was100at80°C.PLLA-b-PCL copolymers were thus easily produced by4f. Moreover,4c can promoteε-caprolactone and lactide random copolymerization.