Lactide as the Playmaker of the ROP Game: Theoretical and Experimental Investigation of Ring-Opening Polymerization of Lactide Initiated by Aminonaphtholate Zinc Complexes

Abstract

A family of homo- and heteroleptic zinc complexes bearing aminonaphtholate ligands was synthesized and fully characterized. Using NMR spectroscopy and DFT calculation, bis-alkoxy-bridged complexes [LZn(μ-OR)] were confirmed to have dimeric structures in solution, analogous to those obtained via X-ray crystallography. Surprisingly, a detailed experimental and theoretical study of the catalytic activity of [LZn(μ-OR)] in the ring-opening polymerization (ROP) of lactides showed that although well-defined alkoxy dimers possess a single-site structural motif, the most active initiator is obtained during in situ alcoholysis of the alkylzinc precursor. These results indicate that rational ancillary and alkoxy ligand design that takes into account its mutual interaction on monomer coordination may be key to the synthesis of new high-performance ROP catalysts.

Highly active Mg(ii) and Zn(ii) complexes for the ring opening polymerisation of lactide

“…Zinc complexes have also been successfully applied to the ROP of lactide, generally being highly active under solution conditions. [66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83] Early work by Coates and co-workers employed a β-diiminate based Zn(II) complex which demonstrated a high degree of heterotacticity in solution. 84 Highly active zinc catalysts in solution have been examined by Williams and coworkers.…”

Homoleptic, bis‐ligated magnesium complexes for ring‐opening polymerization of lactide and lactones: Synthesis, structure, polymerization behavior and mechanism studies

“…As it is hard to remove metallic residues in polymers completely, the resultant polyesters initiated by the complexes of toxic metals such as tin and aluminum may have negative effects on the human body, causing their limited application in the field of green packaging and medical devices. [13][14][15][16][17] At this point, the catalysts with non-toxic and biologically benign metals like magnesium, [18][19][20][21][22][23][24][25][26] zinc, [27][28][29][30][31][32][33] calcium [26] and iron [34] are more suitable and superior catalysts. [35,36] In most organometallic complexes of divalent metals such as magnesium and zinc for the ROP of cyclic esters, the metal centers are supported by a multi-dentate ligand and the complexes are formed as type of LM-X [where X = Et, OBn, OSiPh 3 , O t Bu 2 Ph, N (SiMe 3 ) 2 or NPr 2 ].…”

Synthesis of lactide/ɛ‐caprolactone quasi‐random copolymer by using rationally designed mononuclear aluminum complexes with modified β‐ketiminato ligand

“…So far, a great variety of organometallics have been used as the catalysts for polymerizations of LA and ɛ ‐CL, which range from traditional stannous catalysts to main group catalysts (Na,Mg, Al, and Ca) and transition metal (Zn and Ti) as well as rare earth catalysts . Nonetheless, seldom catalysts can strictly produce random copolymer poly(LA‐ r ‐CL), with the approximately equal in average length of lactidyl and caproyl sequence ( L LA = L CL = 2) .…”

“…So far, a great variety of organometallics have been used as the catalysts for polymerizations of LA and E-CL, which range from traditional stannous 18,19 catalysts to main group catalysts (Na, [20][21][22][23] Mg, [24][25][26] Al [27][28][29][30][31][32][33] , and Ca [34][35][36] ) and transition metal (Zn 35,[37][38][39][40][41][42][43] and Ti 44 ) as well as rare earth catalysts. 2,[45][46][47][48] Nonetheless, seldom catalysts can strictly produce random copolymer poly(LA-r-CL), with the approximately equal in average length of lactidyl and caproyl Additional Supporting Information may be found in the online version of this article.…”